VW Transaxle Folks?

What's it take to do this?

Cut down VW transaxle, used as a diff for something small, light, and bike engine powered.  I guess it's flipped upside down, or not depending on the bike engine rotation, and which end of the vehicle you're putting the engine in.  Select whatever final drive you want your single speed transaxle to be from whatever VW gears were available, and huge bonus, it's got reverse.

$2500 seems a bit steep, but can I do something like this in my garage with the average power tools, a welder, beer, and gumption?

I've never had a VW transaxle apart, let alone had my hands on one.

http://www.transworks.biz/minidiff.html

I mean, you could just get a Porsche 924/944 transaxle, since they're basically similar and already configured for RWD applications. For well under $2500 you could have any gears you want, LSD, etc....

I could see you doing this at home. Cut off the bell housing. Maybe you would have to shorten the input shaft. Flipping the diff is easy-peasy (I've done it). The shifter went in the end of my transmission, and the linkage was fairly long because the engine was mounted in front of the trans, but it worked, just long throws. Adapting a modern cable shifter shouldn't be out of the question. Go for it.

It seems like an interesting solution, but the thing I always get hung up on with bike engines and reverse is that anything heavy enough to need reverse in the first place is probably going to eat a bike transmission in pretty short order.

I am confused what this is used for :)

VW bug trannies with side plates on both sides can have the ring gear flipped to change rotation , 

The late 75-79  or so bug trans only has one side plate so cannot be flipped , BUT the gear cluster can be put in an earlier trans case with 2 side plates, 

The 924/944 transaxles have the added benefit of using a splined coupler to join the torque tube to the transaxle input shaft.

This could be leveraged to help join a motorcycle engine to the transaxle input:

Most used the Audi 016 based 4/5-speeds while some had a more rare Porsche 915 based 5-speed.

Here's some info on their various gear ratios and options:

http://www.clarks-garage.com/shop-manual/trans-04.htm

http://flussigmagazine.com/11/post/2013/12/g31-transaxles-016083-transaxles-and-01e-supplement.html

IIRC, we talked about this diff a few years ago in the Abarth SP1000 thread.   In a 1000-1200 lb sports racer type of car, having reverse is less of a "need" and more of a convenience.   In theory, the gearing would be shorter (thanks to much smaller tires) and not stress the transmission and clutch as much.  I'd also consider a guilbo or Roto-flex type coupler in hopes it could absorb some unplanned shocks to the engine/trans.

A DIY duplicate could probably be done, but it'll likely depend a lot on your access to machining tools and how many prototypes you're willing to go through before you get it right.  The $2500 is not so much the cost of the materials but also the work that went into figuring how to build it.  In that context, the cost seems affordable to me.  

Can the 944 transaxle be gutted so it only has reverse?  If I'm building a bike-engine car, the entire point is to make the thing as light as possible, which is the main benefit of using a bike engine with the integrated transmission.  

For a while they stopped making those. Buggy applications, where a lot of those get used are very hard on diffs, a lot of loading when you land from jumps and such. But the fundamental idea is solid IMO. The problem with using an entire transaxle is all the weight. Plus you're still stuck wih the punky motorcycle clutch. If one could do the Miatabusa setup without such a huge amount of work it'd be pretty epic, tho. 

I wonder if an electric reverse might be a good option for bike engined cars.  I'm thinking of something like a starter motor that engages a ring gear mounted on the drive train somewhere.

In reply to APEowner :

Yes, that's been done.  The Galek J15/Fury uses an electric reverse in the bike engine builds. It is basically a high-torque starter engaging a small flywheel ring gear mounted to the rear diff. From when I talked to Galek years ago at the Carlisle Import & Kit show, the ring gear is from some rather obscure Euro car as it's maybe 12" in diameter.  It's rather clunky to use just enough to back the car out of a parking spot if necessary.

Lawn mower ring gear is only about 8", but the option i always wanted to try is a belt drive starter from an outboard motor.