Here is my transmission mounting bracket. The bracket is a 3/8" thick piece of steel drilled to take two industrial vibration isolators.
I ordered the isolators from a place called DrillSpot.com. I placed the
order at around 10 p.m. one night, and got them 6 p.m. the next day, on
standard shipping from halfway across the county. I was impressed!
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The
bracket mounts to two existing 10mm threaded holes on the tail housing.
This combination puts the transmission output shaft at the same height
as stock (if I measured correctly). Note that both this mounting plate
and the gear shift mounting cover have to be removed for the
transmission to easily slip in between the x-member and the transmission
tunnel brace.
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Here
is the PDF template for the bracket. You could totally make it out of
aluminum, if you want. If I were to make it again, I would certainly do
so. Drilling 3/4" holes in 3/8" steel takes a while, at 1/16"
increments, even with a decent drill press.
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The
two outer holes in the bracket, with the bushings, take two very long
5/16" grade 8 bolts that go through holes in the top and bottom bracing
plates of the x-member. Drilling these holes was not fun, but is
completely doable without removing the body. Here are the holes seen
from above, through the shifter hole in the cabin.
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I
needed 18" of clearance to fit my drill, and I availed myself of my
2-ton hoist to achieve it. Basically, I hoisted the car until the
tailpipe (which is cut on an angle) kissed the ground. I trust my hoist,
but laying under there still scared the crap out of me.
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The
drill was mounted to a right-angle jig (the black posts in the
picture), which was itself mounted to a positioning plate that I made.
The positioning plate is then mounted to the stock transmission mount
support. This ensures that the holes I drill will be straight
up-and-down and follow the centerline of the car -- at least as much as
the stock transmission did.
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Two
six-inch-long 3/8" bolts hold the transmission mounting plate down to
the x-member. For reasons both aesthetic and practical, the bolts go up
from below, so I added a cotter pin so they couldn't fall out completely
if the nut loosens up. The really big washer comes with the isolator
and serves to hold everything in place even if the rubber fails.
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Here is a view of the transmission bolted into place. It's hard to get a decent shot under there.
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This
is a close-up of the same. I'm hoping that the 1/8" below the two
silver bolt heads will be enough. I think it should be. If not, I'll
remove the thick lock washers and use liquid thread locker.
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That's
it. The shifter comes out of the stock hole in the transmission tunnel
centered front-to-back and side-to-side. The threaded end needs to be
turned down and re-threaded to 5/16" - 18tpi for any standard
early-Roadster shift knobs to fit. There are plenty of aftermarket knobs
for the Miata, though, if you want.
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Tuesday, September 6, 2011
Transmission Mounting -
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