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Discussion Starter · #1 ·
the car seemed okay last night, but i took it out today, went around the block, and at the first stop sign the pedal was faded 3/4 of the way down. a second pump and they were rock solid again.

i drove all around and i can find no relationship between driving time, the frequency of braking, and the faded pedal. sometimes it's after 10 minutes of highway driving, other times it's when cruising across a parking lot. maybe once every 50th time i hit the brakes.

someone mentioned the caliper thing and axle play. the rear axles have minute play, they move in and out less than 1/16".

what can i look at next?

:confused1: :confused1: :confused1:
 

· section 8
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you have air some where ! didn't I read you swapped a master ? Providing you bench bled it enough, I am a big fan of gravity bleeding . Park on a level surface or slightly nose up, open each bleeder in sequence for a little while then close. If you have 4 piston calipers with bleeders on only one side lightly tap the oposing side with a small plastic hammer while bleeding. If you did not bleed the master enough , get a helper to hold pedal down , while you slowly open the two lines , farthest away first. Do this until fluid only comes out . Or 3-4 times. If all this fails take a pair of hose clamp pliers and clamp off ea caliper until the pedal feels good , then either leave it there (ha ha) or put a hand vacuum pump on it and pull the air out . if that fails replace caliper. If that fails block off all four calipers and if the pedal is still no good the new master is no good. Yeah I know its new , new does not mean good. If all this fails throw wrenches across the road , drink beer and try again tomorrow. Hope this helps. Bob
 

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Discussion Starter · #3 ·
yes, i have a new master. bled the brakes around 2x with the 2-person pedal method. did it a third time to be sure. reverse bled it last night with the Phoenix gun. only one bubble came out after one pump at the passenger front caliper.

i guess gravity bleeding can't hurt.

:icon22:
 

· FFCobra Fanatic
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Eddie: I've got to believe you have a bad mastercylinder, new or not. A bad cup rubber on the piston is all thats needed to screw things up. Has the MC ever worked properly since you put it on?
 

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Eddie,
Frank is right, I've had renewed master cylinders malfunction straight out of the box. I'd take yours off, mount it in a vice on your bench and test it.
Frank
 

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Ditto the bad M/C. You'd be surprised how often it happens. It's infuriating. I HATE the feel of brake fluid so installing a new master and bleeding the system to come back later to find it mushy gets my goat. Once you get that sorted, if you really want a good bleed, get 2 friends to help and open a front and a rear together (assuming dual masters). Once you're fairly happy, then do a round of pressure bleeds ( you pump the pedal a bit, hold pressure and they will open the bleeders and when your foot hits the floor have them close. 2-3 per and you're good to go. For the ultimate peace of mind, do a hot pressure bleed. Just make sure your help understands not to overtighten the bleeders :)
 

· 2010 FFCars Graduate
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I went through three M/C when I was building my car before I got a good one. :mad:
Good luck. Hope you get it worked out soon.
 

· Official OLD GUY
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Air injection?

Eddie,

Any chance you are having the same issue as this post ( http://www.ffcars.com/forums/17-factory-five-roadsters/297969-master-cylinder-help.html ), air leaking into the system where the reservoir is attached to the master?

Since your master does not have an integral reservoir (like the Jeep MC), there is a chance that the MC is sucking in air when you release the pedal and a vacuum is created by the piston(s) returning to their un-pressured position.

As the brakes are released and the disk piston seals "roll" the pistons back enough to allow a small amount of clearance for the pads, they don't really create any "back-pressure" in the lines to speak of . . . it's the return of the MC piston(s) that draw the fluid back into the master. If there were to be an air leak at the junction of the master and the reservoir. air could be introduced into the master, creating the issue you seem to be experiencing.

Just my 2¢

Also, 1/16th inch axle movement would be in excess for a solid mounted caliper, brake pads only need about .020" to not rub the rotor . . . disk brake clearances are really tight with today's systems. Not sure if this is an issue with Wilwood's, I've always run full-floating calipers so I'm not the one to ask . . . check with Gordon.

Doc :beerchug:
 

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Discussion Starter · #11 ·


it would seem strange that the master cylinder itself is the culprit, because the problem was exactly the same as the old one.

this problem started a short while after i upgraded my rear drums to wilwoods.

the master is a brand new unit from Breeze.

:confused1:
 

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I don't think you have air in the system. If it was air, the soft pedal would be present all of the time. What pedal are you using? One possibility is that the pedal is not retracting far enough to let the piston uncover the vent port. Can your pedal be adjusted to return to a higher point?

Tim
 

· Official OLD GUY
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Pads push-back

Eddie,

" this problem started a short while after i upgraded my rear drums to wilwoods. "

Then I'm going to have to go back to the original idea that the pads are being "pushed back" farther then they would be with a floating caliper, causing you to pump once to extend the pads out to the rotor surface and the second pump to apply pressure to them. Solid mounted calipers need the axle to run true and not move in and out under cornering forces.
If your axles are indeed moving in and out an excessive amount, they will push you pads back to the point that the pedal would seem loose and you would more-then-likely have to press the pedal twice to actuate the brakes. Once to push the pads out to rotor contact, second to apply the braking force.

Any way you can block off the rears and see if you have the same issue? That would tell you if the MC is causing the problem or your new "modification" to the rears.
If the problem persists, it's the MC, if the problem goes away and you have a good solid pedal, it's the wilwood/axle issue.

Be extra careful when trying to stop with the rears blocked off, give yourself plenty of space with no obstructions in your path.

