Ok, I have a puzzling one for the list.

On the way to work today I started a gentle to average stop from around 50 mph to make a 25-30 mph turn. But the brake pedal just started to sink towards the floor and braking power was very low, making the turn a bit scary. (yes, I could have aborted and gone straight)

But as soon as I let up on the pedal and pressed down again, no problems! Brakes as good as they ever were (and they have always been excellent). And they stayed that way for another 20 miles of city driving. Then on the way home, similar occurance. It happened a total of 5 times on the way home (50 mile drive, city/highway driving).

What I have noticed is if I do a gentle braking, it gives this condition. Even at a stop. I tried it about 20 times at home stopped, and could recreate the condition. Fast application of the brakes seems fine, slow application of the brakes seems to trigger it.

ABS seems to be functioning. I jammed on the brakes in the rain a couple times when the problem occured and ABS kicked in and functioned, but pedal was still very far down.

It strikes me as if the piston in the master cyl is leaking. There are no external leaks, fluid level is up, and has not dropped at all. :banghead: FSM was no help. :banghead: 1976 FSM for Olds was no help, :coolgleam:FSM for 1985 Olds mentioned something about a fluid leak to a bypass channel. Repair: Replace Master Cylinder. No clue about it.

Anyone see this type of problem? What was the cure?

Thanks!
Thomas Martin
N0DIH

I would have to agree with your call on the master cyl. I'm not sure if they even sell rebuild kits for them anymore. My car had the same problem, and it was from total neglect of the braking system. (IE a half inch of sludge in the master cyl resivors) When I took the master cyl apart, the cups were hardened, and in my case there was piston damage and scuffing in the bore. It might be just the rubber cups on yours, so a rebuild kit might be a good way to save some money.

I had a similiar problem in my 81 Eldo a couple of years ago, with similiar symptoms, cept pedal sank all the time while breaking. Dropped quite a bit of money on master cylinder, lines, and everything else before we found out that the booster was no good.

I appreciate the help!

I will be looking into it. A new one from NAPA is like $179. REbuild kit shows available, for like $25. I will give it a shot. I have been told that with rebuilding it the bore is typically worn larger, so it never really seals well. But for that price I will try. The car has always been taken care of, but I doubt the fuild was ever actually completely flushed, if ever even bled. Just never needed it, so it didn't get done.

I will be working on it Friday....

Thanks!
Tom

Picked up a rebuilt 6in master cyl and swapped it over the weekend.

Bled the brakes and all is well, despite the rain.....

Thanks for the help!! N@P@ rebuilt cyl at $65. $44 core. Owch. FSM says that service of the master cyl for ABS is replacement only. Non ABS, can be rebuilt.

Tom