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Old 12th April 2018, 10:45 PM
RandyBMC RandyBMC is offline
Junior Member
Join Date: Sep 2017
Posts: 19
Default Gearbox output and diff mounting?

Hello all! I have very much enjoyed the wealth of information here - Chris's, Stot's, and Skov's builds especially.

I was hoping for some help. You can see my full build here:

On to the question. My diff is tilted upward slightly. If I have to, I could shave the rear of the delrin bushings and slot the forward mounting plate in the chassis to tilt the diff downward. See the photo of the angle - about 3-4 degrees from 90. It sits about 7" from the build table surface with the frame raised for the engine mount (doesn't matter - just use that 7" for reference in comparison to the gearbox).

The gearbox can be angled down to within a degree of the diff - 92 or so (see photo on page 11 of my build). It is 6.5" from the build table. If I do nothing and mount the gearbox and diff as is, the diff is higher than the gearbox and about 1-2 degrees off in the Y-plane. It is correct left to right as far as that plane (z-plane?) goes (though obviously offset to the driver side/LHD as all Miata stuff is). I know to avoid vibration you should have both of those axes aligned.

Will I have a big vibration if the output of the gearbox and the diff are 1-2 degrees off?

Is it OK to have the gearbox lower than the diff (usually it seems OEMs go the other way, with the gearbox higher than the diff)?

Thanks in advance for any and all help!!
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