I need more front brake bias!!! [Archive]

Reaper1

02-01-2009, 10:31 PM

I've run in to a point where I've found the brake balance on my car isn't exactly what I need. I'd done a LOT of research a while abck on the different brake systems that were available from the factory on our cars, but I don't remeber some of the info. I *thought* the proportioning valve was the same between the '88 Shelby Z and the '89-'93 11" brake package.

I'd like to get confirmation of this, or the true specs if I'm not right.

Also, if they ARE in fact the same, I need to then find out how to get more front brake on my car...BADLY. It's getting pretty anoying during my auto-x and track day events locking the slightly unloaded rear tire, which in turn unselttle the car more than I'd like at times (not to mention flat spotting my tires!).

So, I'm looking for suggestions. Things I'm considering are(in order, sort of):

-swapping proportioning valve in my car for a true 11" brake system valve
-different pad compounds front vs. rear
-using cross drilled rotors in the rear to lessen the thermal capacity as well as surface area of those brakes
-definatly doing some sort of cooling for the front brakes(applicable to track days only)
-using slotted rotors for the front to try and provide a bit more fresh bite for those pads
-putting on adjustable proportioning valves(need 2 because of the cross-balanced brake system)

I'm due for pads here shortly(a few more auto-x events will probably do them in), so I'm also looking for suggestions for good(race quality, NOT parts store) pads. Currently I'm running Porterfield R4S pads front and rear. At the time I got them(many years ago now), they were the only company I could find that made pads for the front 11" brakes for '89/'90 cars(the '91-93 cars have a different back plate for the pad).

So, if there are any suggestions for these things, I'd like to hear them! :thumb:

tryingbe

02-02-2009, 07:14 PM

http://minimopar.knizefamily.net/perf/brakes.html

Look at the tag color of your proportioning valve.

Vigo

02-02-2009, 07:34 PM

different pad compounds front vs. rear

$12 autozone pads in the rear will fix you right up, i'd bet.

Reaper1

02-02-2009, 10:07 PM

http://minimopar.knizefamily.net/perf/brakes.html

Look at the tag color of your proportioning valve.

If the tag is supposed to be under the brake system warning switch plug on the proportioning valve, then mine is white(well, a discolored white), which matches the site. The Black one would DEFINATLY cause me issues!! I suppose I need to try to find a tan one and try that out.

I have two other thoughts on this issue:

#1 the car was not loaded the way I normally race it. I didn't have my spare in it, which I usually keep in the car to keep some weight in the rear of the car to try and help balance it out F/R. The only thing I can say was that I was having the issue WITH it in as well up at Waterford Hills, just not as bad.

#2 I wonder if I loosen up the rebound adjustment on the rear shocks if that might help keep the tires in contact with the ground better during those transitions? I already readjusted the fronts because after talking with Lee Grimes of Koni, he suggested I was overdamped(at least on the front), so I loosened those up and readjusted them, and now the car not only rides better, but the handling seems to be just as good. Makes me think I might have the same issue in the rear....

Thoughts?

Vigo

02-03-2009, 04:33 PM

well if you loosen the rebound on the rear you might lose some car rotation so it might turn into a flat spots vs fast times thing if you go that route. but its possible you could loosen it some and not lose anything like the front. worth a shot!

Reaper1

02-03-2009, 04:49 PM

I think I will...I gotta mess with the rear suspension anyways..as in my other thread! LOL

Now, what color tag is on the '89 Shelby Daytona proportioning valve?

iTurbo

02-05-2009, 11:42 PM

Good thread! I STILL have this problem of too much rear brake bias on my Omni GLH Turbo because I went against all the good advice here and installed rear 11" vented brake setup from a '91 Lebaron GTC. I like the suggestion about the rear pads; I think I may try that. Not until after I install the '89 Daytona Shelby 11" front brake setup though. The car now has Caravan 10" front brakes, 24mm MC, and a prop valve from my Shelby Lancer. Pads are Raybestos Super Stop on the front and the 911 pads on the rear that FWDP used to sell, and the car also has new braided s/s flexible brake lines. I've scared the crap out of myself braking hard after a run enough times..

Reaper1

02-06-2009, 12:04 AM

WOAH!!! No wonder you have too much in the rear! The fronts are smaller, have less agressive pads, less heat capacity, and the prop valve probably has too high of a pressure split and slope for that car!

I've found out that the '89 Shelby Daytona with 11" brakes comes with a yellow tag on the proportioning valve. This option is not listed on the Mini-Mopar site. However, in my 1990 FSM it DOES list the specs: The pressure split is at 400psi and the slope is .43

I also want to put out there that the P-body(style H24 or H44, which I have no cluse what that means) came with the same Gray proportioning valve as the L-bodies with specs of: split=500, slope=.27.

