Axle shifting on acceleration

[kartoffelpuffer]

I have a '94 C1500 that I just recently picked up. It has 2" drop shackles in the rear but is otherwise stock. Overall the truck runs and drives great. It's quiet, tracks straight down the road and handles well for a 24 year old truck. However, I'm having an odd issue. When I take off from a complete stop I can feel some sort of shifting. The only way I know how to describe it is that it feels like the axle is loose and rotating. It feels similar to issues I've had on linked 4x4's with a worn out joint that allows the axle to shift during acceleration or deceleration.

But this truck has leaf springs so, I don't think that's the issue. It does this even with moderate acceleration so I'm pretty sure it's not axle wrap. Plus it's a 305.... Could a worn out leaf spring bushing cause this? I would think if a bushing was bad it would cause the truck to track funny. I've read a lot of post about slack in the rear diff or slip yolk. Which I've had with other vehicles and there is always an audible clunk with those. I don't really hear anything with this I can just feel it in the seat of my pants.

I'm going to try and get it on the lift this weekend but wanted to see if anybody had an suggestions of what to look at first.

 

[sewlow]

Check the diff.'s U-bolts & the lower plates that they go through.
These trucks are known for those to rust out.
Those lower plates are cupped, so they hold water & any other road crap that lands in there.
The plate's bolt holes can elongate.
The part of the U-bolts that you can't see will get really skinny from rust, too.
Someone installed those drop shackles. Did they do it right? Check those for tightness while you're under there.

 

[Aarong23]

Check the diff.'s U-bolts & the lower plates that they go through.
These trucks are known for those to rust out.
Those lower plates are cupped, so they hold water & any other road crap that lands in there.
The plate's bolt holes can elongate.
The part of the U-bolts that you can't see will get really skinny from rust, too.
Someone installed those drop shackles. Did they do it right? Check those for tightness while you're under there.

I was gonna say it, but sewlow beat me to it. Rusty u bolts is are a problem especially if you live where there's snow and salt. Get ya some new u bolts and you should be good if the bottom plates are good. I'm all about preventative maintenance, so it wouldn't hurt to change the u joint while you're in there working on the ass end.

 

[Hipster]

The leaf pack center pins tend to get crusty and disintegrate allowing stuff to slide around as well

 

[kartoffelpuffer]

Thanks Guy's I'll definitely check the U bolts and plates. However, I doubt its related to rust. I don't think the truck has ever seen salt and the underside is super clean.

I am curious about the drop shackles though. To me they look like they are backwards, but I've never installed any so I'm not sure. But the open side of the C channel is facing the rear. I would have thought it should be facing the front so that you could utilize some of the other holes in the shackle.

 

[someotherguy]

And this is on a truck that wasn't even from a rust area. Just a collection of dirt in the saddles and lots of moisture...

You must be registered for see images attach

Richard

 

[kartoffelpuffer]

And this is on a truck that wasn't even from a rust area. Just a collection of dirt in the saddles and lots of moisture...

You must be registered for see images attach

Richard

I'll definitely check them. I tend to go overboard on the preventive maintenance. So even if something is slightly worn it will get replaced. Especially, since parts for these trucks are cheap.

 

[sewlow]

How mine were installed.

You must be registered for see images attach

 

[kartoffelpuffer]

Not sure if this would cause it but mine is facing the other way.

You must be registered for see images attach

 

[thinger2]

Make sure you dont have any broken leafs in the spring pack.
Sometimes they can split in half and be covered up by the brackets and crud.
It will look fine at first glance but they pull apart under accelleration and then go back in place when you stop
Also check out your transmission mount and motor mounts.
Any problem in the mounts might feel through the seat like diff is moving
If anyone ever did the trans they may have used an impact on the tranny mount which can pull the threads out of the case.
You should never use an impact on a trans mount but they do it anyway.