Dragging rear brakes (2 Viewers)

[Cruisin']

I've noticed my rear brakes (disc) dragging on my truck. The first time I noticed it was after driving about 15min, and finishing with an uphill, followed by a couple of moderate stops. When I got out the brakes smelled, and had developed enough heat that the rear rims were warm to the touch. The fronts were cold, though there was warmth coming off the front rotors.

On recommendation from a mechanic friend (and a good one), I replaced the rubber line between the chassis and rear axle, since he said they can detereorate and get blocked up. I cut the old one up, and it looked fine, so I don't think this is the problem. The caliper slides are lubed, the pistons move properly, and the pads are not binding. I also visually checked all the lines to the front, and none are damaged or leaking. Since checking all these things I have found that the rears are still getting warmer than the fronts, though it hasn't gotten hot like the first time, even after a 30min highway drive.

I'm wondering if the proportioning valve could be causing a problem by either sending too much braking to the rear, or causing the pressure not to release after the brakes are off. The truck has no lift, and is not ABS.

I've searched, but haven't found any info on this particular problem. Any ideas?

 

[FirstToy]

bad wheel bearings?

 

[snowwolf]

Are your bell cranks siezing up? that happened on my rig and warped the discs

 

[Cruisin']

bad wheel bearings?

I ruled those out. With the calipers off they spin freely.

 

[Cruisin']

Are your bell cranks siezing up? that happened on my rig and warped the discs

Bell cranks? Educate me. That's not a term I'm familiar with.

 

[snowwolf]

Have you pumped out the pistons and and lubricated them up, sounds like pistons are jamming

 

[Downey]

I'm going to stick my neck out on this one because I think (could be dead wrong) that all FJ 80's came with rear drum brakes. If I'm right, that means you've converted to rear disc, and if you have there could be two possible problems:
(a) too much residual pressure on the rear brakes, thus keeping them applied slightly all the time.
(b) rear pads so thick that they drag on the rotors all the time. This situation improvers with wear.

If any FJ80's did come with rear disc, then flame my butt up and down the river, and tell me to stick to the FJ40 forum where I stand a prayer of knowing whats going on.

 

[Ebag333]

If any FJ80's did come with rear disc, then flame my butt up and down the river, and tell me to stick to the FJ40 forum where I stand a prayer of knowing whats going on.

I know that some of the early non-US FJ80's came with features that only the US FZJ80's had.

That being said, I don't know if disk brakes were one of those, and I suspect that they were not.



Crusin', have you checked the rotors to make sure they are not warped?

Also, some pictures may help the diagnostic process here.

 

[Cruisin']

I know that some of the early non-US FJ80's came with features that only the US FZJ80's had.

That being said, I don't know if disk brakes were one of those, and I suspect that they were not.

The Japanese model, which I have, came with a FF rear axle, with lockers, and discs.

I have not checked the discs for warpage. There is a slight surging felt when braking, so I would suspect some minor warpage though. Would this cause enough drag to get things hot?

Having said that, its time for an update. I've been keeping a close watch on this, and the problem seems to be going away (I hate it when stuff just sorts itself out, and you never really find anything wrong ). Perhaps the pad thickness comment has something to do with it. I did replace the rear pads recently.

 

[Cruisin']

I'm going to stick my neck out on this one because I think (could be dead wrong) that all FJ 80's came with rear drum brakes. If I'm right, that means you've converted to rear disc, and if you have there could be two possible problems:
(a) too much residual pressure on the rear brakes, thus keeping them applied slightly all the time.
(b) rear pads so thick that they drag on the rotors all the time. This situation improvers with wear.

If any FJ80's did come with rear disc, then flame my butt up and down the river, and tell me to stick to the FJ40 forum where I stand a prayer of knowing whats going on.

No need to flame. As I said in the previous post, the Japanese spec trucks did come with discs.

What could cause too much residual pressure on the rear brakes? This seems like what was happening.

I put new rear pads in not too long ago, so pad thickness could have been an issue, and would explain why it seems to be getting better.

Thanks for the comments.

 

[D'Animal]

Is your rig stock or lifted?


Post #32 in this thread may shed some light.

https://forum.ih8mud.com/60-series-...cing-rear-shocks-my-fj62-found-something.html




or not.

 

[Cruisin']

Is your rig stock or lifted?


