: Noise Source Question



benda
01-08-07, 12:13 PM
new owner of a '79 CDV and i can't figure out the cause of a noise coming from the rear of the vehicle. the noise is cyclical and is dependent of speed of wheels, but cannot be heard at slower speeds. sometimes more noticeable when turning. definitely only happens under engine load, when coasting or stopped there is no noise.

i suspect it could be coming from the rear end, u-joint or a rear wheel bearing, but these symptoms seem to be shared between all 3. any ideas what i should look for to better find the source of the noise?

vehicle info: 1979 coupe deville, 180,000 miles, rebuilt transmission (2002). Purchased the car a few weeks ago, transmission fluid was clean but 2 qts low, rear end fluid was dirty and 1 qt. low. differential gears did not show physical damage or discoloration.

transmission fluid leaks from around pan, but slowly (1 drop per day is my guess). rear end fluid does not leak from cover. all fluids topped off currently. first noticed noise after i had the car a few days, and fluid level checks and changes did not improve the problem - possibly made the noise louder.

thanks.

carnut
01-08-07, 09:25 PM
Best guess, rear u joint. Add some weight in the rear to affect the pinion angle and see if the noise moves to a different RPM range. If I recall this is a constant velocity dual u joint that bolts up to a flat flange on the differential. You might unbolt it and flex the joint by hand to feel if it binds in any direction. Usually a drive shaft re-builder has to repair these because of the re balance issue. Another thought, could you rotate it 90 degrees and bolt it back up? see if that changes the symptom.

brougham
01-08-07, 11:18 PM
That kind of noise can be from a few things. The easiest way to deal with it is to just take it to the garage that youre goign to get to fix it and get them to look at it. If its a u joint you can grab the drive shaft and try to move it around to check for play. And if thats what the problem is anyone who knows what theyre doing can change it it has nothing to do with balancing.

benda
01-09-07, 08:33 AM
thank you, i will look into it this evening.