The J-bodies were available with the yellow and a DIFFERENT Gray proportion valve with specs of: split=600, slope=.43, which is the same as the Tan in the A-body, G-body, and P-body. This could be a typo, but I'm just putting out there what my FSM has in it.

From the looks of it I could try either a Tan or a Yellow proportion valve in my car and have better bias as my specs according to Mini-Mopar are: split=750, slope=.43, which is darn near wha the C-body had WITH ABS!!! It's no wonder I have too much rear bias and why my '90 really didn't have an issue with this same set-up without changing the proportion valve.

Looks like I have to rob my parts car! :D

GLHNSLHT2

02-06-2009, 01:12 AM

what prop valve do you have on your car Reaper? The stock 87/88 prop valve?

Reaper1

02-06-2009, 08:03 AM

what prop valve do you have on your car Reaper? The stock 87/88 prop valve?

Yes, it is the stock '87/'88. When checked the tag the other day it looks an awful like white to me(I had to spray if off pretty well with cleaner to even see the color!! LOL :D ) If that's the case, then it's no wonder I'm having issues if the specs on the white one are correct! :yuck:

My only thing is that being as the car was origionally a disc/disc car, why did it have so much rear bias anyways? Were the old solid disc set-ups THAT bad back there that they needed that much pressure to work? I could be wrong on this, as it's been a long time since I'd done my research, but I thought that hydraulically(meaning pistons sizes and whatnot), that the old disc set-up was identical to the newer one(meaning cam parking brake versus internal drum). If this is the case, then why the HECK does this car have so much rear bias!? :confused:

As an aside, back around 2000, and old aquaintance of mine had an '88 Shelby Z(t-top car). We were messing around with the cars one night trying out his newly gotten G-tech and he hasked me to drive his car. The place we were testing was long enough for the 1/4, but the run-off had about a 30* gradual right hand turn in it probably about 30 yards after where we were getting off the gas and starting to slow down. Well, when I drove his car and started to slow down(of course hitting the turn while I was applying the brakes, but not really that hard), it locked the rear tires and I went for a VERY scary ride(this was before I'd auto-x'd or anything). I slid completely sideways at about 80mph for a good 100-150 yards going around that corner.:wow1: I saved the car and could have come out looking like a hero, but I forgot I could turn around later down the road and kept the wheel locked to try and make the upcoming turn-around and snap-oversteered going the opposite direction for the last 20 yards or so of the slide. I didn't hit anything, and I didn't stall the car, but I was SCARED of that car after that. I refused to drive it. :bolt:

That instance makes me wonder if this is inherant of these cars after what I'm now fighting with my car?

Anonymous_User

02-06-2009, 08:11 AM

Well, for the L-bodies, you could swap to the SRT front spindles, ginormous brakes, 4-piston calipers, etc.

Not sure if I've read of the swap working on G-bodies.

GLHNSLHT2

02-06-2009, 01:00 PM

Yes, it is the stock '87/'88. When checked the tag the other day it looks an awful like white to me(I had to spray if off pretty well with cleaner to even see the color!! LOL :D ) If that's the case, then it's no wonder I'm having issues if the specs on the white one are correct! :yuck:

My only thing is that being as the car was origionally a disc/disc car, why did it have so much rear bias anyways? Were the old solid disc set-ups THAT bad back there that they needed that much pressure to work? I could be wrong on this, as it's been a long time since I'd done my research, but I thought that hydraulically(meaning pistons sizes and whatnot), that the old disc set-up was identical to the newer one(meaning cam parking brake versus internal drum). If this is the case, then why the HECK does this car have so much rear bias!? :confused:

As an aside, back around 2000, and old aquaintance of mine had an '88 Shelby Z(t-top car). We were messing around with the cars one night trying out his newly gotten G-tech and he hasked me to drive his car. The place we were testing was long enough for the 1/4, but the run-off had about a 30* gradual right hand turn in it probably about 30 yards after where we were getting off the gas and starting to slow down. Well, when I drove his car and started to slow down(of course hitting the turn while I was applying the brakes, but not really that hard), it locked the rear tires and I went for a VERY scary ride(this was before I'd auto-x'd or anything). I slid completely sideways at about 80mph for a good 100-150 yards going around that corner.:wow1: I saved the car and could have come out looking like a hero, but I forgot I could turn around later down the road and kept the wheel locked to try and make the upcoming turn-around and snap-oversteered going the opposite direction for the last 20 yards or so of the slide. I didn't hit anything, and I didn't stall the car, but I was SCARED of that car after that. I refused to drive it. :bolt:

That instance makes me wonder if this is inherant of these cars after what I'm now fighting with my car?

