I've tried the search but can't find a thread doing this...I'm betting I'm wrong and there is one....someone please point me?

Ask Dr Evil

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https://www.evilwerks.com

Dr Evil videos are worth the small price.
Klassik Automotive Training School on You Tube is also good, but you need all the expensive tools to do it that way.

Also, the manual is good to read. Any version is better than nothing.

DrEvils videos are great. I also rent out the tools for a rebuild if needed. MarkClick to view attachment

Factory manual is lacking in detail, type o’s and misinformation. If you study the factory manual also read the Sportomatic section as it has greater detail and fewer mistakes. The numbers are completely different but the procedures are the same.
The Dr. Evil DVD is the best source for rebuilding buy a copy and watch it over and over, better yet get a cheap tail shift transmission and practice along with the DVD.
I used to think there was some bad “mojo” inside the 901 box but once you understand what it does, it becomes another mechanical device.

I rebuilt mine with the DR Evil video 10 years ago and its still working good!

Ran with this, thanx guys.... :-)

I have 2 cores, 1 side shift, the other tail shift, so I guess I'll start by pulling the tail shift apart, then pull the transaxle out of my race car (close ratio side shift with 904 main shaft with LSD) and get on with fixing, maybe upgrading depending on what i find....

Hmmmmm....might be doing a couple of these (race spare and IF i build a street tribute)...guess I need to find out what they cost vs. rent...thanx for offering....

I have the LSD but I am jealous of the 904 mainshaft.

I'm told, and have read, this is necessary to re-gear 1st gear, I can't take credit for putting it in, came in the car when I bought it, hopefully it's not broke....

Mark thank you for the offer and I will take you up on this in a few months. I have a few boxes laying around with unknown status and will be getting into them soon.

Thanks again