M37 with Hercules Diesel engine conversion

[MSeriesRebuild]

We are nearing completion of a project to install our 5-speed overdrive transmission behind the Hercules Diesel engines that were installed by us back in the early 90's and later by MARS in Nashville, Indiana. We have done all the necessary conversion to mount an sae#3 flywheel housing on the DT3.7 Hercules engine that will then direct bolt to our 5-speed that we currently use with our Cummins conversions. It has a .69 5th gear overdrive. We should be able to road test it next week as we are finishing up on wiring the truck completely and a few other odd jobs we have to get done before being able to drive it.

If any owners who have the Hercules conversion engine are interested in doing a first rate transmission upgrade with a tall over drive option, please contact us at the website shown below. I plan to offer this in a kit form that can be purchased and installed by owners or their local mechanic. Of course we also offer installation in our shop as well.

[k8icu]

It's a shame that the Herc 3.7 diesel is not really an option any longer. That was always a nice set up. 4BT have gotten so expensive even for used take outs that I'm actually giving thought to useing the GM 6.2. Anyway that sounds like a good set up there Charles and I hope you will follow up with some pics and maybe even a technical write up.

[MSeriesRebuild]

Used DT3.7 engines are out there from various sources. Our new trans set up designed to work with it does away with everything on the back end that always gave problems, such as that huge adapter plate that was part of that original kit. With what we have done, if you had a good used engine or a rebuilt; our system will enable you to install it plus the 5-speed overdrive. This is far better than the original Hercules set up that was designed to be used in conjunction with the original M37 transmission.

[waterloo]

hi all,
I want to point out that the 5 speed trans that charles refers to is the spicer 3053 which is super tough. What is new and exciting is that now for the first time there are overdrive gears available for this trans that brings it from a .78 OD to an incredible .69. This is not like the overdrive most people think of, this is like having another gear to shift into. The ratio is 1:1.45 in the trans. I have this upgrade in my truck and it is awsome.

Tom

[Juan]

I have two trucks with 3053s and the OD ratio is 0.85 not 0.78.

[waterloo]

i can tell you that is wrong. all 3053 us military trans had.78 OD count the teeth and do the math, all parts are the same number, there never was a .85 OD. this error is listed on a couple of major web sites, but they have the wrong information.

tom

[MSeriesRebuild]

Tom is correct about the OD ratio. The military manuals list it as a .85 also, however mistakes are common in military manuals. The civilian manual tells a different story.

I can tell you this also; Tom has certainly done his homework on this transmission, no need in arguing the point, he has it covered.

[Juan]

So, that's where my mistake came from, I have the manuals and since the rpm drop between 4th and 5th was not so great, I thought it was true.

My bad.

[MSeriesRebuild]

This is a very common error. The old Spicer manuals and sales literature listed several different 5th gear ratio possibilities in civilian applications; however when you do research, you'll find that many of the OD ratio possibilities that are listed apparently never did actually exist. I have Spicer components Master Catalogs from back in the 60's that say several things nobody has ever seen. When you look up the supposed part numbers in the genuine Spicer parts manual, that part didn't exist.