driveshaft vibration issues

[detroitmuscle1986]

I have been struggling with a driveline vibration for some time now. I have replaced the u-joints in the rear drive shaft twice with no cure to the issue. The vibration is worst traveling between 40 and 50 mph when you are off the gas and coasting. There seems to be quite a bit of play, both vertical and horizontal, where the slip yoke enters the transfer-case. I took this video today while under the truck for an oil change. Any ideas as to the the issue is would be greatly appreciated. The transfer-case is an NP205.

https://www.youtube.com/watch?v=T_zRf77C1rU

 

[NDT]

Is your rear driveshaft the correct length? Looks like the yoke is hardly in there.

 

[detroitmuscle1986]

I hope it's the correct length! It's what was on the truck when we first purchased it. Maybe some soldier threw a shorter DS on prior to auctioning it off?

 

[cucvrus]

Yes Sir that is definitely not right. That yoke shaft should be in that transfer case further then that. Is this truck lifted? And was the truck on the ground or hanging from a lift with the rear axle unsupported? I think that would definitely cause a vibration up to speed.
I have an M1028 A1 sitting here. Would you like a picture and weld to weld measurement on the rear propeller shaft?

 

[319]

Once had the same issue. Your drive shaft is too short. Yoke should not show that much.

 

[cucvrus]

Yes Sir that is definitely not right. That yoke shaft should be in that transfer case further then that. Is this truck lifted? And was the truck on the ground or hanging from a lift with the rear axle unsupported? I think that would definitely cause a vibration up to speed.
I have an M1028 A1 sitting here. Would you like a picture and weld to weld measurement on the rear propeller shaft? I wanted to add the last part so if you would like I can do this measuring and photo for you.​

 

[cucvrus]

I went out and measured the rear drive shaft on the 1986 CUCV m1028 A1 it is 53" weld to weld. I have some pictures to share. I hope they help. This is the truck I have listed in the classifieds. I also went out and measured an M1008 drive shaft. It was only 48.5 weld to weld. that may be the issue that you have.

 

[MarcusOReallyus]

I think cucvrus probably nailed it. That sounds like something a soldier would do.

 

[61sleepercab]

I had IH truck that would vibrate you out of cab at certain drive shaft RPM We jacked up one side and blocked frame and you could see drive shaft swinging in an arch from too long a shaft tube. Your slop at yoak at speed will alow shaft to start wobbling and raising ****. Get a look at a similar shaft on a example truck and measure right length drive shaft tube. MARK

 

[MarcusOReallyus]

That vibration can tear up a transmission, too.

Don't ask me how I know that.

 

[Keith_J]

View attachment 531106View attachment 531107I went out and measured the rear drive shaft on the 1986 CUCV m1028 A1 it is 53" weld to weld. I have some pictures to share. I hope they help. This is the truck I have listed in the classifieds. I also went out and measured an M1008 drive shaft. It was only 48.5 weld to weld. that may be the issue that you have.

Spot on. Someone swapped out driveshafts without consulting the parts manual.

 

[detroitmuscle1986]

That seems to be the issue! I will have to source a correct driveshaft and take the old girl off the road for a little while. I greatly appreciate you taking the time to take those pictures for me cucvrus and for all the help from the other members.

 

[NDT]

Find a local driveline shop and take your DS in there and have them re-tube it! That is usually cheaper ($200?) than trying to find a DS and shipping it.

 

[detroitmuscle1986]

I was just in the process of finding a local driveline shop online. I will try and get a quote from a place tomorrow. Lately I have been seriously considering swapping in an sm465 in place of the th400. This may just speed up that swap process!