Mystery Clunk When Backing Up Solved!
 

Awhile back I posted about having a weird clunk when backing up. I can find the post, but I thought I'd post that I accidentally fixed/figured out the cause. Last month I pulled my brake pads and scraped off the "glue" type anti squeal and replaced it with anti squeal grease. I did it because I had developed a squeal during low speed braking like in stop and go traffic. Very annoying. I had intended to replace it with new "glue" but my bottle was all dried out and the auto supply store didn't have any. So I went with the grease.

The grease worked and no more clunk when backing up! So, maybe the "glue" isn't the best way to go for anti squeal. I don't know, but seems to work and it eliminated another problem.

Brake pad clunk is not uncommon on many cars, when brake pads get worn. They can shift in the caliper when the vehicle changes direction (forward to backwards etc.).

Calipers with anti-rattle springs on the pad ends are usually immune to this, although they can be an issue if the springs get old and lose tension.

The fresh anti-seize grease may fix it for a while but I bet if comes back - usually does. I replaced my pads when this last happened to me.

Interesting. In my research I found that Akebono pads, which I have, are supposedly prone to this. We'll see what happens. I have lots of pad left.

This video shows the issue, from about 3mins..

https://www.youtube.com/watch?v=zcww690JiKQ

Aren't the anti rattle clips on our brakes there to stop that?

Another thing that can add to the problem is that a ridge of rust develops on the brake rotor after sitting for a while, worse with humidity and different rotor/pad materials, that will get better with driving though.

Aye, that they are.... ;)

The basic issue is that the pads need to "float" in the caliper frame. The fit needs to be loose enough to allow movement for perfect pad-disc alignment but be tight enough not to allow the pad move and make a clunk. There are several springs on the calipers to dampen any excessive movement, but they are (clearly) not 100% effective... :rolleyes:

I suspect that this becomes more of an issue as the guide pins age, wear and get "gunky". This causes the pads to not "retract" from the disc as much as when working properly, allowing the disc to "rotationally shove" the pads back and forth a little in the caliper frame when the vehicle is changing direction or when the brakes are applied. This hammers the pad backing plate and the caliper frame, increasing the clearance and therefore the movement.

Sometimes you can get a small clunk when applying the brakes. Same issue - same cause - the pad has slight play in the caliper frame.

Makes sense.

I’ve been chasing a clunk for months! I know it is not suspension. I’ve gone over lot bumps just to test. I’ve used a large pry bar with wheel weight on and off to check components. I was ready to replace the RR link. New rear wheel bearings will go on soon. I’ll check the pad for movement. I’ll order new slide pins.