Arrrg, brakes!

mike_the_man · 07-28-2003, 09:14 PM

Ok guys, I need your help. I'm having some problems with my brakes. I have adjusted the rear venting clearence, rebuilt the master cylinder, installed a T in place of the proportioning valve and replaced all the fluid with new DOT 4. I have also checked all the hoses, and they look good, no cracks or anything, and there are no visible leaks anywhere in the system.

The problem is, I can't get a solid pedal. I have bled 3 times since rebuilding the master cylinder and installing the T. I bled once using a vacuum pump, once with a friend stomping on the pedal, and once with a pressure bleeder. I can't see any air coming out, so I'm assuming thats not the problem.

I'm stumped, and very frustrated. The only other thing I can think of is that the calipers need to be rebuilt. They don't look like they're leaking, but one could be stuck. Could a stuck caliper cause a soft pedal? And it's very soft, I can get almost all the way to the floor if I really stomp on it.

Any ideas? I'm getting really close to taking it to a mechanic, but I'm to cheap and to proud to do that. I'd much rather fix it myself.

Any and all ideas greatly appreciated.

Amark · 07-28-2003, 10:52 PM

Replace the master cylinder w/ a new one.

Biggy72 · Biggy72's Garage

seems to me like a stuck caliper would lead to a stiffer feel since all the fluid has to go somewhere. A new master cylinder sounds like a good starting point to me.

sixbanger · 07-29-2003, 04:54 AM

I just did a full brake job on my factory six.I would say just keep bleeding them.I had the same problem and thanks to this board and the posts on this subject as I bleed they get better every time.
Also pull the wheels and have someone push the pedal and see if both pistons are moveing at each wheel.
I think I need to bleed one more time.
Good luck
RT.

John Rogers · 07-29-2003, 05:28 AM

I agree with the new m/c idea. Additionally, make sure you have the small clearance between the rod and the back of the m/c piston since if there is no clearance the system can not return to a rest state and you will never get it bled. Finally, the vent clearance works best if it is about 50% of what the book calls for. Good luck.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Make sure you're using the bleeder valves on top of the calipers, not the ones on the bottom.

--DD

durtkillon · durtkillon's Garage

I may be wrong, but if the master cylinder is bad, it will bleed slowly as you stand on it. It's an easy test. Push the pedal hard and hold it. If it continues moving slowly, there is a leak in the MC.

I have to bleed my brakes 2 or three times to get them solid. My car now locks up in the front (even on pavement ;-) )

Scooter311 · 07-29-2003, 07:40 AM

Ditto on Dave - after installing my 911 calipers I kept bleeding the bottom valves, for like 2 days before I realized what I was doing wrong. Bah.

Jim Smolka · 07-29-2003, 08:08 AM

I'll second what Dave said. Though technically not possible, I was able to bleed the brakes w/the valves on the bottom. My local wrench was impressed that the car had a brake peddle

Tidybuoy · 07-29-2003, 09:15 AM

I had a similar problem after doing the 320i brake upgrade.

2 quarts of ATE Blue, and 6 seperate bleed sessions & I finally have a firm pedal.

Of course, I still have the proportioning valve in my car & I think that was trapping some of the air.

Vern

914GT · 07-29-2003, 09:34 AM

Vern - what did you finally end up doing for your 320i calipers?

mike_the_man · 07-29-2003, 11:51 AM

I used the top bleeder valves, so I don't think thats the problem. And it shouldn't be the master cylinder, becuase I did rebuild it (although that doesn't mean that it will work). I'm thinking that it's a stuck caliper. I'm going to check them tonight. Is it possible to remove that brake pads without removing the caliper?

Thanks for all the ideas guys.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

You usually remove the pads before removing the caliper. And when you replace the pads, you generally don't remove the caliper at all.

Knock the pins out (if you're talking rears, pull the clips that go through the pins. Otherwise you're in for a lot of pounding on that punch! BTDT!!) and then wiggle the pads until they slide out.

--DD

M. Hendrix · 07-29-2003, 01:02 PM

Quote:

Originally posted by mike_the_man
And it shouldn't be the master cylinder, becuase I did rebuild it (although that doesn't mean that it will work).

I don't like used brake parts.

M

calbrat · 07-29-2003, 04:16 PM

Master Cylinder should be replaced, however..
When I had my brakes fixed we still had a sluggish action in the pedals... the old bushing in the pedals had brake fluid on them and they were toast! Replaced the bushings and I have never looked back.

mike mueller · 07-29-2003, 04:36 PM

a fellow 914 owner near me had the same problems with his car, except he had a brand new M/C.

I loaned him my pressure bleeder and he still had problems with the system, I thought it was a bad M/C and told him so, he kept saying it was brand new....guess what?

The brand new M/C was the cause of the problems