When I am at a traffic light, my brake peddle slowly sinks down. If I dont add pressure, the truck will start to move forward. (auto) Is this a master cylinder problem? Can these be rebuilt? SHould I get a new one? Aftermarket, rebuilt, Toyota only?
Could it be something else?

 

^likely; yes they can be; i would; any quality brand.
power brakes? maybe a vaccum leak.

if you pump it, does it then slowly fade again? or stay firm?

you have checked the fluid levels, right?
will it stop creeping with the parking brake applied? does this do anything to the feel of the pedal?

 

Almost certainly the MC, leaking past the seals on the plunger.






Fred

 

Fluid is all the way, a little over the max line. It does fade with pumping. Can I just replace teh seals? Or do I have to buy the whole master cylinder?

 

Check the rear wheel cylinders and the front calipers for a leak first. One the rear, slightly pull back the dust covers to see if there is any brake fluid in them. If you cannot find a leak in any of those then it is most likely the master cylinder. I have heard that master cylinders should be honed when rebuilt, but I do not know for sure. I do not think a new one is rediculously expensive, so I would just buy a new one instead of rebuilding.

 

I just had a similar problem and it turned out to be the brake job from hell, but the truck really needed it. I ended up replacing the master cylinder and the both front calipers and the rear wheel cylinders and majority of the brake line. All of my brake components where too rusty. I broke off every bleeder trying to crack open, broke most of the brake lines trying to remove. So, be ready to have a lot of patience.

Jake

 

If ther brake fluid level in the MC is ok (and it is according to him) then it's highly unlikely that he has an external leak.





Fred

 

REplaced my master cylinder in 2 hours and it works good now. It was getting scarey. I have no pads on front brakes, next week's project...