poor braking SLH 1 package

[MoparN75]

Seeking more input so I've started this new thread. I have an '87 Shelby Charger that sat for maybe 4 yrs. When I put it back together I changed the front calipers to a set of mini van calipers I'd had on my Lebaron before I'd upgraded it for a second time to '89 Daytona Shelby specs. Problem is the Charger brakes haven't worked properly since. No matter how hard I push the pedal I can not lockup the brakes. I've driven it like this but it isn't right. If I had to make a panick stop I'd be s.o.l. Recently I've replaced the master cyclinder with a jy 24 mm unit. I've replaced the vacuum booster with one from NAPA and still have the same problem. In re-reading this site http://minimopar.knizefamily.net/perf/brakes.html I'm wondering if I used the proper rotors, can't remember now which ones I used, but if I had to guess I'd say they were from the Lebaron. I don't know...sure has me baffled. I'd appreciate any thoughts you guys might want to share.

[Whorse]

are the calipers clamping fully? Before I did my brake pads in my GTC I had that problem, and it was in fact the calipers not clamping down entirely.

[turbovanman]

Is the pedal hard? after you shut the engine off, do you have a soft pedal for 2-4 pumps then it goes hard? then keep your foot on the brake pedal and start it, it should drop.

[MoparN75]

Is the pedal hard? after you shut the engine off, do you have a soft pedal for 2-4 pumps then it goes hard? then keep your foot on the brake pedal and start it, it should drop.

Let me clear things up. I thought I had mini van brakes on it but I don't. These are calipers from an '88 Lebaron.

No pedal isn't hard. Yes it does have 3-5 good pumps after shutting off engine. It also passes the start-up pedal drop test. Also the booster only loses about 1" in one minute when supply is pinched off and then engine shut off.
Today I pulled front wheels found that pads were shot. Replaced them and rotors with pads and rotors for '88 Lebaron. I was VERY disappointed when I test drove it to find it didn't change.
Well I shouldn't say it did change at all. It brakes quickly to a point, but then I get no additional braking no matter how hard I push the pedal. As before it will not lock the brakes up on any wheel.
I don't have a pressure test kit so I have no idea how much pressure is actually reaching the calipers and wheel cylinders. But I do know that after all the times I've bled the brakes I've got nice clean fluid coming from the bleeders at all 4 wheels when I open them.
http://www.xmission.com/~dempsey/shelby/slhpkgs.htm using part II as a guide.

[turbovanman]

Whats your engine vacuum? if you have a high idle, it will also affect brake booster performance.

[MoparN75]

16" at idle

[turbovanman]

16" at idle


Hmmmmm, that can affect performance. Try this, disconnect the booster and go for a drive-if its the same, then your low vacuum is causing it. If it worse, then you need some better pads or?

[Aries_Turbo]

did you bleed all the lines fully? rear drums adjusted properly? calipers on right side up? the bleeder screw should point up or you cant bleed them...

Brian

[MoparN75]

I just ran to the parts store with it and it feels like the brake pedal travel is being stopped by something. As if the kids toy truck were under it.{ I checked, it's not}. I didn't see anything that would obstruct it's travel, but that sure is what it feels like. If I could just get another 1/2"-1" travel it'd toss me thru the windshield.

[turbovanman]

I just ran to the parts store with it and it feels like the brake pedal travel is being stopped by something. As if the kids toy truck were under it.{ I checked, it's not}. I didn't see anything that would obstruct it's travel, but that sure is what it feels like. If I could just get another 1/2"-1" travel it'd toss me thru the windshield.


Is your pushrod in the booster adjusted correctly?

[MoparN75]

yes, according to instructions that came with the new booster. It simply said I needed a little play up top side of pedal travel and I do.
This is what I've got; pedal is 7" off floor, 3/16th" of free travel, 2" of travel before it hits obstruction which leaves it 4" off the floor.

[turbovanman]

I set it with a helper, its much easier and bang on accurate. Basically, one of you holds the loose mc against the booster, the other moves the pedal, then you can figure out when it moves the mc off the booster etc and adjust as necessary.

[MoparN75]

I unbolted the MC, leaving brake lines connected, had someone hold MC against booster while I depressed the pedal. Seems to be about an inch of travel before MC moves from booster. I then moved MC away from booster enough to check travel of brake pedal. With the rod still connected the pedal moves freely from top to floor with little effort. Bolted MC back on and once again it has the same feel. Feels as if the MC cylinder piston is bottoming out in the bore of the MC. Yet the pedal is still 4" off the floor.

[turbovanman]

Sounds like you need to adjust the pushrod out a bit.

[MoparN75]

I'm not sure that would make a difference, seeing that I have 4" of travel left before pedal would touch the floor. This really is a weird situation. I asked my wife, who was helping me bleed the brakes, if the pedal was moving all the way to the floor when I opened the bleeder and she said it was, so why would it feel like I'm encountering an obstruction now? Man I'm stumped.

[MoparN75]

I finally got around to adjusting booster rod. Moves it out {longer} two turns, made no difference.:confused:
It had appeared to be about the same as the original before I moved it.

[mpgmike]

Try a different prop valve.

Mike

[MoparN75]

Yeah that's what my next move is. Actually turning the booster rod out 2 turns did make a difference...the right front drug bad. Left front got a little warm but rears didn't seem to be effected.

[4cefedomni]

how bigs your master cylinder bore it could be its too big and not allowing you to put enough pressure on it, thats the only regret from my brakes on my car i used the master off an e350 van, a 1 ton, and its huge like inch and a quarter and it doesn't allow for very much pedal travel or feel, one of these days i'm swapping in a smaller master

[turbovanman]

Yeah that's what my next move is. Actually turning the booster rod out 2 turns did make a difference...the right front drug bad. Left front got a little warm but rears didn't seem to be effected.

Ok, so back it back off, now the MC isn't releasing.

[MoparN75]

No, I think 2 turns was just too much and was simply keeping the brakes applied. Once I backed it off they stopped dragging. I removed and cleaned up the proportioning valve this week, it didn't really seem very dirty. Put it all back together today. It's braking a lot better now and it doesn't feel like the MC piston is bottoming out in the bore any longer {not that it ever was actually happening, it just felt like it}, but it's still not right. I'm considering replacing both front calipers next and maybe going back to the smaller MC.

[turbovanman]

Its not the larger MC, I am running one and its one of the best mods I did.

I don't feel like rereading, what MC are you using now?

[MoparN75]

24 mm, it my wifes car and that a bit more pedal effort than she needs.

[turbovanman]

24 mm, it my wifes car and that a bit more pedal effort than she needs.


Hmmmmmm, that shouldn't give you issues like that. I am running the 1 1/8 bore one and its unreal. Larger MC gives you a harder pedal and less travel.

[MoparN75]

yeah, with these calipers I can use the original 21mm M/C. I think she'd like that better.

[fargo59]

pinched flow in a flex line? i had that problem after i replaced the calipers on my 92 van. thought it was a seized caliper, changed them, and couldn't bleed the right front wheel unless i pounded on it with full vacuum assist. changed the flex lines and it was fine. for 30 bucks each, why not? rubber doesn't last forever.