Clunk when braking in the rain

brakes

#1

First, thanks to all who gave me feedback with the vibration in my 87 Dak after changing the u-joints and carrier bearing. That problem is in the rear view mirror.

This problem is recent and only happens when it rains. When braking to a stop, I get a thunk or two. I only having hearing in one ear, so I have no idea where the sound might be coming from. I ruled out loose things knocking around. The last time I was driving in the ran, I got the thunking only the first one or two times I braked, and then nothing. Other times I have gotten it repeatedly in a single drive. I have never gotten it while braking except when coming to a stop. I don’t get it when merely slowing down in traffic or the freeway. I back into my driveway and I am wondering if braking in reverse has any bearing on this problem.

I searched here and on the internet. The problem exists out there as I have described it, but no posts that I can find have identified the problem. The truck has disc fronts and drum rears. I took the front tire off on the drivers side when I re-seated the front wheel bearings. I was going to repack them, but didn’t feel like pulling the caliper, so I just re-seated them. I repacked them not that long ago and didn’t feel it was worth the trouble at the time. I didn’t bother to pull the tire on the passengers side. While I was at it, I greased all the ball joints.

I can’t recall exactly when I first started hearing the clunking, if it was before or after the whole U-joint/carrier bearing campaign, but I became acutely aware of it afterwards, perhaps because that’s when we got a lot of rain. There is absolutely no driveability issues at all, just the clunk when braking to a stop in the rain.

If you have any suggestions on what to look at, or any experience with a similar behavior, please feel free to respond.

Jack


#2

Could this have anything to do with it?

http://www.clublexus.com/forums/car-chat/670071-why-you-get-temporary-brake-noise-after-wet-conditions.html

This site talks addresses a scraping/grinding noise, not a clunk, which is what I am getting. But the idea that a thin coating of rust on the rotors, which wears away after a few applications of the brakes fits right in with what I am experiencing.


#3

SOLVED - This is a weird one. It turns that the clunking is coming from the windshield wipers, and it only happens when the wipers are on and I am braking to a stop, under 10 mph. A few weeks ago the passenger side wiper got disconnected from the linkage. This happened years ago and I fixed it. I haven’t got around to fixing it this time. The rain hasn’t been intense and the driver’s side wiper works and procrastination set in. So it rains again today, and there’s the clunk when stopping again, only this time I notice that it is in rhythm with the wiper, so I do an experiment. I turn off the wiper and brake to a stop. No clunking. I turn on the wiper and brake to a stop. Clunking. I repeat with the same results.

I haven’t yet tore into the wiper linkage and motor, so I have absolutely no idea why the wipers are clunking only when braking under 10mph, but there it is. Being deaf in one ear, as I am, I cannot locate sounds and had no idea where the clunking was coming from, but my sense of rhythm is undiminished, and that is what enabled me to pinpoint the source of the clunking.

Jack


#4
A few weeks ago the passenger side wiper got disconnected from the linkage.

This would seem to be the cause of the noise (loose link hitting something)…let us know.


#5

But why do you suppose that the clunking only occurs when braking under 10 mph? With the wipers on, there is no clunking under any other ccondition. Before I tear into it I want to try one more thing. I want to see if coasting to a stop, without braking, produces the clunking.


#6

Who knows…it’s all guesswork…fix the linkage and go from there.
If that fixes the clunk, the ability of the loose linkage to move must have been a function of the forces applied to it under a certain range of deceleration G’s.


#7

It was the broken wiper linkage. Fixed that and no more clunk.