rear brakes dragging

[Mike82ndABN]

I changed out my diff output seals, and while I was at it I also replaced the rear brake pads.

I twisted and pushed the pistons back in until they bottomed out.

When I put the new pads in and bolted up the caliper there was plenty of slack between the pads and the piston, which I took up later with the brake pedal.

I'm noticing that the rear rotors are getting really hot when driving and the vehicle shudders when coming to a stop, when I jack up the rear I can feel the pads binding on the rotor when I spin the wheels. I can pry the pads away from the rotor and get it to freewheel nicely, but as soon as i engage the parking brake they cinch up tight (which is good), but they don't back off.

I thought maybe I need to push the pistons in some more, so I took the calipers off again and pushed the pistons back in, short drive and they are binding again.

Parking brake seems good (its on the caliper), I have them set as light as possible at the moment and the spring loaded arm on the side of the caliper that the parking brake cable pulls on is resting against the stop on the caliper, so it shouldn't be engaged, there is no tension on it.

What am I doing wrong?

 

[Retiredwarhorses]

These are known issues with these trucks.....did you replace your guide pins?
did you put caliper grease on the pins and on the caliper brackets where the caliper rests?
once released, the pads just float and should rise and drop when no brake is applied.
its common to hear clicking while Coasting from the brake pads rising and dropping.
where did you get the pads? Factory pads should be beveled on the top and bottom edges to prevent shutter...does not always work though if it all tight till they wear in...which can take some time.
and then there is a damaged caliper...which may have happend when you compressed the piston...it works on a ratchet type system inside.

 

[HUMVEE1]

Some possibilities.....
does your pedal feel firmer after you have gone around the block ? Less pedal travel to accuTe the brakes when "hot"?
could be air in the line and as it heats and expands the air pushes the fluid both directions making the pedal feel excessively firm and slightly accuating the calipers.
Bleeding the brakes with proper fluid and backing off the master cyl. Plunge rod a turn could solve your problem.
Brake systems need a bit of play in them to compensate for heat expansion.

 

[Mike82ndABN]

I greased the pins, after cleaning them up with fine sandpaper, no rust, no pitting. Cleaned the teflon sleeves.
Pads are civilian, but they have a bevel cut on the leading and trailing edges. They also have a anti-squeal backing plate which probably takes up a bit more space.
I feel confident I didn't force the pistons back in, a little turning, then a little pushing, back and forth until they bottomed out.

These are known issues with these trucks.....did you replace your guide pins?
did you put caliper grease on the pins and on the caliper brackets where the caliper rests?
once released, the pads just float and should rise and drop when no brake is applied.
its common to hear clicking while Coasting from the brake pads rising and dropping.
where did you get the pads? Factory pads should be beveled on the top and bottom edges to prevent shutter...does not always work though if it all tight till they wear in...which can take some time.
and then there is a damaged caliper...which may have happend when you compressed the piston...it works on a ratchet type system inside.

 

[Mike82ndABN]

I may bleed them tomorrow to rule out air bubbles or other issues.
I am curious if it could be master cylinder related, I understand that when i hit the pedal it pushes fluid that can't be compressed, which in turn moves the piston, but what exactly retracts the piston ever so slightly so that it doesn't keep rubbing?

Some possibilities.....
does your pedal feel firmer after you have gone around the block ? Less pedal travel to accuTe the brakes when "hot"?
could be air in the line and as it heats and expands the air pushes the fluid both directions making the pedal feel excessively firm and slightly accuating the calipers.
Bleeding the brakes with proper fluid and backing off the master cyl. Plunge rod a turn could solve your problem.
Brake systems need a bit of play in them to compensate for heat expansion.

 

[HUMVEE1]

The primary and secondary return springs in the MC.

 

[Mike82ndABN]

Ok, so i'm thinking...

if i crack the bleeder valve and the brake caliper DOES release, then the MC likely isn't doing it's job and releasing pressure when i let off the pedal.

If i crack the bleeder to release pressure and the caliper DOES NOT release, then my piston might be stuck/seized (internal ratchet/screw on rear might be damaged).

