Tech Blog Custom Retrofits

Here are some photos of a custom built GMTH400 transmission to be installed behind a Mazda 13B rotary engine.This transmission was custom built for a customer in the United Arab Emirates.For this job we had to make a special adapter plate that on one side mated the original Mazda bellhousing to the GMTH400 transmission case on the other.We also had to design a custom torque converter that on one side mated the original GMTH400 input shaft,stator tube and pump drive to the Mazda flywheel and crankshaft pilot hole on the other.Special thanks to master machinist Dave Minton and Joe Rivera Jr. of Pro Torque for their patience and assistance with this sucessfully completed hybrid transmission.  

Using a sophisticated Renishaw probing system the center of the pump bushing bore location in the pump body is located and recorded.Then a precision register is milled into the pump body that is concentric to that location.This allows the adapter plate to share the pump bushing bore as a centerline ,and not the pump bolt holes drilled in the pump. Due to manufacturing tolerances they are not concentric to the drilled and tapped pump retaining bolt holes in the case.Although the bolt holes need to be slightly oversize due to tolerances,the Renishaw uncovered the bolt circle is off as well.Because the factory 400 case includes an integral bellhousing this is of no consequence when using production parts and assembly methods.In this case the hole locations were needed to provide mounting provisions and not for indexing parts. The adapter plate is counterbored to within .0005"of the pump register for super accuracy.

Once again the probe is used to locate the center of the pump bushing bore of the original MB bellhousing and is recorded.The original bellhousing has 2 tapped holes for 2 alignment dowels used for lining up the bellhousing to the pump and case of the original MB design.We fitted these locations with 2 precision ground 10 mm. dowel pins to locate the bellhousing to the adapter plate with super precision .This is because the original cast holes in the bellhousing to pump mounting holes have no concentricity to the bushing bore.These 2 dowels are what aligns the bellhousing to the already trued pump body and adapter plate.The probe also recorded the locations of the additional original 17 cast bolts holes that are used to attach the bellhousing to the original MB case,or in our set up the bellhousing to the adapter plate.The inside diameter of the bellhousing is machined to clear the torque converter and pump.Special thanks to my colleague Mike Frabrizio.I had no drawings,only hole locations I collected with the Renishaw probe.Mike flipped the bellhousing over on a piece of cardboard ,traced it and had a sketch in 5 minutes.In another 15 minutes he had my previously recorded locations reversed and recorded on the cardboard.In one hour the profile locations were recorded and I was ready to fixture and program the job.The whole task took 20 hours from start to finish and was completed in 4 days.

HERE IS A GM 4L80E FOR A TOYOTA SUPRA. IT UTILIZES AN ALUMINUM ADAPTER PLATE AND THE STOCK BELLHOUSING.THESE SWAPS ARE BECOMING MORE AND MORE COMMON.THIS ONE WAS FOR A CUSTOMER IN NEVADA.

HERE IS A GM4L80E INSTALLED BY A CUSTOMER IN WASHINGTON STATE.