Brake Caliper Rebuild Problem

BT911 · 04-13-2007, 08:10 AM

hi.. i have an 88 carrera and i jsut rebuilt all the brake calipers. now when first step on the pedal, the pedal goes low but if i pump one time the pedal is in the normal position. i aligned the pistons correctly i pressure bled and manuelly bled the brakes as well. everytime i bled the brakes the pedal does get better. any ideas what i am doing wrong or something i missed. thanks

tonythetarga · 04-13-2007, 08:39 AM

Sorry if this is a basic question, but did you put the calipers back on the correct sides? The bleeder needs to be on top of the caliper.
Barring that, using the manual method can sometimes damage the m/c if you travel the pedal to the bottom during the bleeding. Power bleeding eliminates that result.
Also are you bleeding in the correct sequence?
RR, LR, RF, LF

BT911 · 04-13-2007, 08:43 AM

yeah..i put the calipers in the correct position and i bled it first with a pressure bleeder.

CharlesJones · 04-13-2007, 08:47 AM

My pedal felt a little squashy after I rebuilt my front calipers and changed my front discs recently, even after repeated bleeding, but seemed to firm up after a bit of driving. I have heard it said that the pedal will be slightly squashy for a little while after renewing discs and pads. If it's not too squashy as to feel unsafe maybe you should put a few miles on the car and see how you get on? My pedal feels fine now (although perhaps I'm just getting used to a squashy peddle!).

spinner · spinner's Garage

Assuming you don't see brake fluid leaking anywhere, you still have air in the lines. Normally after rebuilding calipers, I flush/bleed at least 3 times. I pressure bleed using cheap fluid and drive around the block exercising the brakes. Use a rubber mallet and bang the calipers to loosen up any trapped air before bleeding. Pressure bleed again and drive around the block. For the last time, I normally bleed the old fashion way using ATE blue/gold for that nice firm pedal. It's a real PITA but you'll get your brakes back.
Good luck ;-)

BT911 · 04-13-2007, 08:58 AM

i have no brake fluid leaks. i tried the bang on the caliper method and it did get better but not to it's normal posistion. i do agree that i have air in the system somewhere. i just i should just pressure bleed it again. what pressure are you using when pressure bleeding? thanks in advance

spinner · spinner's Garage

12-15?? I don't remember. You don't need much. I believe exercising the brakes at slow speed before bleeding again helps. Just save the good fluid for the last bleed session.

01sport · 04-13-2007, 09:21 AM

I had similar problems when rebuilding my calipers until I replaced the bleeder valves. Installed new speed bleeders and got good pedal.

Tom '74 911 · 04-13-2007, 09:55 AM

I've had the same issues after rebuilding my calipers too and posted similar questions here as well. Here are some of the responses from memory:

1. Standard air in the system response - same info and solutions as already posted, but probably still valid. I use a pressure bleeder and seem to have to bleed the system a bunch of times - like 3+ - before my pedal firms up. Maybe I'm doing something wrong. I usually bleed 'till no bubbles appear, drive for a day or two, bleed again, drive a day or two, bleed again etc..

2. After rebuilding, it takes some driving time for the pistons to seat themselves properly. The new seals spring the piston back away from the pad when there's no pressure on the pedal, so the pad has a longer initial travel to reach the disk when you first press on the pedal. This makes the pedal feel soft as you use up a lot of the initial pedal travel just getting the pads to the disk. A solution is to take the pads out, pop the pistons out a tad (be careful not to pop them out all the way!) and then squeeze the pads in so that they're as tight to the rotors at rest as possible.

3. My suggestion, as long as the car is safe to drive as mentioned above, is to just drive it and exercise the brakes a lot. My pedal was soft for a few hundred miles or so, but after some usage and a few bleedings, much better.

I'm no expert. This is just my experience.
Tom

randywebb · 04-13-2007, 10:23 AM

I have a related question -- if rebuild a caliper on one side, is there any reason to rebuild the other side at the same time? The one that needs a rebuild is on the rear, BTW (the rubber dust shield is breached).