That explains a lot Reaper. Every 87/88 Z I've driven likes to lock the rears prematurely. When I went to 89/90 11" brakes I replaced the whole system. The rears still lock up 1st but probably more so because the difference in tires vs bias. I can trail brake pretty late and just start to lock up the inside rear. I'd suggest swapping out the prop valve for an 89 piece. Then play around with brake pad compounds. I assume you have 4 of the same tires too?

Vigo

02-06-2009, 04:58 PM

Keep in mind that if you loosen the shocks enough to keep the tire on the ground, you can still tune out some grip with tire pressures.

Im still suggesting the autozone pads as the cheapest idea!

but the info thrown out about the prop valves is stuff ive never seen before, which is cool...

iTurbo

02-06-2009, 08:43 PM

WOAH!!! No wonder you have too much in the rear! The fronts are smaller, have less agressive pads, less heat capacity, and the prop valve probably has too high of a pressure split and slope for that car!

Yup, all the chassis/suspension/brakes were all done at once in a Big Bang style upgrade, so I knew it wouldn't be very well balanced right off the bat but I would just adjust from there. I have some 11" fronts that I'm going to install but need to find a machine shop with an overhead mill to prep the knuckles for L-body use first. After that, I'll experiment with pads and the prop valve. Car stops wonderfully except for high speed braking the rear will get tail happy in a hurry! For this reason I don't let anybody else drive the car.

Reaper1

02-06-2009, 11:36 PM

That explains a lot Reaper. Every 87/88 Z I've driven likes to lock the rears prematurely. When I went to 89/90 11" brakes I replaced the whole system. The rears still lock up 1st but probably more so because the difference in tires vs bias. I can trail brake pretty late and just start to lock up the inside rear. I'd suggest swapping out the prop valve for an 89 piece. Then play around with brake pad compounds. I assume you have 4 of the same tires too?

Ah, ok, so it IS inherant to those cars, and after seeing the specs for the prop valve I see why! I will definatly change out the prop valve. I think my parts '90 car has a yellow tag on the prop valve, so I *think* I'm good. If not, in the words of a good friend of mine: I have a metric f*ckton of parts...I'm BOUND to have something in there that is of use! LOL

Oh, and yes, I do have 4 of the same tires: 225/50/16 Kumho MX mounted on Enkie RPF wheels.

After seeing Mike Stimac's car this summer, I'm wondering now if I can fit Viper brakes under those 16" wheels? I don't know if they'll fit with the 13" rotors or not, but if so, THAT would solve my issue!! :thumb::evil:

csracer

02-07-2009, 12:39 PM

Reaper, 16" wheels won't fit over the 13" rotor / Viper Caliper we tried it on Mike's car. When you get ready to do new pads check out Carbotech, I run their XP8 in the front (11" Vented) for track days. In the rear (11" vented) I don't go any more aggressive than a premium street pad like Hawk HPS. The difference in friction coefficient between the two pads seems to keeps the rear lockup to a minimum. Oh, mine has the yellow tag prop valve .

Reaper1

02-08-2009, 12:00 AM

Thanks, Chris! :thumb:

I actually was looking at those exact pads for my car, though I was still in the air for the rears. I think I might follow your lead with that combo.

I'm going to go back to my house probably either next week, or the week after that to get more parts and such so I can make this thing right. I'm due to bleed the brakes anyways, and it'll be easy to get to the prop valve with the tranny out while I'm doing the clutch, so I might as well do all of that at once!

overboostmotorsports

02-14-2009, 01:53 PM

run ebc red stuff in the front and parts store brand in the rear

Reaper1

02-14-2009, 08:13 PM

EBC does not make pads for the '89/90 11" brakes. Otherwise I would have been running Green Stuff pads a LONG time ago! :thumb:

Reaper1

02-14-2009, 08:46 PM

Oh, on another note...while I was messing with the rear suspension today trying(and succeeding) in fixing the noise it was making, I also readjusted my rear shocks to a less firm setting. I backed them down to only 1 turn firm and this seems to have made the rear of the car a little more stable. I can tell that it will still lock a wheel if I were try to turn as I could feel the rear of the car dancing, but I'm fairly sure I didn't lock a wheel in a straight line, which is an improvement! :thumb:

My trials were from 45 and 60mph panic-type stops.

