Rear Differential Bushing Removal/Install
The differential on a Miata attaches through two giant bushings to a cradle mounted to the body. The entire rear suspension also mounts to the cradle, so it is best to take care of the differential bushings while you have the control arms removed. To replace these bushings, you must remove the rearend housing. First, you need to detach the PPF and driveshaft.
We found it was easiest to remove the entire PPF by removing the three bolts on the transmission and the two long bolts with captured nuts at the top that run through the differential. Also, there is a locking washer on the front bolt of the diff — you will need to pry it out once you remove the bolt, then the PPF should come free. As for the driveshaft, we took out the four bolts mounting it to the pinion and slid it over out of the way (don’t remove it unless you have something to cork the rear of the trans).
There are three bolts on the transmission and two on the diff that need to be removed to detach the PPF. Note, the front bolt on the diff has a locking washer/sleeve that must be pulled out to free the PPF.
Once that is done, you are ready to remove the differential housing itself. We used some penetrating lube to free up the nuts holding the bushings in place. There are two locating studs and one large bolt that hold each side in place. Once we broke the two little locating nuts free, we used an impact gun with a long extension to break the large bolts loose and out came the rearend.
Now the fun begins! You need to reuse the metal part of the lower bushings, so you will have to remove all of the rubber bonded to it. Without a press, it is time-consuming, dirty, messy, and (can be) smelly.
A torch is definitely needed for the lower bushings to debond the glue holding the rubber to the metal surface. Energy’s instructions state to heat the metal until you see light smoke coming from the side of the bushing, signaling the bond is broken. As usual, none of us remembered to read the instructions until we had pretty much cooked all the rubber off of the first bushing — it smelled like the drag strip! After looking at them, we did the second one the correct way, and it was a cinch!