June 21 2008
Drive systems trial fit.
It's time to try to try to finalize how and where all major components are going to fit. Initially I though of using famous tough Ford 9" (or is it 229mm?) differential because of variety of ring and pinion ratios available for it and it's very common: no matter where you call everyone and their brother has one. I knew that hot rods and drag racing vehicles use this part and you have to try very hard to break it. This means it is likely way overkill for me, but as long as it fits, I may as well take advantage of it. So I needed actual part to try before starting serious shopping. I called to Dutchman Motorsports and Keith graciously allowed me to borrow old 9" differential. Dutchman is well known in racing circles and they will make custom half-shafts for me. They can do all kinds of shafts, hubs, splined adapters and generally can mate anything to anything.
So I made a cardboard mock up of the motor, bolted its front flange to the diff's yoke, rolled it under lifted vehicle and raised up to the front and then to the rear to see how (and whether...) it's going to fit. The outcome of trial was interesting; here are few photos of what I found.
This is Ford 9" differential - real monster compared to stock Audi one.
Approximate shape of the motor bolted to the yoke. There is no allowance for the motor shaft and this will be taken into account later. Actual motor is square in crossection (245mm per side) with rounded corners. Note on the photo that when the motor "shaft" is coaxial with pinion shaft, the bottom of even this big differential has to be raised by about 20mm to line up. This means the motor will be the lowest point of the setup, especially so if the diff I'll end up using is smaller.
The view from rear toward front suspension of the vehicle This diff now is in the right height position where stock half-shafts flanges were, and it doesn't quite clear the underbody bottom. It has to be raised.
However, there is bigger problem here - the pinion shaft is so low that there is no way I can fit any kind of shaft adapter here, not to mention that there is no space for the motor - the front suspension cross beam is on the way.
Obvious option is to flip the diff up side down - high pinion reverse cut gear sets are available for some differentials including this one. But, the bottom of the diff and the motor are still too low. OF course it is not a strict requirement to keep half-shafts flanges at exactly stock height, so I have some options here. But first conclusion so far is to try to find smaller differential with high pinion option.
Overview of this option. Since the pinion shaft is offset to the left (diff is flipped), the half-shafts will be uneven lengths, or the motor will not be centered. Either way it's doable, I'll think about pros and cons of each option. Depending on the weight distribution under hood if I can offset the weight of the off-center motor, this may work well.
Top view of this setup. I can see that in front the motor will not fit length wise if I want to retain stock front radiator. That would be nice but not really a strict requirement.
The distance between motor bottom and the cross beam is only 15mm. Enough for some sort of cushioning material.
Let's assess the situation with rear suspension. Because of the stock differential is narrower, stock half-shafts are longer and will need to be replaced with shorter ones. Also clever Audi engineers managed to make differential without offset to one side, the pinion shaft is right in the middle between half-shaft flanges. Ford didn't bother, so the same story here - either motor will be offset to one side, or the half shafts will not be equal length. Oh well.
The differential is raised as high as it will go. Way too low, it still sticks under body by about 40mm.
Side view. Rear stock diff support interferes with round cover of Ford one. It has to be removed.
The rear support is out and that allowed to raise the diff higher. It is already touching the cross beams so won't go any higher, but the position of half-shafts flanges is where the stock was.
Another photo of this set up - the web cast on top of the diff is touching black round beam. If I want the differential to sit where the stock was, some of the web will have to be grinded off.
Now, however, the real bad luck. My cardboard motor does not fit height wise! You can't see on this photo, but to be able to bolt it coaxial to the yoke, differential had to be lowered. The body floor here is too low here - if the top of the motor touches the floor, the bottom sticks lower than underbody by 25mm. Provided that the touch is mot allowed and it has to be some sort of vibration insulation between motor and body floor, the floor has to be higher by at least 50mm. Inside above motor there is back seat cushion. It can accommodate raised floor. This is regardless of the differential type or location - the motor is just too large to fit under body and clear it. So I'm in for some body surgery - the interfering section of the floor will be cut out and new raised floor will be shaped and welded in to restore structural strength and allow enough clearance to the top of the motor. This is major body work (and may not be the only one needed, more on that in the battery fit section later), but to do it right this is what has to be done. Once the motor is in right position, I can play with the height of the differential. I will use flexible coupler so the motor and pinion shafts don't have to be strictly coaxial.
Closer photo of this step - the motor is supported by a wood stick to stay in highest position - it touches the floor Closer examination reveals that the floor here has slight slope - it lowers toward rear and the motor body is 25...30mm lower than underbody near differential. IT is lower by 15 or so mm on the opposite end. It doesn't matter now as this part of the floor will be cut out.
View from the rear. The camera positioned exactly in the center, and so is the motor. You can see the differential offset toward left side.
What is the situation with power inverters? For the rear drive its location is clear - the only sensible place is behind rear seat back cushions - next to the rear battery box. However, in front it is tempting to put inverter in the transmission tunnel - otherwise this space is lost. Let's check this out.
The EVI-200 inverter is on its side and ready to be raised.
It is plenty wide up front - the stock transmission is obviously bigger than inverter. However, it gets narrower toward middle of the car.
Barely fits, but goes all the way in. Also clears the underbody just right, so this will be the spot for it. If I were to try to mount the front motor here as I thought, this would require widening the tunnel and moving throttle pedal assembly - doable but too much trouble. for little gain - then inverter would swap places with the motor anyway. Now the tunnel is utilized 100% so will stick to plan A - the front motor is in front of the front differential.
Well, time to prepare floor to be modified, this means removing rear seat and wiring.
Rear cushion raised. There is cushion heating wire harness that has to be disconnected. Bosch impact sensor (I think that's what it is) in the middle will have to be moved to the top of newly installed floor later. Moves out of the way for now as well.
I can tell it is used car. It is very clean everywhere where it can be reached for cleaning, but under cushions there were spots of sticky dried Coca Cola spilled years ago.
Wiring removed, floor cleaned and prepared for cutting.
Same photo from the rear door. All I need now is to protect carpets on the sides from welding mess and take care of sound deadening compound removal - it is flammable. Welding is scheduled for next week.