Brake problem - only happens shortly after startup
 

Help! I have a strange problem that both my mechanic and I can't seem to figure out.

The problem is that when I pull out of the garage and get onto the street in the morning, the brake pedal will go all the way to the floor, and the car won't stop at all. If I step on the pedal a few times, the brakes will come back, and it's good for the rest of the drive.

I did a search on here, and I don't think I'm boiling the fluid - I don't drive it very hard. The last brake fluid replacement was about two years, and it currently has Motul in the system. According to the mechanic, it's at 4% water, which he says is higher than it should be.

The mechanic checked for vacuum leaks, but didn't find anything. He thinks it's a problem with either the master cylinder or the brake booster. If it was the brake booster, though, wouldn't the brakes still work? And if it was the master cylinder, wouldn't the problem be there during the rest of the drive?

Anyone have any thoughts or suggestions? Any help would be appreciated!

A problem with the brake booster would be brakes which require more effort to stop. But the booster itself doesn't effect brake travel.

Your problem is either at the master cylinder or one of the slaves (caliper).

Did you do anything to the calipers recently? If they were rebuilt with new seals or the pads were replaced, often times the pistons need to be "reset" to get them close to the pads. Otherwise, you have a gap between the pads and the pistons. It usually takes a full pump of the pedal or more to get all of the pistons pushed up against the pads and close those gaps.

Thanks. No, there hasn't been any work done on the calipers (or anywhere else, as far as the brakes are concerned). I'll tell the mechanic to take a look there, just in case.

If it was the master cylinder, wouldn't the problem exist at other times during the drive, and not just at the beginning? I'm just trying to avoid swapping it out, and still not fixing the problem.

Sounds like it could be the starting positional gap at the calipers, Kevin noted.

I'd plan to have all of the calipers checked (rebuilt, if never done) and a fresh flush/bleed. NOT a waste of time, at all. I'd check the date stamps on your flex brake lines and make 'em new again if they're aged. THEN, you'll have the 4 corners ready to go..

Then, go from there to the other possible cuprits, such as the MC.

BEST!

Doyle

The master can still work even if it's got a leakage issue. My mothers 1996 Olds Aurora had a master cyl problem years ago. It would do the same thing as you describe. Out of nowhere there'd be no pedal. Then it'd magically return. Coincidentally that Aurora had a Ate master cylinder. So it wasn't some piece of junk.

Do this test on the brake pedal. Press it down with some good force to the point where it resists you from pushing further. Hold it firmly. Car can be running not running, doesn't matter. Does the pedal hold pressure or does the pedal ever so slowly approach the floorboard as you maintain force against it?

I've witnessed a similar problem when someone put something other than brake fluid in reservoir. Seals swell up and cause intermittent sealing issues.

Thanks everyone for the replies. On a somewhat related note - how long do master cylinders typically last?

A bit of an update. The mechanic, while checking out the car again last week, noticed that one of the calipers was slightly sticking. Would that have caused the original problem? Or do most folks still think it's related to the master cylinder? In any case, I'll update if/when I learn more.

You may have found the culprit.

If that doesn't do it, it is your MC.

How long do they last, as long as it is properly serviced, for a while, but poor maintenance and wrong fluid will damage the seals and weaken the function and fail.

Thanks. I'm hoping that it's just a flex line or one of the calipers, and not the master cylinder, as that'll be the most expensive to replace.

Just an update on this, in case anyone else has the same problem in the future.

Ended up replacing the master cylinder, brake booster, and the proportioning valve all at once. Seems to have done the trick, and now my brakes work great. Only problem is that I don't know which of those caused the problem, so I may have some extra functioning parts that I don't know what to do with.

I will buy the proportioning valve. :D

brake booster does just that, assist with mechanical force. it would not be part of this problem, MC was my guess. What was the cost of the booster?

MC!

Doyle

+1 mc
 

Usually sticking clipers are progressive, perhaps sticking a bit more one time than another.

The Mc is the bottom of the hydraulic well, so most of the water and some of the debris goes there. Bleeding the brakes manually often times will cause the caliper seal to ride over a prior bump of accumulated crud, which often causes seal failure.

I'd do the flusingig once a year.

good luck,
chris