Best RWD transmission for TDI Swap

[bigsexyTDI]

So I have poured through the sticky with all of the build thread links, but I can't really find the answer I am looking for...

If you were starting from scratch, what is the best overall transmission for a TDI powered RWD vehicle?

I have acres of old trucks and tractors and other farm equipment and a half a dozen TDIs, and I want to start Frankensteining some sort of rat rod together. It will likely be on an S-10 Chassis as I would actually like to drive it quite a bit when finished and with the use of that chassis for many Hot Rod projects, I know the parts availability will be good for a long time to indefinitely. Also this will allow for decent handling and good brakes, etc.

So all that said, imagine an S-10 frame with a healthy @burpod tuned 11mm pumped, .260 nozzled, GTD17/18/20something turboed ALH with say a '48 Diamond T cab on it... or something completely custom with some old tractor sheet metal... many possibilities. But what transmission?

Best gearing, Best shifting, ease of availability, cost... whatever the factor is for your choice, let me know what ye think. Thanks!

Edited to add that I would likely use an 8.8 Ford rear axle again for the aftermarket support, and because there are a zillion gearing options, so thoughts on gear ratio please add as well.

 

[PickleRick]

The 2wd ax15 from the xj is almost a free transmission if you can find them. I believe Novac transmission sells them new.

 

[GlowBugTDI]

The 2wd ax15 from the xj is almost a free transmission if you can find them. I believe Novac transmission sells them new.

Came here to say this, and instead am going to upvote your post lol. I agree with this, though I'm not 100% sure what kind of HP/torque these trans can hold above the stock rating. I imagine it's a decent margin. I met a guy who was using one in a mini drift truck build using an alh. Never heard end results and if it's lasted.

 

[PickleRick]

300 ft/lbs of torque is the rumored max rating on the ax15.

 

[caffeine]

Could always use an AWD Audi transmission and weld the center diff (usually fairly easy to access). That way there's no adapters or special clutch/flywheel needed. Downside is the chassis-mounted shifter, which would have to be adapted in, maybe shift rods lengthened/shortened depending on the application.

With RWD you can change the final drive ratio relatively easily, so you can get good highway RPMs pretty much no matter what transmission you end up with. The ideal ratio will depend on what gearing is in the transmission.

 

[adamss24]

Use vw crafter transmission

 

[d24tdi]

Use vw crafter transmission

Would be great if they existed on North American shores. The Crafter was never marketed here. But maybe they are common enough overseas to be cheap and easily available? Wonder if the cost of buying one and shipping from UK or Europe would end up less than the price of the adapter plate kits out there for using other gearboxes? What do these transmissions sell for where you are?

Especially in the case of the OP who doesn't already have another gearbox lined up to start with and is beginning with a clean sheet, could make sense. Always nice to have an OE solution. Although are you sure the Crafter trans is drilled for the 4cyl TDI bell? Not certain what the Crafter engine choices were but I believe the older gen LT platform only used the 2.5L 5cyl and 2.8L 4cyl TDI engine lines, which are configured differently. Maybe they had some 2.0L 4cyl choices in the Crafter era?

Interested, as I keep thinking a RWD half ton pickup would make a good work truck with a detuned TDI but don't like most of the adapter choices out there..... Especially for use with the old VE type engines that require a flywheel reference for setting timing, impossible when using a different mfg's trans with an adapter plate.

 

[86turbodsl]

Could always use an AWD Audi transmission and weld the center diff (usually fairly easy to access). That way there's no adapters or special clutch/flywheel needed. Downside is the chassis-mounted shifter, which would have to be adapted in, maybe shift rods lengthened/shortened depending on the application.

With RWD you can change the final drive ratio relatively easily, so you can get good highway RPMs pretty much no matter what transmission you end up with. The ideal ratio will depend on what gearing is in the transmission.

Actually i think Audi/VW AWD trans rotate opposite direction of most common OEMs. Have to stay with same oem.

 

[caffeine]

Actually i think Audi/VW AWD trans rotate opposite direction of most common OEMs. Have to stay with same oem.

Source? Maybe you're thinking of old rear engine transmissions? The AWD Audi transmissions rotate the same direction as the engine, like pretty much everything.

 

[jimbote]

Source? Maybe you're thinking of old rear engine transmissions? The AWD Audi transmissions rotate the same direction as the engine, like pretty much everything.

Nope, the output rotates opposite engine rotation. Looked into this a few years ago for a cheap and easy rwd swap. No gonna work unless you flip the rear diff.

 

[86turbodsl]

I've heard there may be another oem with same rotation, not sure. Nissan maybe?

 

[oilhammer]

If someone (with money, and connections), would just tool up and make a proper cast+machined bellhousing for something like a Tremec we'd all be set.

TKX 5-Speed Rear-Wheel Drive Manual Transmission (tremec.com)

These are simple, sturdy, widely available (still being built, you can buy a brand spanking new one!), and would happily gobble up anything that any 4 cyl TDI could possibly throw at it... and the gear spacing is generally favorable to other high torque/low RPM engines (domestic V8s), so a TDI would work great.

Instead, we're stuck trying to kluge adapters against integral bellhouse manuals from whomever, that certainly "work" but not always the cleanest and certainly has some drawbacks.

