Default Drive train jarring while coasting in gear 

Old 04-25-2018, 06:29 PM   #1
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1979 CJ5 | Chevy 350 | T150 | Dana 30 | Performance Cam

In a failed attempt to locate source of my problem on the forum, probably for not using the right adjective (i.e. - drive train jarring, clanking, slamming back-n-forth etc.. ), I'll ask the question on a new thread..
Thanks in advance for any feedback!

While coasting in any of the 3 gears, I'm getting a lot of play (back-n-forth) slamming action from the rear end to tranny.
I'm sure some of this is attributed to the cam, causing a forward (jump) jerking action which then sends me on a roller coaster, slamming back-n-forth until i depress the cluch.
It only tends to happen when the tranny is aligned with the differential in a state when it doesn't know if it wants to accelerate or slow down.

I've had the rear end and pinion inspected; u-joints replaced. The tranny has been gone through as well.
I have noticed I have about 1/4 inch play when manually twisting the driveshaft by hand back-n-forth. but everything else seems tight.
I have read that this is normal, so long as there is not any up/down or in/out movement

Thanks again for any feedback that may help me pinpoint the problem area.

 

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Default Re: Drive train jarring while coasting in gear 

Old 04-25-2018, 06:51 PM   #2
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1/4" seems a bit much for back lash, but not egregious. Do you have a lift? What kind of driveshaft do you have? Stock, double cardan? What is your driveshaft slope angle? If you have a big lift with a stock driveshaft and an incorrect driveshaft slope, you could be putting the U joints in a bind.
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Default Re: Drive train jarring while coasting in gear 

Old 04-25-2018, 07:02 PM   #3
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Trying to describe your issue can get tricky, but that all we have to go on. The suggestion that Bass made is a good start. Are you getting any driveshaft vibration? You might also want to check the front wheel bearings for any play also. A picture of the rear driveshaft setup could help if you could.
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Default Re: Drive train jarring while coasting in gear 

Old 04-26-2018, 11:32 AM   #4
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Have you pulled the rear diff cover and inspected the R&P gears along with the carrier?
Are you SURE, you're in 2WD?
LG
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Default Re: Drive train jarring while coasting in gear 

Old 04-26-2018, 06:51 PM   #5
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Check your transmission mount really good. Motor mounts while you are at it. Love to see your driveshaft angles for reference. Do you have weak rear springs? Possibly causing axle wrap issues?

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Default Re: Drive train jarring while coasting in gear 

Old 04-26-2018, 08:23 PM   #6
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Thanks to all for the feedback!

I've included pics links below to help with the description.

It's a 3 inch lift, I believe the drive shaft is stock. I recently had the tranny dropped 3/4 inch with spacers (shown in pic) to reduce the amount of angle and stress on U-Joints. (Both u-joints have been recently replaced)
I will have to check the exact angle, what is the max angle one should use?

No driveshaft vibration to speak of.
I believe i could use new wheel bearings. However, I can say that the amount of jarring is not related to wheel bearings.

Positive i'm in 2 wheel drive. Which sparks an interesting thought.. When in 4 wheel drive the problem is minimal and almost unnoticed.

I can verify all mounts are solid as they were replaced with the new engine.
I don't believe axle wrap issues are a concern.

https://drive.google.com/open?id=0B4...8xQXV3aHIzOUY4

https://drive.google.com/open?id=0B4...dHQWZnclM0Uk00

https://drive.google.com/open?id=0B4...YwYy1RcXRZSFdv

 

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Default Re: Drive train jarring while coasting in gear 

Old 04-27-2018, 10:50 AM   #7
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I always mount the DS slip-spline buy the t'case to protect it from damage when off road.
Remove the front DS and go for a drive.
While you have the DS's out-Make sure the u-joints are 'clocked' at a true 90* to each other.
3" lift, is where I would think about using a shim under the axle pads of the rear axle for sure.
LG
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Default Re: Drive train jarring while coasting in gear 

Old 04-27-2018, 06:48 PM   #8
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Quote:
Originally Posted by Lumpy Grits View Post
I always mount the DS slip-spline buy the t'case to protect it from damage when off road.
Remove the front DS and go for a drive.
While you have the DS's out-Make sure the u-joints are 'clocked' at a true 90* to each other.
3" lift, is where I would think about using a shim under the axle pads of the rear axle for sure.
LG
Thanks for the tips, I will check

 

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