Gearbox/Transmission Mount Replacement

Start by removing the exhaust so it would be clear for lowering the cross member. Depending on your car’s setup this may vary but for me it was easiest to drop the entire exhaust. With that out of the way I could focus on the gearbox cross member and associated bits. My setup includes a stay bar, so I removed that bolt at the front, I then put in a floor jack to take the weight while I removed the four 9/16^ths bolts that hold the cross member up. I could then lower the gearbox gently, so it sat on the fixed cross member, and this is all the extra working space you’re going to get.

Using a long extension and a wobble piece I then removed the two 1/2-inch, nuts that are on the threads of the rubber mounts. It’s kind of a fiddle but just move yourself around to get a comfy position and angle and it will be fine. You may have to pull down on the cross member a bit. Also on mine, being a later model car, on the passenger side is the grounding strap, so make a note of where that is fitted. It basically must bypass the rubber mount to keep the ground functioning. Early cars have this ground strap in the engine bay, essentially doing the same thing.

Remove two more 1/2-inch bolts in the bottom of the cross member that connect to the mysterious Y piece bracket. With these removed I was able to get the entire cross member out of the way and be ready to work on the mounts. This is possible because I have slotted the cross member bolt holes. I will explain and show that a bit later.

Getting to the two 1/2-inch bolts holding each mount in place is now easy. If the mounts are bad and mushed up, you may have to work a little bit to get a socket on the bolt head. Just move the rubber a bit if you need to and remove the bolts so you can then easily remove the old mounts and start to install the new mounts.

Before you install the new mounts, spend some time with the threads on the stud. This is is molded into the center of the rubber mount. I think these probably get paint and some amount of rubber on them in the manufacturing process. Once these are ready install the new mounts and made sure to get the ground strap in place.

With an overdrive gearbox the refit process can be a real pain. There are various options suggested to make this easier. I have implemented part of these with slotting the bolt holes on the cross member. This allows you to easily remove the cross member. It is also easier to install the new mounts without having to pre-attach them to the cross member. Doing so gives the nightmare of getting the four bolts installed into the gearbox to hold everything in place. If you have a standard 4-speed gearbox this is not nearly as much of an issue. But with the overdrive it makes things very hard. Yes, it can be done without modifications and I have once. But if you value your sanity, I suggest slotting the holes in the cross member.

As you reinstall everything, get all the various nuts and bolts in place loosely, so things have room to move. Then you can raise the gearbox with the floor jack and work on mounting it with the 9/16 ^ths bolts. Work on getting all of these started and on which ever side you do second be prepared to use a pry bar or other leverage to get things to line up. It’s unlikely it will go up squarely and some finessing will be required. Be careful to get these bolts in straight and correctly so these go in easily with the captive nuts in the frame rail. Tighten these up and check all the other nuts and bolts on the mounts and into the Y piece and the stay bar (if you have this).

While you are under the car and the gearbox is lowered, take a few minutes to check Tom’s Knob for debris. This is the drain from the vent/grille just in front of the windshield. If this gets blocked, you can get water coming into the car near the floor vents etc. It’s easy to get to while you are under the car. Just open the bulb piece and let any debris out and maybe carefully poke around to get everything out and cleaned up. It’s on the passenger side and just inside the start of the gearbox tunnel. As your are doing a gearbox/transmission mount replacement this is an easy item to do.