Rear brakes locking up before fronts

[skokie]

I had a break job done on the 68 1/2 ton. Its power drum/drum. New shoes, master cylinder, rotors, everything. When I slam on the brakes the rear locks up before the fronts. Do I just need to adjust the fronts a bit?

[Pont406]

I can't help you much, but my 69 c10 does the same. I tryed everything and it still does it.

[tcb-1]

hummmm, I have a couple of thoughts.

the front and rear brakes may need a bit of adjustment.

or

you may need an adjustable proportioning valve aft of the existing proportioning valve. but if you haven't touched the factory master cylinder and prop valve, something changed.

or

you can also try rebleeding.

[powell72]

The rears will always lock up before the fronts. When you stand on the brakes it takes the weight off an already light rearend as the front dives. Assuming whoever did your brake job did it correctly, you shouldn't need to adjust yet (you sound like it was recent). How does the pedal feel? Is it high and firm? Jack up the truck and see if there is some drag on the wheels when you spin them if you are concerned.

[Sammy]

After putting everything in my brakes new including drums, I noticed one of my drums was getting super warm. Come to find out one of my drums (new) was out of round. Never know what U get now days. Jack her up & check it out.

[skokie]

Originally Posted by powell72

The rears will always lock up before the fronts. When you stand on the brakes it takes the weight off an already light rearend as the front dives. Assuming whoever did your brake job did it correctly, you shouldn't need to adjust yet (you sound like it was recent). How does the pedal feel? Is it high and firm? Jack up the truck and see if there is some drag on the wheels when you spin them if you are concerned.

Will give this a try and see.

Thanks

[Rollie396]

did you back up and hit the brakes a few times to adjust the rears?

[cobb_ben]

That should not be a problem. It should actually be safer, because if the fronts lock up then you can loose your ablity to steer! That is not good!

[NGN]

just a short time after buying my 67my rear driver side was locking , i was told the brakes had low miles but where done awhile back . put the truck on stands to check out the brake system. fronts drums frist , all the pads are new no lecky brake-cyl , clean . what we found in the rear drums was that the new pads were put on wrong , the two longer shoes on the rear driver side with a wet brake-cyl and the two shorter on the pass side . replaced the brake cyl's and pads bleeded the system and that fix it . be safe check it all out good luck

[70GMCer]

There is not prop valve for drum/drum brakes. It has a distribution block. Brakes systems are designed to have the fronts lock up before the rears. That keeps the rear of the vehicle from swinging around and going out of control. Read your manual on adjustments & how the brakes react to sudden stops. It sounds like you have the rear adjustment tighter than the fronts.

[72hotrod]

You always want the front brakes to lock up before the rear to keep from losing control. The closer together the better, but fronts first.

On a drum-drum system, the size of the brake components (front vs rear) provide the proportioning effect. If your rear wheel cylinders or brake drums and shoes were to be upsized without changing the fronts, your brake bias would increase toward the rear.

DPI Racing supplies a dampening valve for the rear called the Stewart Lock-Resistant Brake System (LBS) that is used by NASCAR teams to help prevent lock-up at the rear during hard braking. It just goes in the line at the rear hose on the frame. I don't know how good it works, but I am looking into it, as trucks need a lot of help in this department. They cost about $90.

[bb1979]

I prefer the backs locking up first, I find it much easier to control than having the front slide out on you

[OrangeCrush1970]

You never want to lose your rear end unless you know how to pull yourself out of it. Try backing up and pumping the brakes whlile bringing it to a complete stop (do this several times). We have self adjusting drums - this should help you out as I had the same situation on my last brake job.

[skokie]

Originally Posted by OrangeCrush1970

You never want to lose your rear end unless you know how to pull yourself out of it. Try backing up and pumping the brakes whlile bringing it to a complete stop (do this several times). We have self adjusting drums - this should help you out as I had the same situation on my last brake job.

I tried that and it didnt do much. Maybe I didnt do it long enough times. About 5-6 times or more than that?

[Arad68]

I advise switching to front disc if you can, but an adjustable brake valve will make a huge difference.

Our trucks, or any pickup truck for that matter, are inherently light in the back

[OrangeCrush1970]

Originally Posted by skokie

I tried that and it didnt do much. Maybe I didnt do it long enough times. About 5-6 times or more than that?

Try backing up and slamming on the brakes a few times (watch your head and the back glass!)…it may take 5 or 6 times depending. Also, seeing as they are new brakes, they may just need a wear in period, that’s just a thought though-

If this doesn’t work you may just need to manually adjust the rear drums. It's a little easier to do on the front than the rear, but essentially you want to make sure that your rear brakes aren’t set too tight. Block your front tires, jack the rear up and put it in Neutral, etc. If you get your rear wheel off and your drum won’t pull off freely, then it is probably just set too tight. ….if you spin the rear hub and you can hear the brakes rubbing then they are probably set too tight. Adjust until there is as little friction as possible.