A few Suburban questions...finally bought one.

[311Hemi]

So I finally picked up an 01' Suburban with 140k on it. I am a nut for trying to make sure everything is up to par (or better)...so I have to be somewhat careful not to start dumping a ton of money into this used truck. It's high mileage so I have to accept it's not going to be perfect. So, a few questions:

1) The truck has a vibration that is noticeable at 70+ mph. I have yet to have the tires balanced, rotated, and alignment checked which will probably be the first step to figuring this out. Aside from that, the rear driveshaft u-joints are solid but the front front output shaft seems to have a little play in it. Because of that play it's hard to tell if there is a loose u-joint. How much (if any) movement is acceptable for the front output shaft? I have heard there is a TSB for a new yoke due to yolk wear or something...but have not yet located it. Anyone know of one or have any other ideas?

[Macgyver55]

I'd still pull the drive shaft and check the rear joint if balancing the tires doesnt take care of it.

A tight/binding joint will sometimes vibrate as much as a loose one.

[311Hemi]

I had the tires balanced which did not resolve the issue. I also pulled the front drive shaft and drive the truck and the vibration remained....so it appears the be from the t-case or rear of the vehicle, or the front end. I will have the pull the rear drive shaft and check the u-joints. I can tell they have both been replaced in the past. I do feel movement or a clunking noise if I push up on the drive shaft at the rear output pf the t-case.

One question, I installed new rear rotors this weekend and noticed that the rear axles have a little vertical play (maybe 1/16")...is a little play normal or should the axles not be able to move up and down at all?

[Jeremy airjer W]

Does it have the aluminum rear drive shaft?

[Bigtom]

can you tell if there are any wheights on the drive shaft the could have got knocked off so the drive shaft is out of ballance.

[311Hemi]

I don't know if it's aluminum or not, it's a Three Rivers drive shaft which is a GM one....same as the front.

The front of the rear driveshaft has a weight on it, the rear does not. I didn't see anything making think the rear had a weight...I will have to look closer when I get it out.

I may take the rear DS in to get the balance checked when I have it out.

[311Hemi]

Pulled the rear drive shaft tonight. One u-joint is fine, the other I am not sure. In one direction it moves smoothly, the other direction it's definitely loose when the joint is mostly centered but gets tighter (but not super tight) when the shaft is moved to more of an angle...either direction.

I think I am going to try to have it looked at tomorrow and balanced while I am at it.

Also, I think it is an aluminum shaft as it is very light for it's size.

[Macgyver55]

Pulled the rear drive shaft tonight. One u-joint is fine, the other I am not sure. In one direction it moves smoothly, the other direction it's definitely loose when the joint is mostly centered but gets tighter (but not super tight) when the shaft is moved to more of an angle...either direction.

The joint should move smoothly in both directions. Even a small amount of looseness or binding can cause a vibration, and it will soon get worse if its at that point now. It should be replaced, even if it doesnt cure the vibration you are heading off a problem in the near future.

[311Hemi]

I got the one u-joint changed and the drive shaft balanced. The shaft was way out of balance and they needed to add a good amount of weight to it....I'm not even sure how it is possible that it was that far off as the shaft is not bent. This has resolved 80% of the vibration...so that is good and it's much better to drive now.

I still have a slight vibration in a very small speed range 68-73, and it's more pronounced when I let off the gas. I can deal with this but will continue to troubleshoot as I have time. I did pull the front drive shaft again after installing the rear and the slight vibration still remained. Shifting into neutral at these speeds did not change anything. So, not sure where that leaves me.