Modifying a ZF 6-Speed to fit a M73

[C3Ferrari]

Hi all, I am installing a BMW V12 engine in a 1969 Ferrari 365GTS4 replica, built on a 1977 Corvette chassis. The bolt pattern on the back of the V12 is different from any other BMW engine, and BMW never installed an M73 with a manual transmission. I did not want an automatic transmission in my “Ferrari” so I had to figure out a way to adapt a manual transmission to the engine. I was able to secure a ZF, six-speed (GS6-53BZ) out of a 2005 645CSI, so I decided to modify that transmission to mate with the V12. I thought it might be helpful/interesting to outine how I did this in case anyone else might want to try.

My first step was to cut the end of the bellhousing off of the original transmission. I did this with a simple sawzall, since the final cut on this part would depend on measurements taken off the manual transmission:

The next step was to build a fixture to mount and hold a miter saw so I could make a cut on the manual transmission that would be perfectly parallel to the original mating surface of the bellhousing. I made the fixture out of ¾” plywood by screwing in a 3’ x 4’ piece perpendicular to a 4’ x 8’ piece and then bracing it so that it would stay perpendicular. The miter saw was mounted to the 3x4 piece so that the blade was parallel to the surface of the 4x8 base. This was verified by using a level to set the blade. I then determined that I needed to cut off 4 inches of the manual transmission bellhousing, so I made a raised “stand” which was exactly 4” below the saw blade. That stand was permanently screwed into the base for rigidity. The circular piece of thin plywood seen in the picture was used to help spin the transmission during the cutting process, and to achieve the exact height measurement:



The saw was then powered up and the transmission was slowly rotated so that the bellhousing was cut evenly all the way around:


The small sections of uncut material seen in the photo are the structural ribs used inside the bellhousing. They were trimmed off with a hand saw to remove the end of the bellhousing from the transmission:



A similar cut was then made on the section of the automatic’s bellhousing so that it could be welded to the manual transmission in such a way as to provide the correct spacing for the input shaft to fit into the pilot bearing when the transmission is bolted to the engine. Here are all the pieces ready to be welded together:


In order to make sure the two pieces are welded together so that the input shaft of transmission would be properly aligned with the pilot bearing on the engine, the piece of the bellhousing from the automatic transmission was bolted to the engine:


Then the engine was rotated up such that it was standing on the front of the crankshaft and the transmission was set on top in the position it would be used:


This is a view looking inside the bellhousing showing the transmission input shaft mated with the pilot bearing:




The entire assembly was being held steady with an engine hoist and blocks of wood. At this point, the bellhousing was tack-welded to the transmission to set the alignment:


The entire seam was then welded together:


I had a custom flywheel and clutch setup manufactured by Spec Clutches, and now have the engine and transmission installed and running in the car. So far, so good!

[ponchiz318]

Wow, great work! Any pictures or video of said replica?

[C3Ferrari]

Thanks! Here's a picture...

[Tim Mc]

And I have issues aligning a standard bellhousing on a Gen I SBC! Serious job.

Neat project-Miami Vice on steroids!

[C3Ferrari]

Thanks. I got tired of people saying "yeah, but it sounds like a Corvette". Not anymore!

[rusefi]

and now have the engine and transmission installed and running in the car. So far, so good!

How is it going? How many miles do you now have on this setup?

I am mostly curious how did you get things to align - the input shaft has to be _really_ parallel and concentric to the crankshaft? Was it pretty much just eyeballing or else?

I understand you've put some effort into making both cuts parallel, but how did you get concentric?

[Liquidity]

I’d like to point out that the M70 most certainly was mated to a manual transmission - the Getrag 560G in the 850Ci. Obviously a bit too late for OP, but not for people looking to do this swap that come across this thread.

[FlyWulf]

Very interesting thread. Plenty of good old fashioned all American ingenuity.

I would also like to mention that there is also an adapter plate and flywheel combo that can be purchased to mate a BMW v12 to a number of BMW 5 and 6 speed transmissions. It is manufactured by a company called PMC Motorsport in Germany. One can order direct from them or from a vendor in Poland that has these items listed on eBay here in the States. The Aftermarket Flywheel must be used with the adapter plate. It can use the OEM BMW clutch or there are aftermarket single and multi disc clutches available. If you need a bolt up solution it is available. I am not affiliated with these companies in any way. Just letting it be known for those who are not inclined to do this kind of work on their project.

Cheers,

FlyWulf