I need more front brake bias!!!

[Reaper1]

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!

[tryingbe]

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

Look at the tag color of your proportioning valve.

[Vigo]

different pad compounds front vs. rear

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

[Reaper1]

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]

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]

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]

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]

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!

[GLHNSLHT2]

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

[Reaper1]

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 ) If that's the case, then it's no wonder I'm having issues if the specs on the white one are correct!

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!?

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. 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.

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

[Anonymous_User]

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]

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 ) If that's the case, then it's no wonder I'm having issues if the specs on the white one are correct!

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!?

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. 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.

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]

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]

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]

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!!

[csracer]

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]

Thanks, Chris!

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]

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

[Reaper1]

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

[Reaper1]

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!

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