60 series diffs on a 40 (1 Viewer)

Joined
May 20, 2013
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628
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Orange County, CA
I threw 85 60 third members into my 76. Bolted right in with no modifications. Since you're going to be taking apart the front, you might as well do a knuckle rebuild.

Best upgrade ever! Brought my rpm's down and the engine is greatful!
 
Joined
Aug 24, 2014
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Woodinville Washington
SBG-- the 60 series axle housing is about 3 inches wider than the 40 housing. Using the 60/62 housing will require, either modifying the 60 housing (notching the pumpkin to move the spring perch over, seems to me like more work), or outboarding the spring mounts on the frame. The outboarding is about 1 3/8 Inch if I remember correctly. I have an empty 60 series housing here (for future use) if you need any measurements.

Don

Thanks Don, it's funny, I posted that than may have found a '60 front end that night... I'm not using leaf springs on my '40, the front will be 3 link, the rear 4 link double triangulated (read, just like ICON)
 
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Apr 1, 2014
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128
Hey Bikersmurf can you tell me how much better the 40 runs with 370's instead of 410's? Also you said it was super easy right?
 
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Oct 7, 2011
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Location
Austin TX
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I didn't do the mods, but my '79 FJ40 has the entire differential from a mid-80's FJ60 at the rear. Didn't have to worry about the gearing because 40's from '79 on up already have 3.70 gears. Switching the entire rear end allowed the use of the FJ60 emergency brakes mounted on the rear axle housings. I also have the split-case and H55 tranny. It is a much quieter riding 40 than most I have been in. The right rear wheel sticks out almost an inch farther than the left wheel. 3200 rpm at 85 mph with 31" tires. (The speedo is accurate.)
 
Joined
Jan 12, 2007
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Houston, TEXAS
Doug, I am honestly surprised that your fuel needle isn't blurred in your pic.

This is on my list as I anticipate making my 40 somewhat of a DD. Thanks everyone!
 
Joined
Apr 2, 2008
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Location
Victoria, BC
Hey Bikersmurf can you tell me how much better the 40 runs with 370's instead of 410's? Also you said it was super easy right?
3.70s bring RPMs down 10%. With 33s, 25% lower than stock. Randy's ring and pinion has rpm calculators for different speeds... 50 mph is about 2000 rpm. My SBC is happy with the gearing.

Yes, easy swap, but time consuming to swap both 3rds.
 

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