86 2.8 brake issue (Page 1/1)
stevep914 APR 13, 12:46 PM
Tried to run the car today after a week parked, and the brake pedal goes to the floor before I can stop the car. Checked all lines, master, and all connections, and no leaks. Brake fluid was down a bit in the reservoirs, but I haven't checked it in a long time. When the engine is turned off, I have lots of stiff pedal. When the engine is on, the pedal goes soft and no amount of pumping brings it back up to normal. Brake booster? I really don't understand how that works. I have not bled all the lines yet, as there didn't appear to be leaks anywhere.
theogre APR 13, 03:53 PM
stiff/hard pedal, engine off, means nothing. After engine off, you only have reserve vac to push pedal easy 1 to maybe 3 times before you are fighting the Big spring in the Booster.

Floored pedal then have a leak somewhere, you allow MC tank to run dry so MC is sucking air, or MC is bad internally.
See my Cave, Brake Service

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

stevep914 APR 14, 04:18 PM
Thankyou! I found no vacuum leaks, and according to info in your cave, the booster and mc are functioning normally.i gravity bled all four corners, and found significant air in the left rear line. The others had none. After the bleed, I have solid pedal again. , I have no visible external leaking and fluid loss from the reservoir, should I assume , over time, I have some kind of small leak internally in the mc? The car runs for an hour once a week- sits the rest of the time. I last bled the brakes over a year ago.
theogre APR 14, 07:54 PM
Air doesn't get in even a car sitting for years. Brake fluid can't evaporate out of a system.
IOW you have a leak somewhere.

MC can leak externally and often you find fluid eating paint under it and/or on front of the Booster.
Internal leaks won't let air in but leaks fluid between sections. Read rest of MC in the cave on brake page or follow map there.

Line w/ air or caliper is good start to look for problems.
Very small leak can drip fluid over time but let a lot of air in the system and you will bleed again soon.

You can Have a firm pedal w/ very small leak but keep pressure on it for a while like emulate long red light for traffic or a train.
Likely you find the pedal slowly sinks and won't stop sinking.
With Small Leaks, Fluid may not drip on floor/ground but have a wet spot somewhere to see/feel.

Warning: Bake Fluid is a "minor" HAZMAT and bad to your skin etc. Wash your hands quickly after touching it.
Read any MSDS/SDS for any DOT3 4 or 5.1 Fluid.

[This message has been edited by theogre (edited 04-14-2020).]

stevep914 APR 15, 11:26 AM
Thank You ! I will continue to search for a leak; it must be extremely small.
olejoedad APR 15, 11:37 AM
Check for a leak where the rear brake line runs through the rear cooling tube clamp on the passenger side.

Very common place for corrosion failure.
stevep914 APR 18, 09:13 PM
Still not finding any evidence of fluid leaking; have the car in the air and search is ongoing.
olejoedad APR 18, 11:18 PM
Pull the Master Cylinder and look at the seal near the vacuum booster.