Reaper1

03-21-2009, 02:26 AM

OK, I wanted to update this! I got my new brakes installed...all new front stuff is '91-up 11". The new pads are Carbotech XP8. I did get the new proportioning valve in(yellow tag). I took it all apart and cleaned all the nasty gunk out of it too. Good thing I did, it was pretty bad!

Tonight I beded the new pads in. WOW!!! That's all I can say! The initial bite on those pads is AMAZING! Plus, they just keep working when they get hot! I had a hard time getting them hot enough to produce the slight amount of fade that they wanted to see during the bed process!

I did try a few panic type stops...here are the initial results: when the pads are hot, I can lock the front with ease. When they are cold...still have the rear lock issue, but honestly, if I have to stand on them that hard there is something SERIOUSLY not right! The car slows down so fast with the new pads up front that it really isn't needed to stand on the brakes.

So, I'm still contemplating getting some cheapy rear pads. I don't really know if it'll be worth it or not....possibly so since the brakes won't get hot enough during auto-x to be able to lock the fronts first.

I also used ATE Super Blue brake fluid and bled the system using speed bleeders and a "bleed kit". I was able to do the entire system in about 30 minutes by myself!!! I don't think I could have done it that fast with another person helping me!!!

Anyways, there's the update....once I get an alignment on the car I'll test it again and take better notes of the behavior under certain conditions.

BTW, if anybody wants to use these pads, they DO squeel when used lightly. I don't mind it because I know why they do that, but others would be bothered by it...

inmyshadow

03-21-2009, 06:43 PM

Alright, I've stayed out long enough.

First, the RS4 pads are too aggressive for the rear. I used those pads front and rear on my old 92 Daytona IROC. I autocrossed the daytona for several years. I would experience rear lock up at times. Mostly when I was hard braking with the car unbalanced. The worst times was when it was wet out. I had a 720 spin across the finish line, causing everybody around timing & scoring to run. The course was tight with a turn just before the finish line and rivers of rain across the in front of the finish line.

I also found the RS4 pads to be too cold for the street. I had a highway commute, keeping my brakes cold. I had to warm up the brakes before I got to the typical choke points on the highway to avoid "oh ----" stops. For autocross, I dragged my brakes to the starting line or the pads would be to cold for the first couple of turns.

I did love those pads though. They did no harm to the rotors at all. The rotors looked brand new after several seasons of autocross.

I just finished off my 11in brake upgrade on my 91 Shadow convertible. My shadow had a yellow tag on the valve. I swapped out the yellow valve with the green tagged valve from my 90 Shadow ES with solid rear disc.

After I spent the two hours doing the job, I found the specs in my 91 FSM. It listed the yellow tagged valve for both disc/drum and disc/disc cars. I have no clue what the specs are for the green tagged valve. I'm not experiencing problems when I went on my test drive today.

WOAH!!! No wonder you have too much in the rear! The fronts are smaller, have less agressive pads, less heat capacity, and the prop valve probably has too high of a pressure split and slope for that car!

I've found out that the '89 Shelby Daytona with 11" brakes comes with a yellow tag on the proportioning valve. This option is not listed on the Mini-Mopar site. However, in my 1990 FSM it DOES list the specs: The pressure split is at 400psi and the slope is .43

I also want to put out there that the P-body(style H24 or H44, which I have no cluse what that means) came with the same Gray proportioning valve as the L-bodies with specs of: split=500, slope=.27.

The J-bodies were available with the yellow and a DIFFERENT Gray proportion valve with specs of: split=600, slope=.43, which is the same as the Tan in the A-body, G-body, and P-body. This could be a typo, but I'm just putting out there what my FSM has in it.

Reaper1

03-22-2009, 02:38 PM

Thanks! Good to know about the rear pads. I suppose I might drop a little more coin to get some less aggressive rear pads on before I hit the track. I don't know what a "green" tag is either, I don't remember seeing that in the FSM. Also, the yellow tag is installed on both disc/disc (11" anyways) and disc/drum cars. My '90 was a disc/drum...yellow tag. My '90 parts car is the same thing. I know my buddy's '89 Shelby Daytona (factory 11") is also yellow.

I suppose we'll see. I'm still getting used to the bite of these new pads. They don't need much effort at all!

As for the RS4's, one the street I never really had an issue, I just had to use a bit more pedal at first. On autocross I found that because I did have to use so much pedal that modulating them was a little difficult and that their characteristics changed during the run as they warmed up.

