Author Topic: Rear brake issue  (Read 5149 times)

Offline 86454

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Rear brake issue
« on: August 25, 2012, 12:29:18 AM »
I have an 86 3/4t pickup that will stop on a dime and an 85 3/4t Suburban that won't. Both have identical brakes with the big 13" drums. To make it short, on the Burb,I have replaced lines,cylinders, shoes,mc, prop valve, and bypassed the height valve. Basically everything I could think of.

I have "searched"brake issues and on a couple of them it mentions to make sure the primary and secondary shoes are placed correctly. How do I know which is which and what happens is they are reversed? I might go through the hassle of pulling the drums to check but I would like to know how to tell if they are correctly placed.

Offline zieg85

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Re: Rear brake issue
« Reply #1 on: August 25, 2012, 07:16:26 AM »
The primary shoe goes closest to the front and is the smaller of the two.  You may have a weak power booster.
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline bd

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Re: Rear brake issue
« Reply #2 on: August 25, 2012, 01:58:13 PM »
X2
If you have vacuum power brakes, make sure the vacuum hose to the booster isn't collapsing and a strong pull of vacuum is reaching the booster.  Check the SPID label in the glove box for your specific brake option to ensure you purchase the correct replacement booster (e.g., here's a dual diaphragm booster for use with JB7 brakes...  http://www.autozone.com/autozone/parts/Cardone-Reman-Brake-Power-Booster/1985-Chevrolet-C20-3-4-ton-Sub-2WD/_/N-ijk97Z8kn7z?itemIdentifier=44449_0_7889_3329).
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 454Man

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Re: Rear brake issue
« Reply #3 on: August 25, 2012, 02:20:34 PM »
I  replaced my booster and now mine stops on a dime. what pads did you go with?

Offline 86454

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Re: Rear brake issue
« Reply #4 on: August 25, 2012, 05:53:23 PM »
These pictures are of the drivers side so it appears that the bigger shoe IS on the back. I haven't checked the other side yet. Does anyone see anything obviously wrong with the brakes?  I have Wagner Thermoquiet on the front and back.  I am not sure when or if the booster has been replaced.  The front pads seem to wear quicker than I feel they should and I just think the rear brakes aren't engaging enough.

I seem to have a rear brake "clunk" when I take off from a stop. That is the only time it makes the clunk. It has been doing it for as long as I can remember but my pickup doesn't. I am certain the noise is not from the driveshaft spline.  Maybe it is something in the differential. Any suggestions?

Offline bd

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Re: Rear brake issue
« Reply #5 on: August 25, 2012, 06:44:16 PM »
Front pads will wear ~3:1 over the rear - that's normal.  The brakes/springs/links in your images are assembled correctly.  The only thing suspect is the placement of your jack stand.  It should be under the axle tube or frame - NEVER under a spring.  A spring is a 'live' piece of metal and can move.  Otherwise it looks fine.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 86454

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Re: Rear brake issue
« Reply #6 on: August 25, 2012, 07:30:44 PM »
Thanks for confirming that it is correct...well except for the jack stand. In my defense I did have a floor jack on the axle but
I know those aren't 100% fool proof.  I will keep that in mind.

Offline 86454

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Re: Rear brake issue
« Reply #7 on: August 25, 2012, 08:15:20 PM »
Regarding the power booster suggestion- can those get weaker over time? I thought either it worked 100% or it leaked.
I have had the Suburban 10 years (about 120K miles) and never replaced it. I have painted it at some point however so it does look real nice :D

Offline zieg85

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Re: Rear brake issue
« Reply #8 on: August 25, 2012, 09:09:34 PM »
You mentioned rear brake clunk... That could be the flexible rubber hose running to the rear end.  I have had them act like that... a delayed rear brake release if you will.  After I changed the hose which must have been swollen inside the rear brakes came alive.  This was several years ago and the end results were night and day.
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline 86454

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Re: Rear brake issue
« Reply #9 on: August 25, 2012, 09:30:08 PM »
Delayed brake release is a great way to describe it. I did replace all the rubber lines last year and it did make a difference but I still had that clunk sometimes.

However, after I put everything back together tonight and adjusted the rear brakes I drove it around few miles and didn't notice the clunk. It was all flat ground where I had stop signs etc but maybe my adjusters need replacing. I know have I checked them and put a dab of grease in the tip in the past  but maybe the threads are not new/clean enough to adjust correctly. I will have to see how long it is before it clunks again.

Maybe the booster is weak and that is what it needs to be top notch. Short of buying another one how can you tell? I replaced one on our 77 Firebird but it was obvious it was bad...you could hear it leaking.