Driveshaft slope/angle

[rivermtnman]

I've got a '88 K5 with a 4" lift, 10b, 700r, NP208, 36" TSL's. We just put the lift in and the steeper the climb it goes up I get a noticable "thumping" sound from the driveshaft or the rear end. On level to moderate steepness no sound, but start getting a little excessive and you can hear it.

I was reading the article on pirate someone posted here, but not sure I understand. I borrowed a digital angle finder and here's some measurements I came up with:
tranny slope= 2* down
driveshaft slope= 23* down
pinion slope (has tapered lift block on rear)= 12*

which means my front u-joint has operating angle of 21* and the rear has 11*

Can I bring the rear pinion angle up more or am I gonna have to look at a cv driveshaft? Will shimming the rear more have much affect to the front joint?

I've not read alot of discussion on here about driveshaft problems with a 4" lift, which has me kind of puzzled about mine. We took the lift from another truck, and I'm not sure who made it.

This is an offroad only ride, so I'm hoping for the cheapest way to fix...

 

[Chaddy]

Is it your drive line hitting the cross member?

 

[rivermtnman]

No its not close to the crossmember, just got back from climbing some rocks around the farm, didnt magically go away, lol. Took a pic...

 

[resurrected_jimmy]

if its u-joint bind at the pinion you ought to be able to see where it rubs on the yoke...... another thought is that you are having some axle wrap trying to climb up steep slopes

 

[RedBrute]

Try lowering the transfer case by dropping the crossmember. If the truck is original, the crossmember mounting bolts will have spacers on them above the frame. put the spacers between frame and crossmember for the transfer case mount. This should relax the front angle a bit more. Also, are the ujoints original? might be a good idea to install new ones because they are running thru a greater range of motion than they have for the last 18 years.

 

[rivermtnman]

Thanks...
I noticed the spacers on the crossmember today, I'll try that next time I'm working on it. The front u-joint is original, cant find any slack in it, but was thinking the same thing about replaces it. I cant see anywhere the ujoints are binding, but they are close, especially the front one. I just thought a 4" lift on the blazers was straight forward and wouldnt cause other problems like drivelines.