Author Topic: Rear Drums Sticking Only Going Forward  (Read 4972 times)

Offline Jon87V20

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Rear Drums Sticking Only Going Forward
« on: December 11, 2019, 08:56:53 PM »
Hi everyone,

Have a weird situation going on with my '87 Suburban V20.

About 300 miles ago, I had the gear ratios changed in both differentials and had the rear one rebuilt as well. They told me the drum brakes in the rear were shot and offered to replace the shoes and turn the drums while they were in there.

Today on the way home from work I felt what I thought was the rear passenger brake sticking a bit with each turn of the wheel and noticed there was an audible squeak each time it was grabbing.

When I got home, I jacked both rear tires up off the ground. I left it in neutral and made sure the parking brake was fully released. When rotating the wheel, sure enough I could turn it but there was a spot that it would grab quite a bit each time around. It was hard to figure out if it was happening on the passenger or driver's side because with the new LSD, both wheels have to turn.

The weird thing is, it doesn't seem to get stuck if I rotate the wheels backwards, only forwards. Both drums slid off pretty easily and nothing in there looks out of place to me, but I'm not sure.

I tried messing with the adjusters after putting the drums back on and it seems like the driver side is adjusted okay, but the passenger side, no matter how far out I run the adjuster, when I spin the wheel forward it gets really hard to turn. Since I messed with the adjuster it seems way worse now. I did make sure that the adjuster was going in the right direction, but all that does is change it from impossible to turn, to almost impossible to turn.

Even when it's almost impossible to turn forward, it will spin backwards all day with no trouble. I can't figure it out. The people that did the gears and brakes are over an hour away and I can't drive it there for fear of fire or overheating other components.

Any ideas?

Thanks!
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline Irish_Alley

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Re: Rear Drums Sticking Only Going Forward
« Reply #1 on: December 12, 2019, 08:04:13 AM »
from what i understand youll get less resistance from the emergency brake when you rotate the tires backwards. you can alleviate the issue with one tire turning backwards by setting one tire on the ground. to me it does sound like its an issue with the passenger side emergency brake. it maybe hanging up a little even with the parking brake released
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Offline VileZambonie

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Re: Rear Drums Sticking Only Going Forward
« Reply #2 on: December 12, 2019, 05:38:07 PM »
Post pics and ID which side is which in your pics.
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Offline Jon87V20

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Re: Rear Drums Sticking Only Going Forward
« Reply #3 on: December 15, 2019, 11:40:44 AM »
Vile,

I didn't see your post until I had put everything back together. Another thing I should've mentioned was only the front shoe is extending on the passenger side when the pedal is pressed. It almost seems like the wheel cylinder may be stuck on the rear facing shoe. Or is it normal for only the front one to move? Doesn't sound right, but I didn't know if that was by design.

Unfortunately, I didn't go compare this to the driver's side as I forgot to check that.

Maybe I just need to go pick up some wheel cylinders as they weren't replaced during the servicing?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline MIKE S

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Re: Rear Drums Sticking Only Going Forward
« Reply #4 on: December 15, 2019, 03:15:52 PM »
Make sure the shoe with the shorter brake lining is on the front shoe. I would search the internet and get a good understanding of the type of drum brake system these trucks use. They are called duo servo. When going forward and applying the brakes the rear half of the wheel cylinder is ineffective on this type of brake. I used to work on some old Fords back in the day with this type of system that only had half of a cylinder that only applied the front shoe and self energized the rear thru servo action.

