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Brakes long pedal

Jay Laifman

Jay Laifman

Donation Time
I'm a little at a loss here and wondering if anyone has a suggestion.

I put on Dan's fantastic rear disc brakes. I absolutely love them. They work great. Every once in a while, in the morning, my pedal is longer that it should be. My feeling is that one of the brake pucks is getting stuck retracted for some reason. I would suspect it is a front caliper - as Dan's are brand new and I rebuilt the front ones about 25 years ago.

I do not have any fluid loss. I bled the brakes extra well when I put in the rear discs, using BOTH of my sons, one in the car, one at the master filling the reservoir, and me at the bleed valve.

This was happening only after sitting for a bit, and would not be a problem as soon as I started moving. Recently it seems to be staying in the longer. I am not getting any pulling either.

I looked at the rubber hoses and none of them seem to be ballooning out. The rear one is new. The front ones are probably 25 years old.
 
A

Asm109

Donation Time
Buy the 2 psi residual pressure valves from Wilwood. Mount them mount where convenient. Before any tees of course
 
Barry

Barry

Diamond Level Sponsor
Jay Laifman said:
I'm a little at a loss here and wondering if anyone has a suggestion.

I put on Dan's fantastic rear disc brakes. I absolutely love them. They work great. Every once in a while, in the morning, my pedal is longer that it should be. My feeling is that one of the brake pucks is getting stuck retracted for some reason. I would suspect it is a front caliper - as Dan's are brand new and I rebuilt the front ones about 25 years ago.

I do not have any fluid loss. I bled the brakes extra well when I put in the rear discs, using BOTH of my sons, one in the car, one at the master filling the reservoir, and me at the bleed valve.

This was happening only after sitting for a bit, and would not be a problem as soon as I started moving. Recently it seems to be staying in the longer. I am not getting any pulling either.

I looked at the rubber hoses and none of them seem to be ballooning out. The rear one is new. The front ones are probably 25 years old.
Click to expand...



Jay,

I suspect that you have excessive rotor run out / pad knock back on one or more rotors.

When you push on the brake pedal and apply hydraulic pressure, all of the caliper pistons "extend" to force the brake pads into contact with the rotors. With a standard Series Alpine brake pedal arm, a 3/4" master cylinder and no brake booster, a force of 50 lbs. on the brake pedal results in a hydraulic pressure of about 480 PSI which results in an extension force of about 1,700 lbs. for the Series Alpine front caliper pistons and about 585 lbs. for the Saturn rear caliper piston. Short of a completely seized caliper piston, it is safe to assume that the caliper pistons / pads are fully extended when you push forcefully on the brake pedal.

The only thing that should cause any of the caliper pistons / pads to retract is "knock back" from rotor run out.

With your combination of components, just 0.010" of pad / piston knock back on just one side of just one front caliper will require almost 3/8" of brake pedal travel to "take up the slack." With 4 rotors and 8 pads, you can get a long pedal in a hurry.

The other potential culprits are a "lazy" cup seal on the MC piston or sloppy MC push-rod.
 
Jay Laifman

Jay Laifman

Donation Time
260Alpine said:
Jay, is your Ebrake adjusted to 3-4 clicks?
Click to expand...
Hmmm. I just made sure that they were adjusted so that the cable was not causing the brake to drag, and I got full engagement when applied. Was there some different adjustment I should do?

And Barry, double hmmm. The rear discs are brand new. The front discs are pretty old. I do not feel any pulsing when braking. But if merely a .010" kickback can cause issues, I have no idea how I'm going to find that! I'll look there for something more obvious.

The master is brand new. I have a .75" from Wilwood. I can see if the piston itself is sticking. Hmmm. Actually now that I think about it, I noticed that my pedal was a little low, causing my mechanical brake lights to go on even when my foot wasn't on the pedal. You may have something there.
 
H

hdar5702

Platinum Level Sponsor
Check your front wheel bearings for proper adjustment.If a wheel bearing is worn or not adjusted correctly the brake rotors will not stay 'true'
and push the caliper pistons too far back into their bores.
 
9

911tr8r

Gold Level Sponsor
Dumb luck I should happen upon this thread. I just had a shop change all the lines and front calipers on my SV v6 conversion. Was not cheap like $1750. The BMC is a Centric for a 72-76 Courier ( Model 130.45501) SInce then when I step on the brake the front calipers stop nicely EXCEPT calipers would not release. It got so bad that I was spinn
Asm109 said:
Buy the 2 psi residual pressure valves from Wilwood. Mount them mount where convenient. Before any tees of course
Click to expand...

ing the rear wheels and the car was just standing still. The mechanic is giving me all kinds of excuses. like bring him back the BMC and he would adjust the piston in the master. That did nothing. I am wondering if the MBC is just wrong for the car?

Would the 2PSI residual pressure valve do anything for my problem? Nothing I expect cause Jay's problem is opposite of mine. In fact the way I got the car home when the brakes were locked up was to relieve the pressure at the banjo bolts and used the E brake till I got home. Scary!
 
