Gearbox mounting

#1
Hi Everybody

Just wanted some advice on mounting the transaxle. I spoke with the engineer and he said to only use three points of mounting, two for engine and one for gearbox. I am using an audi 012 gearbox and it has two mounts on it. What have you guys done for this? I assume you use both gearbox mounts but just tie it back to one point. I am using a sub frame under motor and gearbox to bolt up into car. So would I tie it back down to the subframe below or up to car chassis?

Thanks
Marcus
 

Clayton

Bronze Supporter
#3
Marcus
The RF1 used the cradle style of mount with a stabilizer bar to stop for & aft movement (picture below of one).
I used four points in a rigid chassis to eliminate the stabilizer bar and help control torque twist.
Has worked well so far.
The mount in the photo above will allow the rear of the transaxle to swing sideways a bit if using std engine mounts. Needs to have another link to form a triangle or be fabricated as one piece.
If you are using a solid gearshift linkage, you'll need a stabilizer bar otherwise it will pop out of gear on accel / decel, IMO.

Clayton
 

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#4
Thanks for reply Clayton

Oh yeah I see it now yes that would swing.

Is yours a race car where you have mounted with four points? Mine is a road car. I am a bit concerned that it will try and twist the weakest part, perhaps the adaptor plate, if the mounts are different stiffness between engine mounts and gearbox mounts, if I use two on gearbox. Yes I am using standard engine mounts so if this was fabricated as a single piece and just used that rubber it should be ok do you think? So the second and third picture that allows some rotation?
I am planing on using a cable shift.

Thanks again
Marcus
 
#5
Marcus, the gearbox needs to be damped, but properly mounted to the strongest place connected to the chassis. The 012 has side mounts and both should be used, with a proper transaxle mount - easiest is an L bracket with a rubber mount under the bottom of the L.

If the mounts are too soft you can get some shudder under launch. If the mounts are too rigid then you get a lot of vibration. There is a happy medium. One thing to keep in mind, rubber in compression works but tends to transmit a lot of vibration. Rubber in shear does a lot better in this regard, but the shear load has to be carefully engineered. Said another way a rubber donut works OK, but a proper mount working in shear is better.

Unless your chassis is really flimsy you shouldn't have to worry too much about flex/bend. Think about it - say, 400 ft/lbs of torque spread across 24 inches (typical) between engine mount and transaxle mount isn't a lot of force.
 

Clayton

Bronze Supporter
#6
Marcus
Its a street car with over 14000 trouble free km's.
There's no vibration, the engine mounts are fairly rigid as well.
I used superpro shackle bushes for both engine and gearbox mounts.
I didn't want to run a stabilizer bar, hence the design of the engine / gearbox mounts. I've added extra bars to stiffen the chassis, so minimal flex.

If you are going to run std engine and a single gearbox mounts I would highly recommend a stabilizer bar to stop fore and aft movement.

Clayton
 

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