'87 Carrera: No Brake Pedal.

[dufer]

Sadly, my '87 Carrera still has no brake pedal.

What I experience is:
1) No brake pedal for 1-2 pumps (goes down to the floorboard).
2) Some to semi-solid 1/2 brake pedal in 3-4 pumps.
3) After 3-4 pumps, the brake pedal will hold with no fade.
4) All four calipers are providing braking.
5) Once the brake pedal is released, it's back to no brake pedal

What I've done is:
1) Replaced the master cylinder (performed a good bench bleeding)
2) Bled the four brakes lines repeatedly in every way known to mankind (honest)

What might the following convey?:
1) At the master cylinder, I remove the brake line connection to the front brakes and insert a plug into the master cylinder. Doing this gives me an extremely solid brake pedal (almost zero movement).
2) At the master cylinder, I remove the brake line connection to the rear brakes and insert a plug into the master cylinder. Doing this gives me no brake pedal. [This is with the front brake line returned to normal, non-plugged functionality.]

I have pretty good confidence that the master cylinder is good (hours and hours of work and testing leads me to this conclusion). I've bled the brake lines in every conceivable way with various pressure applying devices, etc. No part of the braking system is leaking.

What's not working? What am I missing? Is there something to consider other than the master brake cylinder and brake lines? A regulating value? Something? Anything?

Any guidance will be greatly appreciated.

Thanks.

Dan

[Steve]

Dan,

Those cars DO have a proportioning valve close by the MC and it may be stuck.

Do you pressure bleed the system?

[Arne]

Another thought - was the replacement master cylinder new, or rebuilt? In my experience rebuilt MCs are worthless, despite any warranty it may carry.

[Steve]

[Arne]

I agree 100%, Steve. I've been out of the tire, wheel & brake business for over 15 years now. But back then, I refused to install rebuilt MCs, period. At best, it would be a guaranteed come-back. At worst....

But despite the number of professionals who won't touch them, still a lot of DIY will try a rebuilt. Generally only once, but they will use them. That's why I brought it up.

[Steve]

[dufer]

Steve:


It's no accident that I posted this plea for assistance on your web board; it's your guidance in which I seek (and respect). I've been reading the Rennlist forum for the past 12 years and your responses to the questions of others; I don't post much stuff as I don't think I usually have much to say.

I purchased the MC from Pelican Parts @ http://pelicanparts.com/catalog/shopcar ... htm#item11 and nothing I see references the MC being new or rebuilt (from what I could find); maybe the price tells all. I don't know the true cost of a new MC.

In bench bleeding the MC and depressing the actuator, it had about 80% fluid out the front connection and about 20% out the back. When the front drain tube was pinched off, it had immediate and solid flow out the back connection.

Of the many brake bleeding efforts I've tried, I did the following this weekend:
1) I applied a Motive pressure bleeder at the master cylinder
2) I opened one of the rear (stock) caliper bleeders into a drain tube fluid collector
3) I applied a syringe fluid injector system at the other rear caliper

I did the above to apply pressure coming from two directions to force brake fluid out the third of the "T" connections. I then reversed the process between rear calipers. I did the same to the front caliper.

If I applied the Motive pressure bleeder and opened one of the bleeder valves, I got a slow drain of brake fluid. If I applied the brake pedal repeatedly at the same time, I got a flood of brake fluid out the drain tube with each press of the pedal. This was the same result for each corner. I've not seen air come out any of the four corners for the last 10+ brake bleeding efforts I've tried.

I am a DIYer. I do want to know this stuff. I run my car at the track and I want to know firsthand how things function. I am coming your way as a last resort. But that's meant in the most respectful of ways. Before asking for your guidance, I've tried, tested, pondered, re-tired, re-pondered, and tested again. Then I repeated the same. And the was just day one of ten in trying to get a solid brake pedal.

From what I've been able to convey, do you have any recommendation of what to attempt next? If that's the MC, so it shall be.

Arne: Thank you for your feedback also; it is greatly appreciated.

Dan

[Steve]

Dan,

Thank you for your kind words about my contributions on Rennlist, I've simply tried to offer something constructive for people.

The bottom line here is that if the pedal will not hold pressure, there is either a leak somewhere in the system or the MC is defective and is allowing fluid to "shuttle" between chambers. Before you ask for a replacement, I would suggest you make certain that the vacuum booster is OK.


FWIW,....We also provide parts for people as well.

[dufer]

Steve:


Thank you for your feedback. I'll address my braking system again this weekend for diagnostics and (hopefully) resolution. Thank you for pointing me in a couple directions.

Dan