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PostPosted: January 5, 2020, 1:31 pm 
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Hello, all.

I' new to the forum (although I been a reader for years now). I'm mechanical engineer and work as suspension engineer in a auto supplier. I finally decided to put in motion my intention of designing and building a BEC Locost. Wanting to make it as light as possible (OfC) I'm researching components.

Can you guy give me suggestions for IRS differentials with aluminum casing, preferably with LSD available as OEM of aftermarket?

Thank you,


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PostPosted: January 20, 2020, 8:17 pm 
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Hi Folks,

Doing a lot of surfing and researching I came across Audi Quattro vehicles differentials. I found several applications like A4, A6 and A8.

I will check in more details about ratios, splines, etc, but can you guys give me an opinion if there is any reason these differentials are not suitable for a Locost?

Did anyone considered or succeeded using them?

Thank you,


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PostPosted: January 21, 2020, 8:45 am 
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I used a Ford 8.8 IRS out of a Mustang Cobra. Swapped the cover for one off an Explorer, which has big "ears" that made for a better mount. If I had it to do over, I'd just get the Explorer unit to begin with, but when a friend gives you one out of a Cobra, you go with it... :mrgreen:

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PostPosted: January 21, 2020, 10:52 am 
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The Ford diff Gonzo mentions is a good choice. It has a lot of parts available for it, multiple types of limited slip from multiple manufacturers.

I did what Gonzo suggests, be aware that the diff case determines the halfshafts that you use with it because of things like oil seal diameter. The diffs are identical ( sort of ) but the cases are not.

I thought the Explorer parts were big and heavy but when I measured them they were not, I think they are the standard 100 mm CV joints, but I don't remember right now.

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PostPosted: January 21, 2020, 7:52 pm 
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Any diff that accepts standard porsche/vw cv and axles is way ahead of anything else imho. Allows you to buy off the shelf half shafts. Best to have matching uprights.

I'm not aware of any fords using standard cv joints but it looks like the audi's do and I know they have in the past.

Use a hardened steel driveshaft adapter to replace the hardened steel sprocket on the bike output shaft.


The longer the driveshaft, the larger the od should be, not necessarily thicker walled.

You can use fwd or rwd uprights if they accept a cv that matches the diff.

While the diff case is light alloy, the spinning insides are not as light as smaller ring gear applications.

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PostPosted: January 23, 2020, 12:18 pm 
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Well I welcome some talk here because it's an area I need to stop being stalled at in my Car9 build. At the light end we have the Hitachi R160 from Subaru at 55 lbs. Then there is the Miata at 65 and the Big Ford diff at 75 lbs. My guess is the Audi is in the 65+ lbs. area.

Thomas, if the diff in the picture is on your garage floor, that's a petty big plus. Pay some attention to where the mounting holes are when you design that part of your frame. All of the drivetrain torque shows up on the diff mounts.

The Ford diff doesn't come with stubs for VW/Porsche style joints, but everything is available for that diff. It would be nice if the world choose a smaller Ford diff, but they didn't. They adapter stubs cost about $750, so not cheap or maybe I'm wrong on the price. When I measured the balls and cages etc. in the Ford halfshafts they were the same stuff as the moderate size Porsche units. I imagine they are basically world standard. They are one size bigger than the VW base stuff on my Formula Ford's transaxle.

So the stuff from the Ford Explorer IRS that looked so big and bulky really wasn't when I measured and weighed the parts. Overkill for many of our cars but not the turbo or V8 ones. Where I got lost was in the details of things like oil seals and also uprights. THe Thuderbird stuff is good but I resent they charge more for it now. It seems like you could mix and match the halfshaft parts but I haven't gone far down that road.

Along with this there is the possiblities of the stuff the off road folks use which is sometimes referred to as micro-stub ( ? ). This involves making your own upright with a bolt on bearing assembly. SOme catalogs sell a dozen variations on parts for this...

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PostPosted: January 24, 2020, 8:06 am 
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Quote:
It seems like you could mix and match the halfshaft parts but I haven't gone far down that road.
With Ford stuff, you can. I have "hybrid" half shafts on my car, with the splined inner piece from an Explorere (matching the diff) and the outer one from a Cobra axle. Dis-assembly of an old greasy CV is a job best done in latex gloves on an old piece of plywood, while wearing a shirt you plan to throw away afterwards...

:cheers:
JDK

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PostPosted: January 24, 2020, 11:13 am 
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I've used the aluminumC5 Vette diff in a few applications. I had an input shaft machined that allowed me to eliminate the transaxle and run a drive shaft. I had a thick aluminum plate machined that bolted to the front of the diff, provided for a support bearing. The plate bolted into my chassis.

I think the late model Camaro uses an aluminum diff.

I had 4 of the diff to driveshaft conversions made. I have 2 extra.


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PostPosted: January 24, 2020, 9:38 pm 
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The Audi diff turns backwards from other diffs


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PostPosted: January 25, 2020, 1:06 am 
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Quote:
The Audi diff turns backwards from other diffs


Well sometimes we have people ask for that too! You can see the driveshaft is offset a bit towards the driver's side.

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PostPosted: January 26, 2020, 1:03 pm 
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Unless you want to go really fast backwards.


horizenjob wrote:
Quote:
The Audi diff turns backwards from other diffs


Well sometimes we have people ask for that too! You can see the driveshaft is offset a bit towards the driver's side.


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PostPosted: January 27, 2020, 12:11 am 
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slappynuts wrote:
Unless you want to go really fast backwards


Seems like the perfect solution if you want to do a front engine rwd setup with an older Honda engine (B, H, D, or F series) since they spin backwards.


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PostPosted: January 27, 2020, 8:54 am 
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Also some shaft drive bike engines might use this...

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PostPosted: January 27, 2020, 6:56 pm 
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There are some bike motors with right side sprockets that would work with that. I think Honda shaft drives would also.

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