Squishy pedal after caliper rebuild

[SpeedracerIndy]

Need some help diagnosing my brake problem after rebuilding my front calipers.

I had a slightly squishy petal before the rebuild, and the car was pulling pretty badly to the left. I disassembled the calipers and found surface rust on the pistons and bores of the left caliper, along with completely disintegrated dust boots on all pistons. I polished them up with some 0000 stainless steel and reassembled with silicone lube. They polished up very well, and there was no pitting. All went back together well, and I bled each caliper 3 times while tapping on the calipers all around with a hammer to dislodge any air bubbles. I used about 3/4 of a quart of DOT4 fluid during the bleeding process. I then pumped up the brakes to extend the pistons and fill the calipers with fluid. I then filled up the reservoir and bled them again. I pressed the brake pedal in while I started the car to verify that the brake booster was working correctly. Then I went for a test drive. The car stops fine, and I am able to lock up the front wheels easily. It stops straight and true, and doesn't pull to one side. But, the pedal has to be depressed almost all the way to the floor to engage the brakes. And, it almost feels as if they are over boosted. The pedal used to be very stiff and engage at the very top. Can someone offer assistance on what to do next to get my high, stiff pedal back? Things that I have done to the brakes relatively recently:

-new master cylinder about 3 years ago (~7,000 miles ago)
-new rubber brake lines about 3 years ago
-new pads about 5 years ago (they are about 60% now).

Edit: I also noticed a "clicking" sound coming from the left caliper, then a few seconds later from the right caliper when I pumpped up the brakes to extend the pistons. I was a little concerned at the sound, but everything seemed to be working ok and the dust boots looked ok when I checked them.

Car is an 81 SC RoW.

[daddygo]

You might want to inspect the brake hoses. When they get old, they can lose their stiffness so that when you press the brakes, your are expanding the hoses...contibuting to a squishy feel. Feel them with your hands. Look for dry, cracking or any areas that are distended. Of course, now that I re-read your post, it says you replaced them within the last 3 years, sorry.

[barndoor]

my guess ,is that you still have air in the system (front calipers).I would keep bleeding.

[rdrr]

I've had the same problem after caliper rebuilds. In my case re-bleeding improved the situation a little, but not a lot. My mechanic recommended putting pressure on the pedal and leaving it overnight, i.e. depress the pedal with a suitably sized piece of wood and wedge it between the seat and the pedal. This improved it a lot. A bit of spirited driving improved it further.

The reason for the problem is (I believe) that the new dust boots are initially not fully seated and pull the piston further back than normal. You then get longer than normal pedal travel. Once the boots are fully seated, the problem dissappears.

[rusnak]

definitely air in the system. You have to try different methods. I have a few, some are desperation methods that would be controversial if posted, so I'm just going to say use a Motive style pressure bleeder.

[john70t]

The brake hoses do go bad. They are probably due for a change if it hasn't been done recently, and could cause slight pulling.

The symptoms happened over a short period of time, and I'm going to suspect the phase "all the way to the floor".
When the piston in the master cylinder is fully extended, it sweeps over rough/rusted areas in the bore which tears the internal seal.

It might be necessary to bleed the brakes some more to see if that helps. It sometimes takes a while.
If that doesn't help, then a MC replacement might be necessary. Pre-bleed it by cutting and wrapping a brake line back into the resevoir and pump it through several times.

[SpeedracerIndy]

Originally Posted by rdrr

I've had the same problem after caliper rebuilds. In my case re-bleeding improved the situation a little, but not a lot. My mechanic recommended putting pressure on the pedal and leaving it overnight, i.e. depress the pedal with a suitably sized piece of wood and wedge it between the seat and the pedal. This improved it a lot. A bit of spirited driving improved it further.

The reason for the problem is (I believe) that the new dust boots are initially not fully seated and pull the piston further back than normal. You then get longer than normal pedal travel. Once the boots are fully seated, the problem dissappears.

This sounds like my situation. I did try some spirited driving with a few hard fast stops and it seemed to stiffen up the pedal for a few miles, so it sounds like the same problem you were having.

The rubber hoses and MC are practically new (~7,000 miles) and feel and look like they are in very good shape. All of my brake bleeds were done using a motive pressure bleeder at about 10-12psi. I think I will try depressing the pedal over night and bleeding again after some spirited drives and see if that helps.

[RoninLB]

the piston ring has a V type edge that pulls the piston away from the rotor.

I install the pads when the pistons & pads are so tight that I need a small hammer to get them in.. otherwise, just wait it out.

[Zeke]

Why not hold off on the "spirited" drives until you understand the problem? It's easy to get trapped air in the system and not get it out successfully until all methods have been employed. For instance, if I do anything to the brake system. I bleed it all, front and rear. Well, reverse of that, of course.

