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PostPosted: November 28, 2017, 11:41 am 
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Joined: October 10, 2010, 10:26 am
Posts: 988
Location: Bakersfield, CA
Hey guys.. I'm kicking around ideas for a new project, and I'll likely need a small-ish, light IRS pumpkin that can handle about 100hp/50 ft lbs torque..

Any ideas where to source one? I'm thinking an off-road (side-by-side) diff? Maybe some light-duty tractor I've never heard of? I'll likely have to go 'out of the box' for this one.. above all else, it must be light- this project won't tolerate the weight of a typical iron diff..

You guys are a tremendous wealth of knowledge, so I thought in your travels maybe you've come across just the thing I'm looking for?- With all of the cool toys/vehicles being made, I'm sure one of them is using what I describe, I just don't know where to look..

**My project car will be rear wheel drive, and around a (3.0:1) to (3.5:1) ratio should work (I can't go much higher than 3.5 though- I want to use a Miata diff, but the 4:1/4:3 ratios are a killer)... also, I could likely use a FWD pumpkin and flip it to get what I need?!..

Any thoughts are appreciated :cheers:

thanks-

-ccrunner

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PostPosted: November 28, 2017, 12:47 pm 
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Joined: December 29, 2007, 10:41 pm
Posts: 855
Location: Vancouver, BC
Would a rear diff from a RAV4 work for you? I did a quick google search and it appears the early ones had a 2.928:1 ratio, but the I have no clue if this is accurate, nor could I find out how heavy they are.


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PostPosted: November 28, 2017, 1:08 pm 
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Joined: April 12, 2012, 11:56 am
Posts: 621
Location: Pemberton, BC
Similar to Rod's idea, the older Honda Civic 4WD had a small rear diff.

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PostPosted: November 28, 2017, 2:08 pm 
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Joined: January 10, 2008, 4:47 pm
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Location: Massachusetts
Consider a Subaru diff at 55 lbs.? It's an R160. What weight are you looking for? Otherwise look into the ATV stuff as you mention...

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PostPosted: November 28, 2017, 7:49 pm 
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Joined: December 17, 2010, 1:24 pm
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Location: Gainesville, Mo.
You might look at some riding lawn mowers, the older tractor style ones, not the zero radius turn type. Don't know about gearing or strength, but they appear to be plenty light with (usually) an aluminum case. Maybe they're the same as the UTVs.

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PostPosted: November 29, 2017, 1:23 am 
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Joined: June 8, 2010, 8:02 pm
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Location: White Rock, BC, Canada
front diff from an ATV? They're light and cheap and should handle those loads. Not sure what direction they spin though.

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PostPosted: November 29, 2017, 11:50 am 
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Joined: October 10, 2010, 10:26 am
Posts: 988
Location: Bakersfield, CA
Thank you guys for the suggestions.. of all that are mentioned, I've dug around on each, and cs3tcr's suggestion of the Toyota rav4 keeps coming back to the top.. the later generations are all aluminum, they're a 2.928:1 ratio (which is ideal), and might offer an unexpected gain :D ...

Because the rav4 is an 'on-demand' 4wd, there's an electronic drivetrain coupler (aka "Electric Control Coupling") on the snout of the rear end's pinion (red box).. The little bit of research I've done shows this to be an electronic/magnetic device for engaging/disengaging the rear end (as the car's computer dictates the need for either 2 or 4 wd... it's actually pretty sophisticated, as the rav4's computer decides how much current to feed this coupler, thus giving it a percentage of engagement, depending on the torque/traction needs of the rear end)- This coupler is bathed in diff oil, and I'm getting the impression this coupler is actually a little wet clutch in it's own right(?), although I'm learning that it's not a typical 'viscous coupler' as it's electronically controlled..

I'm wondering if I could just feed this coupler 'full' current (100% engaged) when my car's key is on, basically locking the diff 'on'(?) (in the donor vehicle they do in fact have a 'lock' button, which "When engaged distributes the maximum torque limit to the rear wheels").. The advantage I'd get for my project, is when the car is turned off (no power to the coupler), it would disengage the rear end, allowing me to easily flat tow the vehicle, which in my case would be a wonderful little bonus..

Question is, is my assuption right?- feeding this coupler 12v will 'lock it up' and give me a truly engaged drivetrain?

As always- thanks :cheers:

--ccrunner


Attachments:
rav diff.png
rav diff.png [ 221.46 KiB | Viewed 495 times ]
rav diff 2.gif
rav diff 2.gif [ 57.07 KiB | Viewed 495 times ]

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My '72 Honda N600 build log (bike engine in a microcar)...
viewtopic.php?f=36&t=14452

My '63 Volvo 1800 with a turbo inline 4 build log (LNF Ecotec compliments a Svelte Swede)
http://locostusa.com/forums/viewtopic.php?f=36&t=16309
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PostPosted: November 29, 2017, 3:18 pm 
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Joined: October 23, 2010, 2:40 am
Posts: 1022
The Rav4 unit looks interesting with good mounting options. Is there a differential function between the two wheels or is it locked? Is there a limited slip option?

Can the clutching mechanism and housing be removed to reduce size, weight and rotating mass? This would require some sort of adapter plate and pinion flange.

Interested to hear more about your new project. :cheers:

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