With the engine in place I could finalize placement of the rest of the drivetrain downstream.
Transmission bolted up without issues. The trans has a mount in the rear that bolts to a crossmember which ties in with the framerails, so leave the framerails unmounted until you have the transmission bolted up to dictate their placement.
V8R uses an energy suspension poly bushing in the rear diff mount. Here’s the mount bolted up without the crossmember in place:
**Note the ratcheting strap: the chassis is strapped to the lift front and rear, with everything down to the subframes going in/out multiple times you don’t want to need to keep track of how much weight is on each end of the car so it doesn’t fall off the lift.
Here’s the crossmember added. The crossmember interfered with the passenger side corner of the transmission tunnel and floor, which you can see in this pic:
Taking this notch out of the crossmember fixed the interference and then everything could square up:
With the crossmember bolted up, the framerails could be bolted in their final resting place. Lots of drilling and then torquing bolts (2 person job – one person in the car with a wrench on top):
Checking the transmission angle. It’s sitting at 1.7° nose-up here. With the rear trans mount torqued down it cinches down to 1.6°:
Moving on to the diff!
V8R’s diff mount kit includes a bracket that bolts to the two ears on the back of the Getrag diff which then slide up on to the same two long studs in the rear subframe that the Miata diff bolts to. The kit also includes two bare steel tabs that get welded to the subframe for the Getrag’s front mount.
V8R’s instructions are to weld the front mount in so that the pinion angle is 1.5° nose-up, which looks perfect now that we know the transmission’s angle.
Bolt the rear mount to the diff and then bolt that to the subframe. I forgot to specify I wanted the diff’s factory mounting bolts when I got the diff from the yard so I had to source some – they’re M14x2.0, two 45mm long for the rear and one 90mm for the front plus lock washers for all three and a nut for the front.
The rear mount has roughly the correct angle preloaded into it, so with the diff mounted to the subframe you just shim the nose as necessary to dial in the exact angle. I needed to shim the nose down a bit, you can see the shim stack in the background of this pic:
Also pictured is the fun discovery that the front factory bushing was completely shot – it just popped out in my hand. Obviously this had to be replaced. Despite most of the bushing already being out, the tough part of the bushing removal was still to be done. You have to remove the steel sleeve that the bushing was once connected to. It does not come out gently:
The factory design is prone to fast wear under hard use because it’s soft and has a lot of air gap around the center sleeve. On a street car you’ll want the factory bushing (Moog PN K200641), but for track use I chose a poly replacement. There are a couple on the market, I settled on one from Creative Steel – this is the “street” durometer which is 75A. We air-hammered this in which was nice and easy. I don’t envy someone trying to press this in considering the proximity to the housing:
With that lovely side-track behind us, back to the front mount…
The two steel tabs are identical, but I found they both needed some grinding to clear the housing better. The front just got a bit of clearancing on the outer radius by the hole. The rear tab needed to be notched:
More than one way to tackle setting the pinion angle prior to welding, my method to eliminate variables as much as possible was to set the whole assembly on the bench and shim the subframe to dead level and then shim the diff to the 1.5°:
Then tack-weld the tabs in place:
Rear tab tack welded in, you can see why I notched that tab:
These are tack welded ONLY at this point. Always test fit in the car and measure before finalizing. The car might not be dead level on the rack or jack stands, and that transmission angle that was measured is relative to actual horizontal, not to the car. Measure many, many times and weld once.
Turns out, the car is level on the rack ! Diff sits at 1.5° nose-up, matching the transmission’s angle within 0.1°:
Subframe comes BACK out again, and final welding can happen. Diff is removed from the subframe for this of course. I cut a length of steel tube to match the length of the diff’s front mount and bolted that between the tabs while welding to prevent warping. Don’t leave the diff in there to serve that purpose, you’ll melt the bushing.
That’s it! Subframe will get cleaned and painted now along with some other parts.