Brakes are "clunking"

[Knightspirit]

So I just upgraded my brakes to Defender calipers, rotors and pads. Before I did this, I had already replaced the master cylinder, proportioning valve and modulator unit (used one). So I had been having this weird clunk after stopping and releasing the pedal - feels like something didn't get bolted on or something - but of course everything is good. I thought maybe it would go away after installing the new calipers - but it is still there. My guess is the modulator unit - but I really have no idea what would cause this. Meanwhile the new brakes work GREAT - wow! They just have that weird release clunk. Anyone else experience this? I have the old modulator that I can re-install - just don't want to guess...

 

[Knightspirit]

Automatic gear box? How are the u joints.

Not that kind of clunk - it's in the brakes...

 

[LRDONE]

I would have someone get in the driver seat and replicate the clunk while you feel and look at everything. If you've gone through the brakes, its likely not the brakes. I just had a similar clunk with mine, my rear diff is now rebuilt and going back in this weekend. I would let off the brake and "clunk". While having someone else replicate it I could put my hand on the rear diff and it was obvious. That clunk resonated though the whole truck.

 

[Jimmy]

Not that kind of clunk - it's in the brakes...

It's this kind of thinking that will keep you from finding the problem.

Is it happening with the truck in park/neutral and sitting still, meaning is the suspension unloaded?

 

[robertf]

I had to replace the bushings on my pedal. had a clunk, but more important it wouldnt always return to the brake lights off position

couldnt find new ones, had to settle for less used bushings

 

[Knightspirit]

Let me redefine the "clunk" - might be a bit confusing. There isn't any kind of metal sound - like in the diff or in the U-joints. It's more like a releasing of pressure suddenly that you feel in the pedal, which is why I think it is the braking system and not something else - although I will definitely check those other things! It does not happen if you just push in the brake pedal while at rest - only after a complete stop - and not if you stop gently and release the pedal slowly as you stop. Very strange - in that it happens once you are completely stopped, and only after you remove pressure from the pedal. it's not like a U-joint or diff where you put it in gear and there is a clunk. Never felt anything like it - almost feels like the caliper isn't bolted and it slips. (yes - both calipers are securely bolted!) Also - and this could be coincidental - it only started after replacing the parts I listed (master, proportioning valve, modulator).

Update: Thump happens on release of brake after stop going FORWARD - and happens at the beginning of braking when going in REVERSE. WTF?

 

[Knightspirit]

I would have someone get in the driver seat and replicate the clunk while you feel and look at everything. If you've gone through the brakes, its likely not the brakes. I just had a similar clunk with mine, my rear diff is now rebuilt and going back in this weekend. I would let off the brake and "clunk". While having someone else replicate it I could put my hand on the rear diff and it was obvious. That clunk resonated though the whole truck.

Wow -that could be it, sounds exactly like what it happening. I will try that and see if I can feel anything! Thanks

 

[Knightspirit]

It's this kind of thinking that will keep you from finding the problem.

Is it happening with the truck in park/neutral and sitting still, meaning is the suspension unloaded?

Nope - not happening just sitting. Only when braking in forward or reverse - and then it changes from the release of the brake when going forward to the beginning of braking in reverse. Weird!

 

[robertf]

see if it goes away with difflock on

 

[Jimmy]

Nope - not happening just sitting. Only when braking in forward or reverse - and then it changes from the release of the brake when going forward to the beginning of braking in reverse. Weird!

To me, this screams not the brakes. Sounds tied to the loading and unloading of the drivetrain.
I need to wake up some more to wrap my head around what's going on. Lol.

 

[Siia109]

Since we are "spitballing" here - thinking of the forces the axle is seeing under braking (rotation) - could this be "slop" in the bushings of the lower link or the A-frame? if not its in the drivetrain.

Good news is there is not much back there that it could be. Of course expect the unexpected - I was hunting around for a metallic rattle when I hit bumps I was sure it was the shocks or loose muffler. Turned out to be the rear hydraulic step that no longer stayed up tight to the underside that rattled!

 

[Knightspirit]

I am going to start taking things apart at this point and look at every bushing etc. even though I have already replaced all of them. It seems like it is getting worse - so it should be easier to figure out! Still does it with the center lock engaged, although I am not sure what that tells me, lol. I'll post back when I get something....

 

[robertf]

check the splines under the rubber caps on the front axle.

 

[DiscoClay]

by chance, did you tune the master cylinder plunger depth in the booster diaphragm? There's an allen head in the plunger rod that (or the diaphragm seat..I forget which end it's on). That rod length is critical because if not calibrated correctly then the diaphragm will not release the master cylinder plunger and your breaks will stay engaged (or even clamp with more progressive force)... I only point this out because there may be a spot in the engagement threshold that may cause the diaphragm to flap open/closed.

*this is just a stab in the dark. But I have made the mistake of installing cheapo master cylinders and swapped boosters...without calibrating them first... only to regret the dramatic brake clamping that occurred. There are two valves that could cause slamming: the vacuum check valve and the internal biasing valve. It is a similar action as the slamming that occurs in waterpipes (in buildings). Again, not sayin it is.. but it may be worth a look.

 

[DiscoClay]

Also, maybe I missed it in the posts to this thread: if it only happens when the wagon is actually moving then you may want to check the radius arm bushings up front, and the trailing arms out back.. oh, and the A-arm balljoint on top of the rear diff.

 

[Knightspirit]

Also, maybe I missed it in the posts to this thread: if it only happens when the wagon is actually moving then you may want to check the radius arm bushings up front, and the trailing arms out back.. oh, and the A-arm balljoint on top of the rear diff.

DING DING DING DING! Just found the culprit:



New poly bushings coming! I guess I didn't replace these when I did all of my bushings - or if I did, I used factory bushes and they got eaten up by my 2" lift.

 

[Tugela]

Good find. You may need to replace the poly bushings again sooner than you expect as they tend to have a shorter service life than rubber bushings. I put poly bushings on my RRC but only kept it for a year after the changeover so not enough time to find out how they held up. Performance-wise they felt fine.

 

[DiscoClay]

DING DING DING DING! Just found the culprit:
<melted/worn-out radius arm bushings pic>
New poly bushings coming! I guess I didn't replace these when I did all of my bushings - or if I did, I used factory bushes and they got eaten up by my 2" lift.

w00t! The sun shines on a dog's ass every once in a while

 

[Knightspirit]

Whew - all done. What a pain! Not easy replacing the bushings in these parts and getting them back on. The good news is that all clunking, rattling and steering issues are now gone! Riding smooth...

 

[DiscoClay]

SWEET! Okay, so give us the details! Which parts did you change out? Just the radius arms or ..?