Weird problem with brake pedal engagement and touchy rear brakes

k1n3k

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Alright, this one has me stumped. I am by no means an inexperienced mechanic. I have worked as the lead fabricator in an offroad shop building high end crawlers, built more engines, axles, doublers, transmissions, t-cases, etc, than I can count, I worked as a machinist for years and have been heavily into turning wrenches professionally and as a hobby for over two decades.

However, this one has stumped me. There is 5 feet of snow outside and I no longer have a garage. I have exhausted my ideas and before I drive an hour to the nearest garage and tear this thing apart for the 4th time looking for this issue, I'd like some advice from Jeep TJ experts.

I have a 1999 TJ with a dana 44 rear. every single suspension component is brand new with a factory replacement. Springs are a 2" lift and the whole thing sits on a set of 31s. Its my DD. On random occasions with no rhyme or reason, when I hit the brakes, the pedal has a quicker engagement and the rear axle will bang, with the rear brakes getting extremely grabby. The bang is similar to leaving the rear seat folded then having it flop down to the floor. Its attention getting, loud, and can be felt through the vehicle. I have made sure the latches were latched on the rear seat, I have disassembled the rear brakes looking for any issues or fluids, and it checks out. I checked the drums for cracks, I checked the control arm bolts for correct torque. I have excellent pedal feel all the time but on the occasion the brakes get grabby there is a less travel. When the rear end does bang, the pedal drops to its normal place. When it does happen, if I apply the brakes lightly I can keep them from locking. when they do grab, it locks the whole rear axle. This whole scenario is random. I'd say 10 our of 1000 brake presses, but they happen in clusters, still random but with more frequency then they pretty much go away for a while. I don't believe it to be a issue with the read diff because I can modulate it. Every single time it happens, its below 35 mph. Never has happened above that.

I am stumped. Any ideas are welcome.
 
Can the proportioning valve be a factor?

Can the e-brake be doing something screwy?

Just throwing it out there with a bump to keep your thread alive.
 
I'm waiting for Mr. B or Jerry to school us...but my guess is the e-brake is snagging on something.

How's the corrosion situation?

-Mac
 
Alright, this one has me stumped. I am by no means an inexperienced mechanic. I have worked as the lead fabricator in an offroad shop building high end crawlers, built more engines, axles, doublers, transmissions, t-cases, etc, than I can count, I worked as a machinist for years and have been heavily into turning wrenches professionally and as a hobby for over two decades.

However, this one has stumped me. There is 5 feet of snow outside and I no longer have a garage. I have exhausted my ideas and before I drive an hour to the nearest garage and tear this thing apart for the 4th time looking for this issue, I'd like some advice from Jeep TJ experts.

I have a 1999 TJ with a dana 44 rear. every single suspension component is brand new with a factory replacement. Springs are a 2" lift and the whole thing sits on a set of 31s. Its my DD. On random occasions with no rhyme or reason, when I hit the brakes, the pedal has a quicker engagement and the rear axle will bang, with the rear brakes getting extremely grabby. The bang is similar to leaving the rear seat folded then having it flop down to the floor. Its attention getting, loud, and can be felt through the vehicle. I have made sure the latches were latched on the rear seat, I have disassembled the rear brakes looking for any issues or fluids, and it checks out. I checked the drums for cracks, I checked the control arm bolts for correct torque. I have excellent pedal feel all the time but on the occasion the brakes get grabby there is a less travel. When the rear end does bang, the pedal drops to its normal place. When it does happen, if I apply the brakes lightly I can keep them from locking. when they do grab, it locks the whole rear axle. This whole scenario is random. I'd say 10 our of 1000 brake presses, but they happen in clusters, still random but with more frequency then they pretty much go away for a while. I don't believe it to be a issue with the read diff because I can modulate it. Every single time it happens, its below 35 mph. Never has happened above that.

I am stumped. Any ideas are welcome.

From what you describe, the shoes are grabbing from too much slack at the anchor pin. How are you adjusting them? Be very specific.
 
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Sounds like the top edge of the leading shoe is getting into the drum before the rest of the shoe makes contact.

To get a good picture of what's going on, pull the drums, clean up the shoes with brake cleaner, shoot them with a light coat of primer, put the drums and wheels back on and lightly drag the brakes for a bit....then pull the drums back off and lets see what the shoes look like.
 
From what you describe, the shoes are grabbing from too much slack at the anchor pin. How are you adjusting them? Be very specific.

Had similar issues on my 97 f150 rear brakes when they would be out of adjustment. A specific model of forklift would do similar things as well. Only the ford had similar pedal touchiness.
 
Also, it obviously has not been doing this since day one....when did the problem begin to occur, and what changes/services/etc occured directly before that point?
 
Alright, Improper adjustment seems to be a common thought here. More Backstory on this rig, I have not owned it long at all and have never done the brakes on it. I did check the adjusters to see if they were free HOWEVER as the pedal felt good I have never adjusted them. The E-brake is out of adjustment as well indicating it has been some time since the last service, but there is still about ~1/4" of material on the shoes. Maybe 3/16", somewhere in between those two.
So with that said, what is the proper adjustment procedure for the rear drums? I'll run through that after I replace the radiator... And maybe get the heater relay plug swapped out, and replace the clockspring, and fix the sliding window latches, and replace whatever is squeaking in the accessory drive... This thing has a list.
 
Just for the record you’re on the best forum if you want good practical experience- I say that because it’s impressive that you would come to us with what you do- And I wanted you to know you’re not at the wrong place.