Barry

Barry

Diamond Level Sponsor
911tr8r said:
Dumb luck I should happen upon this thread. I just had a shop change all the lines and front calipers on my SV v6 conversion. Was not cheap like $1750. The BMC is a Centric for a 72-76 Courier ( Model 130.45501) SInce then when I step on the brake the front calipers stop nicely EXCEPT calipers would not release. It got so bad that I was spinn


ing the rear wheels and the car was just standing still. The mechanic is giving me all kinds of excuses. like bring him back the BMC and he would adjust the piston in the master. That did nothing. I am wondering if the MBC is just wrong for the car?

Would the 2PSI residual pressure valve do anything for my problem? Nothing I expect cause Jay's problem is opposite of mine. In fact the way I got the car home when the brakes were locked up was to relieve the pressure at the banjo bolts and used the E brake till I got home. Scary!
Click to expand...



Classic symptoms of the master cylinder piston not fully retracting when the brakes are applied and then released. Possibly a defective MC, but more likely because of the brake master cylinder pushrod being too long / mis-adjusted or the brake pedal arm not fully returning when released.
 
Jay Laifman

Jay Laifman

Donation Time
911tr8r said:
Dumb luck I should happen upon this thread. I just had a shop change all the lines and front calipers on my SV v6 conversion. Was not cheap like $1750. The BMC is a Centric for a 72-76 Courier ( Model 130.45501) SInce then when I step on the brake the front calipers stop nicely EXCEPT calipers would not release. It got so bad that I was spinn


ing the rear wheels and the car was just standing still. The mechanic is giving me all kinds of excuses. like bring him back the BMC and he would adjust the piston in the master. That did nothing. I am wondering if the MBC is just wrong for the car?

Would the 2PSI residual pressure valve do anything for my problem? Nothing I expect cause Jay's problem is opposite of mine. In fact the way I got the car home when the brakes were locked up was to relieve the pressure at the banjo bolts and used the E brake till I got home. Scary!
Click to expand...

I assume your MC is a dual circuit MC, right? And no servo. Seems odd that only the fronts would lock up because of the MC. Also seems odd that both sides of the front are locking up - like not a ballooning rubber hose affecting one side. But then that does seem to point to a problem with the front circuit of the MC - unless the servo is hooked up to only the fronts, which creates a problem.
 
Jay Laifman

Jay Laifman

Donation Time
Very strange then that you are getting lock up on front. I would think that whatever is causing that issue from the master would do the same for both circuits. But since they are dual circuits, and you are getting that, and it is both front wheels it sure seems like the MC is the source. But I'm not sure how that can happen. It's just a plunger with two holes and two seals.
 
9

911tr8r

Gold Level Sponsor
brake rod has about 1/8" play before contacting the back of the MC so spacer would not help. In the AM plan to swing down one caliper to see if pistons move freely.
 
B

Bill Blue

Platinum Level Sponsor
Jay Laifman said:
Very strange then that you are getting lock up on front. I would think that whatever is causing that issue from the master would do the same for both circuits. But since they are dual circuits, and you are getting that, and it is both front wheels it sure seems like the MC is the source. But I'm not sure how that can happen. It's just a plunger with two holes and two seals.
Click to expand...
Jay, I had a similar problem, only with the rear brakes. All it takes is one piston to not fully retract, therefore blocking fluid return. I've never seen a piston setup where the rear piston pulls the front piston back. It is all spring pressure. While my problem was on the rear brakes, it was very effective.

Bill
 
Jay Laifman

Jay Laifman

Donation Time
Bill Blue said:
Jay, I had a similar problem, only with the rear brakes. All it takes is one piston to not fully retract, therefore blocking fluid return. I've never seen a piston setup where the rear piston pulls the front piston back. It is all spring pressure. While my problem was on the rear brakes, it was very effective.

Bill
Click to expand...
But if he had one piston with a problem in the front, he would get obvious pulling. On the rear, since it is a solid axle, there would not be pulling.

Also, you said you did not have a piston fully retract, which blocked fluid return. I think that is also different for front and rear discs. On the fronts, if a piston does not pull back, there will be fluid in the cylinder and it will not go back towards the master. But that doesn't mean it is creating pressure in the system. That means that one piston is stuck, and one pad may be up against the rotor. But not necessarily clamping on the rotor. I don't know. Would that cause the front end to total lock up? I'm thinking it would not - only make the car pull in one direction.

On the rear disc calipers, with only one pad connected to the one piston, and the other side connected to that, there would be stronger clamping force if the piston gets stuck in the out position. Is that what happened to you?
 
B

Bill Blue

Platinum Level Sponsor
Jay, the brakes are plumbed so that front brakes are on the same circuit, rear brakes on a separate circuit. So unequal pressure would be between the front/rear brakes, not left/right.
Bill
 
Jay Laifman

Jay Laifman

Donation Time
Right. But you said it was a piston problem. So that would be left and right. That's what I"m trying to help explore. Is it a caliper issue or a MC issue?
 
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