I should bleed these things and see how much junk comes out, I just saw a youtube video where someone had rust and junk in the lines and it was acting as a one way check valve, preventing the pistons from retracting. When I pushed the pistons back in to install the new pads, I don't usually open the bleeder (I know some people do it that way but I try to keep the system closed), I could have pushed some junk back up the lines, especially with all the bending I did on the lines moving the caliper around.

 

[HUMVEE1]

Well maybe that's your problem. You put in thicker pads but still have the same amount of fluid In the lines and a simple brake bleed is all that is required.

 

[Mike82ndABN]

When you push the piston in, it just pushes it back up to the master cylinder, where the level gets higher (and I take out excess with a baster). I don't think you can have extra fluid since it doesn't compress. The fluid in the reservoir on the master cylinder isn't under pressure, system will work with the cover off.

 

[HUMVEE1]

That may be. I am basing my experience on a British sports car that had the brakes lock up last weekend during a race (of all times). Heck of a time to tell ya but I don't know squat about Humvee brakes. Just British sports cars.
Still, bleeding your brakes might help or solve your problem.

 

[Retiredwarhorses]

That backing plate is not used....I also ONLY use AM general and Hawk pads. This is what's used on the the Hummer H1 as well. The pads must free float. Did you replace the rotors?

 

[Mike82ndABN]

Bled the brakes, took out the shims on the pads, worked the pistons in and out a couple times to try and loosen them up in case they are sticking.

Still seems like they are dragging, the pads don't float, they stay tight against the rotor.

Has to be one of two things...
1. both pistons are seizing, whether it be due to corrosion or internal caliper damage.
2. brake pressure is not releasing, maybe junk in the lines or an issue with the master cylinder and the return springs or return vents, or the MC pushrod doesn't have enough slack to fully return to it's home position.

 

[Retiredwarhorses]

Disconnect one of the calipers. And cap off the line...then drive the truck.
those calipers are known to seize up...it's not uncommon. But it's also just as common for them to shudder for some time till the new,pads break in.....did you do rotors too?
i personally don't do pad swaps....I always do the rotors at the same time, or at least have them turned.
its cheaper to replace the rotor then to have them turned....or pretty close.

 

[Mike82ndABN]

I didn't replace the rotors, they are in good shape. I only changed the pads because I was doing the rear output seals and it seemed like a good time to put new pads in.

It definitely shudders. I've been checking rotor and pads temps after a drive, they are around 200 without heavy braking. Maybe this is normal and I am thinking they are seizing.

If i disconnect one caliper and drive it capped off, what am i checking for with that?

 

[Retiredwarhorses]

I thought you only had one sticking caliper? anyway...those brakes get hot, just from drving, especially when new.
i just did a set on a truck and just up and down the street they couldn't be touched, way to hot.
yoi could alway put the old pads on and see if you are having the same issue, not sure how worn they were.
and its always possible the pads are not to spec as they are after market....I only use AM general pads or NOS pads.

 

[Mike82ndABN]

It's both the rears. The main symptoms seems to be the shuddering once they get hot and the rotor temps being higher than the front rotors.

I'm tempted to try and bleed the master cylinder, i saw two methods, one was to remove it and use short hoses to feed the fluid back into the reservoir, and pump it until the air is gone. The other leaves it in place and has you crack the lines loose and pump to remove air.

Thanks for the input so far, if the shuddering is sometimes normal with new pads, i may just drive it more and keep an eye on rotor temps and see if it works itself out.

 

[Retiredwarhorses]

Is it shuddering only at low speeds? Usually when coming to a final stop is what I have experienced.
my 98 did this for years, would shudder badly at low speeds,in parking lots when the pedal was lightly applied, worked fine for regular braking....one day, it just went away.
but not till both calipers were replaced, both stub axles in the diff, both rotors, pads ....it was,under warranty back then from AM General....just didn't fix it....till several years later, now it's not a problem. But my hummer get less then 50miles a year on it.

 

[Mike82ndABN]

yea low speed coming to a stop, might just need to get driven more.

 

[Retiredwarhorses]

Sounds like it just need to be driven...this can happen if your rear diff stub axle are worn. That's is why the dealership replaced them. It's annoying as ****. Just drive around and ride the ebrake. If the rotors are over heating, they are going to discolor and glaze over.

 

[Retiredwarhorses]

You said the edges were beveled....you can always bevel them more with a grinder.