1988 GMC 4X4 305 eng. K1500

And the condition of the pedal return spring is...?

Weak? Broken? Unknown because it is missing?

When you fixed the brakes... what did you do?

I don't know were the spring is located. I put a master cylinder on and a brake switch and bleed the brakes and now the brake pedal does not come back up and the lights stays on, until i bring the pedal back up .

Did you bench bleed the master cylinder prior to installation?

Did you bleed each wheel cylinder, starting with the cylinder with the longest tubing run from the master cylinder and working to the shortest? Generally, this would be RR, LR, RF LF.

Yes, I did all of that.

Roxie, I found another discussion forum where this has been discussed and resolved. It boils down to (most likely) the activation rod between the MC and the booster.

Read through this thread. I think the answer to your trouble lies there.

Doorman, I have not showed him this message yet. But He is outside working on another problem ,He just put brake shoes, pads whatever the name is for that year.LOL Also new brake calipers He said that .the brake pedal will not return to it's full position,without lifing it up with your hands . So the brakes are still on and the lights ,while the brake is on, he has worked on it for 3 days now . and getting pretty mad. I thank everyone for any answers you can think of for the problem.

Also, I forgot he put a master cylinder on it too . Could it be the difference in the piston travel in the master cylinder or the booster? Maybe they gave uys the wrong one! Just a thought!

Did you try the link in #5?

If your read the entire thing, quite a bit is revealed about what the trouble really is, why it happens, and what to do about fixing it. It doesn't sound like a big deal.

Oh, and my comment about the pedal spring is WAY off... there isn't one.

I think I read it right . My husband did not mod.his truck it is factory. it only has 84,000 miles. everything needed replaced because the woman that owed the truck never did anything to it. Thanks for all your help!

He took off the MC and I took it back and got another one to try and it still does the same thing. The brakes work fine, but they will not come all the way back up to the resting point. And other idea!

There is a spring inside the master cylinder. And there is the first place to start looking.

very common. the parts store gave you the wrong application master cyl late 80's trucks had many options that look simaler but are differant get your old one back if possible and compare bore size stoke length stepped bore or straight when you carefully remove the new note if piston has returned to the snap ring