u joint woes

[chunk40]

I have a 69 GMC long ved that I did some trading for.....the guy I got it from cut the front coils to lower it and removed a few rear leaf spings in the back to drop it a total of 3 inches.....the problem I am having is I am destroying rear u joints.....it is a two piece drive shaft.....help me please

[crossfire84]

How much driveline angle is right for my application?

Thats a loaded question. The best answer is....the least amount of driveline or u-joint angle is the best amount of angle. Try to achieve the least amount of u-joint angle but don't make it less than 1 degree. A little known fact about u-joints is that they require about 1 degree of operating angle to get the needle bearings rotating. If they do not rotate they will fail. Too much angle will also cause them to fail. The type of rear suspension also plays a big part in setting the angles as well as the engine/transmission angle. Leaf spring cars have a need for more downward pinion angle due to spring wrap-up while coil spring cars control the situation better. Hard acceleration as in the case of a drag race car requires a different setting than a street driven car. Traction bars, ladder bars, 4 links, independent rears all have special needs and requirements.

this was taken from Dennys driveshaft.

[chunk40]

thank you the guy I got the truck from did on nasty hack job and I have sheard two ujoints on on the way to the easter show in st louis

[PGSigns]

Sounds like you need to start at the front and work your way back. One thing you need to check is to make sure the two drive shafts are phased correctly. If he put the rear one on in the wrong place on the splines it will be hard on the joints.
Jimmy

[gofastnut]

If everything on the front side of the drive shaft checks out OK, you can by wedge shaped shims that slip in between the mounting pad on the axle and leaf spring. I think they come in .5 or 1.5 degree increments. Hope this helps.

[chunk40]

thanks for all the advice

[Robznob11]

Carl's racing has shims up to 4* , as already stated check phase first and then try and get your angles with in two degrees. If it has been lowered a lot I suspect the rear may sit higher than the bearing causing a compounded angle. Look at it from the side the pinion points up in stock form, now when you move the whole rear straight up it put s the shaft actually running up hill towards the back that will put a hard angle on the pinion u joint. Mine was like that and I had to go with a full 4* wedge. Of chorse mine is one piece but the principal is the same. Be sure you check all angles with ground level to ride hight. Many try to level the frame and that's a whole other arguement, hence why the other person said it's a loaded question lol. Lots of people debate this subject.