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U-Joints and Vibration

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Transmission & Drivetrain
Forum Description: If it's between the engine and wheels, it goes here
URL: https://theamcforum.com/forum/forum_posts.asp?TID=88489
Printed Date: Mar/29/2024 at 2:56am
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Topic: U-Joints and Vibration
Posted By: CamJam
Subject: U-Joints and Vibration
Date Posted: Jul/12/2017 at 8:35pm

I replaced the U-joints on my '72 Javelin today trying to cure a drive line shudder.  While I made a big improvement, it's still not perfect.  I have the same problem to a smaller degree in my '69 AMX and wonder if it's something I'm doing.

I made the mistake in the past of tightening the u-bolts too tight and distorting the bearing cups, so I know not to do that, and I marked the position of the driveshaft today when I took it off to make sure that the yoke and drive shaft went back together oriented the same way.

I also know to make sure that the U-joints are not binding after they are pressed back together.

I did notice that one of the U-joints I got today was made in China.  The other (a Spicer) was US made, and the cups seemed to be stronger. Anyone else had problems with the Chinese U-Joints from places like O'Reilly's and/or Auto Zone??

I'm going to try switching the drive shaft 180 degrees tomorrow, but just thought I'd ask for some ideas from you guys before I start chasing my tail.


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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD




Replies:
Posted By: 304-dude
Date Posted: Jul/12/2017 at 8:53pm
I donno, but long ago some where I read about how  to check balance of the drive line (Chilton or AMC) on installing a large band clamp may assist in seeing if there is an out of balance.

Marking 1/4 sections with a marker and placing the screw end on the mark. Rotate 180, 90 either way to see  were between the marks to place it. Some times 2 bands is needed for balancing.  


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71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker


Posted By: CamJam
Date Posted: Jul/12/2017 at 8:57pm

Thanks, James. I do know that trick. 

I'm also going to loosen the U-bolts just to make sure I got the cups properly seated in the saddles.


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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: POWERSTROKER7.3
Date Posted: Jul/12/2017 at 8:58pm
When does the shudder appear? Is it when you accelerate from a stop, on deceleration or is it a constant vibration reguardless of vehicle speed? Does it change if you are at speed and put the vehicle in neutral does it go away or still there? Is it at slow speeds or high speeds? These answers will help with the diagnois of your issue.


Posted By: Airdrie AMX
Date Posted: Jul/12/2017 at 10:33pm
If you haven't already, check and see if there is any weights missing of the driveshaft on either end they are usually welded on washers. A couple of other things to look for is a worn or broken trans mount, movement or worn splines on yoke, tailshaft bushing, driveshaft too short (not enough spline contact), loose pinion/ carrier bearings. Could be anyone of a number of things, just some things i'd look for.

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72 amx javelin 401 4spd


Posted By: CamJam
Date Posted: Jul/12/2017 at 11:48pm

This shudder is sort of a pulsation, and the frequency of it increases with speed for the most part.  Seems a bit more pronounced under acceleration. It's still there when coasting in neutral or decelerating, but it becomes more constant rather than pulsating.  You don't notice it under about 40 mph.  I can wedge my hand under the rear seat while I'm driving and the vibration feels quite strong there. That's right about where the rear u-joint is.

Thanks for the tips so far. There is a weight at the back of the drive shaft. I don't see any at the front.

I'll check the tranny mount first as that's an easy one.

Guess I should also check that the rear diff has enough gear oil.  I just bought the car a few weeks ago and haven't gone through everything yet.



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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: CamJam
Date Posted: Jul/14/2017 at 10:12am


The TSM does have some good information on diagnosing this problem.  I checked my pinion angle measurements and don't see anything out of the ordinary there, so I'm going to pick up a dial indicator from Harbor Freight today so that I can check the shaft run out too.




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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: CamJam
Date Posted: Jul/14/2017 at 5:09pm

I actually think I might have two things going on here.  I have some wheel wobble on the left rear.  It's not the wheel, so it's either a bent rear axle or hub-- and I have some engine vibration too.  When I'm going down the road, at highway speeds, at a certain speed it seems the two get in phase, which is when I get a sort of cyclic shudder.  

How much engine vibration is normal, I don't know, so I'll have to have someone more knowledgeable than me check it out.  When the car is parked it causes the steering column to vibrate at what I estimate to be around 2,500-3,000 rpm. There's no tach in the car so that's just a guess.

How hard is it to replace a bent rear axle and/or hub?  I guess I should just replace both pieces?



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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: mmaher94087
Date Posted: Jul/14/2017 at 6:43pm
Cameron, pull the rear wheels and see if the hub balance-weigh is interfering with the seating of the rim against the hub.

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Mike


Posted By: CamJam
Date Posted: Jul/14/2017 at 7:36pm

That's a great thought, Mike. I'll check it out in the morning.   I don't remember the drum having a weight, but I could be wrong.

In the meantime, I made things a whole lot better by inverting the drive shaft 180 degrees at the rear U-joint.  I also ran the car in gear on some jack stands and added some hose clamps to the drive shaft (following the instructions in the TSM) until I found the sweet spot.

I also found a vacuum leak causing a little miss in the engine.  It's not perfect yet-- I think I need to replace the carb spacer-- but it's an improvement.

Anyway, all-in-all the vibration's much better, though the LR tire is still definitely wobbly, so I'll look for a weight on the drum.


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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: mmaher94087
Date Posted: Jul/14/2017 at 8:51pm
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.

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Mike


Posted By: tomj
Date Posted: Jul/14/2017 at 10:22pm
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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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com



Posted By: CamJam
Date Posted: Jul/14/2017 at 11:38pm
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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'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD



Posted By: Buzzman72
Date Posted: Jul/15/2017 at 8:45am
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.

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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.


Posted By: 73Gremlin401
Date Posted: Jul/15/2017 at 12:35pm
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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73 Gremlin 401/5-spd.
77 Matador Wagon 360/727.
81 Jeep J10 LWB 360/4-spd
83 Concord DL 4-dr 258/auto



Posted By: tomj
Date Posted: Jul/16/2017 at 5:37pm
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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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com



Posted By: CamJam
Date Posted: Jul/16/2017 at 8:02pm
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.


-------------
'73 Javelin 360 (current project)
'72 Baja Bronze Javelin SST
'69 Big Bad Orange AMX (2018 Teague Heritage Award) SOLD




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