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U-Joints and Vibration

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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 Topic: U-Joints and Vibration
    Posted: Jul/12/2017 at 9:35pm

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.
'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Jul/12/2017 at 9:53pm
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.  
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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/12/2017 at 9:57pm

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.
'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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Post Options Post Options   Thanks (0) Thanks(0)   Quote POWERSTROKER7.3 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/12/2017 at 9:58pm
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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Airdrie AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/12/2017 at 11:33pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/13/2017 at 12:48am

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.

'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2017 at 11:12am


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.


'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2017 at 6:09pm

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?

'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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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 7:43pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote CamJam Quote  Post ReplyReply Direct Link To This Post Posted: Jul/14/2017 at 8:36pm

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.
'69 Big Bad Orange AMX 390
'72 Baja Bronze Javelin SST
'70 Opel GT
'07 BMW 335i
'13 Ford Focus ST
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