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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: Jon87V20 on December 11, 2019, 08:56:53 PM
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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!
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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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Post pics and ID which side is which in your pics.
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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?
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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.
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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.
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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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This ^^^^^
Make sure the lands aren't deeply worn, causing the shoes to stck.
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Sorry if this is a dumb question. What are the "lands"? I'm not familiar with that?
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The raised pads on the backing plate on which the shoes rest. They are thrust surfaces that must be smooth.
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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...
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Check and make sure they didn’t machine the drums too large
Might want to try a new drum
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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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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.
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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
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Bruce can you remind us (well, some of us) what FF stands for? I know I'm going to feel dumb... :o
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Full Floater
The axle is simply a mechanical coupling to the wheel hub and supports no weight of the vehicle.
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Thx VZ, I'm smarter now ;D
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Sorry for reviving such an old thread, but I’m not sure it was worth creating a new one.
I pulled the drums off and completely disassembled the driver side. It looks like the lands are pretty beat up. Is it okay to try and clean them up with sandpaper? I really don’t want to pull the axles and replace the back plates right now. I just spent $270 buying new drums, shoes and hardware and the back plates aren’t cheap.
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It depends on how deeply the backing plate is grooved. If the grooves are shallow, using a sanding disc on a right-angle die grinder should work. Otherwise, the grooves can be filled by brazing and then trued flat with a sanding disc. Be sure to lube the lands with a dab of grease during reassembly.
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Thanks, bd. There's a pretty bad ridge on one of the lower lands on the side that wasn't even sticking so the other side is probably worse. That's a bummer. If I take the axles out to change the backplates, that doesn't involve any of the tolerances etc. that a professional has to set up right? You can just slide the axles in and out once you remove the pin? I just paid thousands of dollars to have both the front and rear differentials redone and don't want to mess anything up.
I was also wondering, is there a certain type of grease I should be using for the drum brake hardware, or is normal bearing grease okay?
Thanks again. I appreciate the help.
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Frankly, I would braze it up in place using a nickel silver brazing rod. No need to disassemble past removing the shoes. Viscous, white lithium grease is generally used to lube the lands and self-adjusters.
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I don't have any experience with brazing. Is that something anyone can do with a decent tutorial video or something?
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If you can solder or weld using a flame, you can braze rather easily. Otherwise, it's not a difficult skill to learn fairly quickly, but I recommend practicing on some scrap metal initially to get the hang of it so that you feel comfortable. Practice with flux coated brass rod on scrap pieces then switch to flux coated nickel silver rod to repair the backing plates. The biggest expense is in preparing if you don't have any of the equipment. You will need welding goggles and gloves, a torch setup, and gas(es).
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Just wanted to throw an update out on this. After finding most of the lands on the backplate were pretty beat up, I elected to just sand them a bit to take off any sharp or rough edges and put some fresh lithium grease on them. So far, things seem to be going well. However, I do still hear a bit of a squeak after several slow downs on the highway then rolling slowly in gridlock traffic.
I'm also still getting shuddering from the rear end under heavy braking. I'm wondering if maybe this has something to do with the combination valve (proportioning valve?). The reason I say that is, I've noticed when braking, I can feel a slight resistance in the first few inches of pedal travel where I can feel the truck actually begins braking, then further down with more travel, I hit harder resistance and there's significantly more braking force.
Could this be that the drums are that first grab I'm feeling happening way before the discs grab as well? I'm thinking the shuddering is maybe the drums are being way over-engaged by the time I have my foot hard into the pedal like that? To be clear, they are NOT locking up though.
By design, all four brakes in theory should be engaging at the same time correct? Isn't that the main function of that valve?
Hearing this, would anyone recommend looking at replacing the combo valve?
Thanks!
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Sounds like you need to resurface the drums.
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I just put some brand new ones on. They claimed to have resurfaced the old ones too.
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...and?
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I just meant that as a reply to what you said about resurfacing. Everything in there is new. Drums, shoes, and all the hardware. Still having some symptoms albeit not as bad as before.
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So you replaced the drums and it's still the same? If everything is as you say, it sounds like it's your front brakes.