The new ones just have a LOT of bite and I'm going to have to adjust accordingly. I don't need nearly the amount of pedal to get the same and even MORE stopping force than with the RS4's.

jory

03-29-2009, 12:35 AM

Thanks to this thread I saved tearing into that part of the brake system twice. My Laser had a black tagged prop valve and I will be using 11" front/rear brakes. I remember from my Spirit that the stock yellow tag valve had great balance with the 11" big disc brakes. The brakes were very easy to control if a wheel was to skid, just let up a tiny bit and get back on them. It felt like the car was kind of squatting during braking thanks to the bite of the rears, but rear lockup was never an issue. They only locked if I slammed on the pedal, and then all 4 wheels would skid. So I pulled a yellow valve from the yard today, and it will be going in tomorrow. The hardest I ever pushed those brakes I was running with a turbo GTI or some such and I out braked it from 120, I stopped right on the white line and he was half way through the intersection when he stopped. Talk about a rush :)

GLHNSLHT2

03-29-2009, 01:26 AM

I'm glad I'm not the only one to feel the car squat on all 4's when you nail the brakes. What's great about that is that if you're busting the speed limit and a cop just happens to be coming the other way you can dynamite the brakes and the car doens't do the nose pitch thing, just squats on all 4's and it's like you hit a dip or something. I've gotten out of being pulled over a couple times because of that I feel.

Reaper1

03-29-2009, 11:34 PM

Yeah, mine used to squat quite a bit, but now with the new pads and proportioning valve it does nose dive a little.

As an update to the pads...I LOVE them as far as perforamance is concerned. I feel I NEVER have to worry about if I can stop the car. What I don't like is they dust....a LOT! I figured the dust that was on my wheels before I cleaned them was just from bedding them in...normal. However, I cleaned my wheels the other night(both front and back as well as waxed them), then drove to Orlando(about an hour drove from where I am) and then drove back. That was enough to make it so I could wipe my finger on the wheel lip and you could tell a VERY significant difference between clean and dirty! Oh well, I suppose I'll just have to find some REALLY good wax for my wheels and wash them more often...

Reaper1

04-06-2009, 07:39 PM

OK another update!! After my track weekend I figured out that I STILL have this issue!

After the first day I sourced some Pep-Boys 'El-Cheapo rear pads to replace the Porterfield ones.

Even after this change the rears STILL lock WAY before the fronts. It's not as bad and I can put more force in to the pedal and get WAY more braking than I had before now, but it STILL locks them up!

After talking with my instructor and Chip Herr about this the conclusion is I need a bias of around 70/30 front/rear respectively.

The adjustments I've tried are:
-swapping proportion valve for the "correct" one, evidently there is a Gray and a Green valve that I might be able to try as well...specs unknown for the Green valve
-swap pad compunds
-adjusted rear rebound
-lowered rear tire pressure

I think I'm going to try and source the other two proportion valves and try those. If that doesn't work the only other thing I can think of is either getting a custom valve made, or installing an adjustable unit or units.

Does anybody have experience installing adjustable units on a FWD cross-balanced system? I know it can't be that hard, but I've never seen it done personally. I'm wondering how bad it would be to eliminate the cross balance and just go front/rear? I know WHY they cross balanced the system, I'm just curious....

Anyways, input would be appreciated once again. This issue was one of the reasons I didn't get bumped to a more advanced run group sooner. It wasn't my driving, it was the car! ARRGGHH!!!! :mad:

inmyshadow

04-07-2009, 08:49 AM

What kinda of speeds are you at as you reach the braking zones? When you lock up, what is the angle of the course?

Right now, I'm using Satisfied Pro Ceramic Pads PR524C that I got from tirerack for 8 bucks. Even with the store brand rear pads, I haven't experienced any rear lock ups. I've tried some fast, late braking tests. My tests were all done in a straight line. I haven't attacked any on ramps yet.

Only time I was able to lock the rears was after just swapping the 11in rear disk with the 10in front rotors. I also had the yellow tagged proportioning valve.

Now I'm full 11in brakes with green tagged proportioning valve and rear stainless steel brake lines.

I'm wondering if you you need to work on our threshold braking. You just need to find the sweet spot in the brake pedal.

OK another update!! After my track weekend I figured out that I STILL have this issue!

After the first day I sourced some Pep-Boys 'El-Cheapo rear pads to replace the Porterfield ones.

Even after this change the rears STILL lock WAY before the fronts. It's not as bad and I can put more force in to the pedal and get WAY more braking than I had before now, but it STILL locks them up!

After talking with my instructor and Chip Herr about this the conclusion is I need a bias of around 70/30 front/rear respectively.

