Help with vibration

[RJB44]

Hello -

I have a 91 GMC Jimmy with 4-inch lift (springs) and 35 inch tires. I bought the truck less then a year ago through a local government auction. Based on the background info I got, the truck had the new lift, tires and wheels added in 2006, as well as complete bodywork restoration and new paint. The truck runs beautiful and looks great.

The main problem overall I have is that it has a vibration in the driveline upon low acceleration (10-25 or 30 MPH) then smoothes out when I get into the 40-45 range. It stays smooth until I get to about 65, then it starts to vibrate again, although not as bad as the early acceleration. I recently replaced the rear drive shaft u-joints, but not noticing any change. I am pretty sure that there was no work done to the stock driveshaft, so being at the angle it is for the lift may be one issue. I had a front-end alignment and balancing, so were good there. My local mechanic said that all the other joints looked good. (Front). I would like to know what I could further assess to help resolve this driveline issue. I have been thinking about getting a new, custom drive shaft, perhaps from Tom Wood. Feedback appreciated.

 

[suntadz]

I used the HAD driveshaft and was very happy. I had the same type of vibration on a similar lift and it all went away with a few of the right axle shims.

 

[tvonloss]

More than likely drivline angle problems. It can get technical getting it right but basicly the front and rear U-Joints nee to be running at the same angle but if the angle is too high it will vibrate no matter what. I ended up having a driveshaft made with a CV styl joint in front and setting up a zero degree angle in the back to make it smooth again. Same basic setup as yours. 6" lift/4.88s and 35"tires.

 

[Thunder]

If ground clearance is not a big issue.You could try dropping the transfer case. it is simple to do and free. Look at the Trans/transfer case crossmember and see if there are spacers on the bolts between the frame and cross member. If there are. your crossmember/Tcase has already been dropped. If not you will see the spacers on the bottom side of the bolts that attach the crossmember to the frame.
You will only loose about 1" of clearance by dropping the xfer case.
Dropping the xfer case wil help to get your drive line angles better and may help with vibrations.

 

[Mudstud]

First thing to check is to see at what angle your t-case yoke is at and your rear end yoke. They should be within 2* of eachother. If not, that is your problem. If you don't understand how to measure this just ask. It is quite simple and probably can be done with the shaft still in.

 

[rx7gslse]

I'm dragging up this thread vs starting a new one...

I'm having teh exact same issue.. vibration under load worst aroun 20-35mph..

The trick is, I've been running this lift this way for about 3yrs now, and the angles haven't changed... It just started doing this two day ago..

U joint bad? driveshaft out of balance? something else??


help!

 

[tvonloss]

more than likely U-Joint. Look for rusty looking powder around the joints, thats a dead givaway. If not pull it out and check them by hand for smoothness/tightness.

 

[Mudstud]

With the truck in nuetral and on level ground and the wheels shocked a few inches from the tires get under it and grab the d-shaft and turn it both ways, Any slop? There will likely be some in the slip yoke but you are trying to see if it's coming from one of the joints.

 

[guz71]

I would check and see what angle your pinion is sitting at and if thats not the problem then you might have to go to a CV style driveshaft

 

[isaac]

i had the same issues after lifting my blazer i tried shimming the axle i thought i got the right angles but it still had slight vibrations. after messing with several different shims i finally broke down and a local drive shaft place make me a cv drive shaft the best 200 bones i ever spent. it was like night and day driving my truck after i installed the drive shaft.

 

[obijuan]

200!?!! the local driveshaft place is $450 starting for a cv shaft blazer size!! not even 1350! OMG.

 

[isaac]

yep all they did was use my old drive shaft components retube add the cv and balance... i think it was like 230 with tax out the door.

 

[rx7gslse]

eh, pretty sure it was the front u-joint..

but didn't really matter, as the new owner bought it before I got a chance to fix it.... Not my issue anymore!!

(of course, neither is the truck )