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U-Joints and Vibration

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mmaher94087 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mmaher94087 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2017 at 9:51pm
I may have missed where you said which wheels you have on the car but a few washers on the wheel studs may give enough clearance away from the hub to eliminate the problem.
Mike
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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2017 at 11:22pm
i dunno -- if you have possible multiple sources you just gotta get down and eliminate them (as possibilities) one at at time.

are you SURE your wheels are OK? how do yo know? if they're old steel AMC wheels i'd bet that they are bent.

jack the car up, put it in neutral, lay on your back, and shake the s**t out of the driveshaft at each end. if it moves AT ALL replace the U-joints. if it moves .010", less than the thickness of the cardboard in a book of matches, it will vibrate. and if the driveshaft is 40+ years old you mighty consider getting it balanced. 

jack the rear up, both wheels on stands, take the wheels OFF. (put on a couple lug nuts to hold the brake drum on flat and square. put it in gear and run it. 20, 30, 40 mph. if THAT vibrates, it ain;t the wheels, they're on the ground.

in neutral, not moving, engines do NOT vibrate. if the air cleaner is rocking all over the place you need a tuneup or something. you should be able to put a bowl of water on the engine at 600, 700 rpm idle in a stock engine and the water will ripple, maybe the bowl will vibrate a bit and fall off in a couple minutes. it shouldn't get tossed off. thats a problem.

bad motor mounts dont cause vibration, imbalanced cylinder firing causes vibration. bad motor mounts can cause weird problems and if bad enough allow the driveline to get out of line enough to cause vibration on the road. a half-fast test is to put it in gear with the brakes on hard, rev it up slowly (load it up) and see if the engine moves! a sligt shift is OK but if it lifts an inch or something mounts are bad.

on old cars that haven't been solidly gone through, very often problems like this have multiple, simultaneous overlapping problems that all interact. the only way to approach them is start on the obvious stuff -- old rusty steel wheels, bad U-joints, etc -- and go from there.

many times you end up going through some system entirely nto sure if its the problem, just to ELIMINATE that problem. most of 'em shouldn't cost too much (U-joints) and rarely will it be a waste of money.


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CamJam View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 12:38am
Thanks for your tips, Tom, but if you go back a couple posts you'll see that I fixed most of the vibration problem.  I had already changed the U-joints but that didn't help.  What finally fixed it was swapping the drive shaft 180 degrees at the rear U-joint, then using some hose clamps to re-balance the drive shaft.

I also had a vacuum leak that was causing some motor vibration.  As you said, they were indeed multiple, interacting problems.

I verified that the steel wheel was not the problem by changing it out with an extra aluminum one I had in the garage.  I'm going to measure the run-out right at the hub tomorrow with a dial indicator and that will tell me for sure whether or not the axle or hub is bent.  I think this might be responsible for the small amount of vibration that remains.

Mike, I did check the drum and hub and there is no weight interfering with the wheel. Good thought though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 9:45am
In '73, my brother had a '71 Gremlin. He was bound and determined he was going to run a set of 14x6 Cragar S/S mags. He discovered that, to make the mags sit flat, he had to remove the drum balance weights

Obviously, AMC didn't just randomly decide to tack a weight to the drum. The weight would have served a purpose. Minus those weights...what degree of imbalance was induced? Maybe not a lot, because the ride wasn't intolerable.
Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 73Gremlin401 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/15/2017 at 1:35pm
Since what is being described here is a cyclical harmonic vibration, not a constant one, part of the problem is radial tires.  AMC dealt with this issue on the large body cars with rather massive rubber encased steel weights that were bolted to the underside of the cars driveshaft tunnel about where the rear seat is located on Matadors and Ambassadors ordered with radial tires from the factory.  You'll find an explanation of this 'fix' in any AMC TSM from 76 on up, perhaps earlier.

My 73 Javelin AMX, a 3-speed/304 car that came originally with bias-ply tires had this exact same cyclical vibration when I installed a set of BFG Radial T/As.  I was able to get some of it gone by having the tires dynamically balanced on the car, a technique that so far as I know has gone the way of the DoDo, but was fairly common in the 70s and 80s.

I do agree that if you have a bent axle/hub on the rear, that part of your problem lays there.  But you may always have some degree of harmonic vibration in the car - something I'd put up with over going backwards in time and putting bias plys back on it. Handling and safety are far more important to me.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Jul/16/2017 at 6:37pm
Originally posted by CamJam CamJam wrote:

Thanks for your tips, Tom, but if you go back a couple posts you'll see that I fixed most of the vibration problem.

oops sorry, i read back, but enoug time passed i shoudl have started from the first post. sorry for the redundancy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/16/2017 at 9:02pm
Originally posted by tomj tomj wrote:

Originally posted by CamJam CamJam wrote:

Thanks for your tips, Tom, but if you go back a couple posts you'll see that I fixed most of the vibration problem.

oops sorry, i read back, but enoug time passed i shoudl have started from the first post. sorry for the redundancy.

No worries... you had some useful tips in any case.
'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
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