|[an error occurred while processing this directive]||Short Cuts|
By: Jim O'Brien - 5/2000
|Drilling new holes|
|Adapter after drilling|
|Modification for nut and bolt clearance|
|Hole in floor for clearance.|
During the installation of the 4.3l Vortec engine, I had to relocate the transmission mount. I took this as an opportunity to revisit my skid plate with the goal of increasing the clearance under the skid plate.
My old skid plate was made out of 1/4" plate steel and was pretty much indestructible. The only issue was it had a 3" drop in it to provide clearance for the D300 drop. Since I was installing a new transmission (a SM465) and I had the transmission separated from the transmission, I decide to index (or rotate) the transfer case counter clock wise to provide additional ground clearance.
This isn't a very difficult project, just one that takes some thought before you do it. For instance, in my installation, the transfer case was about 3 inches further forward with the 4.3L/SM465 then the old 4.2L/NP435 setup. This caused some clearance issues that I could only resolve by cutting access holes in the floor/transmission tunnel.
So, to index the D300, I did the following: I removed the 3 studs from the D300 housing so all 6 mounting holes were empty. I then installed in each hole a pointed set screw (I picked them up at the local hardware store for about 32 cents each) with the points facing out. I then installed the D300 (making sure to leave enough clearance so the set screws didn't score the adapter) on the transmission adapter to determine where I would need to cut access holes in the floor. After cutting the access holes, I used a jack stand a shims to rotate the transfer case up to the desired position. During this process, it became clear that I would need to modify the shifter mount that comes off the transfer case above the front output yoke. This was due to the sheer size of the SM465.
Once I was satisfied with the location of the transfer case, I took up the slack between the set screws and the adapter. The goal here was to transfer the center marks for the mounting bolt holes to the adapter for later drilling. I used a rubber mallet to make sure the marks were transferred to the adapter. I then removed the transfer case. All in all the worked out very well.
I removed the transmission adapter and drilled the new holes in the adapter. I also chamfered the new holes in the same manner as the original ones. I could only drill 5 holes, as the sixth one would not have been reachable. If this turns out to be a problem (like leaking oil for instance) I'll move the bolt hole in the transfer case. I also then had to grind the back side of the adapter to make sure there was clearance for the mounting nuts/bolts.
I then dry fit the adapter on the transfer case, and had to make a minor adjustment to one of the holes. I was pretty pleased with how things had gone to this point. It was time to reinstall the adapter on the transmission. This was done in no time. Now for the test, install the transfer case on the adapter while its on the transmission. This took a bit of effort (a D300 gets heavy after while when lifting it by your self!), but I got it installed.
The images to the right show samples of the process. I think the most dramatic images are of the D300 in the stock location and the new indexed location. In the stock location the D300 hangs down below the frame rail at least 2.5 inches. Now its above it by about 3/4". I worked on laying out the new skid plate today and with a little luck I think I be able to run a completely flat skid plate! An additional benefit is that now the rear output shaft bearings should be self lubricating when flat towing.
I still have a lot to do on the engine swap and when I get it done (the motor runs...) I'll come back and spend some time with a sheet metal brake and some 16 gauge sheet metal to close up the uglies I made in the floor. Hopefully, when that is done, it will look like it was meant to be that way, its just the passenger who will lose a little foot space.