Back Brakes lock up before the Front Brakes.

[bwlyon]

I have a 1967 F250 with Drum/Drum brakes, I have went through the brake system completely. New front shoes springs adjusters, rear brakes have been inspected thoroughly and all parts in good working order, and I just installed a new master cylinder after finding the pedal to be spongy after fresh brake job on truck. Master cylinder bench bled, all wheels properly bled. The brakes work great now, but the back brakes lock up before the front brakes. I haven't even been able to lock up the front brakes except on gravel as I don't want to flat spot the new back tires. With all that said, my question is that normal since there is only a distribution block on the drum/drum set up and no "metering valve" to restrict pressure to the rear brakes. Again, the brakes work quite nicely it is just locking up the rear brakes before the front on "panic braking".

[two-bit]

No....thats not normal.
I would suspect that your front shoes are not set correctly. Odds are they are close. Just not close enough.
When you installed the front brakes, did you adjust the front shoes after you installed the drums ?
If not, you still have to much shoe travel.

My '72 has 4 drum also. When i did the fronts, i put everything together. Bled it all out. Then adjusted the fronts one more time.
Front tires off the ground. Appropriately bent screwdriver in hand, i made a mark on the inside sidewall of each tire with a grease pencil.
Then i reached up with one hand and spun the tire. I watched how far the mark went around. also listened for "shoe drag". When i was done, I adjusted each front so that the grease mark on the tire would spin from about 12:00 to 6:00 or 7:00 ish. (In less than one rotation) Yes, there was shoe drag noise. Yes the tire gets hard to spin laying on your back !
After i did this, i carefully took my first test drive. Feel out your brake pull. Odds are good that it will pull to one side or the other. If it pulls left, tighten the right front a little, and vice versa. It took a few times, but i got that monster to stop straight from 45 mph with just a little pull to the right. Could have been the crown of the road also doing that.
If you get the fronts right on, and the rear still likes to lock up first, you could back off your rears a "click" or two if you like.

The tire that skids or slides has less resistance to the road and will always want to get in front of the tires that have more resistance. Thats why the back end of your truck is trying to pass the front end when you brake right now.

Other suggestions for setting front drums i have heard are to bottom out the adjuster, and then back them off an even number of turns.
I have never used this method because you are dealing with friction/wear parts. No two set ups will be the same, shoe thickness, drum dia, spring tension rates, ect... Lots of variables.
We all like to go....we all need to stop. As effectively as possible. Otherwise other things stop us, and that tends to bad

Good luck with it !
Two-bit

[Mach428]

What you're describing during panic braking is quite normal. Hard braking shifts a great deal of weight toward the front thus easily locking up the rear.

You should check the adjustment and bleeding on all four corners but I doubt you will get all four to lock up at the same time

[bwlyon]

Well, after careful inspection of the rear brakes it need new wheel cylinders, so I replaced rear wheel cylinders and drums. Problem solved. Thanks for all the replies.