Whats wrong with my brakes
 

I have an '86 short bed and its having braking broblems. I need help on deciding if it is the master cylinder or the booster. What is does is sometimes when i press the pedel it just keeps on going all the way down and the truck just barely slows down while other times I can press the pedel and after about an inch or two of travel it feels normal. It is never hard to press at all, just sometimes it is very soft and keeps right on going.(especially the first time it gets drove that day) It has been this way for a while and never gotton any worse but I had a close call the other day and decided I better fix it now. I'm thinking it is the master cylinder. Thanks for any input

Jeremy

I'll start the replies off with saying I agree with you - - I would say the master cylinder is bad. Having said that, I have never experienced a booster problem myself, so I don't know what the signs would be...

:canada: :bowtie: :flag:

You are loosing pressure somewhere. If there is no fluid leaking anywhere then it has to be internal. More than likely it is the master culinder, but it could be a wheel cylinder too... :cool:

It's probably not the booster. If he had hard pedal pressure then that would be a symptom of booster problems. More than likely the seals are blown on the master cylinder.... :cool:

When is the last time you changed your brakes? Did it start then?

That has happened to me. It is the master cylinder.

Grrrr.. I was about to start a thread with this question. I Just replaced my whole front end brakes... rubber hoses, steel lines, pads, rotars, ect. All xcept the master cylinder and calipers... so im guessing its the master cylinder because if it was one of the calipers it would pull? right? hah. Well Thanks for beating me too the punch with the Q and thanks for all the replies too.

another thing... how long could you go without it? will it mess it up if i ride like that for a few weeks or so? because the budget is stupid tight right now. but i still want to be safe. Btw, it is my daily driver, so thanks for any help.

hotrodhomi, It did get worse when I replaced my rear brakes and wheel cylinder.
I bled them throughly. Could this have an effect on something?

I put on my new master cylinder today, bled it by mounting it to the booster and screwing in the plastic plugs and pumping/holding the pedel while loosing a plastic plug until all the air was gone. The problem is still there!! I even tried bleeding at the wheels... it didn't help. Where should i go now?

Could it be a wheel cylinder even if it is not leaking? Because Like I say it really started when I did a rear brake job and replaced two leaky wheel cylinders.

Thanks guys for the information
Jeremy

im not a brake specialist or anything but dont you have to press a button or something on the pro. valve up front ???????????

I seen there was a button on that thing, but i have no idea what its for =D lmao

Cailpers for these trucks are really really cheap I wouldnt skip them.

does any one know what the button on the pro valve??? mentioned above is far? Where is it and does anyone know what it does? I'm new to this one.

I'm going to replace the calipers tomorrow and see if that helps matters any.

Thanks
Jeremy

Here's a past thread that contains some information on the metering pin located on the proportional valve.

BOXRODZ,
I see the button you are talking about, but I tried to push it in and it will not push at all. The little rubber cover over the pin is very soft, I can feel the pin underneeth it, but I cant make it move. I assume my proportional valve is bad? Maybe this will take care of my problem. I went ahead and put on new calipers this afternoon and a new mastercylinder yesterday and the brakes feel exactly the same as before. I do think air is my problem though b/c it did not start until i put wheel cylinders and shoes on the rear. Do you think it is worth a shot to replace the porportional valve? Looks like it could be a job getting all of the lines hooked back up.

Thanks for all of 'yalls help
Jeremy

How well did you bleed the system? It sometimes takes a few cycles to purge the air out of the lines. You may be right... You may still have air in the lines. Also, could it be possible that you reassembled the rear cylinders/shoes incorrectly (ie. automatic adjusters)?

It doesn't take much to depress the metering pin. If it's stuck, it may be clogged. But, I haven't heard of one being stuck. A faulty metering valve could cause excessive pedal travel. But, I'd try check the rear brakes and bleed the system first.

Thanks everyone. I pulled the drums off this afternoon to be positive the wheel cylinders were not leaking...they wern't. However I did tighten them up a little (with the adjuster) and it seemed to help my problem a lot. They wern't realy loose though b/c I had to loosen the adjuster to get the drums off. I'm gonna re-bleed the whole system tomorrow. The problem still seems to be there somewhat especially when the engine is cold(??) If you slam on them it will stand on its nose and drag the rear tires, but it is when you gradually slow down and keep slowly pressing the pedel that I notice it. Anyhow maybe after I bleed them again tomorrow it will good enough where I can live with it.

Thanks
Jeremy

If it pushes all the way down when you push real easy, but hooks up when you push hard, it's the master cylinder.

I just replaced the master cylinder though. Could it be bad also? (a re manufactured one from O'Reilly's)

How about the vaccum line from the intake or carb? How about the vaccum valve on the hose that goes to the master cylinder?