drive train vibration

Hi Guys, another short question:
I'm getting horrible vibrations, worst in third (When engine to driveshaft ratio is 1:1). Think it's the driveshaft (or rather the rear U-joint, seems not quite round and is missing a few needles). How do I find out what U-joint I need? I've heard that they like breaking suddenly if chosen too weak and my car weighs 5000 lbs. Can't seem to find a number on it either... It's a 1983 G20 van, the shaft seems straight though. I also got a new damper, so it can't be that.
And another question regarding this vehicle:
I'm getting pretty poor mileage out of it, but massive acceleration and early gearchanges. Think I might put a bigger rear gear in it. What's the biggest you can get that'll fit in a standard differential case?
Would appreciate any input. Thanks a lot,
MadMax

If you suspect a u-joint is going bad, don't waste your time changing just one, do them both. Sometimes a bad u-joint will not be detectable by the usual method of just trying to turn it to see if there is any play in it. If there are alot of miles on the vehicle, or you carry heavy weight, or tow with it, it's probably time anyway. As far as changine the gears for better mileage, I'll leave that up to someone else.

You find out which U-joint you need by going to your local auto supply store and telling them what vehicle you have, and which U-joint you want. If you have missing needles, now would be a good time.

Changing gears is really expensive. However, you should be able to get something in the 2.70 - 3.00 range for that van.

Oh dopey me, I must have misunderstood his question. When you go to the parts store, like was just said, see if they list a heavy duty version for your truck.

Don't the G20 vans have a two piece driveshaft? My last Chevy van had a two-piece driveshaft with a support bearing in the middle. Is my memory going bad or has Chevy changed?

Quote:

---

Originally posted by Henry Rifle
Don't the G20 vans have a two piece driveshaft?

---

They did have a two piece driveshaft (I think befroe 1979, not quite sure about the exact year) But mine is definitely one piece. Might have it rebalanced, too. Does the driveshaft really cause that much vibration? seems like the thing's about to fall to pieces at some RPMs. I guess I'll just give it a shot, the only problem is finding a chevy-shop here in Germany. But he who seeks shall find ;-) THX!

The G20 Vans had both a two piece driveshaft, and a one piece, depending on the wheelbase. In either case the u-joints are all the same. I don't know what brands are available to you over there, but if you need some major U.S. brand part numbers, let me know.