Do I really need a fine spline rear?

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I can get a 1968 J40 rear diff for a good price. It will be behind a stock SBC with a TH700. Just normal off road stuff, not a rock crawler. Thinking of using a Toyota T-case for reduced driveline angles. What do you guys think??

John
 

Mace

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It depends.. A lot of guys have great luck with the coarse spline pinions..

If you keep axle wrap to a minimum then you will probably be fine ;)
 

Poser

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welcome.


In the V8 trucks that I have owned, it was not ever an issue....I did not beat on them offroad like I do the Red truck however...


I would not worry about it, unless you are SOA, and going to be rodding on it.


Good luck!


-Steve
 

Eskimo

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Of the 3 I've broken, one was from axle wrap. The other 2 were both times when I was on the stupid pedal trying to get up something, and the tires suddenly caught grip.

I agree with Mace - keep the axle wrap in check, and you should be fine.
 

woody

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pretty sure I get zero axle wrap with my rear 4-link, and I junked one stock coarse spline rear pinion and one cryo-treated coarse spline rear pinion. I can change a rear pinion in 45 minutes....I'd hope no one else ever gets that good....I wish I'd only broken three...

For street, it's fine...for light offroad it will be too...but if you get into ANY climb situations or rock/bind situations, you'll regret it.

Hell, I've got fine spline in there and still carry a spare one, just in case....
 

Eskimo

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Change the pinion in 45, or the whole third? Either way, you're fast with the wrenches!

I imagine the axle shaft will break before the fine-spline pinion... I hope.
 

woody

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Eskimo said:
Change the pinion in 45, or the whole third? Either way, you're fast with the wrenches!

I imagine the axle shaft will break before the fine-spline pinion... I hope.

Pritchetts Canyon, CM04....stock coarse spline rear pinion, 4-link elliptical, stock rear FJ40 axle and shafts. Rear pinion snapped on the last climb out, I was 5th in line out of 25 trucks....by the time Jeremiah was at the top with the last truck, we were topping off the diff with fluid....

jack the truck, pull both tires, drain the fluid, pull the cover, pull the calipers, pull the clips/shafts, pull the entire diff out, pull the bearing caps, remove the trashed pinion, pull the spare pinion out of the tool bag, drop in carrier, install bearing caps, reset backlash/adjusters, re-install diff, reinstall shafts/clips, reinstall calipers, install tires, set pinion nut, install driveshaft, install rear cover, refill with fluid......didn't even change the pinion seal.....

~45 minutes....C and I....

busted that pinion a month later (early June)....installed a cryo-treated coarse pinion....busted that a year later (May 2005) and installed a used 62-series fine spline setup.
 

TxCruzr

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Eskimo said:
when I was on the stupid pedal trying to get up something, and the tires suddenly caught grip.
I know that feeling. Done it once or twice more and the fine spline seems to take the punishment alot better.
 

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