Could it be the brake booster?

Toyota pickup, 1987 2WD 22R engine. At a stop light the brake pedal slowly (1 min. or less) goes to the floor. I obtained and installed a rebuilt master cylinder and bleed the entire system. The pedal still sinks to the floor. Let's assume the rebuilt replacement is OK. I am now suspecting the brake booster. Are these customer rebuildable? Or is it just another part to buy already rebuilt? I am prepared to get inside it myself.

Reply to
imola23
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You have a bad master cylinder. Try to find a new one instead of a rebuilt. A bad brake booster would cause a hard pedal because you would have no assit. The only thing that would cause the pedal to go to the floor would be a bad master cylinder or a leak.

Reply to
Mike

I bet its a wheel cylinder.

Bend down and look at the inside of your tires. If you see one or more wet, you've found your problem.

Reply to
Jim Smith
[quote] The only thing that would cause the pedal to go to the floor would be a bad master cylinder or a leak.[/quote] I was thinking it might be an air leak from the booster.
[quote] I bet its a wheel cylinder.

Bend down and look at the inside of your tires. If you see one or more wet, you've found your problem.[/quote]

I should have mentioned that I am not losing any fluid
Reply to
imola23

I was thinking that the booster could be losing air.

And I should have mentioned that the system is NOT losing any fluid.

Reply to
imola23

I assume the rebuilt is NOT okay.

Did you bleed the new MC while it was still on the bench? If not, it can hold pockets of air that will affect braking performance. Having said that, a sinking pedal is the result of leaky seals within the MC, or a leaky seal at a wheel cylinder/caliper. If the leak was at a wheel, the fluid would be on the outside, and you could see the trouble. There should be enough on the outside that it would be painfully obvious.

I completely discount the brake booster as a source for your trouble.

Reply to
Jeff Strickland

If you are not losing any fluid, then you replaced a faulty MC with another faulty MC.

Reply to
Jeff Strickland

If the booster was loosing air ( actually vacuum ) you would have a hard pedal. The booster helps apply the brakes so you don't have to press on the brake pedal that hard with your foot. If the brake booster wasn't working you would have to press on the brake pedal very hard to get the truck to stop.

If you are absolutely sure you are not losing any fluid then you have a bad master cylinder. Some rebuilt master cylinders are of such poor quality that you may end up purchasing several before you get one that works. That is why I would always recomend you buy a new one.

Reply to
Mike

Faulty rebuilt master cylinders and unfortunately not uncommon. If only seals are replaced without a good honing of the bore then an internal leak can occur which causes loss of hydraulic pressure without a leak being visible. Bench bleeding is often required before installation too. A crude test of the brake booster is to push hard on the brake pedal with the engine off. Start the engine while continuing to apply pressure to the brake pedal. If you feel the pedal go down slightly once the engine starts, the booster is probably working as it is applying boost, i.e. vacuum, to the pedal. You could also try taking the vacuum hose off the booster and seeing if there is brake fluid inside. It should be dry. Good luck. Al

Reply to
al

Reply to
forte

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