Rear brake issue
#1
My buddy has a 69 Mach 1 with a weird brake issue.
The left rear drum brake will not lock up. The disk brakes in front and the right rear lock correctly but the left rear will not.
Here is what we have done.
New master cylinder, proportioning valve, wheel cylinders, lines. Bleed the brakes somewhere around a dozen times. ? Adjusted rear shoes. Removed the left rear line from the wheel to the brass block and blew it out with air. Pumped the pedal while the line was off to be sure we were getting full flow thru the block.
Can not get that one wheel to lock up.
Any thoughts would be great.
Thanks
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#2
Have you by chance installed the self adjuster backwards? This would render it useless, or actually back the brakes off when applied??? Find a picture online, and look at the assembly for the left rear, (drivers side) and make sure you have the cable route correctly and the adjuster turned the right way. About all I can think of. Hope it helps.
 

JTS
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#3
It is weird you are experiencing this issue only on one side.  Did you check to see if your wheel cylinder is working when you apply the brakes?
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#4
(04-16-2019, 07:36 PM)Mustangmike Wrote: It is weird you are experiencing this issue only on one side.  Did you check to see if your wheel cylinder is working when you apply the brakes?

Yes, the new cylinder pushes the shoes out when brakes are applied with the drum off.
We are getting some braking from it. But with the brakes applied, you can still turn the wheel by hand. We’ve sanded the shoes to clean any glazing off. Drum surface seems fine.
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#5
(04-16-2019, 01:24 PM)JTS71 Mach1 Wrote: Have you by chance installed the self adjuster backwards? This would render it useless, or actually back the brakes off when applied??? Find a picture online, and look at the assembly for the left rear, (drivers side) and make sure you have the cable route correctly and the adjuster turned the right way. About all I can think of. Hope it helps.
 

JTS

I can check that but this is all being done in shop. Has not been road tested yet.
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#6
Are the brake shoes installed correctly?  The linings are different lengths, short and long, two of each.  The shoes with the shorter linings go to the front, the shoes with the longer linings go to the back.  Are the backing plates grooved so bad where the shoes rub that they do not move smoothly?  After a brake assembly (without drum) is installed onto the backing plate, you should be able to grab the shoes at the bottom and slide the bottom of the complete assembly front to back.

If mechanically and hydraulically everything seems fine and the same from side to side,  you are down to something wrong with the brake lining or the drum.
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#7
(04-17-2019, 03:30 AM)1969_Mach1 Wrote: Are the brake shoes installed correctly?  The linings are different lengths, short and long, two of each.  The shoes with the shorter linings go to the front, the shoes with the longer linings go to the back.  Are the backing plates grooved so bad where the shoes rub that they do not move smoothly?  After a brake assembly (without drum) is installed onto the backing plate, you should be able to grab the shoes at the bottom and slide the bottom of the complete assembly front to back.

If mechanically and hydraulically everything seems fine and the same from side to side,  you are down to something wrong with the brake lining or the drum.

The brake shoes are Indeed installed correctly as you describe. Shorter shoe to the front.
We have not checked the backing plates but did not notice any abnormal wear. 
What if the drum has been resurfaced and too much material has been removed. Would that prevent the shoes from fully engaging the drum because of the reach of the wheel cylinder?
We are really at a lose here to explain this.
Using a proportioning valve tester next to check the new valve for proper operation.
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#8
(04-17-2019, 09:16 AM)dlhurd Wrote: [attachment=12918][attachment=12918]
(04-17-2019, 03:30 AM)1969_Mach1 Wrote: Are the brake shoes installed correctly?  The linings are different lengths, short and long, two of each.  The shoes with the shorter linings go to the front, the shoes with the longer linings go to the back.  Are the backing plates grooved so bad where the shoes rub that they do not move smoothly?  After a brake assembly (without drum) is installed onto the backing plate, you should be able to grab the shoes at the bottom and slide the bottom of the complete assembly front to back.

If mechanically and hydraulically everything seems fine and the same from side to side,  you are down to something wrong with the brake lining or the drum.

The brake shoes are Indeed installed correctly as you describe. Shorter shoe to the front.
We have not checked the backing plates but did not notice any abnormal wear. 
What if the drum has been resurfaced and too much material has been removed. Would that prevent the shoes from fully engaging the drum because of the reach of the wheel cylinder?
We are really at a lose here to explain this.
Using a proportioning valve tester next to check the new valve for proper operation.

Below is a picture of typical wear grooves on the backing plates.  All my old cars had these grooves on the backing plates.  You might want to check your backing plates for this type of wear.  It could definitely cause brake shoes to hang up.

In regards to resurfaced brake drums, if your drums have been resurfaced there is a chance too much material was removed if the drums had excessive wear or have ben resurfaced more than once. Most shops that resurface drums typically won't cut them if this is the case. Did you try swapping the drum on the side that is working to rule this out?

   
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#9
Updates Huh
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