308 brake light came on and fluid came out of reservoir

1980 308 pedal went almost to floor with little resistence and then brake failure light came on. I pumped brake peddle an number of times and pulled over. Brake fluid had come out of cap of reservoir even though cap was on tight. When I stated car again no problem was found. Could this be a master cylinder problem or the brake booster failure. Do not want to chance a failure until I determine the cause of the problem. Any suggestions would be helpful.

 

I have now test driven the car with many starts and stops and no problem evident. Has this happened to anyone else???????

 

be cautious !
I suspect intermittent master cylinder failure. Seal failed only once and when releasing the pedal you pumped back a lot of fluid fast and got the overflowing.
if you cannot find a leak on calipers, brake lines, I'm sure you need a new master cylinder.

Best Regards from Germany

Martin

 

If the pedal went almost to the floor, it can only be a few things of things

- lots of air in the system (this won't heal itself)
- a very big leak in the brake system. check all 4 corners and all the piping (this won't heal itself)
- seals are shot in the master cylinder. As they start to fail, they can bypass fluid one time and work fine the next time. Keep in mind the 308 master seals are not cup or lip seals like so many of us are used to. They are more of a large o-ring (see below) and need to be in good condition to work most effeciently.

Rick
Image Unavailable, Please Login

 

My guess would be a stuck caliper & boiling of fluid. Had you driven it a distance or just started out?
My .02, rarely worth even .01. ;-)

 

AFAICT, there's not a lot of red magic in the brakes, it's a straightforward vacuum-boosted dual hydraulic system like you'd find in about 83 bazillion more mundane cars of the era.

The reservoir caps are vented, so fluid escaping from them indicates that something is pressurizing the reservoir (which shouldn't be happening, of course). The other posters have identified by far the two most likely causes:
- Bad master cylinder seal is letting hydraulic pressure go where it isn't supposed to and not where it is supposed to, which is why you lost the brakes.
- Stuck caliper is boiling fluid in one circuit, which means no braking action and excess pressure at rest).

The former is way more likely than the latter, but the two are not mutually exclusive. Often if one part of a hydraulic system is in bad shape, so is the rest.

 

As already posted, it's the master cylinder seals. Time for an overhaul. While you're in there you should check the bore for scoring. The piston went full travel without pressurising the system and on the return stroke, instead of letting in fluid as it should (to compensate for brake wear) it pushed fluid back into the reservoir.

If it happened once it can happen again. Give the master cyl an overhaul and have peace of mind.

You can buy the seals for 20 quid from Superformance.

 

How does that work? Where does the brake fluid come from?

 

Brian; when the seal fails, the brake fluid which should pressurize the caliper passes the seal and gets into the master cylinder room BEHIND the piston.
While releasing the pedal you make a very fast stroke backwards to the reservoir, pumping this fluid back.
Theoretically it might even create a vacuum in the system, drawing back the caliper pistons.

Best Regards

Martin

 

Yep; and if the reservoir has been topped-up after the brakes have worn down a bit then there's more fluid in the system than the reservoir has capacity for and it spills.

 

Pulling the caliper pistons back is the only way to over flow the reservoir short of boiling. Brake fluid doesn't spontaneouly appear, the system doesn't create fluid to barf it out the top. Now, how far would you have to rectract all the brake cylinders to get fluid out of the top? The reservoir should hold enough fluid to wear out a set of pads from new - that's a lot of piston travel.

 

yes, but if someone tops up the reservoir with worn pads it will overflow when pulling back the caliper pistons.

Best Regards

Martin

 

After a failure like this I would overhaul the complete system, no matter what. 15 years ago I had a master cylinder failure on a car and it was NOT funny. NO brakes whatsoever, without ANY previous warning. 10 pumps later it was "working" again. Uhuh.

In the past years there have been two accidents locally, both where cars went into a gas station by the motorway. In both cases people died, including the drivers I believe. I contribute that to this failure, the failure on my car was also after about 5 minutes of not using the brakes.

If the master has not been overhauled in the past 10-15 years, do it. Brakes are cheap and the adagium "wherever there is doubt, there is no doubt" certainly is true here.

Same with the calipers, after 10-15-20 years they tend to stick even on cars that hardly see rain. Although if the fluid got hot enough to spill back into the reservoir, I'm pretty sure you would have noticed the very hot brakes.

 

great common sense post. Particularly when the rubber parts are literally dirt cheap.

 

Exactly. Once you're hurdling towards that crossroad or a family on a zebra crossing with no means of getting your speed down, it's too late to realise that saving those few hundred dollars was a tad foolish.

A niece of mine went through a highway toll gate at a good rate of speed in her Chrysler Voyager because of the exact failure described. Fortunately there was an empty lane or it would have ended very different from a snapped beam, a new windshield, an hour or two at the police station and having the car towed back home.

I learned my lesson with these scary experiences and replace or overhaul the master cylinder on my cars now when they hit a 10-15 year age mark or 100k miles mark, and do the brake hoses and calipers in the process.