July 01 2011

Suspending Rear Motor

Time to complete rear end. Lots of decisions on mechanical parts to be made. Luckily, stock half-shafts will be reusable as Audi differential is wider than Toyota one. This means I will have to machine spacers to accommodate shorter than required half-shaft. Audi engineers managed to make pinion gear shaft dead centered in respect to the sides, while Toyota's unit is straight forward and its input shaft is offset 30mm to the right. Because heavy motor is centered along the car body, the differential will be off-center by 30mm. This means my spacers will be uneven thickness since stock left and right rear half-shafts I'm re0using are identical length. Bigger challenge is suspending motor and differential using noise absorbing cushions while keeping them strictly coaxial. Don't forget that right half-shaft sleeve linked to Toyota diff was mounted directly to it and because it's more than 600 mm long it acts as a long lever resisting twisting forces when engine torque is applied, so there are no other brackets or attachment points for this purpose. I won't have this anti-torque sleeve, so when the diff will try to rotate around its input shaft, there must be something preventing that. And that something must be attached to the vehicle body  through cushions as well.

After long debate how am I going to hang totally foreign differential and prevent it from moving, what I ended up doing is re-using Audi's cast aluminum anti-torque support beam for its differential to hold Toyota's diff. Since mounting holes of course not only do not match but don't exist on the rear cover of Toyota's unit, I just welded these two parts together. While fabricating motor support brackets as well as differential supports, to keep motor and diff coaxial I temporary linked them with hard aluminum coupler mimicking rubber coupler I'll be using, so the whole assembly acted as one piece. This worked out very well, and I later on did applied the same technique for the front end. The rest of the work, while tedious, was pretty straight forward. Few different sizes of rubber vibration isolating bumpers were purchased from Grainger, thin sheet metal mock up of the brackets were cut and pre-fit, and final parts were made from aluminum and steel. Following photos show the process along the way.

Left spacer as machined
Right spacer. Note it has deeper cavity to accommodate off-center differential.
This is where it goes.
The spacers bolted to the differential stubs.

The steps below may not be described in right order - this work was actually done more than a year ago (I just got time to update the website) so I don't remember exact sequence. But all the steps were necessary, and for some the sequence is not critical - for instance fabrication motor support brackets is unrelated to machining half-shafts spacers so I could have done it before or after. I also recall taking more photos than currently posted here, so I will update this page when I find them.

The stock attachment eyelet on the rear cover of Toyota diff had to be cut off since it interfered with the rear suspension beam. The stock Audi bracket holding diff will be welded to this point. 
Designing rear motor support brackets.
Trial fit. 
Trial fit - side view.
Bending of 6mm thick steel is better done on heavy duty press.
A special die makes the job a snap.
 Initial bend with larger radius round die.
Final bend with sharper angle.
Another simple bracket - right angle bend. Piece of cake for this ancient bending press machine.

After all major components were suspended, final step is to link the motor and differential with flexible torque transmitting disk - this is a shaft coupler from a Mercedes drive train.

Mounting motor-differential coupler.

More photos to follow.

Next - updated battery