black95183

Hello all, I am in need of some opinions/guidance. I have a 86 951 I am currently beginning to restore. First project is brakes. They were terrible when I bought it, you have to stand on them to have very little braking power. I replaced all rotors/pads first. I took all calipers and lubed pistons, all pistons are working as should. Replaced rubber lines with braided. Replaced master cylinder with original ate and primed before installing. Bled entire system very good until all new fluid is coming out. Take it up the road and still have to stand on them for very little braking power. Any advice is much appreciated. Thanks guys

Sixline

Sounds like there might be a problem with the brake booster.

black95183

I was wondering about the booster. Wouldn't I still have good brakes if it were bad, just not the assistance from it? Should still have good pressure without it shouldn't I?? Thanks

GPA951s

My track car scared the crap out of me like that... had to STAND on the brakes,,, good pads new fluid Ect... Ended up rebuilding the calipers... When I took the pistons out of the calipers and scraped them I could not believe the build up on them.. Like 6 hours later.... (16 pistons) Well-La... Good brakes... What a difference... Check out Van Svensons rebuid video on youtube.

Sixline

How does the pedal feel? If you press it a few times with the engine off does it firm up? With your foot on the pedal start the engine, does it sink down a little bit?

The brakes without a properly functioning booster are going to feel weak, especially when you are used to boosted ones. You could do some tests at low speed with it disconnected and connected to see if there is any difference. Have you checked for vacuum leaks also?

MAGK944

Try disconnecting the vacuum from the booster, plug the engine end then go for a drive. If it’s the same then it’s your booster.

black95183

I'll check them out, thank you

black95183

It feels good when I pump them up with the engine off. Good and firm and then when I start it and drive you have to push it to the floor for very little. I'll check vacuum lines. Thank you

black95183

I'll give that a try. Thank you

Breakaway944

Black95183 I am not sure i understand your response above. You say it pumps up firm with the engine off but you have to put the pedal to the floor for any braking action with the engine on. Do you mean you have to push really hard towards the floor or do you mean you push hard enough to make the pedal go to the floor before you get any braking action? If the pedal actually goes all the way down towards the floor from hard pushing while the engine is on it usually means you have a leak in the system. Go back and check all of your connections, they have to be pretty tight.

Gage

Please explain the process for lubing the caliper pistons.

black95183

I pumped pistons out as far as they would go without popping out completely and applied brake grease around piston walls

black95183

When I start car the pedal goes down slightly. Good vacuum pressure at check valve. Could it be the check valve itself? If so what am I looking for in valve when I remove it? Blow through it? I haven't taken check valve out to check it yet. Thanks all

GPA951s

There really shouldn't be any "lube" on the pistons.. There is the "square cut ring" that is the sealing ring that holds back the fluid. The Idea is to get all the debris off the piston. So, Take the caliper off, Blow the piston (s) out with air Clean them really well, (If they are coated you have to use a razor blade and drag it backwards so you don't nick the coating, If you do... game over.. what you are trying to accomplish is the correct Diameter (which is a clean piston with no foreign matter on it) so that it slides in and out easily. the only "lube" you should have on it is brake fluid on the backside.

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aussie944cab

I had exactly the same problem as the OP, bled brakes so many times, even manually activated the ABS valves, replaced brake booster, I had Stop-tech street pads in, I bought the cheapest metalic pads you can buy from Rockauto, fitted them and guess what, BRAKES, now I can stop with pushing my bum off the seat, drive barefoot without dislocating my toes, the confidence has come back, havent tried them on the track but will next month