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Step One: Motor to gearbox adapter plate and coupler

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Motor to gearbox adapter plate and coupler

This is a short description of how I have connected the NetGain 9" Impulse electric motor to the gearbox on the Volvo 440. I am using a clutchless design where the motor is permanently connected to the gearbox. This is possible because we don't need to idle the motor when the car is stationary and when we release the throttle to change gears the motor freewheels.

Some advantages of a clutchless coupler is a simpler design and lower rotating mass which will increase performance.

The gear change is slower because the syncros in the gearbox have to match the motor speed to the gearbox input shaft speed and this will potentially cause more wear on the syncros, but the flexibility of electric motors means gear changes are less frequent.

Here we see the components used to make our adapter. The aluminum plate is 12mm thick and was ordered with a hole for the motor cut out. Also in the picture is the original clutch disc with the friction material removed, a coupler plate with taperlock bush and of course the Impulse 9 inch motor. If required a new clutch disc can be purchased from your local parts store, this one is in good shape. We need it because of the splines in the centre slide onto the gearbox input shaft and the springs act as a damper between the motor and gearbox.

The coupler is a standard industrial unit, it is actually only half of a coupler but it is all we need. In the centre we can see the taperlock bush. This clever device allows one coupler to fit different shaft sizes as you order the bush in the size required. The motor uses an 1.125 inch shaft but here I ran into the first problem. It turns out that British keyway size for 1 1/8 shaft is 5/16 of an inch but the American keyway size is 1/4 inch.

This problem was solved by having a smaller bush bored to 1 1/8 and a 1/4 inch keyway cut. The next problem I had was the hole I cut for the motor was to small and had to be enlarged with a half-round file. by laying it on the motor and giving it a gentle twist it left witness marks on the plate so I knew were to file.

Here you can see the coupler with the taperlock bush removed along with the grub screws and key steel. The 2 grub screws force the bush into the coupler compressing it onto the shaft. To remove, undo the grub screws and screw one of them into the third hole and it pops the bush out.On the clutch disc it was possible to see where the edge of the friction material was. Using this line we centre punched and drilled 6 holes for bolting to our coupler.

With the coupler slipped onto the motor shaft (tightened the taperlock bush just enough to take up any slack) we marked a circle the same diameter as the holes we made in the clutch disc. Gently pressing the dial indicator holder onto the coupler while turning it by hand is all that is required.

Next I made a template using a cad program (a compass and protractor will also do). The goal is to centre punch six evenly spaced holes on the coupler.

Onto the drill press and then tapped the holes for our bolts.


In this picture I have bolted the clutch disc onto the coupler and slid it onto the gearbox. Over this I made a cardboard template of the gearbox and coupler.Also in this picture is aluminum bar that will give us the required space between the gearbox and motor.

The size required will have to be calculated and depends on the distance required. The length of the motor shaft, gearbox input shaft and thickness of the adapter plate all have to be considered. On the gearbox bell housing are several locating dowels.

You will notice in the upper left corner of the picture that I have drilled the hole so it centres precisely on these dowels. We will come back to that later.


Cutting the adapter plate. I have marked out the pattern using the cardboard template I made earlier. I was tempted to go to my local engineers/machine shop and get them to cut it with their plasma cutter and next time I probably will, but I wanted to see if it could be done with tools at hand. So out came the air hacksaw and away we went. By keeping a shallow angle it was possible to pull the blade around the curves as long as I kept it lubricated. Used WD-40 first but it wiped out the permanent marker so after redrawing it I used motor oil. I am sure that this is not recommended as there is danger of snapping the blade. I used a high quality bimetal blade, 18tpi. Wear appropriate safety gear when using power tools.


Next the adapter plate was laid on the gearbox using the coupler to centre it. I hadn't intended the holes to be so close in size as originally I was going to use a NetGain Warp 9" motor which has a 4" hole. The WarP 9" motor was going to cause clearance problems it the engine bay so we decided to use the ImPulse motor instead, This motor is suited to front wheel drive applications as it is the same length as other 8" motors on the market but has better performance because of its larger diameter. using a drill bit through the gearbox mounting holes, I marked and then drilled the holes on the drill press.

It is now time to decide the orientation of the motor, mark and drill the motor mounting holes. I have decided that the motor terminals are going to face up and have drawn a line on the motor and adapter plate while it was sitting in the motor. The circle you see is because I was concerned about clearance between the coupler and adapter and had to enlarge the hole on the gearbox side of the plate. It so happens that the grub screws for our taperlock bush is the same thread as the motor mounting holes. I have ground a point onto a 5mm allen key and cut it off.

Next it is threaded into the hole so it just pokes out.

Then laying the plate back onto the motor we line up the marks we made earlier and give it 1 gentle tap with a soft face mallet. Remove plate and drill hole. Refit plate, rotate 90deg, lining up hole you just drilled with the next hole and repeat until all holes are drilled.

A couple of problems that you may encounter;
1- The holes don't exactly line up. Use a small rat tail file to 'pull' the hole over.
2- Can't remove the grub screw. If you tap to hard the allen key will get stuck in the grub screw. Make sure it's a loose fit before you start and use a magnet and small screwdriver to loosen it and get it back out.

The plate is now bolted to the motor, the coupler secured to the motor and the clutch plate bolted to the coupler. I have tried it in all 6 positions to find the best one, 'pulled' over a couple of holes with the rat tail file and set up the dial gauge to get it centered. I have been able to get it within 0.002 of an inch (0.05mm) which should be fine. The closer the better. The clutch disc is sitting on washers to space it out from the coupler. It is important that it faces the correct way, flywheel side towards the motor because of the damper.

The next step involves setting the gearbox on top of the motor, loosely bolting together, powering the motor with 12 volts and adjusting the position of the motor to gearbox until it all runs smoothly. Once this is done they can be bolted together and then the 2 bars that fit onto the gearbox locating dowels will be bolted to the adapter plate so if we need to take it apart in the future it will go back together without having to realign it (although the clutch disc would still have to be realigned to the coupler if it was removed)

I must state that this has not been put on the road yet, so check back later for more pictures and updates. Back to the Electric Car page