Lightweight Tough Live Axle

Looking at buying a V8 Bugeye and weighing up options for the rear end - it currently has an unknown open diff. Was supposed to be a Mustang II eight inch but it isn't - not a drop out center section. Could be a 6 3/4" Mustang II rear which may be strong enough (mild small block Ford and small tires) but I don't know if LSDs or gear sets are available for them. A 9" Ford seems way overkill and heavy but maybe an aluminum center section and lightweight brakes would negate a lot of that? The choices of gear sets/LSDs and strength are certainly attractive but what other options are out there?

Will obviously need to be narrowed so axle shafts with a constant diameter that can be resplined would be a bonus. Definitely want an LSD and being able to get a choice of gear ratios would be helpful too.

GM 7.5/7.625 is the first thing that comes to mind for being relatively light, and having tons of gear and limited slip options.  Might be slight overkill for your power/weight, but I can't think of any lighter live axle with the same level of customization options. 

Edit:  Might be a Mopar solution, too, but I don't know much about them.  Maybe some old Toyota axles, but probably harder to find, and more expensive.

Edit again:  7.5 axles apparently are not constant diameter, so you may be looking at paying for custom axles.

Ford 8"?

Toyota 8"?

Volvo 940/960

(dana something)

No idea if they are sturdy enough or not, but I am sitting here on my lunch break watching mighty car mods, and they are putting an LSD into a kei truck rear axle, and it has a removable center chunk like a Ford 9".  Might be the right width for a Sprite, too.

I'm pretty sure the Legends/Dwarf cars use cut down Toyota 10 bolt axles, so I'd guess they were chosen at least in part for being relatively light, cheap, and easy to narrow.

My first thought was Toyota 8" and Ford 8".  The Ford likely has more gearing options.

What about Dana 35s from base model jeep wranglers? They should be laying behind every 4wd shop as no one wants the little axles. 

A Datsun/Nissan H190 (510 wagon / Roadster) diff is 96lb complete; that weight is with Aluminum diff carrier and aluminum drums. It's 53" wide axle flange to axle flange. It will handle 300ft/lbs of torque.  You can fit an OS Giken limited slip ($1500 installed) and if you can find the axle itself that will be another $1000.  At that price you could just about get a custom rear axle.

I did some serious wheeling and dealing on the one for my 1200 it I was still out of pocket $1500.  

In reply to Tom1200 :

That came in the 1600?  With ~100hp is the limited slip needed?

sidekick/tracker axles are already set up with brackets for a 4 link and track bar. 

Stampie said:

In reply to Tom1200 :

That came in the 1600?  With ~100hp is the limited slip needed?

Yes, the leaf spring suspension has very limited droop travel and so the inside wheel spins.

It's probably not an issue on a street car but remember Datsun made race parts for every model of car they made back in the day.

You will be re-engineering a bit anyway as you are starting with a quarter elliptic car - a semi-elliptic is an easier conversion.

What is the output of the engine?  With a light car with limited adhesion, you will be more likely to spin tires than break axles, but anything from the later style MGB on would work, if shortened to the right track width.  It would be nice to get a Japanese axle with an LSD, too.

I stuck with an early MGB axle as my output on my V6 was only about 200 bhp and I am a conservative driver.  What sort of power do you expect this car is putting out and how do you intend to drive it?

The Ferd 8.8 seems to be the go-to choice for many these days--still easy to find in a junkyard, as sub-modern Exploders and Mustangs are still pretty plentiful.  You might still be able to find an actual old-school 8" like the one that came in my Falcon (and Broncos/Mustangs w/V8s), but people seemed to start liking them and seeking them out some years ago . . .

My 9" with aluminum housing, 10" solid rotors, and aluminum calipers (VW A4 chassis: Golf/Jetta/New Beetle, may also be shared with front wheel drive B5s) weighs 190lb.

The Mazda 7" I took out weighed 160lb with 10" vented disks and pure unobtainium iron calipers.

The 8.8 would have been a better option weight wise but there were other considerations.

For my RX-3, I was considering a Ford 7.5.  They are plenty strong for a light car and they are very light.

Rx7 gsl-se have been used narrowed in bugeyes for years. Hard to get gears below 3.90 though lsd options are pretty good. 

In reply to Teh E36 M3 :

You can get 4.08, 4.09, 4.44, and 4.78 as junkyardables.

I have an unmolested GSL-SE rear with calipers, rotors, cables, and stabilizer bar, but am hesitant to sell because the thing is $2500 now.  If I want one later, it will be even more.

I meant numerically lower ratio. But yeah- pretty good support. I frankensteined a 4.44 Kia front cwp into a Miata housing with an RX-7 clutch diff. Worked beautifully. 
 

