at that point wouldnt it be cheaper to build a steel casing?

 

Ken,
I think that's getting a bit complex. The bearings are at the ends of the case so the case ends is only where you need the anti-stretch device. Molding and/or fitting around the fins could be a pain. Not sure I'd want to weld on the case either due to chance of warping.

 

I thought the GV unit looked familiar in the pics, I used to rebuild them many years ago for Triumphs & Volvo's (used up to the late '80s at least)
The G.V. unit as they say is a Laycock de Normanville overdrive as used on Jags. ,Volvos, Triumphs, AMC's & others , see the info on this web site.
overdrive info, Overdrive Repair Services
Could somebody find out what model GV use ?, probably a J or LH, secondhand units for Jags/Volvos etc. should be cheap & plentiful.
New the Overdrive Repair Services units are £695 / $1216
The company say they can manufacture parts, so maybe more helpful than GV
I will get some pics of a Triumph one I still have in a garage somewhere. IIRC the whole unit is only 12" long max including prop. flange

 

Martin,
Thanks for the additional information. The insides of the Laycock unit looks like the insides of the GV unit right down to the flat bottom oil reservoir. I see that the Overdrive Repair Services does offer a retro unit which could be fitted to a variety of vehicles. The price is good. Could be that one of these would work for the 928 after a lot of mods to the torque tube and drive shaft. I'd wonder if the units that may be obtained from a used vehicle with a lot less torque than 928's develop would be strong enough. Maybe one from a Bently would be ok.

 

This is REALLY INTERESTING.. Thanks Martin..!

Louie,

Do you think if the TT were to be shortened and mated to the ORS unit it would be doable..? I am thinking that a flange could be bolted or welded to a shortened TT with a mounting plate for the OD unit.. The OD would go just behind the Flex plate like the 'Vette unit from GV... If you think this could work, what kind of fabbing would be necessary to get it to work, and would you be interested in making something like it...?

Thanks,

 

Yes, it would all work. I don't see the torque tube shortening and adaptation as much of a problem. I do see the driveshaft adaptation as a challenge. You'd need to make an input section that would adapt to either the flex plate, or clutch disk/pilot bearing and to the ORS unit. Then do the opposite on the output end to adapt to the drive shaft. It may be easier for the output side to make an entire new drive shaft from larger, more robust, material. Unless someone else does this, it will be on my list of stuff to do soon as I get my car running and sorted out. Hopefully in a year. If this unit can't be used as an "under drive", and the only choice is as an overdrive, then you'd need a 2.73 final drive in place of the 2.2. I see people thinking the 3.09 final drive as a cure all. However it seems to be a bit too low and mostly would negate 1st gear just as Mark Kibort has preached. I guess if your motor was really puny, you might need the torque multiplication.

 

Thanks Louie,

Good to know.. I was thinking of this setup, and as I am building a TS SC motor, I think the 2.2 may be fine even if the unit were only O/D. I could switch the O/D off in 4th, and be happy with 1-3 over and 1-4 reg to give me 7 fwd gears... My guess is that if the motor got 500 at the tires, I may even be able to use the 4th O/D..

I will do some research on the thicker driveshaft... Am I correct to geusstimate that if a new Flex plate coupler were fabbed up to say a Vette coupler and input for the O/D, I would only have to be concerned about the O/D output shaft coupler to the modded driveshaft which would need to have 928 splines on the end to couple to the Trans.....

Thanks again,