Did you bleed the rears?

[rusnak]

You have to diagnose the problem. If you can get the pedal to firm up with multiple pumps, then you have piston rings retracted too far. If you have a squish pedal, as the thread title indicates, then you have air in the system. If you have a pedal that starts out firm, then drops clear to the floor, then you have a leaking MC.

I think you have air probably trapped in the calipers and behind the brake proportioning valve. You need to move a lot of fluid and try tapping to dislodge the air bubbles. Try a plastic mallet on the calipers, and if that does not work, then maybe try a two person brake bleed with one person on the pedal, and the other person working the bleed screw to shoot the air bubbles out with pressure.

And trust me, do not go for spirited drives with bad brakes

[The Curator]

I ran into a similar (air) problem and had to bleed them over and over again, my mechanic insisted that the mc was bad but I kept trying and all the sudden it was back to normal but only after multiple tries.

[SpeedracerIndy]

Thanks all for the advice. I will limit the spirited drives until I am confident I know what the problem is. I have replaced countless calipers, and bled brakes more times than I can count, and I am very confidant that the air is out of the system. I fully intend to bleed them again after they are working correctly. I intentionally bought cheap fluid from autozone for this round because I had planned on replacing it with some super blue when I'm done with the repairs. I really feel that the problem is that the pistons are retracting too far into the caliper. I took the wheels off again to check the dust boots, and noticed that there is about a 1/8" gap between the pads and the rotor, and the pads wiggle around freely in the caliper. Shouldn't they be resting practially on the rotor?

Perhaps I should change my description from squishy to "light". I wouldn't say that the pedal feels spongy like when there is air in the system, it just feels very light. There is much less effort required to stop the car than before the rebuild.

[Eric_Shea]

The reason for the problem is (I believe) that the new dust boots are initially not fully seated and pull the piston further back than normal. You then get longer than normal pedal travel. Once the boots are fully seated, the problem dissappears.

No way.

There's probably still air in the system. Have you checked the actuator end play at the pedal cluster/MC?

[rusnak]

one more post, then I'm out.

Try one of these from Kragen or Pep Boys:



It's a brake pad spreader. It fits in the space where the spring steel goes. You basically take the spring out, put the pads and pins back in, and tap the brake pedal to overextend the pistons. Then you use the spreader to spread the pads just enough so that the caliper fits back onto the rotor. Now you have a correctly adjusted brake pad clearance to the rotor.

[Flieger]

My brake pedal travels farther and smoother/lighter now that I have rebuilt S calipers from Eric. I think it is just that the pistons move much more now than they did when the caliper was frozen up with corrosion. I bled them one weekend and they felt good. I used a rubber mallet and the push the pedal method. I have stainless steel braided brake hoses and a stock 19mm master cylinder. I have M calipers in the rear. I did a few spirited drives with the brakes in "good" and safe condition, then bled them a second time the next weekend. The pedal felt more responsive and was firmer. The quality was "great".

The brakes have since firmed up a bit as they have become bedded in on the rotors which had odd wear patterns from the corroded calipers.

I would drive normally if the brakes feel safe and bleed them again on the weekend. You will probably find a little bit of air but that can make a big difference.

No comments about the adjectives, I'm just a kid

Here's Eric's work:

[midnight911]

another vote for more bleeding... I wouldn't distrust that piston seating theory but air is more likely the culprit.

[Pingo]

Calipers mouted wrong side/up side down? The bleeding screw should be on top...... ??

[Eric_Shea]

Calipers mouted wrong side/up side down? The bleeding screw should be on top...... ??

Naaaaa... your monitor is upside down. Try this picture:



Max, check the MC actuator on the pedal assembly. Now that the brakes have bedded in you may want to make sure everything is within spec there.

E.

[AHartz]

I am struggling through the same issue. I rebuilt all four calipers. I have driven it a couple hundred miles and pads are fully against the rotors (no light visible between them). Have bled & bled & bled the system using all the tricks that I could find on this board (gravity bleed, traditional pump-the-pedal method, beat the calipers with mallet, force the pedal down overnight, seal threads on bleeder screws with grease, etc.). Still have a spongy pedal and little confidence in hard braking situations. Master cylinder was replaced with new one two years ago.

I haven't tried a pressure bleeder yet - that's my next step. Knowing that the master cylinder is only two years old, I'm convinced that there's still air in the system. It's hard to believe it knowing that I've run about 1 gallon through the system!

81 911SC Targa

[midnight911]

gallon of fluid...that's about what I've consumed too. :-) I do too wonder, even having said it is the air, why it takes so long to get the air out? New cars off the factory line do not have the problem. why us?
but i try not to worry about it too much. although i still THINK my pedal is a little spongy, the car does slow down fine and very well controllable at track situations.