Hey all...
First off, truck is a '93 W250, 4WD, 12V Diesel.
Truck has 1 ton axels, and 4 inch lift.

Here is the issue:

Under light driving conditions, I have no problem. Basically keeping the boost under 4 PSI. However, it doesnt matter what speed I am at, anywhere from 10 to 70 MPH, if I start to put my foot down at all, the entire truck starts to shake violently. If I back off the throttle, it goes away.
Under light or no load conditions, there is no problem. Putting the truck in 4wd doesnt affect it at all.

So far, I removed the rear drive shaft. I checked the u-joints on both ends, both have fresh grease and move perfectly. The slip yoke also has grease and slides no issue there. Nothing seems loose either.

With the DS out, I grabbed the input flange to the rear diff. I wiggled it around in all directions, I could feel no play here.
I did the same to the transfer case. There was some play in the circular direction, but nothing that seemed abnormal. I believe it is chain driven, so I little movement would be expected.

I took the truck out for a drive with no rear DS installed. For some reason I could hardly keep it on the road... or get my speed up... I think I may have an alignment issue. However, when I put my foot into it, there was no shake.

So, all in all, I know I have an issue somewhere between the transfer case and the rear wheels. Unless the DS is completely out of balance, then it can be ruled out, and I think that would be noticeably all the time.

Can anyone tell me what could be causing this? I dont know what else I can check without tearing things apart, which I dont want to do at all if I dont have to. For reference, the rear axel is a DANA 70 with power lock.
The lift kit isnt that high, so the angle in the DS doesn't seem very excessive.

Any advice at all would be very helpful. Thanks!

 

One other thing... Rear tranny mount looks good and solid. I havent tried putting a jack under it but it looks fine.
Here is an odd thing. I just went out and lay down in the snow. I put the jack under the rear diff and lifted the whole rear axel up in the air. (the DS is still off) I then rotated the one tire, and both turned together. I then went underneath and turned the flange on the diff. Both wheel appear to be locked together through the diff... I cant get one to stop rotating or for them to move independently from each other... there is absolutely no play through the diff to the wheels... but it seems odd. I dont know if the Power-Lok is supposed to work this way... or if someone has modified the rear end... or if possibly the locking diff is stuck on?? ANy thoughts?

 

sounds like you have a limited slip differential if both tire spin the same direction. that is a good thing. it will help your truck get better traction. i know my ramcharger takes off real good with the LSD.

 

Ok update:

I got stuck on the front lawn... 6 inches of snow and no rear wheels lol... i got mad and threw the rear drive shaft back in... I still had the rear end in the air so I started her up and ran it through the gears... everything felt good. I left it in gear spinning and walked around the truck... looked good, good DS alignment. Put it back on the ground and took her for a rip... it was perfect! It was smooth as can be! I dont know what was going on before, but something was obviously misaligned or something... I changed nothing... I didnt mark the DS position, so it is possible it is 90 degrees from where it was but thats it... it drove like a champ!

Thanks for all the input! Seriously... im very pleased right now.

Also, with regards to the diff, I did some googling and found that I have a locked diff... so its never free to spin... sucks for turning, but great for snow and what not.

 

if it sucks turning then you are not going around the corner fast enough lol. have you taken it around a couple corners? if you go fairly slow around a corner you will notice the wheel hop it may have a locker. if you don't have the wheel hop then you most likely have a limit slip differential which only really lock when you stomp on the gas or are able to freely turn the rear axle.

 

Lol... Yup, for sure a locker.... Hops all over... The short wheel base and big tires make it more noticable...

 

lets just hope it is not a lincoln locker in there. you only do that to demolition or off road vehicle. not very nice when they eventually break free.

 

Not sure, but i dont want to open to find out either.... Im just glad she isnt shaking like a paint mixer anymore

 

It could be your injectors. My dads f250 7.3 would shake really bad when you got on it and we replaced the injectors and that fixed it.

 

I am going to bet it was the DS 180 out. I had that problem with my first Chevelle SS after I replaced the U joints. I could not figure out why the thing shook so violently when under hard accel. Well, I had stuck the DS back in 180 out of where it came out. Took 15 minutes to fix and I was so happy when it turned out to be so easy!