Non-Thunk: Noise/Clank; Does this explanation make sense (1 Viewer)

[ebod]

I get a noise in my 2004 LC that I've described in the past in the paragraph below. It's different from the driveline thunk. I took my truck to TLC 4x4 (local high-end landcruiser experts) and they told me not to waste $200 for them to inspect the suspension because they know what it is and it's a common problem. I'm sure I'm losing much of the technical explanation, but does the following description make any sense and does anyone else notice the same thing? TLC says that the noise occurs because either the ABS sensor or the brake fluid (I forget which they said) gets hot and causes a very slight delay in the pads hitting the rotors and then the pads kind of "slap" into the rotor. They say that the anti-vibration shims (or something) that are part of my brakes make the problem less bad, but don't eliminate it. Can anyone with actual technical skills interpret what I'm saying and tell me if it makes any sense?

DESCRIPTION OF NOISE. Noise when decelerating after a weight transfer (i.e., when decelerating after hard acceleration or when starting down a hill--it seems more connected to front/rear weight transfer than lateral weight transfer). The noise happens towards the beginning of deceleration when the vehicle is still moving but when weight is transferring from back to front (compared to driveline thunk which happens at stop/start). The noise is higher pitched than the driveline thunk. You can "feel" the noise a bit in your feet through the floorboards/or pedal. The noise happens only after I've been driving my car for a while.

For what it's worth, I haven't changed or turned my rotors for the past several brake jobs (rotors are thick enough to meet specs) and I do get a bit of a shimmy when decelerating at freeway speeds (from either pad deposits or slight warping). I'll probably change the rotors on my next brake job, but I've got a lot of brake life left. Any suggestions as to how to try to address the noise in this situation?

Thanks in advance.

 

[OregonLC]

Are you actually hitting the brakes or just letting off the gas? If it's the latter it has nothing to do with ABS, pad shims, etc. I'd be thinking something in the driveline, like perhaps a tired CV, wheel bearing, or u-loint. You could start isolating the problem by having a buddy ride with you to listen to see where the noise seems to be occurring - front, rear, or center. But you're right, driveline thunk is not harmonic. If you're feeling it in your feet it's something else.

 

[ebod]

It is when I hit the brakes (and only after I've driven for a while and heated things up). It does not occur merely by lifting off the gas.

Thanks!

 

[lexi4darin]

Have you considered that one of the calipers might be sticking? I've not heard of the explanation from TLC4x4 before. Nor does it make a lot of sense to me on the surface.

 

[OregonLC]

Have you considered that one of the calipers might be sticking? I've not heard of the explanation from TLC4x4 before. Nor does it make a lot of sense to me on the surface.

if it's the front they're not floating calipers so there's nothing to stick (four pots, two inside, two outside). the rears are single pots and do float.

 

[agaisin]

if it's the front they're not floating calipers so there's nothing to stick (four pots, two inside, two outside). the rears are single pots and do float.

Pistons can stick on a fixed caliper design, right?
I understand that floating calipers are notorious by design for having calipers sticking but at the end of the day even with fixed calipers, the pistons move in and out and if they are not moving freely (rust, dirt due to bad seals/boots or moisture in brake fluid) you can end up with sticky pistons - same effect.

Just curious to understand it better.

Thanks!