The adjustments I've tried are:
-swapping proportion valve for the "correct" one, evidently there is a Gray and a Green valve that I might be able to try as well...specs unknown for the Green valve
-swap pad compunds
-adjusted rear rebound
-lowered rear tire pressure

I think I'm going to try and source the other two proportion valves and try those. If that doesn't work the only other thing I can think of is either getting a custom valve made, or installing an adjustable unit or units.

Does anybody have experience installing adjustable units on a FWD cross-balanced system? I know it can't be that hard, but I've never seen it done personally. I'm wondering how bad it would be to eliminate the cross balance and just go front/rear? I know WHY they cross balanced the system, I'm just curious....

Anyways, input would be appreciated once again. This issue was one of the reasons I didn't get bumped to a more advanced run group sooner. It wasn't my driving, it was the car! ARRGGHH!!!! :mad:

Reaper1

04-08-2009, 12:03 AM

OK, I was seeing anywhere from 105-120mph right at the start of braking in the braking zone.

We(my instructor and myself) were braking in a straight line going in to turn one. I had a better feel of how much I could ask of the brakes the second day, so I didn't have as much of an issue, but I also know that I coold have gotten more out of it if I didn't have to worry about the rears. Toward the end of the weekend I was able to use it to my advantage to rotate the car, but I still feel there is more that can be had if this issue wasn't as bad.

I was starting braking at the 400' mark going in for turn 1, but I was also slowing WAY down to make it becuase I was having issues with my turn-in point. Turn 1 and 2 are connected and is a decreasing radius turn, so you double apex it. I got turn 2 fine, it was turning in to 1 and hitting the apex that was killing me.

My instructor on lap 3 decided that he was comfortable enough to dive in to the 300' mark before braking. That is where he was braking in his race car, and it would have been fine had the rears not locked! The fact that I KNOW the car could have done that with no issues on street tires if it didn't have this issue says volumes to me. I KNOW the car can do it, I just need to fix this!

I've only gotten the front brakes to lock before the rears a few times, and that was during bedding in the race pads on the front. After that I've not been able to do it.

I agree that threshold braking is something I need to work on, but I can't do it with the brakes messed up like this.

I REALLY wish I could get the fronts to lock first, then I could practice my threshold braking a LOT easier(and safer). I mean, this works OK for rotating the car, but there's no way I can dive bomb a fast corner right now and know with comfidence that I don't have to worry about the rears locking and a possible spin....Part of that IS driver, I know, but if the car doesn't work the way it's supposed to, as my instructor proved, there's nothing you can do about it!

inmyshadow

04-08-2009, 08:26 PM

What is the brake compound of your rear pads? I wonder if you can get an organic brake compound in a rear pad. Or you can try different brand pads to find which one has less bite.

MP use to have offer an adjustable brake bias device. Other saying that, I don't have much experience in using adjustable brake bias devices.

OK, I was seeing anywhere from 105-120mph right at the start of braking in the braking zone.

We(my instructor and myself) were braking in a straight line going in to turn one. I had a better feel of how much I could ask of the brakes the second day, so I didn't have as much of an issue, but I also know that I coold have gotten more out of it if I didn't have to worry about the rears. Toward the end of the weekend I was able to use it to my advantage to rotate the car, but I still feel there is more that can be had if this issue wasn't as bad.

I was starting braking at the 400' mark going in for turn 1, but I was also slowing WAY down to make it becuase I was having issues with my turn-in point. Turn 1 and 2 are connected and is a decreasing radius turn, so you double apex it. I got turn 2 fine, it was turning in to 1 and hitting the apex that was killing me.

My instructor on lap 3 decided that he was comfortable enough to dive in to the 300' mark before braking. That is where he was braking in his race car, and it would have been fine had the rears not locked! The fact that I KNOW the car could have done that with no issues on street tires if it didn't have this issue says volumes to me. I KNOW the car can do it, I just need to fix this!

I've only gotten the front brakes to lock before the rears a few times, and that was during bedding in the race pads on the front. After that I've not been able to do it.

I agree that threshold braking is something I need to work on, but I can't do it with the brakes messed up like this.

I REALLY wish I could get the fronts to lock first, then I could practice my threshold braking a LOT easier(and safer). I mean, this works OK for rotating the car, but there's no way I can dive bomb a fast corner right now and know with comfidence that I don't have to worry about the rears locking and a possible spin....Part of that IS driver, I know, but if the car doesn't work the way it's supposed to, as my instructor proved, there's nothing you can do about it!

Reaper1

04-09-2009, 12:29 PM

The rear pads are now some cheapy Pep-Boys pads. I *think* they are organic...

