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Old 05-17-2010, 10:27 AM
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Ring gear spacer in a GM 8.5" 10 bolt

Did a little searching over the lunch hour and couldn't find much info out there about people's experience using ring gear spacers to put 3 series gears in a 2-series GM 8.5" 10 bolt, specifically in 450hp-and-below applications. I've got one in my ride and I have not taken it on the road yet to break in the new gears. Richmond says drive for 10 miles at highway speed, stop for 30 minutes, repeat 3 times and the gears are good to go. Not sure if anything special is req'd for the spacer, like re-torque at certain intervals.

Other than a few comments about broken ring gear bolts, didn't find much. I imagine that if the spacer were machined with proper flatness tolerance then fastener fatigue due to bending would not be an issue. I work for a company that installs utility equipment on upwards of 24" diameter shear-ball type bearings, and we never use spacers because flatness is critical to bolt life.

Does anybody have any experience with these spacers? Specifically interested in maintenance, do they need to be re-torqued frequently, or just the first 500 miles or so? Or is it a big enough deal I yank the rear end and rebuild with a 3-series Eaton?

Thanks!

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Old 05-17-2010, 11:02 AM
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Read this. http://www.nastyz28.com/forum/showthread.php?t=185113
There are a lot of un needed comments in this thread, but there is some good information too.
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Old 05-17-2010, 11:27 AM
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A spacer is not the preferred method. There are no "thick" 8.5" gears to make a different series diff accept a a different series gear (like for the car 12-bolt, for example), so if you are going to use the 3-series gear, you will need a spacer or a 3-series diff.

If the spacer is machined "perfectly", and the alignment is spot on, and there's nothing- absolutely NOTHING trapped under the spacer/ring gear (including any garbage that might be lurking down inside any of the threaded holes, etc.) and the power level isn't excessive, the spacer will work.

I would suggest making some studs by taking the heads off of some long bolts, slot them so they can be removed as needed w/a screwdriver, and use them to get the ring gear/spacer exactly aligned to the diff. The gear is a tight fit, it's easy to get it misaligned if you're not very careful.

The bolts have LH threads.
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Old 05-17-2010, 11:56 AM
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Quote:
Originally Posted by cobalt327
If the spacer is machined "perfectly", and the alignment is spot on, and there's nothing- absolutely NOTHING trapped under the spacer/ring gear...and the power level isn't excessive, the spacer will work.

I would suggest making some studs by taking the heads off of some long bolts, slot them so they can be removed as needed w/a screwdriver, and use them to get the ring gear/spacer exactly aligned to the diff. The gear is a tight fit, it's easy to get it misaligned if you're not very careful.

The bolts have LH threads.
Unfortunately it's already built, and not by me. My brother had it built it up about 5 years ago while he was in ASE tech school. His Powertrain teacher "supervised", said he had installed spacers before and he would make sure it was done properly. The guy was in his 50's, said he had been rebuilding trans and diffs for 30 years then became a teacher. Sounded like he knew his stuff, and I was looking for any way to save a buck at the time (full time school + part time job = no money to support expensive car addiction). I did get to see the pattern, runout and backlash measurements. Don't remember the exact #'s but I do remember they were right at what Richmond spec'd, and the pattern looked exactly like the instructions showed.

I was just concerned there might be a solid consensus that these things are garbage. I'm thinking I'll do the 10mile/30minute rest break in procedure per Richmond's instructions, then drop the cover and inspect, maybe check the contact pattern, runout, backlash and ring gear bolt torque while I'm at. Might give me some assurance the ring gear didn't shift.

Assuming it survives break-in, do you think I should make a habit out of checking on it every oil change, or something like that?
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Old 05-17-2010, 12:13 PM
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Sounds like it has as good a chance of any at lasting. If you were to really hook it up (drag strip-prepped launch pad w/slicks, for instance), you could break it.

But if it doesn't make any noise and the pattern is good, I'd not worry about it. No problem looking it over when the cover's off, but I wouldn't really want to retorque it, it should have been assembled w/threadlocker and all retorquing will do is break the threadlocker loose.

