Brake problems

[K1500Baloney]

I have had problems with the brakes on my 1990 K1500 since I bought my truck. I have replaced the booster, master cylinder, deleted RWAL, replaced front and rear brake hoses, calipers, rotors, brake pads, rear shoes, and wheel cylinders. Not only that, but I feel like the only thing I haven't done is replace the proportioning valve. Despite this, it is very difficult to stop the truck sometimes. The pedal is hard, and sometimes when I come to a hard stop and press the pedal hard to the floor, the driver side caliper gets stuck. This has happened before and after I replaced the calipers up front.

 

[FullBlowncustoms]

Sounds like a bent kinked line maybe? I used the those copper / nicad? lines on my 95, no rust, easy to bend. check for vacuum at booster? Bled the lines in correct order? Bleed the master before bleeding the system itself? does a 1990 have ABS like a 95 K1500?

 

[Erik the Awful]

Did you replace with the stock parts, or did you "upgrade"?

 

[K1500Baloney]

Did you replace with the stock parts, or did you "upgrade"?

I used standard replacement parts for the truck. Its all parts store quality nothing fancy. I tried the nbs master cylinder but oddly it made it worse in ways.

 

[K1500Baloney]

Sounds like a bent kinked line maybe? I used the those copper / nicad? lines on my 95, no rust, easy to bend. check for vacuum at booster? Bled the lines in correct order? Bleed the master before bleeding the system itself? does a 1990 have ABS like a 95 K1500?

I could definitely look at some of the lines closer. From what I can see everything looks ok. I have replaced the booster and the replacement was bigger than what it had and looked much more suited for the truck. I can pull the vacuum hose off after a day and it still has a vacuum at the booster. I have also done plenty of bleeding in different places on the truck too. I had the dump valve but no ABS. I deleted the dump and now I have Master cylinder -> proportioning valve -> hard brake lines to all the brakes. Its basically the same now as something from the 80s.

 

[Schurkey]

WHICH brakes does this truck have?

Unless it's an extended-cab, you could have the crappy JN3/JB3 brakes--the weakest power brakes ever installed on a GMT400 vehicle.

Look at the SPID sticker inside the glovebox, verify the JN/JB series of options.

It's insanely common for the 254mm (10") rear brakes to be out-of-adjustment. Generally accompanied by seized park-brake cables. DOES YOUR PARK BRAKE WORK OK?

Make the LF caliper lock-up. Loosen the bleeder screw. Does the rotor now turn freely? If it does, you have a hydraulic problem unless dicking with the bleeder screw jiggled the caliper enough to un-stick it. If it doesn't, you have some sort of caliper-mounting problem.

Make a hard stop from highway speed. Faster is better, but be safe. Get out, feel the hubs/wheels. Both rear wheels about the same temp? Both front hubs/wheels about the same temp? Everything is at least warm, maybe HOT?








I'd pay money (not a lot, but some) if the moderators would edit the thread(s) suggesting the "NBS" master cylinder downgrade on any vehicle with low-drag calipers--pretty-much every 1500, and some of the light-duty 2500s.

 

[FullBlowncustoms]

Only think I can think of is a valve block stuck? Booster problem? or a pinched line or plugged?. All would cause a HARD pedal with no stopping. Fluid not flowing freely or returning, releasing etc... wheel bearings ok? Booster use a rod? if so is it bent or correct length? Is the hard pedal the same with engine off, engine at idle, engine revved? vacuum line on or off? is booster holding air? etc..... lift it up, put foot on brake pedal, have someone see if all four wheels will not turn, release pedal see if one sticks? Sit on LEVEL road, at idle let foot off brake, see if truck starts to move on it's own at idle.? hit brake and then see if it starts to move again at idle? Only time I seen a hard pedal is problem at the booster or valve or pinched, collapsed line etc.. With vacuum line off the booster, engine running, is there GOOD vacuum? and does it seal nice in the grommet? When you replaced the calipers did you clean it all up scale etc.. nice so they slide free? new bolts? not bent etc... just shooting out ideas... good flow coming out of the proportioning valve? no bubbles?