# Direct drive without driveshaft?



## Woodsmith (Jun 5, 2008)

Assuming your diff is chassis mounted and not in a live axle it might seem like a good idea.

However!

Problems can arise as the motor/trans is usually rubber mounted and will have scope to move in all three directions, roll, pitch and yaw, and also bounce. The diff will not. Added to which there will be some chassis flex.

By only using one UJ between them you will have used a drive component to restrain the pitch, yaw and bounce movement of the motor/trans. This will probably lead to early bearing failure and UJ wear.

It would be better to have a very short shaft, almost two UJs back to back, that will allow that movement without stressing the transwarp motor tailshaft or diff.
It would be worth ensuring that the motor mounting is still flexible but not too flexible to be outside the range of misalignment for such a short shaft.

There will also need to be some axial movement through a splined shaft. That may already be incorporated in the transwarp setup, but I don't know.

I would also make sure the motor is mounted on at least three points so that it is stable and self supporting and aligned. Don't be tempted to hang the motor on two mounts and use a UJ to hold the end of the motor up.


I've never used this set up BTW but I have tried running a single UJ between an ICE and transmission to a rigidly mounted transfer box in an off road vehicle. It didn't work too well (for all the reasons above) so I changed to two UJs back to back on a sliding shaft. That worked well.


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## kerrymann (Feb 17, 2011)

Woodsmith said:


> Assuming your diff is chassis mounted and not in a live axle it might seem like a good idea.
> 
> However!
> 
> ...


Thanks Woody. I should have specified it was to a fixed diff not a live axle. Only a crazy person would have a 9" motor on a live axle.....  When I did it on my leadwing trike the chain actually took up a fair bit of mis-alignment (though it was showing wear) and they were very rigidly connected.

I think you and I are one the same brain wave as far as the single u joint. I was hoping that I could build a frame that would tie into the diff mounts and support the motor. The diff mount is obviously going to be fairly rigid and a good frame would keep the motor aligned to the diff independent of chassis flex. A short shaft would work for sure but it would still be at least 30cm long. That would move the motor too far away to be supported by the diff or suspension subframe mounts. It would be easier and arguably better to go with a more conventional motor mount with a decent drive shaft (~1m) that can easily soak up any misalignment or flex. A rubber donut type ujoint might be better as it can take up small amounts of radial misalignment but I am thinking it's a losing proposition.

I like the idea of a single u joint but don't think it would actually work out. Now if someone has made it work, I'd be happy to be proven wrong.


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## Tesseract (Sep 27, 2008)

kerrymann said:


> I am curious if anyone has tried connecting a transwarp with the TH400 tailstock directly to a differential with just one u-joint? ...,


It's my understanding that U-joints need to be used in pairs to cancel out the changes in rotational velocity that occur in proportion to the deflection angle. If you want to use just one "articulating" joint then it has to be a "Constant Velocity" type.

Using just one U-joint will basically result in a lot of vibration and early failure, is the gist.


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## Woodsmith (Jun 5, 2008)

I think if you had the diff and motor on a stiff subframe and aligned straight you could probably try using a single rubber doughnut joint. It would be a bit like low power applications using a Lovejoy type coupling.

There is a doughnut close coupled to a CV with sliding action as used on the Lada Niva, between the main transmission and the transfer box, that might be a good option.









I have one that may or may not get used on my tractor to go between the transfer box and the axle.


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## aeroscott (Jan 5, 2008)

Mercedes uses rubber flex disks on all ones I've seen . Including 700 + hp models .


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