g80 rear diff hop

[h45wt]

I had my g80 rear axle lube changed at 2500 miles. They used some brand of synthetic and added friction modifier that I had asked them not to do as I was told by others it was not needed. It seems to have been fine. I changed it again at 79,000 miles just before we started out on a 14,000 mile cross country trip. I used M1 75w90 LS synthetic. About half way through the trip I was making a 360 turn in a parking lot. There was a puddle of water part way through the turn and when the outside rear wheel hit the puddle there was a slight jerk. I duplicated the turn and the same thing happened. I believe it was the locker transferring power from one wheel to the other but I had never felt that before. This is happened in 2wd.

When we got home in the snow and ice it felt like the locker was grabbing and causing some jerking in the snow and ice.

I also felt some hop in the front end while turning in 4wd. I have never noticed it before on ice and snow although you do feel it some on pavement.

1) Is there a problem with using the M1 75w90 LS in the G80? Should I add some friction modifier or is what I recently noticed normal. Odd that I had not noticed it before in 79000 miles.

2) I suspect there may be a problem in the front drive line causing the front to hop. On my older Fords it was usually a front u-joint going bad but I don't know how the Silverados are set up in front. Perhaps it is also a u-joint problem.

So please give your thoughts.

[crashz]

Shouldn't be an issue using that lube in the rear. Some use a 70-140 for towing heavy in hot weather, but probably won't have any noticable difference when driving. Actually, it sounds as if the truck is acting normal. When in 2wd and a wheel slips, the locker will engage if the difference in wheel speed (left and right) reaches 100 rpm.

When you turned in 4wd, you may have hit a dry patch or so. Since the front and rear wheels take a slightly different track when driving in a turn, a driveline bind will wind up unitl relieved by wheel slip. If all tires have good traction, the one with the least will slip, usually causing a hop on a good surface, but unoticable on a slippery surface. Severe bind will damage components, so be careful.