Chevy & GMC Vans

i have what seems to be alot of slack when i move my rear yoke by hand.
the pinion nut and shaft both move with the yoke, doesn't seem that the pinion nut is loose but i havn't put a wrench on it either. There is no fluid leaking from the seal.
I'm changing out the u-joints because the van kicks a little sometimes while shifting and i have a vibration which starts about 55 mph. The u-joints dont have anything obvoius wrong with them although the caps are pretty rusty, the caps i was able remove had grease in them and move freely so now i'm worried its the pinion bearings or carrier but i'm gonna see how it goes with the new u-joints.
Wheels on the ground and driveshaft is removed obviously, 2 wheel drive with the g80 & 3.73
sorry for the dark video but you will get the gist of it.

http://www.youtube.com/watch?v=pyBDtFi6 ... e=youtu.be

While that seems to be quite a bit of rotational movement, I don't know if it is excessive. You could pull the diff cover and inspect the gears with a flashlight and also inspect the old oil and magnet for debris. Some fine powder-like material is normal. Before removing the cover, make sure the fill plug will come out. Once in there you can check for backlash with a dial indicator to be sure the gears are ok. The rotational movement you get is from the movement between the axle shafts all the way to the pinion.

That looks pretty normal. If the rear end isn't making any unusual noises then it's OK. Do what Dean suggested. It never hurts to take a look inside. Like Dean mentioned, be sure you can remove the fill plug. They can be a real chore sometimes.

Put the new u-joints in pulled cover off the diff and inspected.
Magnet had fine grey particles all over it but no shavings anywhere and the ring gear looked really nice, old oil was fairly clean, refilled with gl-5 rated full synthetic.
Took it for a drive and the vibration is way worse now on the highway, especially while off the gas. I marked everything before i dropped the shaft so i couldn't have put it on wrong, it also has a master spine on the tranny side but i noticed with the rear section still disconected i could install the tranny side in a few different positions, how could this be with a master spline ?
Tranny fluid is a little low.
Anyways im not to happy right now to say the
least.
Its going to the driveline shop thursday, we will see what they come up with.

When the new u-joint got installed, did you make sure it moved freely? I have had them end up tight causing vibrations. I have never had an issue with lining up the slip yoke to the original splines as the driveshaft should be balanced. I always have my local Fleetpride replace u-joints and balance the shaft at the same time.

Ya the new u-joints move around nice and free, i had the day off today but brought the shaft to my workplace to use the tools, i did the rear one first and almost gave up cuz it was stiff, i figured i would have our mechanic have a look before i throw in the towell, so i walked it over and he said " oh it just needs to be set" he put it down on his bench and tapped around the caps with a small hammer then it moved around nice and free, i thanked him and went back to install the front side..
I have to say that removing the stock u-joints was a major pain with the amount of corrosion i had to deal with plus the nylon pin things which i melted with a torch.
One thing i'm questioning though is the fact i have only 2 c-clips installed on the rear connection to the pinion yoke, i will have another look tomorrow but i guess you just line up the slip joint and keep the caps centered as bestest you can while attatching the ubolts.

The diff yoke should be stepped, so the caps can not move or come out once you bolt the uclamps down.
They shouldnt fit if they arent sitting in there right.
Sounds like the other cap was just a bit over pressed, so he just tapped the thing a bit to push it back in.
I bet he could see one c-clip bulging out a bit from the pressure. anyways, once he set back into place, it takes away the play you were feeling as vibration.
Hope it works out for ya...

I'm not having any clunking while moving the shifter around in the driveway or any low speed issues but sometimes get a random hard shift or kick while it upshifts, highway vibration is the main concern for sure.
Ya im thinking i may have cranked that first one too much, i have another u-joint so if im up to it tomorrow i'll throw it in and see what happens.
Happy New Year !!

Ok i dropped the drive shaft to inspect everything again since the vibration was worse after changing out u-joints yesturday, it sure looks like all 4 clips must be installed for the rear u-joint , even where the caps are held in place by the u-bolts ( i read somewhere here they are not needed for the 2 held by u-bolts). so i put the clips in and went for a drive, the bad vibration i had yesturday is gone, however i am only back to square one it seems as i do still have the origoinal vibration starting around 55mph. so all said and done, i have new u-joints and diff fluid but no change as far as the vibration goes.

On some pinion yokes you will find a couple small tabs on the outer edge that will hold the u-joint centered. On these they do not do this all the time so you need the internal "C" clips to center the u-joint in the yoke.

Next step would be to rotate the tires and see if the vibration moves.

I had new tires balanced and mounted less than 2 weeks ago but will check the pressure and possibly rotate as suggested.

Was it vibrating before the new tires?

Before the new tires went on the van rode really ruff, the tires on the van when i bought it were bald and created all sorts of noises including some vibration, i honestly never drove it much
until getting new rubber, i think now that most of the wondering and tire noise is gone i possibly
notice it more now.

maybe tighten the pinion nut? i had similar issues with my 97 cargo, after new fluid, and u joint, it still happened. i got about a half turn on it. Worked perfectly after.

Not mentioned yet are the balance weights that are spot welded to the driveshaft. There can be one at each end of the driveshaft. I have had them come loose and create a vibration.