I don’t have a lot of drum brake experience and I’m not going to embarrass myself pretending, but stay on here and you will get good advice.

I was thinking earlier that it might be a good idea to just disconnect the emergency brake completely short term and take that out of the equation in case it is acting up.

Good luck and we are honored you logged on.

Andy
 
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... what is the proper adjustment procedure for the rear drums? ...

With the resume you posted at the top, I would think we should ask you that. It's the same procedure for any drum brakes for the last, oh, 70, 80, 90-ish years.

But I see you're young, and maybe haven't messed with drum brakes much. There is a FSM available here, and there is an adjustment section at page 5-27.
 
With the resume you posted at the top, I would think we should ask you that. It's the same procedure for any drum brakes for the last, oh, 70, 80, 90-ish years.

But I see you're young, and maybe haven't messed with drum brakes much. There is a FSM available here, and there is an adjustment section at page 5-27.

Thanks for the FSM. That is always helpful to have.
I ask for the procedure *because* I have worked on a ton of drums over the years. Some are different, but most are similar. As I'm sure you're aware, adjusting the brakes on a 1953 beetle is not the same as a 1970 Chevelle, and different still from a 1987 samurai. But in all cases, I've found the best result is to just ask the experts or RTFM. Brakes are important, and not something to guess at.

When I inspected the rear brakes, I simply pulled the drum off, inspected wear on the drum and shoes, inspected the hardware for damaged, loose or missing components, and slid the drum back on. I had deemed no adjustment needed as the pedal feel was good. Usually when they are out of adjustment there is excessive pedal travel.

I'll have the brakes apart again this weekend, I'll post an update on what I find.
 
Could one of the pistons in a wheel cylinder be hanging up causing it to grab if its adjusted right? Something violent like that should become apparent on the shoes or hardware rather quickly.The way you say it locks up the whole diff is odd though. I'd probably pull the cover and have a look see at everything.

Jack stands or a lift,stethescope and a buddy might help you recreate and pinpoint the bang?left,right etc
 
The way you say it locks up the whole diff is odd though.

I did neglect to mention it has an LSD, or... something. The previous owner had put a new read diff in it 10+ years ago, and he *thinks* its a grizzly but I've not had any of the oddities occur that typically happen with an auto locker. So I'm not sure what it has but there is for sure something in there. From my research on this rig it came with an LSD from factory and it drives like it has an LSD rather than a full locker.
 
I would look at the upper control arm connection to the rear differential. That point may be oblong and causing the intermittent issue of banging when engaging the brakes,

When the suspension unloads it goes back to the normal position for it to happen again


II’m spitballing here, but that sounds like a suspension issue
 
All of this is kind of similar to what's going on with my 99. - @mrblaine?
Except when it happens, it pops, does a whew-whew-whew little squeaking, and makes the front right grab and jerk.
Randomly. And then it drives and brakes smooth as silk for a bit. Then Randomly starts again.
Everything up front is new, all brake components are new, new tires, all balanced, 26 psi, new steering, new steering knuckles, all brakes fluid flushed multiple time, all ball joints new, all U-joints new, every single rear brake drum components, all adjusted and checked multiple times, everything except Proportioning valve, and the rear center brakes line have been replaced, and that's next.
Only 5k or so miles on all that, and this is driving me nuts, at the end of my wits with this.
@AndyG Has seen all of the work done to it.
Any advice is welcome,
 
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Have not forgotten about this thread, and still have not fixed the problem. Shortly posting this thread, the petcock on the radiator decided it had enough of life and proceeded to break. Then after getting the Jeep home, we ended up getting storm after storm until the jeep was buried to the top of the mirrors in snow. Soooo being as I had my truck and no desire to replace the radiator in the cold, it sat. Last week the truck failed me, and the radiator was the easier fix so I gravitated toward the jeep again. No issues with the brakes yet on the jeep since the snow. Will update this as I find more info.
 
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Have not forgotten about this thread, and still have not fixed the problem. Shortly posting this thread, the petcock on the radiator decided it had enough of life and proceeded to break. Then after getting the Jeep home, we ended up getting storm after storm until the jeep was buried to the top of the mirrors in snow. Soooo being as I had my truck and no desire to replace the radiator in the cold, it sat. Last week the truck failed me, and the radiator was the easier fix so I gravitated toward the jeep again. No issues with the brakes yet on the jeep since the snow. Will update this as I find more info.

What? No pictures of the Jeep buried?

-Mac
 
All of this is kind of similar to what's going on with my 99. - @mrblaine?
Except when it happens, it pops, does a whew-whew-whew little squeaking, and makes the front right grab and jerk.
Randomly. And then it drives and brakes smooth as silk for a bit. Then Randomly starts again.
Everything up front is new, all brake components are new, new tires, all balanced, 26 psi, new steering, new steering knuckles, all brakes fluid flushed multiple time, all ball joints new, all U-joints new, every single rear brake drum components, all adjusted and checked multiple times, everything except Proportioning valve, and the rear center brakes line have been replaced, and that's next.
Only 5k or so miles on all that, and this is driving me nuts, at the end of my wits with this.
@AndyG Has seen all of the work done to it.
Any advice is welcome,
I believe I finally figured it out, fingers crossed, so far so good.
Finally realized that the PO had bent the backing plates on the rear drum brakes.
So after much work and days I won't describe here, I straightened, bent, ground, trial fit, replacing drums again, new axles, new spider gears, and after three years, smooth, no noise, no vibration stops.
PO probably pried on the backer plates, trying to remove stuck drums.
They have to be straight, because all the working parts ride on them.