Crafter was never sold here, and that gearbox is clearly not ideal for a car or small pickup (it's tall, and geared low, because it's for a giant commercial vehicle). The longitudinal VAG AWD units won't work because the output spins backwards, and they also have some other ratio changes that would have to be dealt with, and they also were not intended to apply full engine output to the rear... although they are probably more robust than the Subaru units that people have attempted to make RWD drift cars with (they all broke).

 

[jimbote]

I've heard there may be another oem with same rotation, not sure. Nissan maybe?

We're talking VW/Audi longitudinal boxes that bolt right up to the tdi. Those boxes are reverse rotation output in relation to crank rotation.
Nearly every other longitudinal rear drive trans rotates the same as the crankshaft. So yes, nissan would fall in that category, as well as toyota, jeep, ford, chevy, dodge, etc... pretty much everyone except VAG.

 

[86turbodsl]

I did some research into this a while ago since i'm into Audis and wanted to know what was possible for engine/trans swaps. With the reverse rotation on longitudinal audi trans, any other oem swap into an audi means you have to either stay with an audi longitudinal trans or swap to a different rear end. Since we're talking about engine swaps using AWD trans with reverse rotation outputs in something non-VW/AG it becomes relevant. Either the trans changes or the rear end changes.

 

[oilhammer]

Something tells me you'd also have to carry the now useless front diff in the case, or the bellhouse will just crack like an eggshell the first hole shot you gave it, LOL....

 

[bigsexyTDI]

If someone (with money, and connections), would just tool up and make a proper cast+machined bellhousing for something like a Tremec we'd all be set.

TKX 5-Speed Rear-Wheel Drive Manual Transmission (tremec.com)

These are simple, sturdy, widely available (still being built, you can buy a brand spanking new one!), and would happily gobble up anything that any 4 cyl TDI could possibly throw at it... and the gear spacing is generally favorable to other high torque/low RPM engines (domestic V8s), so a TDI would work great.

Instead, we're stuck trying to kluge adapters against integral bellhouse manuals from whomever, that certainly "work" but not always the cleanest and certainly has some drawbacks.

Crafter was never sold here, and that gearbox is clearly not ideal for a car or small pickup (it's tall, and geared low, because it's for a giant commercial vehicle). The longitudinal VAG AWD units won't work because the output spins backwards, and they also have some other ratio changes that would have to be dealt with, and they also were not intended to apply full engine output to the rear... although they are probably more robust than the Subaru units that people have attempted to make RWD drift cars with (they all broke).

Exactly... my brother is a CAD Engineer for one of the big defense contractors... I guess I will just recruit his services...

I was just hoping it was already done and I was missing it somehow...

 

[jimbote]

Something tells me you'd also have to carry the now useless front diff in the case, or the bellhouse will just crack like an eggshell the first hole shot you gave it, LOL....

Does the diff provide that much strength? Seems the pinion would be self supporting enough to toss the diff.

 

[oilhammer]

Well that's the thing, I don't know.... but clearly that big chunk of iron filling several holes in the aluminum casting probably does something.

 

[jimbote]

Well that's the thing, I don't know.... but clearly that big chunk of iron filling several holes in the aluminum casting probably does something.

When i was considering this, I was going to toss the diff. It seems the pinion is more than adequately supported. Planned to weld or plug the axle holes and reinstall diff cover.

 

[PickleRick]

Not sure how strong the audi/VW AWD transmissions are but the WRX guys don't seem to mind abusing them after welding the spider gears.

 

[adamss24]

Not sure how strong the audi/VW AWD transmissions are but the WRX guys don't seem to mind abusing them after welding the spider gears.

I have a mate that is runing a rear wheel drive b6 audi a4 2.5 tdi quattro with a few mods. So far hes welded the centre diff and it seems the rear diff is hokding pretry well to the abuse! He wants a gtb2260v adapted off a f10 bmw so we will see if it stands the abuse any longer! Dont know what possesed him to downgrade from quattro to rwd but i guess if we all be the same world would be a really boring place!

 

[caffeine]

If someone (with money, and connections), would just tool up and make a proper cast+machined bellhousing for something like a Tremec we'd all be set.

TKX 5-Speed Rear-Wheel Drive Manual Transmission (tremec.com)

These are simple, sturdy, widely available (still being built, you can buy a brand spanking new one!), and would happily gobble up anything that any 4 cyl TDI could possibly throw at it... and the gear spacing is generally favorable to other high torque/low RPM engines (domestic V8s), so a TDI would work great.

Instead, we're stuck trying to kluge adapters against integral bellhouse manuals from whomever, that certainly "work" but not always the cleanest and certainly has some drawbacks.

There are already adapters available to work with the GM metric bellhousing and SBC bellhousing, no? One of those bellhousings (for a T5 or older 5 speed) should bolt right up to a TKX, and should be pretty easy to find.

 

[oilhammer]

Yes, an adapter, not an actual bellhouse. So you have engine --> adapter --> bellhouse ---> transmission. Wouldn't it be nice to just have engine --> bellhouse --> transmission?

 

[jimbote]

Yes, an adapter, not an actual bellhouse. So you have engine --> adapter --> bellhouse ---> transmission. Wouldn't it be nice to just have engine --> bellhouse --> transmission?

QuickTime made a bellhousing for tremec to VAG inline. This was a few years ago. Not sure on current availability.

 

[jimbote]

Discontinued...

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