MattAlpha · MattAlpha's Garage

I just re-built all of my calipers about a month and a half ago. Wide A and Wide M. I couldn't get a hard pedal until I took the front calipers back off and "exercised" them. I used compressed air from my air compresser (I held the nozzle to the end of the hard line) to exercise the pistons. I placed an old rotor in the middle of the caliper so my pistons did not pop out. This also allowed me to make sure the separation between the pads and the rotors was correct (it will be too wide if you have compressed the pistons completely into the caliper). I exercised each caliper at least 10 times. Each time I did it, the piston moved easier. After the brake pads compressed on the rotor, I let the pressure build to 60 psi and then removed the air line from the caliper's hard line. After I re-installed the calipers, I bleed them all again and I was left with a hard pedal. After a few weeks of driving I bleed them again and the pedal got even better.

It takes a while for the new (rectangular) seals in the calipers to brake in as well. You will notice a difference when everything has broken in, but it may take a while.

I didn't exercise the rear calipers, but I'm going to in a couple of weeks. It can't hurt, it just means some more bleeding.

I hope this helps,
Matt

timcantrell · 04-13-2007, 10:56 AM

After completely draining the brake fluid as with a caliper rebuild, you end up with small air bubbles in areas that are hard to clear. Large air bubbles are bled out fine. Small air bubbles are not so easy to remove. I learned a trick while bleeding motorcycle brakes. They are much more diffucult to bleed since the M/C is directly above the calipers. Anyway, If you apply pressure to the brakes overnight or for a couple of days, the small bubbles that remain will combine into larger bubbles and can be bled out. This may sound crazy but it works. Pump your brakes up. Figure out a way to keep pressure on the system (i.e. work out something to lodge against the seat and keep pressure on the brake pedal. Leave it for 1-2 days, then bleed. You will be amazed.

defcon65 · 04-13-2007, 01:11 PM

That's a good tip, Tim - I'll try it, since my lines have been completely drained. The spongy brake phenomenon I've been able to solve in the past with repeated bleedings over time. Hopefully your method will shorten the process, thanks.

Regards,

DanielDudley · 04-13-2007, 01:21 PM

I really don't like to drain the system. I will plug the lines, and have gizmos for various cars. When the lines are dry, I have found that it is often helpful to loosten the lines at the MC and bleed there. I have been known to crack the bleeders and let gravity do it's thing for a while. I also have been known to pre fill the calipers before bolting them on, esp. if I have plugged the lines.

EAP · EAP's Garage

One more tip from experience...

You may want to check the condition of the master cylinder. It is possible for the MC piston to allow fluid by now that you have installed new seals at the calipers, the piston seal becomes the weak link in the chain.

djpateman · 04-13-2007, 04:53 PM

Are you fellows lubricating the O-rings and pistons with anything when you rebuild the calipers? I am hearing of this problem a lot, and yet with all the calipers I rebuild I never seem to have that problem. Perhaps the reason is that I use a special seal lubricant during my assembly process.

Monza_dh · Monza_dh's Garage

I also just did this for the first time. Rebuilt front calipers on my '88, as well as replaced bearings, races, rotors, hardlines and did a full flush. I bled them at least three times with a vacuum bleeder. I initially had the same issue as you but each bleed I got closer to a complete firm pedal. Take your time, I bled them a few different times over a long weekend not expecting to get it perfect the first time.

hcoles · 04-13-2007, 06:43 PM

Monza and Tom 74 911 sound about what has gone on with me. I've done lots of bleeds and about 2 full caliper rebuilds and use pressure bleeder without fluid.. I just use the fluid in the resovoir.. haven't had many issues.. a bit spongy to start with with new pads and square "O" rings installed... the "boots" burn off after the first track day :-) so I know those aren't hanging anything up...

-Henry
89 911 - daily, track, AX - fresh top end DIY

rick-l · 04-13-2007, 08:05 PM

Quote:

Originally posted by djpateman
Are you fellows lubricating the O-rings and pistons with anything when you rebuild the calipers? I am hearing of this problem a lot, and yet with all the calipers I rebuild I never seem to have that problem. Perhaps the reason is that I use a special seal lubricant during my assembly process.

+1 I used Sil-glide and had no problem.

Are your wheel bearings adjusted correctly and the rear ones tight?

sithot · 04-14-2007, 05:39 AM

The pistons need to "realease". You can do this a couple of ways but I've used something like a very worn out set of pads to give the piston something to push against. Once the seals "release" you can push them back, install your pads and do the brake bleed again. No more problems should arise.

Tom