Brake Light On Need to Drive Truck Tomorrow
 

I just finished a full suspension and partial brake system refresh. I installed all new brake lines and rear brakes/wheel cylinders. The front brakes are about 6 months old and they worked fine before the rebuild. Master cylinder is fairly new, booster and proportioning valve are original and they worked fine before the rebuild.


So far I have bled the brakes solo using the gravity method and the bottle/hose method. I am getting fluid out of all four bleeders. Pedal seemed firm before I drove it. While driving the truck the brake light on the dash came on. The brakes work but they are weak. After driving the truck the pedal is much softer than it was before I tore it apart.

The master cylinder is full and there are no leaks anywhere. I tried pushing in the button on the proportioning valve but it doesn't want to move. I'm pretty sure it didn't move from it's original location anyways. Any ideas on where to start? Should I just re-bleed the system at each wheel? Should I pull the master and bench bleed it?

I need to drive the truck to the exhaust shop tomorrow and I want to make sure its safe.

Re: Brake Light On Need to Drive Truck Tomorrow
 

Look at the backing plates and see if there is any signs of brake fluid around any of them.

The light usually means that one of the brake systems has failed, front or rear. I have never done this but I read that if you take the switch out of the distribution/combination valve (where the wire connects) that you can reset the valve with a small screwdriver or punch by prying it whichever way it needs to go. I will see if I can find the thread on it.

You can check this thread out to see if anything there helps you.

https://67-72chevytrucks.com/vboard/...d.php?t=758471

LockDoc

Re: Brake Light On Need to Drive Truck Tomorrow
 

If there are no obvious leaks, stomp on the pedal real hard to try to reset the shuttle valve in the distrib block. However, the fact that it came on WHILE driving rather than right after you bled the system is more an indication of a leak rather than a shuttle valve that got off center due to the bleeding process. But never know til you look! If it is on and you have a leak - you still have either front or rear brakes (assuming they aren't ALL leaking :))

Re: Brake Light On Need to Drive Truck Tomorrow
 

I thought about pulling the switch out of the proportioning valve and manually centering it but I was unable to get it to break free. I ended up pulled the master and bench bleeding to verify that there was no air in it. I test drove it after I put the master on and it was doing the same thing.

Once I got the master back on I also tried stomping the pedal as hard as I could. It actually made the light go off for a bit but it would intermittently come back on.

After staring at it for about 20 minutes I thought to check the rear brakes and make sure they were adjusted properly. Turns out I forgot to open up the star adjusters so the rear shoes were barely making contact with the drums when I was hitting the brakes. I adjusted them and now the truck is back no normal and the brake light is off. Fortunately I didn't damage a wheel cylinder.


Thank you for your suggestions. Ended up being an error on my part. Now the truck can go get full dual exhaust with some dynomax mufflers

Re: Brake Light On Need to Drive Truck Tomorrow
 

Good deal! glad you figured it out.

LockDoc

Re: Brake Light On Need to Drive Truck Tomorrow
 

Good update, thanks for the solution post.