Unless there is another option from MP I don't know about, the adjustable bias is the same thing you can get from Summit, ect..., which is what I'd be looking at installing...

Juggy

04-25-2009, 02:10 AM

BUMP

hey chris...maybe im ignorant to the thread, for tryin to read up to make sure i say this but....

have u thought about champhered brake pads in the rear?? i was going through some brakes and founda set of champhered ones, with a huge assss champher, they are only going to hold as much pressure as what contacts. you could start champhering things little by little until you found the perfect champher. but of course youd haev to take the pads off every here n there to re champher due to wear.....just throwing it out there.....could be a nice alternative to switching back to solid rear rotor, that way u can keep the cooling properties of the vented, for auto x-ing

like if u take 1/2 the contact surface area of the pad, its going to greatly reduce the braking pressure on the rear

Juggy

04-25-2009, 02:20 AM

They only locked if I slammed on the pedal, and then all 4 wheels would skid. So I pulled a yellow valve from the yard today, and it will be going in tomorrow. The hardest I ever pushed those brakes I was running with a turbo GTI or some such and I out braked it from 120, I stopped right on the white line and he was half way through the intersection when he stopped. Talk about a rush :)

this reminds of my buddies shelby charger with the SLH 3 setup....we were buzzed up n hit taco bell for "4th meal" lol

he gassed the car and catapulted the 2.5 S60 charger to 100 mph then slammed on the brakes to make the red light. lets just say i wasnt wearing my seat belt and i flew from the passenger seat into the dashboard, tossing my pepsi all over his car, only to land on the floor with a face plant into his lap :yuck: lets just say he got more excitement out of it then i did :o

at least we both had a good laugh :clap:

SLH 3+ (11" front w/ vented rear) for the win!!! lmao

Juggy

04-25-2009, 02:23 AM

PS love the Z.....i hate white but your car def can pull it off!! thats a clean ride u got there....even when it is covered and numbered in blue masking tape :P

would love to see ya at SDAC again this year....jagr bombs FTW!!!

Juggy

04-25-2009, 02:25 AM

ya ya ya i know im blowin this thread up lmao

Reaper1

04-25-2009, 09:50 AM

^^Somebody's havin' a good time! LOL

I guess I forgot to update this thrread..I thought I had, but anyways.

So, I went to rotate my tires after the track day and when I did I found something very interesting. While my instructor was driving and we had our little wild ride we BOTH thought the rear brakes locked. Well, according to what I found on my tires that was NOT the case! The two front tires had MASSIVE flat spots on them and they were not like that when I rotated them up there. One was so bad that it went through the tread, down in to the carcass! These tires *had* 2/3 tread left on them too! So, that kind of thing could only be caused by sliding a long distance, or a moderate distance at high speed...hmmmm.

So, the moral of the story is that the front tires did indeed lock before the rears, and it's not advisable to lock them up like that at those speeds. The result was that I had to replace both of those tires, and will eventually be replacing the other two for a complete set. The tires I replaced them with are the Kumho XS, one step up from the MX's I was running. There are several reasons for this, as I really wanted to try the Direzza's, but that'll have to wait.

Cory, thanks for the compliments on the ride! :thumb: The pictures make it look a heck of a lot better than it does up close, but I'm picky too, so...

http://photos-c.ak.fbcdn.net/photos-ak-snc1/v2508/159/4/1335150140/n1335150140_30191418_5492616.jpg

I'll post one of the tires too in a little while! :D

Reaper1

04-25-2009, 10:30 AM

Here are the two tires I replaced. These were taken after they were dismounted off the wheels...

This is the worst of the two. You can see where it ripped through the tread and down in to thr carcase. There's also some marbles left on it from the track! LOL
http://farm4.static.flickr.com/3409/3472757229_6ac123e3a5_b.jpg

This one wasn't as bad, but bad enough where it was't "round" anymore! LOL
http://farm4.static.flickr.com/3305/3473569126_8600db5714_o.jpg

In both cases you can see that I am running just a tad more negative camber than what is optimal for maximum braking, but it works very well for cornering and keeping the tires happy in that situation, especially with the amount of body roll. The body roll isn't horrible, but our suspension design is not vert good at keeping a consistant camber arc with roll, so a decent amount of negative camber is needed. If I had some stiffer springs I could get away with less...

In the picture I posted of the car above it can be noted that my tires are pretty far up in the wheel wells. Keep in mind the car sits pretty darn low to begin with, so that isn't too far from how it normally sits, and if I'm not mistaken that picture is of me going around turn 3 where you pull alot of consistant cornering g's there.

