I have a 1999 k1500 breaks locked up wont relese

[Natedawwg]

99 k1500 replaced master and booster brakes locked up and wont relese. Wheel cylinders wont go back in. Were the shoes ride on it. Like the pedal is constanly pushed down but its not Rebuild brakes past summer no issues at all untill this. Bench bled correctly abs bled power bled manual bled. Still nothing but it did let go a little. New abs mudule within last year all new lines, hardware

 

[Nad_Yvalhosert]

Have you tried loosening the bleeder screw and compressing the wheel cylinders?
Did you verify the pushrod length from the pedal is the same?

 

[Schurkey]

Did you verify the pushrod length from the pedal is the same?

Yup. Master cylinder primary piston probably not returning to it's proper "at rest" position due to misadjusted pedal-to-booster, or booster-to-master pushrods.



You did install the correct master cylinder...right? Not some crazy conversion to a master cylinder from a newer vehicle?

 

[deadbeat]

99 is the first year of the gmt800 for the 1500 series trucks, seems like an easy year to mess up and get the wrong part for.

 

[Pro439]

Rear only I wonder if something is wrong with the proportioning valve. If the rod length is correct for the pedal that is what I would check. I would open the bleeders and see if you have psi which you shouldn’t have when the pedal is not pushed. If you open the bleeder and it releases psi I would close it and pump the brakes 1 x’s and see if it’s still locked up. If it is I would try bypassing the proportioning valve and see if it still does it that will tell you if it’s the new parts you put on or not. I wouldn’t think the ABS module would cause this issue as that’s what it’s made to prevent

 

[any4xx]

Once upon a time I had this happen with my ‘97. Turned out a brake hose was collapsed internally.

 

[Nad_Yvalhosert]

Rear only I wonder if something is wrong with the proportioning valve.

3 channel ABS system. There is no external proportioning valve. Its internal to the ABS module.

I wouldn’t think the ABS module would cause this issue as that’s what it’s made to prevent

The rear brake circuit takes its signal from the VSS in the t-case. If the rear is locked up when it's not moving, there's no VSS signal to make the ABS dump pressure.

 

[skylark]

Start at the master cylinder and loosen the fittings. If it still locked up then tighten the fittings and move to the next fittings down the line. When the brakes finally loosen up you know that the problem is just upstream. Starting at the back is just guessing and losing fluid.

 

[Pro439]

Wow!!!!! I absolutely didn’t know that gm did that. Learning new things all the time

 

[GoToGuy]

If you don't have the factory service service manual, you should, it's free to download here in forum. Just do search and get your year , make life easier. Coffee break now, wheel brake later.