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Old 03-19-2003, 04:23 PM   #1 (permalink)
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No rear brakes

I have a '76 Blazer with 3/4 ton axles and my rear drums aren't working properly. They work fine when I use the ebake but they are lacking when I use the pedal. The problem is severe when I'm towing and my Front brakes will lock up if I need to brake hard. Just normally I get some bad brake steer.

My theory is the truck is still running a 1/2 ton master cylinder and it's not pushing enough fluid to the rear. Before I swap in a new master I was wondering if the proportioning valve needs to be changed when doing a .5 to .75 swap or will the new master fix it? Thanks

Travis
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Old 03-19-2003, 04:33 PM   #2 (permalink)
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im in the process of putting 3/4 ton axles in my 1/2 ton and the 3/4 uses a different master cylinder and brake booster.
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Old 03-19-2003, 04:43 PM   #3 (permalink)
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Thanks I know the master on the 3/4 is a bigger bore. I was wondering if the prop valve needs attention too.
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Old 03-19-2003, 07:32 PM   #4 (permalink)
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I would think your proportioning would be OK as long as you have'nt converted to rear disks.
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Old 03-19-2003, 08:17 PM   #5 (permalink)
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Your proportioning valve and master cylinder should be fine. I would look at rear brake lines to make sure there is no blockage or that the rubber line isn't swelling when you step on the brake. Also, make sure your wheel cylinders aren't leaking.
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Old 03-19-2003, 10:01 PM   #6 (permalink)
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Quote:
Originally posted by motorhead72k5
Your proportioning valve and master cylinder should be fine. I would look at rear brake lines to make sure there is no blockage or that the rubber line isn't swelling when you step on the brake. Also, make sure your wheel cylinders aren't leaking.

Really you think the master will be fine? I would assume the 14b brake stuff would dwarf the 12b stuff the master was designed to fill. I'll check the lines but I haven't noticed any leaks. From the pedal feel it just seems like there's not enough fluid getting to those huge brakes. I'll go over the lines before I swap masters. Thanks

Travis
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Old 03-19-2003, 11:20 PM   #7 (permalink)
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Originally posted by Overkiller



Really you think the master will be fine? I would assume the 14b brake stuff would dwarf the 12b stuff the master was designed to fill. I'll check the lines but I haven't noticed any leaks. From the pedal feel it just seems like there's not enough fluid getting to those huge brakes. I'll go over the lines before I swap masters. Thanks

Travis
Yup, I am running 3/4 ton gear under my K5 with the stock master and I have absolutely no problems. At the worst, you will have to use a little more foot. The only difference the hydraulic system will see in the rear end is the size of the wheel cylinder. The system remains full of fluid from top to bottom,. All the master does it pressureize it. The larger master will give you a quicker response, but the one you have should be fine. How does the pedal feel? Is it spongy, or does it fade at all? Did the problem just develop, or has it been there since the axles were swapped in?
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Old 03-20-2003, 12:38 AM   #8 (permalink)
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Hmm good points, I bought the truck in its current condition. I need to go over the lines and make sure everything's flowing well. The pedal feels pretty bad but too be honest I've never driven or owned a Chevy that the pedal felt good to me. I need to do some checking before I start swapping parts.
Thanks

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Old 03-20-2003, 12:46 AM   #9 (permalink)
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Yeah, Chevys are typically a little soft, but it should be reasonably firm. Have you bled the system?
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Old 03-20-2003, 12:43 PM   #10 (permalink)
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If you feel like you loose your rear brakes all together when you hit them hard its your porportioning valve triping. Older Cheveys are natorious for having those things go bad.

But if that is not correct I am guessing air in the lines or the automatic adjustment slack adjusters stoped adjusting. Those things get rusty and crudy and stop adjusting the rear brakes. The brake shoes should be just touching the ware surface on the drum when not pushing on the pedal for them to work properly. I think all of the older cheveys I have owned have had this problem.

EDIT
2 of witch were 1/2 tons with 14bolts swaped in. You don't have to change the master cylinder when swaping rear ends.
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Old 03-20-2003, 01:57 PM   #11 (permalink)
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With the 1/2 ton valve and master cylinder the brakes on my 14 bolt tend to be touchy and lockup if used carelessley.
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Old 03-21-2003, 08:11 AM   #12 (permalink)
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Quote:
Originally posted by rcurrier44
The brake shoes should be just touching the ware surface on the drum when not pushing on the pedal for them to work properly.

They should be tight enough that it takes a little effort to turn the tire and it should make no more that one revolution. I adjust mine so that it almost stops turning when I let go, and that is with a 39.5 Swamper. It should be tighter with larger tires because of the greater rolling mass.
The way you adjust them will work, but industry standard is that they be a little tighter.
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Old 03-21-2003, 08:20 AM   #13 (permalink)
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when I bought my truck I had the same problem and it turned out to be the proportioning value.

good luck
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Old 03-21-2003, 07:22 PM   #14 (permalink)
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Had the same problem on my truck - it was the prop valve.
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Old 03-21-2003, 09:49 PM   #15 (permalink)
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Well I tried to smog the truck today and the truck wouldn't stop the rollers. It has no rear brakes at. If I pull a prop valve out of the boneyard does it have to be trom a 3/4 ton 4x4 or can I just grab a chevy truck prop valve? If that doesn't work I'm considering converting to rear disks. Thanks

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