Vigo

04-25-2009, 11:58 AM

Reaper1

04-26-2009, 12:13 AM

That usually happens on the inside front on a long turn under braking. Sometimes you cant hear it because of the noise the other tires are making. Ive had the same thing happen to me on my dynasty, but my tires were almost full tread.. so it didnt go down that far, but it did damage a near-new tire :(

Inside front or inside rear?

These were both on the front. We were not doing any trail braking at all...all braking was done in a straight line.

These tires WERE 2/3'rds tread! LOL Were were going about 120-125mph and the braking/sliding started at the 300' mark from turn 1...we slid at LEAST 200' of it! :yuck:

GLHNSLHT2

04-26-2009, 12:58 AM

you're way more trusting than I am to let someone drive your car. I would of been pissed.

Reaper1

04-26-2009, 03:52 AM

Well, I'll put it to you this way, I rode with him in his own race car and I knew how he drove. I felt comfortable in his abilities to control the car and I figured he couldn't do mcuh worse than I'd already done. Remember, I'd already spun it twice on the first day!

There are very few people in the world I'll even hand the keys to...he happens to be one.

As for being pissed...again, I knew there was an issue and that I'd already flatted two tires. Not badly, but enough to notice. I bought those tires with the express intent on beating the living snot out of them at auto-x and road course events. It just happens that he beat on them a little more than I did! LOL I honestly can't be pissed for something like that given the circumstances it happened. I laughed about it then, I'm still laughing. It was a learning experience, and I learned a LOT.

If I hadn't felt comfortable with him driving the car harder than he laready had the first two laps out, I would have said something. Neither of us expected the brakes to lock, and knowing what I do now, especially the fronts due to all the issues I'd been having!

Am I irritated I had to replace two tires that were basically good still? Eh, a little, but really besides the money it doesn't bother me. I gained so much from that one track day...I can't wait to do it again. I just need to make sure I truly do have the brake bias fixed...for that I'll be reinstalling my crappy old 15" wheels and doing some test runs so I don't ruin my good tires! :thumb:

Vigo

05-04-2009, 10:24 PM

Inside front or inside rear?

These were both on the front. We were not doing any trail braking at all...all braking was done in a straight line.

Inside front, trail braking, decreasing radius starting from about 80mph and let off the brakes around 45 iirc. Luckily my tires were less than half the price of what you're running now.. : /

Reeves

06-22-2009, 11:20 PM

I don't want to hijack here....but am I reading correctly that L-bodies came with a grey prop valve? Am I also reading that the grey valve had the lowest rear brake pressure of all the other valves?

Where do I look for the color on the valve?

Thanks!

Reaper1

06-23-2009, 12:16 PM

IIRC they Grey valve does have the lowest pressure and ramp. However I don't have my books with me to confirm it.

To look for what "color" the valve is, there *should* be a platic tag around the brake warning switch on top of the valve. The tag's color is the refference to which valve it is.

Reeves

06-23-2009, 01:56 PM

Cool, thanks. I'll check for color tonight.

omnigoestohell

06-23-2009, 02:27 PM

Reeves

06-23-2009, 03:50 PM

Wildwood makes adjustable prop valves, you'd need two for the rear because of the split system but you should be able to soften the bite in the rear that way... or go back to drums in the rear as nearly all of the braking in an l-body seems to comes from up front..

It's Wilwood and yeah, I may have to go that route.

Discs are lighter. Especially when using 87-88 Daytona rear non vented discs and Wilwood 1.4 lb. aluminum calipers.

Reaper1

06-23-2009, 04:05 PM

I still wonder if there is any detriment to getting rid of the diagonal split system and just doing a straight front/rear set-up? I know WHY it's done the way it is on street cars...redundant safety, but is it really something that needs to be kept? I just wonder what happens if you run two adjustable proportion valves and one is just a TAD different from the other? Most of the adjustable valves seem to have set specific positions and no fine adjustment that *I* know of.

Does anybody know?

Aries_Turbo

06-24-2009, 12:02 AM

removing the diagonal doesnt seem to affect my k cars braking at all.

one thing i did notice. i did have the one port going to the front brakes and the other going to the rear. when the rear play was taken up before the front play, the pedal would get crazy hard and the front brakes wouldnt work much at all. this is with a wilwood valve in the rear setup. what i had to do was join the front and rear together and then split to the front and the split through the wilwood valve to the rear.

i did have the rears lock first once on the kcar but that was when i was bedding in the pads and the fronts were fading real bad. i figured that would happen.

brian