Rear brakes are giving me fits.

[Brownsquare]

Is there a way to determine by VIN which rear brakes my truck has? For reference it's an '87 GMC Sierra 1500. It's a 2wd long box base model with a 4.3 V6 and a three-speed Saginaw manual trans. I can't seem to get the correct parts to finish this never-ending rear brake job. When I took the rears apart, the passenger side was stuck so hard it took me an hour to wrestle the drum off. Once it did come off the adjuster was cranked DOWN all the way and yet the shoes were still tight to the drum. The hardware and shoes appeared relatively new, and the rear drums had almost no wear, so I assumed somebody had put brakes on it recently but may have installed the wrong parts.

I went down to the local auto parts store and bought all new stuff except drums. Went back to install it and the drum still wouldn't fit, even with the adjuster turned down all the way. I went back to the parts store and was told there were two different brake types. 11" diameter and 11 5/32" My drums measured 11" so I should have had the correct parts. Even with the emergency brake cable tension taken off completely, I still couldn't get the drums on with the adjuster turned all the way down.

Frustrated, I went back to the parts store thinking maybe a previous owner installed 11" when the truck should have had 11 5/32", so I bought all stuff for 11 5/32" (including drums this time) and went home to install it. The good news was with the 11 5/32" shoes on, the drum fit nicely! The only problem was, that drum and shoes was almost twice the width of the 11". When I slid the 11 5/32" drum over the brakes, it bottomed out against the backing plate before it even reached the lug studs.

I feel like I've tried every combination of parts to get where I want to go, but nothing is working. To further confuse things, a friend who used to work in parts at the local Chev dealer told me it wasn't uncommon to have to machine down new drums to make new brakes fit! In all my years of brake jobs I've never heard that before.

Any suggestions? This is frustrating the heck out of me!

 

[Bennyt]

Not sure about the vin but the RPO tag should designate which option but that only works if nothing has been changed. The original drum you took off should have size cast into it and you can measure the width of the original pads.

 

[rusted nuts]

Is there a ridge on the back of the inside of the brake drum next to the backing plate?? Also would drum turn by hand before You removed it?

 

[fast 99]

Incorrect diameter shoe will not have the same circumference. Should be able to lay a shoe in drum and see the difference.

With new shoes installed are they on the anchor pin?

Did you check emergency brake cables for free movement?

 

[PrairieDrifter]

I had to get brand new rear drums cut because of brake drag. It was 1/2 ton brakes also.

 

[PrairieDrifter]

It would lock my truck up hard

 

[Snoots]

Not sure about the vin but the RPO tag should designate which option but that only works if nothing has been changed. The original drum you took off should have size cast into it and you can measure the width of the original pads.

Got no RPO tag? Since you have an '87 I believe you can still get a build sheet from GM.
IDK the URL off the top of my head but I'll try to find it.

 

[Brownsquare]

Where is the RPO typically located? I want to say I saw something inside the glove box door? I'll have to double check.

Rusted Nuts & Fast 99: No the drum would not turn by hand before I removed it. In fact it was so tight the shoes and hardware came off with the drum. That's when I found out the adjuster was backed all the way off already.

Rusted Nuts: There was no ridge worn in the drums. That's the part that's truly puzzling. It's like they were brand new just installed with no wear at all, yet they were installed that tight and I drove the truck from Ft. Wayne IN to Grand Rapids, MI with no issues.

Even when I removed emergency brake tension completely (to swap a frayed cable) I still couldn't get the drums to go back on. The one thing I haven't tried yet is the cylinders. I'm wondering if maybe I have the wrong ones, as I did replace those. Last night I did confirm that my drums are exactly 11".

The next time it's not raining or snowing here (or both in the same day) I'm going to dig into this thing again. I'll let you guys know what I find. Stay tuned lol.

 

[SquareRoot]

Where is the RPO typically located? I want to say I saw something inside the glove box door? I'll have to double check.

Rusted Nuts & Fast 99: No the drum would not turn by hand before I removed it. In fact it was so tight the shoes and hardware came off with the drum. That's when I found out the adjuster was backed all the way off already.

Rusted Nuts: There was no ridge worn in the drums. That's the part that's truly puzzling. It's like they were brand new just installed with no wear at all, yet they were installed that tight and I drove the truck from Ft. Wayne IN to Grand Rapids, MI with no issues.

Even when I removed emergency brake tension completely (to swap a frayed cable) I still couldn't get the drums to go back on. The one thing I haven't tried yet is the cylinders. I'm wondering if maybe I have the wrong ones, as I did replace those. Last night I did confirm that my drums are exactly 11".

The next time it's not raining or snowing here (or both in the same day) I'm going to dig into this thing again. I'll let you guys know what I find. Stay tuned lol.

Inside glove box. Should have a line with a code of JB1. JB3, JB5...etc.

 

[scrap--metal]

The one thing I haven't tried yet is the cylinders. I'm wondering if maybe I have the wrong ones, as I did replace those.

^ You might be on the right track there.

If the bleeder screws are tight in the wheel cylinders, and the wheel cylinders are at maximum expansion, the drums may not fit over the shoes even if the parts are otherwise installed correctly.

In other words, try cracking the bleeders on the wheel cylinders to relieve pressure, which should get the brake shoes to come in.

The last wheel cylinders I did, non-square, gave me fits. I couldn't get the drum on right; it fit, but not correctly. After lots of dicking around, I discovered that my brand new wheel cylinders were at the maximum extension when I pulled them out of the box and put them on. Even without brake lines attached, they wouldn't compress until I loosened the bleeder screw.

I can't ever remember having a new wheel cylinder come from the box maxed out like that, but now I'm aware and you all are too!

 

[Bextreme04]

That was my thought also, wheel cylinders might be wrong or seized. The rubber hose connecting the axle hard lines to the frame hard line could be collapsed, or you could have a stuck prop valve too. What do the cylinders look like? Are the pads sitting all the way down in them?

 

[Finkaire]

Rear brake lockup! I gave up and took it to a shop. Got it back with the brakes dragging. After three attempt and a bunch of money they work. There is confusion on the OE setup, I’m the original owner. Supposedly they couldn’t find wheel cylinders that matched? Brake line swapped did the final trick. I believe next time for about the same cost I’ll retrofit to discs.

 

[Brownsquare]

Loren, I was thinking along the same lines with the discs. Unfortunately they're not cost effective at the moment. I'm going to try the bleeders. Thanks guys! -Marc.

 

[Rusty Nail]

hey are the '86 parts the same or different?
might be worth a look next time youre at the parts store.

 

[BadBowtie]

Still depends on if this 1987 has standard duty 11" brakes or the optional HD brakes. Build sheet code will answer that- If the rear axle wasn't also swapped somewhere in it's lifetime.

I would THINK with that drivetrain option she has the smaller 11" light duty brake system.

Checkout those wheel cylinders & replace that rear flex hose while you are this deep in....