Tech- Fabricated rear trans mount

One of the big advantages of the frame swap is that I'll be using the entire driveline, from the flywheel back, as it is. This means the rearend, driveshaft, and transmission will stay in their stock positions. For one thing, repair and maintenance will be routine, since it will all be stock. Also important is that driveline phasing will not be affected. Phasing is the relative angular positions of the driveline components along their axis'. In basic terms, if the angles get messed up, the driveshaft u-joints will not work properly, and the driveshaft develops an imbalance (or perhaps it is really a binding) that causes vibration, humming, and in some cases a bad vehicle shake. This can be troubleshoot(ed?, troubleshot?) later, but it can take a lot of shimming and trial and error. I once had this problem and it only happened at certain speeds; never did get that fixed properly. So I am hoping to avoid the problem.


One thing I have to maintain is the position of the transmission. It is held up in the front by being attached to the motor, and has a single mount under the back part all the way at its rear. Taking out the motor will leave the transmission flopping about. Not good. I decided to fabricate a bracket, sort of a bridge, or girdle, to keep the transmission in position when the motor is removed. With the transmission secured, I would only have to make new motor mounts for the electric motor.

In the lead photo, you can see I made a straight bar that goes under the two stock trans-to-motor bolts. I did some grindy-grinding to make reliefs for the vertical trans strengthening ribs. I'd rather take the material out of the bracket than the trans case. Frankly, I don't think it'd matter either way. I made angled pieces that go down to friendly spots the frame rails, and welded them onto the horizontal piece.

I made two tabs to weld onto the frame. The main bracket will bolt to these. I didn't want to weld the main bracket directly to the frame. This way, if it ever needs to come out, it will be easy to do. Plus I am assuming for now that this will clear the F100 floor and firewall. If the whole thing interferes later, we will have to do something else, but at least it will maintain the trans position for now, so I can remove the motor. The tab on the left has a scallop to match where it will go on the frame .

I used through holes and did not tap either the bracket or tabs with threads. I like the simplicity of bolts and nuts.

I also like round the corners off with a "big" radius; notice it does not go tangent to the sides, but still has corners at the junction of the radius and sides. This is the sort of thing you normally get with a mass-production stamping machine, and I prefer that look over the fully rounded ends you would expect with a custom made piece. So I like the unexpectedness and irony of it. Looks more industrial too.

Here is one of the tabs clamped into position for welding to the frame. In reality I had to swing the clamp up to make room for the welder nozzle. You can see that radius detail I mentioned.

I used beefy 1/4 x 1" steel bar. I had considered going with only 1/8" thick material, to save half the weight, but decided against it. This mount will be holding up part of the motor weight too, so it will do a fair amount of supporting. Angle material would give more stiffness along the beam, but there is really only vertical and rotational (radial?) loading, not front-to-back, so the flat bar will suffice here. Look, I'm not going to have to justify every design decision here, am I? Jeesh.

Here you can see one tab welded to the frame, and the bracket in position behind it. I am going to use a transfer punch to mark the bracket for drilling the matching holes. A transfer punch is a center punch that is at the end of a particular diameter rod. These come in a set of many diameters, and you select the diameter that fits tightly into the hole in the first part, in this case, the tabs. You then whack it with a hammer, and you get a center for drilling your matching bracket hole that is exactly centered with the tab hole. This is a big improvement over the "trace the hole with a pencil and try to make an accurate matching hole" method I have used for years. The center punches have vastly improved my fabricating; parts fit together with better alignment and less slop. Way more professional.

Unfortunately they have not improved my ability to focus a camera.

Here is the bracket installed, bolted to the trans and the frame tabs. I took it off and gave it a little zippely-zoot with a spray paint can, and it's done. I like semi-gloss (semi-flat? no, satin) black, it has a factory stock look, and again is also an understated industrial look I dig. It didn't show up well in the photo after being painted. I can now remove the motor and bolt the trans to this in preparation for the rest of the conversion.

This took about 2 hours total to make. Maybe less, but I did other things while I thought about the next step, and I was trying to take photos and plan this post as well. Fabrication is the part I really enjoy most anyway, so why rush through it just to be done?