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Coupler overview
Since I spent a majority of my EV conversion budget on a Lithium battery pack I needed to cut back the spending and save money wherever possible. One of the areas I figured I could save a few bucks was on the home fabrication of the coupler and adapter plate.
I started my quest for a DIY coupler by searching the catalogs of commonly available industrial taper lock bushings. After looking over the many different products that use the taper lock setup I selected a synchronous gear belt pulley and split taper bushing combination made by Browning. I chose the synchronous gear belt pulley to make the coupler since it was made out of steel instead of cast iron and would be easier to machine. The pulley was Browning part No. 24HP100 (Grainger No. 2L700) which had an outer diameter of approximately 3.8” and thickness of 1.25”. The bushing was Browning part No. P1 X 1-1/8 (Grainger No. 3X483) for a 1.125” keyed shaft. I chose the split taper style bushing over the Q-D style bushing because the split taper type has an external key which mates with the pulley for positive drive and greater torque carrying capability. Whereas the alternate Q-D style bushing does not have an external key and relies solely on the friction of the taper and the bolts to transmit the motor torque to the load.
Bushing and pulley as purchased
Coupler CAD dwg
One nice aspect of using a later model donor vehicle such as the A4 Jetta (4th generation) is the pilot-less input shaft in the transaxle. No pilot bushing is required for the transmission input shaft. This eliminates the need to fabricate and install a bushing in the end of the motor shaft or coupler body.
Since I spent a majority of my EV conversion budget on a Lithium battery pack I needed to cut back the spending and save money wherever possible. One of the areas I figured I could save a few bucks was on the home fabrication of the coupler and adapter plate.
I started my quest for a DIY coupler by searching the catalogs of commonly available industrial taper lock bushings. After looking over the many different products that use the taper lock setup I selected a synchronous gear belt pulley and split taper bushing combination made by Browning. I chose the synchronous gear belt pulley to make the coupler since it was made out of steel instead of cast iron and would be easier to machine. The pulley was Browning part No. 24HP100 (Grainger No. 2L700) which had an outer diameter of approximately 3.8” and thickness of 1.25”. The bushing was Browning part No. P1 X 1-1/8 (Grainger No. 3X483) for a 1.125” keyed shaft. I chose the split taper style bushing over the Q-D style bushing because the split taper type has an external key which mates with the pulley for positive drive and greater torque carrying capability. Whereas the alternate Q-D style bushing does not have an external key and relies solely on the friction of the taper and the bolts to transmit the motor torque to the load.
Bushing and pulley as purchased

Coupler CAD dwg
One nice aspect of using a later model donor vehicle such as the A4 Jetta (4th generation) is the pilot-less input shaft in the transaxle. No pilot bushing is required for the transmission input shaft. This eliminates the need to fabricate and install a bushing in the end of the motor shaft or coupler body.