In the meantime, you can be looking for a 3-series carrier, or another diff for that housing. But if your 2-series holds up past break in, I'd call it good to go- at the power levels you spec'ed, and no slicks.
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Old 05-17-2010, 12:22 PM
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Quote:
Originally Posted by big gear head
Read this. http://www.nastyz28.com/forum/showthread.php?t=185113
There are a lot of un needed comments in this thread, but there is some good information too.
Thanks for the link BGH! Now you've got me nervous. I had a rear end lock up on me once and I darn near crapped my pants. Definitely don't want a repeat of that (of either the lock up or the pants-crapping, especially when combined). Obviously you would NOT recommend using a spacer under any circumstance. I will keep an extra close eye on it during and after break in.

If I come across an Eaton 3-series posi carrier will my 2-series guts fit it, clutches, spiders, etc?

Thanks for your help guys!
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Old 05-17-2010, 01:48 PM
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Quote:
Originally Posted by PontiacPhil
Now you've got me nervous.
I suppose that could be a 'good thing'.lol

Quote:
will my 2-series guts fit it, clutches, spiders, etc?
The internals are the same. But a better diff altogether would be better. BGH has a "pet" recipe for a good replacement 8.5" diff and axles, maybe he'll share it one more time.
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Old 05-17-2010, 02:54 PM
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Quote:
Originally Posted by cobalt327
I suppose that could be a 'good thing'.lol
Yup. Usually when you start getting too comfortable with something is when it is the most dangerous.

Quote:
Originally Posted by cobalt327
...BGH has a "pet" recipe for a good replacement 8.5" diff and axles, maybe he'll share it one more time.
A link would be sufficient (unless it was in that last one BGH posted, in which case I must not have read it closely enough). No need to repeat what you've said in the past.

Thank you both!

:edit:

Is it this: BGH - "You will have the 8.5 10 bolt with a 30 spline pinion shaft and 28 spline axles. I'm assuming that you have a standard differential right now and want to upgrade to a posi. I recommend the Eaton Posi. If your axles are worn and need to be replaced then I would upgrade to 30 spline Moser axles and a 30 spline Eaton Posi. The cost is the same for 28 and 30 spline parts, so it's pretty easy to see that this is the way to go."

Last edited by PontiacPhil; 05-17-2010 at 03:03 PM.
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Old 05-17-2010, 05:19 PM
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That's close enought. If I'm building one that will see some drag strip time with slicks I also recommend welding the axle tubes. You can find more information on that here. http://www.nastyz28.com/forum/showth...ing+axle+tubes Bracing the spring perches is also a good idea for drag racing.
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Old 05-17-2010, 08:40 PM
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Quote:
Originally Posted by big gear head
That's close enought. If I'm building one that will see some drag strip time with slicks I also recommend welding the axle tubes. You can find more information on that here. http://www.nastyz28.com/forum/showth...ing+axle+tubes Bracing the spring perches is also a good idea for drag racing.
That was a great how-to. I don't have any experience with it, but I work with a lot of guys who weld cast iron and everyone seems to have their own opinion as to "well I did it this way and it worked just fine". It's good to see what the experts have to say about it.

This is a street machine, no serious drag time planned and no slicks. Running Hoosier QuickTime DOT's most of the time on the street and when I do the weekend (more like monthly for me) warrior thing at the strip. Might slap on the Radial TA's if I feel like cooking some rubber, but otherwise I tend to be a granny compared to some.

I'm going to add the 3-series Eaton with Moser 30 spline axles to my wishlist, along with the thousands of other dollars of "wants". This will probably be higher on my list, though. A dependable diff is more important to me than rumbling exhaust.

Thanks again!
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Old 05-17-2010, 08:59 PM
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Almost forgot!

All the diffs I've had built in the past were always with new gear sets. If I snag a deal on a 3-series, can I put my soon-to-be-used Richmond 3.73's on that carrier with no problem? I assumed this is no biggie as long as the pinion/ring are in good shape and stay together as a set and it's set up properly with a new installation kit, but it never hurts to ask.
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Old 05-18-2010, 06:02 AM
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That should work just fine. Here is another link for that one. http://www.nastyz28.com/forum/showth...ht=change+posi
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