Caliper Rebuild Question - After affects...

[Icemaster]

Installed new braided lines, rotors, pads, and rebuilt the calipers on the front of the '85. Bleed the lines twice so far. Full fluid replacement comes after I do the rears.

The brake pedal has a lot more travel in it and builds resistence further down in the stroke than before. It build pressure (and holds) if I pump it and engages further up, so I'm thinking it's not master cylinder.

Searching here, I found that it's likely the pistons are withdrawing too far back into the calipers, hence the additional effort to pump them up - the additional pump or two on the pedal forces more fluid back into the caliper. That's what I'm putting together anyway...

How do I fix this? Am I mistaken in thinking the MC is OK?

[squelch]

I just did the same job, though I completed all four and replaced the fluid. I am experiencing the exact same thing, as have many others on this board. After reading many, many threads, it seems that it may work itself out after 100 miles or so, as the cylinder seals break in. This is what I am hoping for. I did not pump my master cylinder at all when bleeding the brakes, so I am almost certain it is not a MC problem. I have about 50 miles on mine so far and am going to re-bleed them again this weekend. I'll let you know if mine improves.

[Mitch Leland]

I'd be interested in the outcome as I'm putting mine up on jacks tomorrow to replace the rotors, S.S. hoses, and rebuild the calipers.

Thanks,

[cl8ton]

I had my calipers rebuilt along with new rotors/pads and used the power bleeder sold here on PP.
The pedal travel and feel came back just like before the rebuild.

You probably still have air in the lines, PP has an excellent article on bleeding brakes, just besure to clamp
off the overflow line if using the power bleeder! Seems the article fails to mention that!

My rebuilt calipers...

[JohnJL]

The correct bleeding procedure starts from the left rear and works around counter clockwise. You may have a bubble at the hard line. After bleeding the rears also, at the very end of doing the front left wheel have your assistant hold the pedal 1/4 down while tightening down the bleed screw.

Dont know why it works and maybe its voodoo but it works for me even when using my pressure bleeder.

[tonythetarga]

Originally Posted by JohnJL

The correct bleeding procedure starts from the left rear and works around counter clockwise.

Not to be a pick but you want to start at the RR, then LR BUT then go to the RF and then the LF. You always want to be bleeding the caliper that is furthest from the reservoir and m/c.

[KTL]

The problem is the new piston seals will retract the pistons too much when you release the pedal. Therefore you must extend the pistons out just enough to make it difficult to insert the pads. That will solve your problem. Do a search. It's been documented numerous times. The late Warren Hall (Early_S_Man) referred to it as "hysterisis" and describes the occurrence very well.

[cgarr]

How did you bleed the brakes? What works well is to get some pressure on the pedal, have someone stand on it then crack the bleeder to force the air thru, also you might try and bang on the caliper with a rubber mallet, you may have some trapped air which is common when you rebuild these calipers unless you bench bleed them first.

[nyne11]

Not to further be a pick but if you note where JohnJL is from we drive RHD cars here so....the MC is on the RHS...therefore JohnJL is correct.

Originally Posted by tonythetarga

Not to be a pick but you want to start at the RR, then LR BUT then go to the RF and then the LF. You always want to be bleeding the caliper that is furthest from the reservoir and m/c.

[tonythetarga]

LOL pick away! Point taken, but still it remains that you always want to start furthest from the m/c and move to the next furthest caliper until you're done.

[cgarr]

So down under are the bleeders on the top or bottom of the caliper?

[Bill Verburg]

Originally Posted by cgarr

So down under are the bleeders on the top or bottom of the caliper?

It would be impossible to bleed a caliper if the bleeds are on the bottom

[Tom '74 911]

Originally Posted by KTL

The problem is the new piston seals will retract the pistons too much when you release the pedal. Therefore you must extend the pistons out just enough to make it difficult to insert the pads. That will solve your problem. Do a search. It's been documented numerous times. The late Warren Hall (Early_S_Man) referred to it as "hysterisis" and describes the occurrence very well.