Offline ehjorten

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Re: Rear Drums Sticking Only Going Forward
« Reply #5 on: December 16, 2019, 08:53:16 AM »
Pressure in the slave cylinder doesn't care what is happening outside of the cylinder.  It still applies the same amount of pressure to both the front and the rear cup.  You should see both shoes move when you apply the brakes.
-Erik-
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Offline VileZambonie

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Re: Rear Drums Sticking Only Going Forward
« Reply #6 on: December 17, 2019, 07:45:14 AM »
The hydraulic pressure is converted into mechanical force which has to overcome the seated spring tension on either side, which may not be equal due to many factors. Best thing you can do is strip down the brakes and clean the backing plates, lubricate the lands and replace all of the hardware. Make sure the shoes are in the correct position fully seated on the anchor pin and unaffected by the parking brake and that it is not hanging up. Often someone will adjust the parking brake to overcome improperly adjusted shoes so back off if they are not seated on the anchor. Replace or machine the drums and properly adjust the shoes, make sure the adjusters are clean and lubed so that they move freely. If the wheel cylinders are old and cruddy, replace them too.
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline bd

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Re: Rear Drums Sticking Only Going Forward
« Reply #7 on: December 17, 2019, 08:47:29 AM »
This ^^^^^

Make sure the lands aren't deeply worn, causing the shoes to stck.
Rich
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Offline Jon87V20

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Re: Rear Drums Sticking Only Going Forward
« Reply #8 on: December 17, 2019, 10:13:47 AM »
Sorry if this is a dumb question. What are the "lands"? I'm not familiar with that?
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline bd

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Re: Rear Drums Sticking Only Going Forward
« Reply #9 on: December 17, 2019, 11:24:44 AM »
The raised pads on the backing plate on which the shoes rest.  They are thrust surfaces that must be smooth.
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 Jon87V20

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Re: Rear Drums Sticking Only Going Forward
« Reply #10 on: December 17, 2019, 12:21:32 PM »
Okay thanks. I'll check that out next time I'm in there.

I thought I mentioned this in my first post on this but I guess I didn't. I noticed if I grab both shoes, it's easy to rotate the entire works from side to side. To be more specific, the shoes can move around quite a bit while pivoting on the top pin where the springs are attached to, sort of how a hammock would move.

It's been so long since I've worked on drums, I couldn't remember if that was normal or not. Seemed easier to do on the passenger side than the driver side initially, but seemed to firm up just a bit after I had moved the adjuster some.

Does this seem relevant or point to any issues, or is this normal?

I was thinking this may have had something to do with the vibration I was feeling before the sticking happened...
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline roundhouse

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Re: Rear Drums Sticking Only Going Forward
« Reply #11 on: December 19, 2019, 11:58:47 AM »
Check and make sure they didn’t machine the drums too large

Might want to try a new drum

Offline JohnnyPopper

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Re: Rear Drums Sticking Only Going Forward
« Reply #12 on: December 20, 2019, 11:47:19 AM »
The 'hammock' action is normal, and would indicate that the 'lands' are not rutted and binding.

Keep in mind that when you are not braking, the shoes and related hardware have to rest in a static position inside the drum, unmolested by a spinning iron surface. So the perceived slop is by design.
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Offline Jon87V20

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Re: Rear Drums Sticking Only Going Forward
« Reply #13 on: December 23, 2019, 10:16:56 PM »
Okay thanks guys. It might be some time before the weather gets better here and I feel like taking it apart again. I will post an update and some picture next time though.
1987 Chevrolet Suburban V20 Silverado
350ci TBI TH400 NP208

Offline 75gmck25

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Re: Rear Drums Sticking Only Going Forward
« Reply #14 on: December 25, 2019, 06:56:11 AM »
Several years ago when I had the brakes done on my 14 bolt FF, the shop had trouble finding a brake kit with all the right parts so they cobbled it together from more than one parts kit.  It works fine for braking, but my rear brakes now sometimes stick if I leave the parking brake on and the weather is cold and moist. 

I've learned to leave the parking brake off if parked for an extended time, since it sometimes takes quite a bit of throttle to get the shoes to break loose if it sticks in place.  Its also a PIA to even check the rear brakes on a 14 bolt FF because you have to pull the axle before you can remove the drums.  That little inspection hole doesn't give you much visibility.

Bruce