Ballen

Hey all, this is one of my first posts here, although i have been reading the boards for a while trying to find out all i could about the 8 (even though no new car is in my immeidate future).

My question actually doesn't have to do with the rx8, but more of a general automotive question. I was driving the 1971 Jaguar XKE that my father and I are restoring last night, and right as i was finishing my usual circuit of the windy roads near me, the brakes stopped working correctly. When i pushed on the pedal it went straight to the floor without slowing the vehicle down at all. Pumping the brake pedal helped, but it was still nowhere near the usual braking power.

I didn't have time to check anything out then, as this happened relativly late at night and I had work in the morning, but what do you think is causing this problem? Air in the brake lines, or possibly a leak in the master cylinder come to mind, but I don't know that much about braking systems.

I apologize if this is somewhat off topic, but unfortunatly I haven't been able to find a XKE forum that was nearly as active as this one is, and you all seem to be knowledgeable. Thanks in advance for your help

-B

romulus

I think you have a massive break fluid leak. It could be that you forgot to tight a bleeding valve or a break hose simply bursted because (break peday goes to the floor). Air in the system just make the pedal feel spongy. I had a coworker who had a Dodge fairlane/fairlady? when moving out from the parking lot on his way home had a hose blew off.. lost break because its pedal went to the floor as he applied the breaks. Fortunately, the got that fixed in half hour.

Ballen

Update:
Checked the brake fluid level after work today and it was at the fill line. I moved it around in the driveway a bit and the brakes feel fine now. Guess I'll just have to drive carefully and see if it happens again. Could be a case of how all problems on British cars are intermittent.

Thanks for the suggestions though

-B

Nubo

Sounds like you might have experienced some boiling of the brake fluid. One possibility is that the fluid is old and has a lot of water in it, which can boil if the brakes are heavily used. Drums and rotors get hot. Another possibility is that you have one or more brakes that are dragging. This results in extreme heat and can boil the fluid even if new.

Brake fluid (and even water) are non-compressible, which allows the force to transmit between the master cylinder and brake cylinder. But gas is very compressible. Boiling water/brake fluid results in gas in the line which condenses back into liquid when the system cools. Thus you regain braking and there may be no apparent loss of fluid or any air bubbles in the line.

A complete replacement of the brake fluid may be warranted and you should check carefully for a dragging brake.

w2aew

I agree with Nubo, you probably boiled the brake fluid. Remember that brake fluid is hydroscopic, i.e. it absorbs water. If there's water in the fluid, it will lower the boiling temperature. However, it is possible to boil brake fluid even if there is no water in the fluid (as happened to a friend in his Lotus Espirit B/T during one of his first track days).

Unless you were driving/braking very hard for a long time, I would doubt that you'd boil standard brake fluid - so I'd suspect water contamination. Thoroughly flush the refill the system.