Post #32 in this thread may shed some light.

https://forum.ih8mud.com/60-series-...cing-rear-shocks-my-fj62-found-something.html




or not.

I though of this. I don't have a lift though, so it shouldn't be a factor.

 

[Cruisin']

Have you pumped out the pistons and and lubricated them up, sounds like pistons are jamming

I haven't done what you suggested, however I pushed them in a ways with a c-clamp, and pumped them out a bit by the pedal, and they move freely, so I sort of ruled this out. Would any jamming be noticable by this method?

 

[FirstToy]

parking brake is siezed and dragging, pb pad is wearing down from dragging and freeing up?

 

[Cruisin']

parking brake is siezed and dragging, pb pad is wearing down from dragging and freeing up?

Checked that too. If anything the parking brake is adjusted too slack. As I mentioned earlier everything spins very freely with the calipers off, so I know its the disc brakes.

The other interesting thing to note is that it is both sides, not just one. Things like a seized caliper etc. would be very unlikely to happen to both sides, the same amount, and at exactly the same time. Whatever has been causing this I think must be upstream of the brake line tee on the rear axle. What could possibly cause residual pressure in the rear brake circuit, and not the front???

 

[Cruisin']

Bump and an update.

After a bunch of driving around this weekend, mostly short drives, I have found that the rear hubs/wheels are generally a bit warm compared to the front, and after one stretch the dragging seemed quite a bit more pronounced in that the rear wheels were quite warm to the touch. This was accompanied by some surging suggesting warped rotors.

Here's where I'm at: I'm pretty sure the rear rotors are a bit warped. This is a chicken and egg thing where I don't know if they warped because the brakes are dragging, or if the brakes have started to drag because the rotors are warped. I'm reluctant to get them turned until I know this for certian.

I'm positive the problem isn't wheel bearings or park brake for reasons outlined in previous posts. I also don't suspect calipers since its affecting both sides equally. I think it has to be one of three things:
1 pads too thick
2 LSPV malfunctioning causing residual pressure in the rear brake circuit
3 a master cylinder problem.

None of these are a super cheap fix, so I'm looking for more ideas of what to check before replacing parts. With the amount of mudders out there I'm sure somebody has encountered this before...

Thanks,
Jason

 

[Ebag333]

It certainly sounds like your brakes are dragging a bit. If it's only rear and not front, I'd suspect the LSPV.

For a cheap test you could swap the LSPV with a simple T fitting and see if the problem goes away. Be aware that if you have disc rear brakes they can and will overpower the front brakes, which can be dangerous in a panic stop situation.

 

[Todo]

Hey, thought I'd chime in and give my 2 cents on the topic at hand.

You stated that your parking brakes if anything, may have too much play in them, which got me to thinking. Did you know that our parking brake system is a Drum system? Our rig has a disc/drum setup on for the rear axle. I, just a few weeks ago (only had my 80 for a year) learned this.


The reason I know this and mention it is because I just recently replaced all the pads and rotors on my '96 80. Since I was combining this task with a rebuild of my front axle, I did not readjust/tighten the parking brake.

My thinking was that this would force me have to do the "one week later check everything you did to make sure it's still tight and not falling off yet" check. Much to my disappointment, my parking brake did not think this was such a good idea. I had made a series of short test drives that all went well - no noises, no problems, everything seemed good to go. However, 2 days later I was driving around in the parking lot at my local grocery store waiting for my wife (rather than parking, cause we all know that it's much more fun to drive our rigs than park them, right!). Out of no where I get this nasty grinding sound combined with a real heavy drag. Turns out that somehow the parking brake pretty much locked its self down, making it not such a pleasant experience to drive. I made the short trip (2 miles) home and by the time I got home the rear drum portion of the rotor was too hot to touch. I double checked and made sure that the caliper was functioning correctly and then I adjusted the parking brake. And since then I have had not problems what so ever.

Hope that helps or sheds some light for ya. check out the brake FAQ's for the 80, this one helped me a bit.
https://forum.ih8mud.com/80-series-tech/135349-parking-brake.html

good luck

 

[Cruisin']

Ebag, can you tell me what size/thread the fittings on the LSPV are so I can get the right tee? Its always easier to go into the parts store and actually know what you need!

I think that's the next thing to try anyway.

Cheers!

 

[Ebag333]

I don't know off hand. It should be the standard Toyota size though, they're pretty interchangable....