So i have a nice clank or thunk going into gear and i'm almost positive it is the U-joints. Now i know there are U-joints for the drive shaft and rear half shafts. I was wondering if all the U-joints are the same size between the half shafts and drive shaft? They are all orginal U-joints so i am thinking about changing all of them. 6 of them i believe? Anyone have any tips for this? pretty simple procedure i would think. Any info would be appreciated!

 

I did a little quick research and at least one manufacturer lists the same part number for all six. Over the years I have learned to put the hammer away when u-joints are present! Also be careful to properly support the yokes when pressing the cups in and out. I use my shop vise with appropriately sized sockets as a press. An old timer told me to hone the yokes so the cups go in with very little more hand hand pressure.A brake cylinder hone works great. Since I have been doing this,my u-joints are lasting much longer.
You should be able to do this,it's no more difficult than the front end work you did last fall. Good Luck!
Ron

 

#1 your idle might just be to high, that will give you a clank or thunk.
#2 your bushings at the front of the differential may need to be replaced.
#3 if you don't have this tool www.volvette.com part # TL30 than bolt the half shafts together before changing the U-joints so you don't bend the flange. PG.

 

I just read the two really good replies to your topic and I think they cover your questions well. I especially like the light honing of the cap holes. It's always good to clean up the surfaces of whatever you're working on. Prep is the most important and greatest amount of work in most fixes/rebuilds.
IMO I feel that U-joints w/ grease fittings are the best. The sealed joints are ok, but I prefer pumping up my U-joints w/ fresh grease periodically. And when installing joints w/ fittings, make sure the grease fitting is in the right direction so you can get the grease gun to it. It is possible to install the joint where the fitting can't be gottin to due to it's position in the yoke.
And Good Luck. Sounds like you've figured out the problem, gotten the tips you need and now it's just all about "turning the wrenches."

 

All good advice. Also be sure if using ones with zerks, to put the new one in so that the hole for the zerk is in compression when the shaft is turning in the forward position. That way the joint is not weakened by the hole.

While I agree w/ Texas Jim, sometimes you have to use a needle fitting to grease the U-joint as there just isn't room to get the regular gun fitting in there. At least that's been my experience.

 

I feel, from my experience w/ drag racing and high performance/high power and torque, that the hole for a grease fitting makes a minimal amount of difference when it comes to a high level of torque breaking a U-joint. Unless you have one heck of a high powered application in your 'Vette, this will never come into play. If I'm not mistaken, when the joint is installed where the fitting can be accessed properly, the joint is also in the correct position/installed in the proper direction, as there is one correct postiion f/ the joint to be installed-agreed. (all discussion based on the "proper/correct" installation of the joint)
W/ the situation of room f/ a fitting and ample room f/ a grease gun to lube the joint on the 'Vette, these yokes are set up f/ a fitting to be used and f/ a grease gun to lube them, although a rigid tube on the gun isn't a good choice in the C3's situation. I will agree that a needle is a good method to use when a grease fitting can't be mated w/ a conventional grease gun tip.

 

I had the same problem with my 79 and after changing the U joints and still had the clunk I changed the differential bushing and it solved the problem. The bushing looked fine but it was bad. Lot easier than changing the U joints.

 

Shark, From changing u-joints f/ many years on many rides, it seems that there's only ONE correct position to place a u-joint in-place. Seems that when they're in position to be greased, sometimes needing a flex hose w/ the "short" (the ones that are an inch or so in length sometimes won't get to the fitting) metal coupling on the end of a flex hose to lock onto the fitting, that the joint is installed correctly. I have used a needle to grease certain joints before, but any time I have a u-joint, and the u-joint is installed properly, I can get to it w/ the flex hose and short metal end.
I do feel that you need ALOT of horse power and torque to break a U-joint due to it being weakened by the fitting(zerk) hole. I've broken u-joints at the drag races in the past and torn them apart in the dirt, but never has it been due to that spoken-of hole. Not that I don't think it's impossible, but would take some doing IMO.