QuestionI have a 1988 Toy pick up with 270,000 miles. When I start up in the morning sometimes I have good brakes and sometimes none at all. After driving for 10 -15 miles they come back and are fine all day. I have had new master and wheel cylinders, calipers, hoses, pads and shoes, and compensating valve. There is good vacuum at the booster. I have taken the truck to the repair shop (Tire Kingdom) and they can find nothing wrong. Any suggestions? Thank you.
AnswerSounds like alot of fun to drive doesn't it!
When I'm working on something in a case like this I normally start by re-bleeding the brakes. (No matter how many times it's been done.) And driving around with a vacuum gauge while the problem is going on. That way I can tell if the vacuum assist (brake booster) is operating properly. *Especially* if the pedal is hard while the problem is occuring.
Hold the pedal half-way down & crank the engine. It should go to the floor.
From there I bleed the brakes abit, and use a dye addative in-house & test drive the car fairly hard. Afterwards I do a quick brake bleed, and get someone to run the brakes while I visually inspect all the brake lines in operation.
If there is no leak I Replace the Master cylinder & Brake booster as one unit instead of twice at the same time if a quick look shows no leaks. If there is a leak, I fix the leak & *completely* flush the system.
You must not leave anything like water, or a dye in brake fluid. It must stay pure specified fluid.
I don't really do places like small time repair shops / tire places for brakes. I've heard horror stories too many times & as a child, saw a mechanic pick-up a flat blade screw driver then pop it against the master cylinder / brake booster seal to crack it, requiring a new pair of both.
