HELP GM 8.5 axle rebuild... Will this run?

[FluoFerret]

Hello everybody!
I am currently rebuilding my 8.5 10bolt axle, and I hat to get a new carrier (Yukon), and a new ring/pinion (Motive Gear). And this setup is baking my brain, as I probably can't see the wood anymore because of all the trees. I need fresh new pairs of eyes with their verdict 🙂

I installed the new assembly with a 0,041" (1,05mm) shim-setup. Backlash marked on the ring gear says 0,006", but it sits currently at 0,055". Any further attempt to adjust on the diff-bearing shims throws me to the high end of the backlash-tolerance indicated in Motive Gear installation instructions (0,007-0,009).
Below are the pics of the current pattern.

According to the recommended pattern by Motive Gear, only the coast-side seems to be a bit offset to the heel of the tooth, but the rest looks fine.

However, I can't fully reconcile my result with any other pattern considered to be valid throughout the literature for face milled gears. Here's an example

Can somebody with more experience help me out with his oppinion/knowledge on what I did there?
A big thank you in advance for all your help!

 

[Bonnewagon]

Setting up these gears is a science that few actually can do. Are you experienced at this? Did you read the FSM for the process and tools needed? I think you should start at the beginning and post your results.

Did you use all new bearings? A new crush collar? What pinion gear shim thickness, and the total pre-load you used on it. Did you use a pinion depth setting tool?

0,041mm shim-setup

That is a mistake, yes?

Did you use new carrier side bearings? What kind of carrier shims did you use? A kit of multiple sizes? Did you find zero lash and add the correct pre-load shims?

After all that is perfect, only then should you be looking at gear backlash and tooth contact pattern, adjusting as needed.

If you are experienced at this, I apologize, but you did not give enough info to draw any conclusions.

 

[69hurstolds]

Maybe it's my eyesight, but it APPEARS to me the drive and coast sides are a bit leaning toward the toe. The pinion depth looks pretty good to me, but backlash might need to be increased a hair. Again, to me, it appears ALMOST there. I'm not an expert, though.

That's all I got. Out of all of them, the coast side pattern is the least worrysome. In other words, if the drive side is set fairly centered, that's the most important part of the equation.

Ask an expert. A guy named Jim goes by the username "monzaz" on a bunch of car forum sites. Don't recall his last name. He is someone I consider a valid expert on ring and pinion stuff. He's only done about 10,000 rear ends. And didn't have to go to prison to do it. 🙂

They got a forum there. Contact him there and if he decides to help you, which he most likely will, he can just look at what you got and tell you what's what. Yeah, he's THAT good.

Home

To join the forum there, or just read up on stuff (you're not the only one that's had questions):

www.jdrace.com - Forum Home

 

[FluoFerret]

Did you use all new bearings? A new crush collar? What pinion gear shim thickness, and the total pre-load you used on it. Did you use a pinion depth setting tool?

Did you use new carrier side bearings? What kind of carrier shims did you use? A kit of multiple sizes? Did you find zero lash and add the correct pre-load shims?

After all that is perfect, only then should you be looking at gear backlash and tooth contact pattern, adjusting as needed.

If you are experienced at this, I apologize, but you did not give enough info to draw any conclusions.

Don't worry, I am a bloody noob at this, out of necessity. There is no more mechanic-shop around here I can entrust my US-Cars to anymore. Most shops only hire "spare-parts replacer", and good mechanics have become impossible to find. The inevitable doom caused by modern cars where a computer makes a diagnose and tells you which part to swap out, in accordance to some procedures cooked up by engineers at the factory (rant over. lol)

Basically everything is new, except for the axle-housing. I had to do it, because the old carrier-assembly got badly refurbished by a mechanic-shop who also managed to put the wrong oil in (engine oil instead of heavy gear oil). the spider gears were eaten up and clunked a lot, and turning while going up made a terrible grinding noise. it was a carnage.

The shims i used to set up the carrier were made by Yukon, kit SK SS10. Here's what I did:

1. Dropped the carrier and bearings in
2. Pushed the carrier into the pinion until I didn't feel any backlash anymore and thickened the shim-sandwich on the ring-side until i needed a firm but not excessive pressure on the thumb to push it in, keeping zero backlash on the gears.
3. Started to shim up the pinion side of the carrier until it was tight, but not binding.
4. Removed the thinnest shim from the ring side, packed it over to the ring side, and installed the bearing caps. Everything felt snug and tight but not binding.
5. measured torque on the pinion needed to turn the differential. it was about 25-26 inch-pound. (no crush sleeve, but a spacer-kit by Yukon)
6. measured backlash and checked the pattern.

I hope this helps you a little bit to understand what I did. 😆

 

[MrSony]

If you got all the parts, aint no shame in taking it down to someone with a shop and a bit more experience. Plus if it blows up, you know where they work.

 

[565bbchevy]

If you got all the parts, aint no shame in taking it down to someone with a shop and a bit more experience. Plus if it blows up, you know where they work.

I think the issue with that is he is in Luxembourg not the US

 

[Bonnewagon]

OK, I get it. You are forced to attempt it because, well, you are the last resort. No problem. I used to do it with just a set of feeler gauges. First off, there is a wonderful explanation of all this in the Factory Service Manual. You really need to read up on this or you may make some very expensive errors. Is that a 1980 Pontiac? Nice. Any FSM for a G or F body from that era will have the 8.5 rear differential section. They are all set up pretty much the same. I would take the carrier out and double check the pinion pre-load just to be sure.

You must first understand the concept. The pinion and carrier are held in suspension by having an amount of pre-load on them. That way they will stay in alignment under the torque from the engine. If they move, they lose the relationship of the pinion and ring gears, then they wear, or break. So you first assemble the pinion gear and bearings, check the pinion depth, set the pre-load, and then leave it alone. TIP: I have always checked the pinon depth with a factory depth tool. It has never been off from the original pinion shim by more than a thousandths of an inch or two. Thus, we usually re-use the original shim. Also, check the pre-load without the carrier in place. You just want the pre-load on the pinion gear. The reason they used a crush collar is that as you tighten the pinion nut, it crushes the collar. Once you get the correct pre-load, checked with an inch pounds torque wrench, you stop turning the nut and the collar is now the exact size to maintain that pre-load. The reason that a shim might be used is in racing, when they take rears apart and put them back together and speed is essential. The shim is only good if the pre-load was first set with a collar, removed, measured, and a shim the exact same size put in. Otherwise, how can you know what shim to use?

So, please find a manual, read it, and go back to the pinion setting. Ebay has them as well as factorymanuals.com. Worst case I find one and ship it to you.

 

[Bonnewagon]

https://www.ebay.com/itm/3745287201...pid=5335822911&customid=&toolid=10001&mkevt=1

 

[64nailhead]

.005 backlash is too tight. No less than .008" is recommended and if it were .012-.013 it will work just fine. I target .008-.010. Think of backlash like crank bearings - too tight and everyone knows, a little loose and no one knows.

When you're measuring rotational torque -be sure to not have the pinion seal installed.

When installing the carrier shims, if you can push them in with your fingers, then they are loose. Add a couple of thousands to each side until they can be tapped in (not hammered in, but tapped in) with a small hammer. I put the diff in, with the pinion not installed and figure out how much total shim I need for both sides combined, then record that number. When you're all done, be sure the carrier shims equal that number or .002-.003 greater.

So looking at your pattern knowing the backlash is too tight and carrier shims are too loose is somewhat of a waste of time in my opinion.

 

[MrSony]

I think the issue with that is he is in Luxembourg not the US

Germany doesnt have a publicly available drivetrain service shop?