Actually, you can do this up on blocks or stands . . . you'll know if the pedal is soft just pressing on it (after re-bleeding the fronts and the line to the rears to your test blockage). Best place to add a plug(s) is the "Tee" at the rear. That way you test the master up to that point in the system.

Tryin' to help, Ol' Buddy . . .

Doc :beerchug:
 

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Discussion Starter · #14 · (Edited)


Pete:

the very first time it happened was the morning after, i backed out of the driveway, went around my (short) block, cruising steady in 2nd, going maybe 20mph, steady, no brakes. the block is "short", but i did two HARD left turns (like close to a pac-man right angle turns) then a quick HARD right turn, and then at the stop sign, - that's where the pedal was almost completely faded.

i think you may be onto something. i am going to try to duplicate this exact scenario and see what happens.

plugging the "T" for the rear is a brilliant idea. i made a plug from a fitting and JB weld... i used it so the brake fluid would not leak out of the front T when i was doing the master. my T and rear flex line/splitter in the rear is up high under the trunk, so it's a higher point and i won't leak out too much fluid.

correction: my axle play is 0.020". this was controversial when i did the rear disc brake retro, some were saying my whole axle should be rebuilt. some said their brand new hi-po rear end had 0.020" as well. a mechanic i talked to said 0.020 play is perfectly fine and nothing to worry about. as usual, i am :confused:

i will try going around the short block with a series of small, tight turns, or possibly try it in a parking lot. plugging the brake lines will take some time.

:beer:
 

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Hey Eddi, just a thought to build on what Big Blocker is suggesting. Would it be possible to jack up the back of the car and then try to move your rear wheels in/out (mine move in and out 1/16" or so pretty easily) to see if you can knock the pads back in and then try your pedal to see if this recreates your problem? Just a thought for what it is worth. Regards Scott
 

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X2

What johnnybgoode said,
Try putting the car up on jacks and pressing the brakes, even if it takes two or more presses to get them to be hard.

Start by pressing on your brakes (even if you have to do it twice to get a good feel) and then release them . . . wait a few seconds and try to press them again, they should be hard the first press.

Now, go rock your axles back and forth . . . then go press on the pedal again and see if you have to pump them up or do they still have a hard feel the first time.

If they are soft, the axle movement has moved your pads back far enough to cause your two-press pedal issue . . . you'll need to work on eliminating that free-play. "C-clip" eliminators are supposed to be a good thing, although, meant to retain an axle should you experience an axle break during hard acceleration or turning. Maybe they would eliminate your free-play to an acceptable amount.

I can't say from experience that I've ever had an issue with your symptoms before . . .
On the expensive side, there's always the conversion to tapered bearing ends for your 8" rear end.

" i did two HARD left turns (like close to a pac-man right angle turns) then a quick HARD right turn, and then at the stop sign, - that's where the pedal was almost completely faded. "
This tells me that the pads are being knocked back . . . Try this same scenario without the hard turns, go straight as possible and see if the pedal is hard the first time, every time.

" my axle play is 0.020". this was controversial when i did the rear disc brake retro, some were saying my whole axle should be rebuilt. some said their brand new hi-po rear end had 0.020" as well. a mechanic i talked to said 0.020 play is perfectly fine and nothing to worry about. as usual, i am <confused>. "

Eddie, if your rear end was OK up until you swapped out to your Wilwoods, there is nothing wrong with your rear end. You issue is with the fact that the old calipers would float with the runout of the rotor, not effecting the pads. Your new calipers are solid mounted and do NOT follow the rotor, so any in-n-out movement in the rotor
(like making hard turns) causes the pads to be pushed back into the caliper piston bores.

.020" isn't your problem . . . 1/16th" (.0625) is, especially if this is the "play" on each side.

Doc :beerchug:
 

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Discussion Starter · #17 · (Edited)
i am sure the above procedure won't work, because the pedal will always be rock-hard once it's in the garage. i'd need the brakes to stop in front of the house, and another tap once pulling in.

the best i can do is take the wheels off, and look carefully at the calipers and see what's going on when a friend depresses the pedal.

for what it's worth, my rear end may be the only donor thing left on the entire car that is not fully rebuilt or replaced.

when i did my 3.55 gear swap, the mechanic did replace the bearings and crush sleeves. is that considered a "full rebuild?" when i did my pinion seal, i replaced the seal only, and re-used the bearing and crush sleeve, but i don't imagine that section relates to axle play.

:icon22:
 

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Eddie, i know you have wilwood rears. I also know they are different then ours... but, ours you need to remove the caliper and put it in the 3 or 6 O clock position and bleed it. It makes a wicked huge difference. Hope you get it figured out.
 

· Blue Oval Scribe
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Eddie, what do you have for front brakes, spindles, and control arms? I've seen this issue on some Mustang II front suspension setups on street rods/classic Mustangs, where the front floating caliper is actually pushed from the back side by a sway bar, control arm, etc. and compresses the piston, causing a "no brake" pedal to the floor moment. Pump it and then the brakes are fine. This would only happen on turns that were far enough to hit the caliper. You could drive for an hour on the highway straight, but make a sharp left at the end of the off-ramp and bam, no brakes at the next stoplight.

Post up some pics, or try turning your steering wheel with the suspension at ride height and see if your front calipers are hitting anything.

HTH...
Mark
 

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Discussion Starter · #20 ·
Hi Mark:

i have 100% '90GT Mustang Front. the problem started after the Wilwood rear retrofit, and with the old master cylinder.

changed master cylinder, same problem. reverse bled brakes, same problem. so now i suspect the rear brakes are the problem.

interesting to read your comment about the Mustangs. i will check the front brake interference.

:icon22:
 
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