Noise diagnostic advice needed

[TJM70's_48]

I took our my P15 for the first time this season.

When driving and in gear I have a metallic clunk noise when I take my foot off the gas pedal. Happened in all 3 gears and at all speeds and it sounded like it was coming from the area under me or firewall area. It almost sounds like two ceramic dinner plates clunking together.

The engine is running very well, I did a tune up a few weeks ago...it's starting well and driving nice and strong. I did change my transmission oil from hypoid oil to GL-1 yesterday. Noticed the noise after this. Probably a coincidence? Near the end of the season last summer I heard something similar on one or two occasions. But, this is more pronounced.

Any diagnostic advice that you can give me to help track this down? It does not sound good to me. If I have bottom engine noises would I hear them at idle? My biggest problem is always that I have nothing to compare to.

[Plymouthy Adams]

have you gave time to inspect the rear mounts both sides of the bell housing..could be a bit of rocking on loose/compressed rubber attributing to the noise

[TJM70's_48]

I will check anything you suggest!

I thought maybe the drive shaft was loose, but I can't get any movement by hand...I really didn't know where to suspect or begin looking. I would like to be able to create it manually while I'm under the car or at least come close so I get the right thing.

[Don Coatney]

You should also inspect your rear suspension. Could be a spring shackle or bad bushing. Also inspect the U-bolts that attach the rear axle to the springs.

[desoto1939]

If you have stopped the car and the engine is running. Then put it in reverse start to back up do you get a clunk sound or do you get the same when taking off from a dead stop.

This would more likely be the universal joints and if you have the old style pin and trunion then then might need some lubricate in the housing or might need to replace the ujoints.

Rich Hartung

desoto1939@aol.com

[Young Ed]

If you have stopped the car and the engine is running. Then put it in reverse start to back up do you get a clunk sound or do you get the same when taking off from a dead stop.

This would more likely be the universal joints and if you have the old style pin and trunion then then might need some lubricate in the housing or might need to replace the ujoints.

Rich Hartung

desoto1939@aol.com

That type of noise can also be from rear drums not tight enough and moving back and forth against the keyway. If you have that you will only get 1 clunk per switch from reverse to forward. The original poster said he gets the noise in all 3 gears so I don't think thats his issue.

[TJM70's_48]

No...the noise I am experiencing only occurs when the car is moving. Not upon acceleration but only on deceleration; when in gear and just about at the time I lift my foot from the gas pedal. It happens when the car is in any gear - not only when gearing down or when in second for example...

Other than a visibly bad or missing bushing, how else can rear suspension issues be diagnosed?

[greg g]

exhaust pipe hitting against the frame some where???

[1947PLEVY]

Drive it about 25mph and tap the gas pedal. If it makes noise then...probably a u-joint. If it does it under a load probably a mount or exhaust system. Possibly spring from pressure plate.. So many possibilities..Wheel bearing????

[maverick]

it might could be that the thrust washers on the cluster gear in the transmission are worn causing it to move back and forth in the housing.

[TJM70's_48]

I knew I would get a lot of possibilities...I just don't have the experience to even narrow it down to a list of suspects. So this help, based on my vague description, is very appreciated.

Some of these things I can figure out myself, some tests where indicated in a post...if none of these turn up the culprit, then I'll have to find a mechanic who can help.

In about 2 weeks I'll have some time to devote to working on it and will be sure to post results and additional questions.

[P-12 Tommy]

It's a shame none of us could be there to listen. Sounds like u-joint. My 2 cents.

Tom

[Don Coatney]

Other than a visibly bad or missing bushing' date=' how else can rear suspension issues be diagnosed?[/quote']

then I'll have to find a mechanic who can help.

You answered your own question.

[TJM70's_48]

Don...I'm trying to do the work that I can do on my own...so if I can figure it out I'll tackle almost anything. I just have a lot of learning to do. I messed around with cars a bit as a kid, but then have only done oil, brakes and the occasional odd job like a gas tank or sensor here and there on my new cars.

Those of you who have been around these cars, or cars in general, to build up a lifetime of knowledge are very fortunate. I agree with P-12 Tommy...one of you could listen and probably nail it right away.

I crawled under there last night and my rear spring mount on the drivers side does not have a bushing. Maybe that's a lead in the right direction. In any even, it's something else that needs to be fixed. On a growing list.

Thanks again for the helpful comments and for the info. I appreciate all of them.

[Niel Hoback]

If you don't have a bushing, (silent block), in a rear spring, you have found your problem.

Changing from coast to accel to decel makes the axle move forwards and backwards under the car. No bushing means metal to metal as the axle moves the spring front to rear.

Just for fun, cut yourself a piece of an old tire and jam it in there just to see how much quieter it is.