Strange knocking noise while coasting

[thrnelson]

I know, I know its hard to diagnose noises over the internet however I am going to throw it out anyway. I have been driving my Comet most every day now that I have the steering sorted and overall it has been driving quite well. With the exception of a strange knocking. When I accelerate it does not do it, when I am actively braking it does not do it but when I am coasting to a stop light it starts knocking. If I give it a little gas it stops. Has anybody experienced this.

[Rocket989]

I can't remember - does your Comet have a stick or auto?

[thrnelson]

Auto. What I believe is a "green dot" C4. If you put it in D then you have 2nd and 3rd gear. If you put it in "2" then you have all three.

[poboyjo65]

could be exhaust.

[thrnelson]

Loose exhaust it easy to check. I will look tonight. That would be nice because it should be easy to fix.

[poboyjo65]

Not necessarily loose ,just too close to something .

[CALIFORNIA CALIENTE]

I agree with John,sounds like something moves while coasting,hitting on something close,it does not take much movement to cause noise!! ROY.

[Lou's Comet]

Check your U Joints in the driveshaft.

Lou

[thrnelson]

I did not see any locations that should have been knocking on the exhaust. The U-joints are on the winter list. I will check them this weekend. I really want them to last until November when the salt falls and I start my long winter list of repairs and updates.

Thanks for the response.

[popscomet]

IF YOU HAVE BAD U-JOINTS.... don't put them off,,, they need to be replaced sooner then later....pop

[thrnelson]

Understood. Dropping a U-joint on the road would be ugly. I just hope its not the case and you know what hope can get you.

[lavron]

we always rocked the car back and forth to check for u-joint if it was in park or 1st just push and see if it will roll a bit forward and back, sometimes you can hear them that way as well, of course can get under and look but that means crawling under and trying to push and look.

See Ya,
Mike

[thrnelson]

I got under the car today and tried turning the drive shaft, it did not turn. Next I tried moving the shaft up, down and side to side. It moved about 1/16". It did not feel sloppy. Does anybody have any other ideas?

[Lou's Comet]

I got under the car today and tried turning the drive shaft, it did not turn. Next I tried moving the shaft up, down and side to side. It moved about 1/16". It did not feel sloppy. Does anybody have any other ideas?

There should be no movement in the U joint,,,,none. How did you check it? On the ground, or jacked up? Was car in neutral when you check them?

Again just guessing but a bad u joint will make noise when coasting, when you accelerate you are loading the joints and they won't make noise and when braking in essence doing the same, but when coasting they are not loaded and will clank/click/clunk if bad.

If you are checking them with car on ground, block wheels so car won't move. Put the car in neutral. If you are putting car on stands still put it in neutral. At front grab driveshaft with one hand and trans yoke with other hand, hold yoke still and se if you can twist driveshaft back and forth and try moving it side to side, up and down across axies of joint. There should be "no" movement in joint. Check the rear same way grab driveshaft and hold pinion yoke still and look for play. Again should be no movement.

Other things to check? Lug nuts all tight? a loose wheel would make noise coasting. Car a automatic? Maybe flex plate to torque converter bolts loose? Is the noise different when coasting in straight line compared to coasting turning left or right? Where does the noise seem to be coming from?

Lou

[vicegrip]

One more thing on u joints...You do everything you can to check while on the car.Everything is tight so they must be good,right? Not necessarily! You pull the joint apart and one bearing cup is dry,not quite bad enough to be loose but bad enough to cause popping and clunking. The only real way to check is to pull them apart.