1990 Chevy C1500 - Front Brake Problems

What would I be checking for?

Typically, blockage of the flexibles and tubing that is preventing the fluid from returning from the caliper. It is not hard to occur. The blockage may be occuring in both directions, but is not sensed due to the hogher pressure when you step on. (I had a problem like this once, but I found out that the master cylinder had an internal leakage instead...)

Does this truck have the anti-lock braking system GM tried on trucks with rear drum brakes?

If so, disconnect it! I had an '88 C3500 with it. I called it always-lock....

I'm not sure when GM discontinued this style of anti-lock I just hope you don't have it.

Not that I know of it does not have it

May have two troubles.

What were reasons you replaced the brakes?

Low pedal is an indication of a bad brake booster unit.

When the RF rotor locks, and refuses to release, then crack open the bleed screw and see if it releases. If so, caliper is probably good; suspect rubber flex line next. Internal line failures common on older vehicles. Interior of hose disintegrates and acts as a one way valve. If not that, then crack open fittings starting from RF, tracing back to master cylinder.

Bleed brakes RR, LF, RF, LF when you complete the repairs. Also, make sure you bleed the master cylinder before you bleed the system. On the bench is best. When you bleed the system, use the factory method.

Make sure the rear shoes are properly adjusted. Just a slight drag when you spin the drum.

Did you use reputable and known brands of replacement parts? Many of the off-shore parts are garbage. Quality (OEM or aftermarket) are best.

DO NOT disarm the anti-lock brake function. Major liability and legal problems can occur. Lawyers look for this kind of stuff. You can get bankrupted doing that.

If you're not a trained technician, I would consult a good mechanic for assistance. You really need to start over and cover the basics for peace of mind. A pedal dropping to the floor is nothing to mess with. Get the system checked completely before taking to the road again.

Ok This is what I have done. I replace the caplier ( eventho it was new, I exchanged it ) I replaced the pads and the hose from the brake line to the caliper. I bled the brakes starting with the RR, RF, LR AND THE FR. wirhout the engine running the pedal is hard, with the engine running the pedal will go almost to the floor. The right front is releasing now. After calling it alot of ugly words I am leaving it along for awhile.

The flex hoses are considerably less expensive than the lawsuit you'll see if you hit someone because of faulty brakes.

Old brake hoses have micropores that allow air in, but leak no brake fluid.

This gives you a "spongy" pedal and delayed release. You should also replace the "distributor valve" it is located on front compartement near the floor wells, and it is not one of those "T" distributors for L and R wheels, (which wouldn't hurt to replace also). The distrubutor valve takes the master cylinder pressure, delivers an even flow and pressure to all wheels and returns fluid back to the reservoir.

google "TSB" for your make and model particular to brakes; checks for recalls or problems.

* TSB - technical service bulletin

wow guys....alot of sugestions for a simple common problem to diagnosis this problem corectley all you must do is remove the caliper in question and try and compress it with the bleeder valve open if the caliper compresses the hose is bad if the caliper dosent compress the caliper is bad and that is all there is to it

What if I put a BB in the brake hose connection?

You are right that is a simple way to diagnose his problem.

First--19 year old flexible brake lines are way past their service life and are 99% certain to have swollen internally to the point of seriously restricting flow. Change them ALL immediately.

90% probability swollen brake hose is causing the very slow release/no release.)

Low pedal--hard or spongy? Spongy means air in the system yet. Probably trapped in master cylinder. That's why they always should be filled and 'primed' before installation on the vehicle. A spongy pedal can also be caused by brake pads that are not yet bedded in to a worn / grooved rotor.

A low, but hard pedal (can be pumped once and pedal rises to normal and is solid) means either rear drum brakes are mis-adjusted (too loose) or : a) a front disk is warped and causing pads to retract too much; or b)new caliper seals too soft and stretching on piston rather than sliding and retracting pads too much when pressure is released.

Ok This is what I have done. I replace the caplier ( eventho it was new, I exchanged it ) I replaced the pads and the hose from the brake line to the caliper. I bled the brakes starting with the RR, RF, LR AND THE FR. wirhout the engine running the pedal is hard, with the engine running the pedal will go almost to the floor. The right front is releasing now. After calling it alot of ugly words I am leaving it along for awhile.

now that you fixed the front check for a leak in the rear...posible wheel cylinder or way out of adjustment...also check the other front caliper for frozen slides that will make the pedal fall also

Abs hydraulic unit or the rubber hose. yes it does have abs. Your best bet is to try the abs hydraulic unit. Trust me I spent close to $400 trying to find out what was wrong with mine. I have a 1990 chevy c1500 5.7 small block and and a 1990 chevy c1500 7.4 big block. The abs hydraulic unit sends an equal amount of brake fluid to each wheel what yours is doing its not taking the fluid back to the master cylinder that cause's the caliper to stick. I hope I helped you out...