Also I believe 3.90. 4.22, 4.30 from Rex-7 and Miata. As long as they have the short pinion from the solid axle cars and Miata's and some other rx vehicles. 

Thanks for the comments and suggestions. A bit more info - it's just intended to be a general fun hooning around car, will probably go down the strip a couple of times to see what it will do but that's not its main purpose and it won't be wearing slicks. Maybe 250-300hp? I think around a 3.50 gear would probably be about right,  tire size somewhere around 205/60x14.

Pete. (l33t FS) said:

My 9" with aluminum housing, 10" solid rotors, and aluminum calipers (VW A4 chassis: Golf/Jetta/New Beetle, may also be shared with front wheel drive B5s) weighs 190lb.

 

The Mazda 7" I took out weighed 160lb with 10" vented disks and pure unobtainium iron calipers.

 

The 8.8 would have been a better option weight wise but there were other considerations.

 

For my RX-3, I was considering a Ford 7.5.  They are plenty strong for a light car and they are very light.

What rotors are you running, are they from an OE application or aftermarket? Are the Audi calipers from the front or rear?

How does the 7.5" compare weight wise with your current set up?

I doubt you'll be able to actually put traction to it, so make sure you don't get wheel hop and you can probably undersize it. A little tube bracing can go a long way.

Personally my vote would be a Ford 8.8. Plentiful in junkyards, cheal, good OEM diffs and gear ratios, lots of aftermarket support, take a ton of abuse and you can get them in leafs or coils. Then if you ever do get traction it won't explode.

In reply to Racingsnake :

I wanted a 4 on 4.5" bolt pattern to match my FC RX-7 front suspension, so I had axles made by Dutchman to my specs.  I also wanted to widen the track by an inch because I was getting tire rub on the inner fenders with the RX-7 axle, and move the pinion over a little to the left because the RX-7 pinion flange hits the right side of the tunnel.  Basically it is an axle for a 58" rear on the left and a 60" rear on the right, for a 59" flange to flange width.

The main reason I used the 9" over anything else, besides very cheap gears and diffs, is the pinion flange to axle distance is almost the same as the short nose Mazda 7".  I acquired a Thunderbird pinion flange and had it machined to take the Mazda driveshaft.

Rotors are from the rear of a NEDCAR Volvo S40 (2004-earlier), like $10 each.  Dutchman doesn't do stepped wheel/rotor registers, so I had the axles made with the Mazda register and had some centering rings made locally that were the same thickness as the rotor hats.  (Being a Mitsubishi design, the rotors have ridiculously large pilot) 

Calipers are from a VW, not Audi - first generation New Beetle and other A4 chassis cars. (Contemporary Audi A4s were built on the B5 chassis - VWAG started their chassis naming convention before they started calling Audis A(x) )  Front drive Audis appeared to use the same beams, or at least the same at the business ends.  The Volvo and the VW both used Lucas rear calipers so the pads are even the same, but the VW calipers are aluminum and the hand brake cable setup was much more adaptable to the Mazda - just trim a notch in the housing bracket, and widen the cable mount slightly.  And clock the calipers roughly 45-60 degrees down so the cables could reach.  Axle housing brackets for some flavor of Wilwood caliper had the same center-center distance so those were cut down to suit the small diameter rotors.

If I were to do it again, I'd have used FC RX-7 four lug rotors so that I could move the calipers more inboard so I could use 14" wheels.  ACTUALLY if I were to do it again, I would ring up Speedway (the shop in California, not Iowa) and have them build me a floater rear end.  It would probably have been about the same expense, and I found that even with the Torino "big bearing" housing ends I was only getting three or four rallycrosses before the axle bearings were hosed.

Hosing axle bearings is a major reason why I stepped away from the RX-7 rears - axle bearings were a constant issue. 

As was, towards the end, just plain breaking axles.  As Opti pointed out, a little bracing goes a long way, the final event where I ran the 7" was the event that I broke an axle brace when the jack slipped while I changed a tire.  Immediately broke the axle on that side in competition.

No hard numbers on the 7.5, that was a project that never panned out.

As someone who spent quite a bit of time wondering about reasonably lightweight upgrade/alternate options for Toyotas originally equipped with 6.3" and 6.7" (aka 10-bolt like the Dwarf cars use) I would think the Ford 7.5" and Volvo with Dana 30 center section (240? 740? Not entirely sure which models) would be decent options.

The Toyota 6.7" and 7.5" are also good on paper, but not so much when it comes to paying for them...everybody wants them, hard to find these days, and they are priced accordingly.

In reply to Pete. (l33t FS) :

I came to the same conclusion after building up mine; I was very close to being able to just have Speedway build one.