CFM928

My brake booster is failing. (The brake pedal depresses more upon startup and there is some assist, but I can hear a hissing sound when pressing it.) I've been quoted prices from 150 to 350 for a replacement booster.

Has anyone used the RockAuto rebuild service. $150 to rebuild. I like the idea of 'keeping the original', not crazy about the additional down time shipping and waiting for rebuild.

Thoughts?

Charlie 1980 928S Out of storage!

jpitman2

If you have your foot on the brake at startup, I would expect the pedal to go down as the vacuum does its job. Its normal to have some hiss as air enters the booster when its operated - there is a filter around the pushrod inside the cabin for the air - usually its not audible over the engine sounds or other ambient noise. If you shut the engine down and push the brake in a quiet environment you can hear it.
Dont see anything in your post to justify a failure diagnosis - either its boost characteristic has changed lately, or it takes more pressure to stop? If the pedal gets VERY hard and less effective, this can be caused by the m/cyl leaking fluid into the booster casing, and the fluid is preventing the booster from stroking as it should - this should show up as a fluid loss in the m/cyl. Check this by pulling the vacuum hose off the booster, and feed a length of rubber in till it hits the bottom, check for signs of fluid.
jp 83 Euro S AT 57k

CFM928

Thanks JP. I checked for fluid in the booster. Bone dry. Still lots in MC reservoir. It just doesn't stop well unless I apply lots of pedal pressure, and I still can't lock up / skid the tires braking in a straight line. (...and I'm a cyclist, strong legs, I mean I'm pressing really hard.) 'Normal driving' they seem adequate, but if I ever need to do a panic stop, I'm hitting something!

jpitman2

No air leaks in the system? Check valve (between inlet and booster) seems OK? When you checked for fluid did you get a big hiss when you separated the hose from the booster - indicating it was holding vacuum? All the pads OK? Any uneven braking - pulling to one side ? Brake hoses have been known to delaminate internally and not flow fluid properly. Also possible for rusty/corroded caliper pistons to cause poor braking - BTDT. No signs of brake drag? Testing for drag - find a safe piece of flat road, and allow the car to roll to a halt in neutral - if there is something dragging you will feel a sort of lurch at the instant it finally stops.
jp 83 Euro S AT 57k

Mrmerlin

buy a new ATE booster,,
Roger has them about 275.00.
also fit a new master cylinder about 295.00 ,
Also 1 liter ATE gold fluid,
4 new SS flex lines 85.00,
and DC111 on the tank MC grommet seats surfaces so the bores dont corrode , and the MC base seal

hacker-pschorr

My 80 had a failed brake booster & I could still achieve full braking with additional effort.

As the diagnosis continues, to answer your original question: I would have the booster & master rebuilt but not from Rock Auto. Instead, I would use White Post Restorations.

I sent a clutch master to them to be rebuilt, and will be sending them a brake master / booster soon:
http://whitepost.com/brake-sleeving-...ding-services/

16vsilverstreak

FYI I just called White Post to inquire about rebuiling an '83 booster. Price was 470.00. The price incuded a new master.

FredR

Your brakes do not work correctly, the car is 40 years old- just do as Stan says and contact Roger or one of the other 938 parts specialists and invest $500 to replace the most safety critical components on the car. Given your issue you should also look at doing the seals in the calipers whilst you are at it and be rest assured you are good for another 20 years or so at least. Discs/pads replace as needed when worn.

hacker-pschorr

Normally I agree with buying new, but Whitepost Restorations reputation in the collector car world is impeccable. Their clutch / brake master rebuilds are better than new since they hone them out and install a brass sleeve that will not corrode like the original ones do.

FredR

Interesting observation- clearly they are not a cheaper option but if you know they give a superior product why not?- particularly so for the master cylinder.