I've been through this before w/my brakes and posted on some of the earlier threads w/the same question. Bleed the brakes a bunch of times, tap on the calipers w/a rubber hammer until you're confident that there's no air in the system. Then, as long as it's safe to drive. . . drive it, and the new seals will seat themselves. Do some more bleeding after you've driven a few miles - seems like I'm almost always able to get even a few micro bubbles out. Extending the pistons out and wedging the pads in will improve your pedal feel immediately, but the only cure I found was miles.

Tom

[Gunter]

The bleeding-issue has come up many times.
I found over many years, and different vehicles, there is no need for a power bleeder or vacuum bleeder.
Start at the fartest caliper, use a small bottle with a clear nylon line over the nipple, open the bleeder, pump the MC reasonably by hand without going to the bottom, watch the reservoir and keep filling, when you see no more air in the nylon line/bottle, close the bleeder and go to the next one all around.

You read correctly! There is no need to close the bleeder while pumping the MC because no air will be sucked back!
Why? Because the slight resistance of the seals in the MC while retracting is to little to pull back the volume of fluid in the brake lines.
In other words, the MC is higher than the calipers and the fluid wants to go down, not up!
Air will not get sucked back.
Try it and see; just don't pump too hard and don't go all the way down with the pedal and push the MC-plunger too far.
JW doesn't use any power bleeder and I know why.
Also, there is no need to clamp the overflow line because it has nothing to do with the internals of the system.
The overflow is there to protect the carpet/metal in the trunk and is just a simple drain.
Of course, you can use a power bleeder if you like. (And clamp the line)

Tom is right about bleeding it again after a while.

[rusnak]

+1 on the calipers being retracted, causing too much travel for the brake pistons to engage the pads.

You can tell right away if the pedal feels spongy or soft, then it's air in the system.

you need to take the pads out, tap the pedal to close the piston gap, and re-install the pads. Use a brake pad spreader to clear the rotor, and slip the caliper onto the rotor and bolt the calipers back.

[Icemaster]

Thank you, thank you all....

I'm figuring I'll just go ahead and do phase 2 and re-do the rears this weekend, then flush and bleed, bleed, drive, bleed, tap, bleed etc.

While it's up, I'll try closing the piston gap and re-insert the pads. I did find one thread where someone beveled the edge of the pads then re-inserted them, I'll be damned if I can find it again tho.

I'll give your method of bleeding a go Gunter, thanks.

[rusnak]

don't go through all the trouble to bevel your pads. Here is the right tool, it's cheap and chances are you can find them at Kragen/ Checkers or Napa, or Pelican Parts, etc.

http://www.pelicanparts.com/catalog/ShopCart/TOOL/POR_TOOL_CAT265_pg28.htm

[aston@ultrasw.c]

I rebuilt my calipers recently and I was warned that I might have this prob, happily I did not!!

Anyway, I was ready to make some plywood spacers about 1/8" thinner than the pad. These would be installed in place of the pads, then after stomping on the brake pedal the pistons would return to the perfect spacing.

I never got to try it ;-) But it might solve your prob without removing the calipers.

[Icemaster]

Thanks Rus,

I borrowed one of those from a friend, I'll give it a go this weekend.

[JohnJL]

Well I'm now having a similar problem.

I had a very firm pedal but poor feel. I rebuilt the calipers, replaced with SS lines and installed new pads.

At first I did not replace the master cylinder as it was new-looking and already the larger 19mm size.

However I got the new engine in and running and went to back out and the brake pedal went to the floor! No brakes at all (except e-brake.)

So I installed a new 19mm master cylinder and re-bled the entire system three times. I stopped getting bubbles after the second time but went around again.

I am still getting no bubbles, but the brake pedal is still very soft. It goes to the floor with little resistance.

I used a pressure bleeder the first time on the old MC and both pumping through limited range and pressure bleeder on the new MC.

I have checked the pads are all in contact with their respective rotors.

Any ideas?