Clunk Noise and Differential Questions

[Prof_h]

Hi Everyone,
Vehicle details: 2010 Tahoe LT, 5.3L 8cyl, 6L80e, 2wd.
I'd like to work on my SUV this week and was wondering....
Does this SUV have a reusable differential gasket? Is Royal Purple synthetic differential oil okay to use in this gearbox?
Does anyone have the "slip yoke clunk"? I've seen several posts on the "clunk" problem on other older chevy/gm vehicles. How about bad motor mounts? Could this cause the "clunk" sound when I am slowing down to a stop? It really doesn't occur that often, but when it does, it is loud and feels like someone slammed into the rear of my SUV.
I know there are lots of questions, but would appreciate any information you could provide.
Thank you,

[kenman1717]

The newer ones should have a reuseable gasket, its metal coated in rubber, price one out and the price should tell you, the paper/cardboard gaskets they have always had are cheap but the reuseable one its like $50, I'm a mechanic in Canada so the price will vary in the states but you get what I'm saying. Royal Purple will be fine as long as you use the 75w90 synthetic gear oil that GM recommends. That clunk your describing really sounds like slip yoke. If an engine mount was bad, it would be slamming and jerking up the hood. Is your slip yoke leaking, I mean from in behind the ujoint but with trans fluid. There are new updated yokes without the plug in the middle of them, They were very common for leaks. The splines of the yoke are supposed to stay lubricated to prevent the clunk. What is the level of your transmission fluid. If its low that could be part of it. I mean your really not supposed to put grease on the splines of the slip yoke but it is pretty common, it usually helps for awhile then you have to redo it. Others have put a grease fitting in the slip yoke so it greases the splines, so they don't have to take the driveshaft out everytime. But if you do that make sure the grease fitting is behind the wear line of how far in slips into the trans under normal operation.

[j cAT]

you may have a re-usable diff cover gasket . I would buy a paper gasket and some permatex formagasket sealer just in case it is damaged . placing the sealer on the paper gasket set on cover allow 30 min to set up then place on the cleaned gear box using mineral spirits . clean the box out good then check for any cracked gear teeth. 75-90wt synthetic is used and should be added up to bottom of the fill plug . label should indicate as to what oil to use.fill to the bottom of hole level ground. drive it a few miles park on a level spot then open the fill plug to allow excess to pour out or perhaps you need more.. this happens because adding the gear oil it can create air pockets , which is why you do the check after some driving after servicing it and check for leaks.. the clunk if like at a stop light , on starting out it clunks , this is usually the drive shaft yoke. over time these require greasing . drop drive shaft and use the moly EP2 grease on the shaft. don't need much . also check those U joints for wear or binding. binding does cause vibs.. wear causes drive train clunks on moving as well as stop/go operation. my toyota 4 runner has grease fittings at these points as well as the U joints .. GM should have had the slip yoke grease fitting for this also. I know of some that had installed these grease fittings esp those that OFF road../ lifts..

[Prof_h]

Thank you for both replies. Update: Took off the drive shaft and noticed a very small amount of weeping TF around the back of the trans. Yoke looked really clean and wet from TF. Since I have the DS out, I'll go ahead and replace the U-joints and grease the inside of the yoke. I purchased GM spline grease for this purpose anyway, quite expensive. I've seen a lot of YouTube videos and have not seen a yoke like the one I have. Right between the shaft of the yoke and the u-joint, there is a steel doughnut ring about 1" thick welded to the yoke. Don't know what that is for, maybe something to do w/balance? Checked TF level and it is fine. Had Tranny serviced recently at the Dealer to see if that would help w/the "clunk". The "clunk/slam" only happens when I'm slowing down to stop. It has never happened when I start off from a stop. Dealer said I needed a new tranny, that I didn't have a 1st gear. Reputable Tranny shop said tranny was fine. Shop said to try and get the "troublesome" intake sensor replaced. Had that done, no difference in problems. Took a look at the motor mount and it looked old and cracked. Tried the motor mount test and the driver's side mm looked like it allowed the engine to lift about 2 inches. That doesn't seem normal to me. Comments? Thanks again.

[j cAT]

driver side MM will do it .. 2 inch lift .......not good...

[Prof_h]

Just wanted to give you all a quick update...changed out the driver's side motor mount and all of the stabilitrak, traction control, warnings went away. This had been a recurring problem for 2 years and not one mechanic suggested I replace my mm to solve that problem. I still have shifting and clunking on occasion, but at least one thing isn't happening anymore.
Thank you to all of you for your input and suggestions. It really saves me quite a bit of $.

[j cAT]

ON my new Toyota there are slip yoke grease fittings and the grease to use is moly grease EP2 .. My 2000 GM truck have no clunks since I dropped the drive shaft and put the moly grease on the splines ,,

it is 4wd ..had this clunk @30K miles .. 175K now no clunk..

2wd trucks the front driver side spring may need replacing and will throw off the drive shaft angle .