I was coming up to a stop sign and mashed the brakes and it felt not normal. I had to mash them very hard before it stopped. When I let off of the brake pedal my brake light came on. This is on my 87 Silverado.

The booster holds air and feels normal so I replaced my master cylinder. I bench bled it and put it on and the brakes are still not working right. Here is how it feels: when I first mash it I hear the normal "shoosh", as I continue to push it right about the time the brakes SHOULD be applying it gets hard and I have to push very hard to stop. I have no vacuum leaks or fluid. What could this be?

miss adjusted brakes? drums on the rear?
ppl being lazy and do the big no no of adjusting shoes up with the hand brake adjuster?

I would look at your brake shoes and make sure a shoe hasnt broken or came loose. Also make sure they are adjusted right.

Hard pedal with power brakes usually means booster is bad. It is like trying to stop without power assist-takes extreem effort to apply brakes.

Hard pedal with power brakes usually means booster is bad. It is like trying to stop without power assist-takes extreem effort to apply brakes.
The booster holds vacuum. I read if it holds and I hear no leak that the booster is good. I may be wrong though.

I will pull the tires off and check the brakes, thanks guys. :thumbsup:

Check your engine vacuum and the vacuum hose. If it sucks flat, the booster won't get enough vacuum. Fuel vapor from the intake can soften the hose. There is usually a steel tube plus small filter in the line to prevent fuel vapor from entering the booster and rotting it. check that air can flow through this hose assy and the booster retains vac with engine off.

I've seen the proportioning valve fail and cause low pedal that feels spongy. Does your truck have the quick take up master cyl? The aluminum one?
David

Check your engine vacuum and the vacuum hose. If it sucks flat, the booster won't get enough vacuum. Fuel vapor from the intake can soften the hose. There is usually a steel tube plus small filter in the line to prevent fuel vapor from entering the booster and rotting it. check that air can flow through this hose assy and the booster retains vac with engine off.

I've seen the proportioning valve fail and cause low pedal that feels spongy. Does your truck have the quick take up master cyl? The aluminum one?
David
The booster held air for a day so I think it is good. My truck does have the alum master cyl. I don't know if it is called a quick takeup one though.

Is the booster a direct replacement? have u checked the dept of the piston in the master cylinder is the same....the rod maybe a couple mm to long

UPDATE

Well I replaced the master cylinder and nothing changed so I decided to bleed out all of the old brake fluid. I started with the driver side rear and the whole line had air in it! Went to the pass side pulled off the drum and saw a slight leak coming from the brake cylinder. I did not think too much about it because it was not very wet,,,,started bleeding that side and air never stopped coming out. Apparently the cyl was sucking in air but not leaking a lot of fluid. I replaced that brake cyl, bled all 4 corners and now my truck stops great. Thanks guys for the help :thumbsup:

It is common, replace a booster or mastercylinder or wheel cylinder, and if the others are not new, they will blow out over the next few months.