Custom Transmission Mount for TJ

As you take your Jeep on the trail, one of the first things you noticing is the lack of ground clearance. Especially as soon as you start doing harder trails. The first major modifications made to most Jeeps is to lift them to gain some ground clearance. The two major types of lifts are the suspension lift, and the body lift. Lifting the body generally allows for more tire clearance and the running of larger tires. Larger tires will lift every component of the Jeep while keeping stock suspension geometry. This is a good thing. However body lifts can only get you so far. With the suspension lift you gain clearance on everything but the front and rear axle assemblies. The suspension lift alters the stock suspension geometry and most lift manufacturers account for this in their kits. Most people find that a combination of both of these types of lifts yeilds the best performance overall.

I have always been a believer in that the larger lifts are not always needed. As you can tell from some of the other articles on my site I took a TJ with a modest 3" of lift, a 1" body lift, 33" tires and front air locker through some of the toughest trails on the East Coast. The point of the articles was to prove that the super high lifts and really large tires are not necessary to get out there and conquer the trails. Also that a Jeep you can drive every day is capable of doing just that, and getting you to work on Monday... in one piece.

Keeping with that idea, I set out to improve on one aspect of the TJ, CJ and YJ that has always bothered me. How low the transmission skid plate hung down from the center of the vehicle. Upon measuring the stock skid plate, it takes up a whopping 4.5" from the bottom of the frame rail to the bottom of the skid plate! That's more than your average lift! If you drop the stock skid plate, you will find your transmission is bolted to it utilizing a rubber transmission mount between the skid plate and your transmission. This is where most of those inches come from. The idea is to transfer this mount to the inside of the frame rails and gain back some inches below the frame rails.

Here you can see the new transmission support. Two tabs were welded to the inside of each frame rail and motor mount bushings mounted between the tabs. Square tubing was used to run across and underneath the transmission. Steel plate was then welded to the tubing to mate up to the transmission in the original location. Also note the re-routed exhaust to clear the new mount. The original converter was used along with an aftermarket smaller muffler.

The bushings used are polyurathane which does transmit a bit more of the motor vibration into the cab. However rubber could easily be used to replace the poly bushings. While I gained close to 4.5" underneath, I did not really raise the transmission that high. Most of the clearance we gained was in the original transmission mount. So there is plenty of room for the transmission and transfer case. Even though I do have a 1" body lift, you could still do this without it. The main things to check for while raising the transfer case and tranmission is clearance between the tranny and the body, the front driveshaft and the transmission mount, and the exhaust.

One of the other things this modification does change is the driveshaft angles. I placed a call to Tom Wood of Tom Wood's Custom Drive Shafts and discussed my project with him. After measuring all the angles twice he had enough information to help me decide on the correct rear driveshaft. The rear driveshaft is now at a 22 degree angle. Fairly steep for a 3" lifted TJ. Tom suggested a high clearance CV joint setup. This shaft will allow for axle drop and an overall angle of about 35 degrees. Tom is a great guy to talk to if you decide to take on a project such as this.

Here are some more pictures of the driveshaft and how to grind the output yoke.

Finally the finished product. Look how much more clearance there is!

The next step is to make a flat skid to protect the transmission and transfer case.

Last updated 6/15/2005

Finally the finished product. Look how much more clearance there is!