caliper rebuild gone awry

[nzaldivar]

Hey Folks,

Had a sticking front right caliper, so I started rebuilding. All calipers were rebuilt and converted from dot5 to dot4/3 (PO had put dot5 in). Before repair/conversion had great pedal feel and car stopped on a dime.

Now since rebuilding calipers and changing fluid, the car's pedal is hard, then spongy then the brakes fade to almost nothing....until I pump again.

There is no leaking of fluid that I can find and reservior is still full.

Some other details:

* If I hold the brake pedal down and start the car the pedal does move some....not alot but some....but the feel is totally different though. HARD before, then Soft.

* When changing fluid i removed the booster and master cylinder so to drain the dot5 that was in the master cylinder.

* I ran about 24 oz of fluid through the system to ensure no air.

* While bleeding, the rear brakes recover after 1 pump, the front take 2-3 pumps.

* I installed new steel lines to replace the rubber ones at the same time.

* I have not driven the car very much, because fear of not being able to stop.

Is it a booster problem or master cylinder problem?

Please advise.

Thanks,
ned
911SC Targa

[PorscheGuy79]

Dont worry too much, it sounds like air still left in the system. Brake bleeding is like black magic...sometimes it works, sometimes it doesnt. This has happened to me before, somtimes I do the same thing a couple of times and it doesnt work at all and then suddenly bam its done like a charm. Just re-bleed the brakes until the pedal feel returns to normal.

If that doesnt work it might be a damaged master cylinder seal which could have happened do due improper bleeding technique but I would try bleeding it a couple more times first because that sounds like the problem.

[MotoSook]

Most likely air in the MC still...lots of discussion on this.

[SC Schrauber]

ditto

How long ago did you rebuild? It takes a few miles for the brakes to adjust. After my rebuilds I bled the brakes at least ten times and still had this spongy feeling. Disappeared after a couple of driving days.

Frank

[nzaldivar]

last week and have driven the car only a mile or 2. seems scary on the brakes to drive.

[Grezdlitn]

What wrong with this picture?



I had the same symptoms as you. I discovered that the front calipers can be installed on opposite sides and with the bleed valve on the bottom air is trapped in the top of the piston. They will work but not well........ my 2 cents worth.

I put them back where they belong and the pedal response was perfect.

[bell]

i did the same thing.......once

[shawn irvine]

I need diagnosis help on my 1984 911 brakes. they seem to drag on the back calipers after I apply the brakes ( just enough that if I were on a slight incline it would not roll) then they let up a bit untill I put the brake brakes on again. Help Shawn

[syncroid]

Hi Ned, I've gotten stung by the spongy brake pedal a couple times. Once you make sure that you have bled ALL of the air out of the system, you should excercise the calipers. You just rebuilt them right? The orings for the pistons need to break in a little before you get a good pedal. Pull one brake pad out at a time. Get a suitable prybar and put it in where the pad is out. (between the rotor and the caliper piston) Have someone gently pump the pedal to bring the piston out about a quarter of an inch and then take the prybar and squeeze the piston back in again. Repeat this about 5 to 10 times for each piston. Your pedal should be back to normal. If this does not take care of the problem then you might be looking at replacing the master cylinder. Sometimes an old master cylinder will die a sudden death when new brake fluid is run through it.
Good luck and I hope this helps you out.

[syncroid]

Originally posted by shawn irvine
I need diagnosis help on my 1984 911 brakes. they seem to drag on the back calipers after I apply the brakes ( just enough that if I were on a slight incline it would not roll) then they let up a bit untill I put the brake brakes on again. Help Shawn

You may have restricted flexible brake hoses. If they are original, replace them.

[MotoSook]

Originally posted by shawn irvine
I need diagnosis help on my 1984 911 brakes. they seem to drag on the back calipers after I apply the brakes ( just enough that if I were on a slight incline it would not roll) then they let up a bit untill I put the brake brakes on again. Help Shawn

Not to derail the original poster's thread...but you may need to rebuild your calipers. Corrosion and worn (hardened) seals will prevent the pistons from retracting..or make them seize.

[911pcars]

Another possibility. You may have trashed a cup in the master cylinder during the bleeding process. Did the pedal go to the floor at any time?

Sherwood

[nzaldivar]

it only goes to floor when bleeding, and then feels spongy and can be pumped for better stoping.

[Wil Ferch]

nzaldivar

look what I ( and "poet" Sherwood) say here about gravity bleeding...especially balanced against the risks of driving the MC seal in too far--->

Question on bleeding brake fluid.

...going to the floor...even once...may not have been good...


Wil

[RoninLB]

Originally posted by Wil Ferch


( and "poet" Sherwood)

he is good.. for sure.

[911pcars]

Aw shucks Wil and Ron. I'm turning red. Errr, my eyeballs anyway. It's 1 o'clock in the morning. Despite our hopeless infatuation with these vehicles, writing tech opinions is a pretty mundane activity when you think about its impact on our insignificant lives. Maybe a little levity and flourish with the key strokes will keep us (me) loose and sane.

Ned,
I hope you get the pressure back into your brake system. My best guess at long-distance troubleshooting is a malfunctioning master cylinder. If by now you've replaced every single component in the brake system except the MC without resolving the pedal-to-floor issues, that's probably it.

Good night and good luck,
Sherwood

[1meansc]

.

[RoninLB]

[QUOTE]Originally posted by nzaldivar

, the car's pedal is hard, then spongy then the brakes fade to almost nothing....until I pump again.
------------- air


If I hold the brake pedal down and start the car the pedal does move some....not alot but some.....
--------- booster confirmed ok

[Dixie]

nzaldivar,

You have air in the system.

Do you mind describing your brake bleeding procedure? I've seen more than one thread where the procedure used was incorect...

[nzaldivar]

I did 2 procedures twice following RL, RR, FL and FR on the wheel position.

2 using the mini-vac and 2 using the 2 man bleed with new brake fluid in the exit bottle.