Who wants to build a transaxle?

I'm just going to throw this out as food for thought.

From my reading on the forum, the availability of 2nd hand G50s isn't what it used to be. I would imagine the current crop of suitable Audi boxes will begin to dry up eventually, too.

There are also people out there who (I assume) would like a new transaxle for their GT40 / Lola / Ultima etc, but price is a major barrier.

In Australia, a new Porsche gearbox is around $18-$23K depending on model. I imagine a new ZF or RBT-6 is somewhere in that ball park. Mendola is at the lower end of this range, but unproven in an application of the kind we are interested in AFAIK. I don't know the cost of the new Xtrac transverse transaxle.

There is a lot of amazing engineering experience on the forum. So, why hasn't someone designed, built and profitably produced a strong 5 or 6 speed transaxle with decent gearing for under US$10K?

Don't shoot me down just yet - listen to my idea. You've may have even thought of it yourself...

Build a prototype based on 2nd hand Tremec or Richardson etc. Make a longer input shaft. Or, even better, make an input shaft extension. Then put a hole in the front of the gearbox and attach an extension for the output shaft (that goes on to the front rather than the rear of the shaft) with a gear on the end. Set an equally strong ATB diff between the 2 shafts (or above the output) with a gear on its input. The diff sits the correct way round and is driven from the gearbox output shaft extension via a reversing gear, so everything spins in the right direction.

I'm sure you can see where I'm going with this. I never said there wouldn't be a lot of machining involved!

Make a frame to support all of this and to take a bellhousing at the very front, over the input shaft extension. Once all the mounting points are properly located relative to each other, have a think about the stresses involved, and use your CAD experience to knock up a case design that mounts between the bellhousing and the gearbox, and that carries (and oils) the diff, and locates and seals all the shafts etc.

You can now produce new transaxles using commercially mass produced bellhousings, gearboxes and diffs, with you supplying CNC'd input and output shaft extensions and the intermediate case, and machining any necessary parts of the gearbox. You could go the whole hog and do a completely new case, but I think that would merely cut into profitability.

Oh, and you might want to consider a business plan before doing any of the above! I'm making assumptions about the costings, but would imagine a unit using new parts would cost less than US$6,000 if much of the machining was done in-house. Add a bit to amortise your prototyping costs, and the rest is profit. Subcontract the intermediate cases out. Low volume, low overheads - the key to undercutting the traditional transaxle manufacturers ...

Why haven't I given it a go, or at least done more research? I'm up to my upper hair folicles in full time work, kids and building my own prototype production car. But if one of you do it, I'll be your customer in a few years time.

So, do you think I'm a complete loon, or is there some merit (you can read genius if you want)?

Ian Anderson

Lifetime Supporter
Ok so who was that looking at producing some engineering stuff in China - How about a transaxle? How many would sell?

I would imagine a fair few

The process does not sound too different from the development of the T44 from the old top loader tranny. However, IMO, to do it rightwould require serious research and development, time and money. And until FFR starts building 20 GTMs every week, the target market is too small to justify such a development effort.

Peter Delaney

GT40s Supporter
Albins Off Road Gear here in Oz (who make most of the custom replacement Porsche gears available) have a 6-speed transaxle setup for off-road use - hugely strong. They are now testing the sequential version, & I am told that the next project is a smaller, lighter version which would be perfect for GT40', Ultimas, etc., and that Stage 2 will be sequential. (Prices bandied about were in the AU$18k bracket).

I wouldn't hold my breath, but if you are at the "looking stage", they might be a reality by the time you need one !

Kind Regards,

Peter D.


GT40s Supporter
In the UK, a company took a pre existing casing but then redesigned the contents completely from scratch. The casing is the useful Renault item that we use in GTD's. The gearbox is now a 6 speed box with all 6 forwrard gears in the main housing with reverse pushed out to where 5th used to be. All shaft sizes have been increased to be stronger.

The benefits are that all mounting points and drive shafts are as before including the gear linkage but you just need to use a different gate. The first to go into a GTD will be during this year.

But the relevance to this thread is that it has taken a good number of years for the deigner to design it and then for Quaife to make all the gears bits.

For G50 users there must be plenty of after market goodies already out there as that is one heck of a good gearbox otherwise why would it be raced with the big power Porsches? If you are a G50 guy, I see no reason to re invent the wheel. Just buy the right bits.


GT40s Supporter
You are right, but teh box has been designed to be used for road work too. It will be interesting to see how the guinea pig gets on. The reason why the box was designed was for Renault Alpines to have better a gearbox and these are driven on the road as much as 40's. The guys who did this do know what they are about. Wendy's Lotus has a dog box (Hewland Mk5)and having driven that, it is very useable.

Ron Earp

Sounds extremely pricey with a low volume, which means production costs would not be cheap. I'd have to agree with Malcolm (since Renault is just not done in the US without extra hassle) - get the Porsche box with the right sutff.

Malcolm what about that company you, Paul, and I got the transaxle flier from at the Festival of Speed? Anything there?


GT40s Supporter
I will have to get Paul to answer that one, Ron, as I can't remember seeing the flier. Sorry, getting old perhaps?
transaxle wish-list

OK, lets see how much interest there is in this idea

If someone was interested in producing a new transaxle what would be the ideal layout?
gear_guru said:
OK, lets see how much interest there is in this idea

If someone was interested in producing a new transaxle what would be the ideal layout?
I would say the ideal layout would be similar to a ZF with a more space-efficient design for the gear selector. It would use a modular bellhousing design so it could be readily hooked up to SBC, SBF, LS1, etc. engines. It would allow the ring gear to be flipped for mid- or rear-engine applications. It would also use as many parts as possible from a readily available, proven existing transmission, such as an input shaft and gears from a T56.
fostereast said:
Does anyone know where any of the old GT40 ZF transaxle drawings can be found?
Hi fostereast - drawings of the ZF internals are on www.rbttrans.com

Mark, your spec looks spot on. I would be looking for a 6 speed, ideally from a donor that has a few ratios available.

The issue of cost of machining has come up a lot in this thread, but I'm not convinced you couldn't significantly undercut the new transaxle manufacturers even (perhaps particularly) with a low volume. I'm definitely not suggesting telling someone with a 5 axis machine and all the other stuff, "This is what I want; build it for me and send me the bill." That would be the expensive way to do it.