Lifted Blazer

[Kooter]

Do you need to extend the rear drive line for a 4 inch lift? I just had the rear u joints done and had the rear end rebuilt and it still has a clunk when it shifts. I was thinking it could be the driveline banging in and out of the
t-case? Anyone else have this sound?

[dmkscott]

Might be in the U-joints, you can purchase pads that are installed in between the leaf springs and the axle mounting pads (look like a 5degree wedge). They increase the angle the front of the axle housing sits and reduces the angle the u joints are running. I have a 6 inch lift on my blazer and it helped greatly due to the short rear drive shaft and angles.

[Jonboy]

You may also want to space the trans/transfer case crossmember down a little bit as well.

[Zoomad75]

Each truck will vary when lifted. My K5 didn't need any driveshaft length adjustments when I lifted it. Mine would chew up rear ujoints like crazy before the lift though. I used a shackle flip which did help in rotating the pinion up slightly and elimintate my ujoint issue.

Go get a magnetic angle finder from sears (under $15). Park the truck on level ground. Crawl under and take a measurement off of the t-case output (rotate the output yoke so it's flat sides are top/bottom). Take the measurement from the topside of the yoke. next, put the finder on the driveshaft and get a reading. Then go down to the axle and make sure the pinion yoke has the flat sides top and bottom too. This time measure on the bottom of the yoke.

Ideally the t-case and the pinion should be within 2 degrees of each other. if they are off by more, you will have driveline vibrations. Some get away with shimming the rear only and others have to drop the rear of the t-case down. Some have to do both.

I'd say check first before just shoving a 5 degree shim in at the axle. The natural tendancy under acceleration is for the pinion angle to point up slightly so if you already have it jacked up 5 degrees you could induce more problems than you are fixing. Besides if it needed that much, I'd split the difference and use a smaller 2 or 2.5 degree shim and them drop the t-case down to get the rest.