How to Make Your own Transmission Crossmember

In the following article, we will examine a step-by-step process for how to make your own transmission crossmember. This is no small task and it takes hands-on experience in craftsmanship. For those looking to get into the world of modding cars though, this should be a helpful guide. You’ll probably need to do some surgery when switching gearboxes as well.

In case you change your gearbox, maybe for a five-speed item or as part of an entire drivetrain swap, you will need to modify the crossmember. But why modify it when you can build a custom-made item? There are simple designs that use readily available polyurethane bushings to provide both a solid and flexible mounting point.

Round and oval tubes work best but you can use just about anything, even if it comes from the scrap bin, which makes it super affordable. Before starting, you need to purchase a set of Superflex bushings.

Some alloy spacers are also necessary to align the crossmember ends when welding. Custom-made is ideal, but if you do not have access to a lathe, you’ll have to improvise with some large spacer washers and clamp everything up tight so that it won’t move.

The Step-By-Step Process

Ensure that there is something to fix the crossmember to. On some cars, the central crossmember will be directly in line, but if yours isn’t then you need to come off the chassis rails and floor with some box section.
Once you’ve determined the mounting position, you need to fabricate the brackets. Ensure that there is adequate clearance all around by working the design out on a card.
After you are satisfied with the design, transfer it to some 3 mm steel plate. Ensure you lay out four of these to reduce waste and unnecessary cutting.
As it’s 3 mm, you will need to use a hacksaw to cut and shape it. After cutting, clean the edges up with a file or similar tool. Be sure to cut them in pairs so that they match each other.
With the hacksaw you can cut the two pieces of tube, which form the ends of the crossmember. Make sure to measure the width of your bushings.
Drill a couple of holes in the brackets with a 12 mm drill and place two spacers, as described earlier, on either side to locate the tube. Then bolt everything together with the tube centered.
Test the brackets on the car and make any necessary adjustments. Make sure there is clearance all around the crossmember end, as you don’t want it to touch the car.
If you are 100 percent satisfied with the positioning of the brackets, tack them in place. Use plenty of fasteners on both sides to prevent any twisting during welding.
Weld all around the brackets, then remove the crossmember end and repeat on the other side. To ensure adequate penetration, make sure the area you are welding to is clean and rust-free.
Now that both brackets are in place, you can measure the tube length required for the crossmember itself. Give it an extra inch so you can trim it to fit once the first end has been welded on.
After cutting the end at an angle, offer it up to the tube and use a file to shape it to fit snugly. You can mount your tube high, but it may vary depending on the application.
Bolt the end back in place and position the crossmember tube. Next, mark the location of the mounting holes, remove them from the car, and center punch the holes.
To accept some 12 mm tubes, the holes will need to be drilled. Using a pilot drill, drill the whole way through, then drill each side separately with a step drill. This will ensure that they line up.
Make two lengths of the tube, insert them into the two holes you drilled, use part of the gearbox support if you still have it, and then weld around the tubes. Take care not to burn them.
We need to cut and dress both tubes after they have been welded in. Because our crossmember is mounting flush with the bottom of the gearbox, they need to be almost flat with the tube.
Having now fitted the crossmember to the car, give it a few fasteners to ensure that it cannot move, and then remove it so that it can be fully seam welded.
On the car, you can fully seam weld the tube end, but make sure to add a few fasteners to the sides you can’t reach while welding to ensure nothing moves.
When it is completely cooled down, it can be fitted with the bushings, which should be a push fit into the tube. A little lubricant may help if your bushings are stiff.
Bushings include a steel tube through which the bolt passes. This tube needs to be pressed into place; use a vice to ensure everything passes through the square.
Bolt the crossmember onto the car and mark the other end of the crossmember. Profile in the same way as before, and then bolt everything back on. Be sure to take your time with the second profile to ensure a snug fit.
Once you are satisfied with everything, fasten it down. Get a secure hold on there as you will need to remove the crossmember to complete the welding.
After it has cooled, install the second bushing and clean up all the welds before painting it. Rather than bolting directly to the gearbox, the crossmember has bushings at the end that cushion the gearbox.

There you have it, a step-by-step process for how to make your own transmission crossmember. This can prove to be challenging and time-consuming, so even if you don’t feel up to the task, don’t give up on your swap dreams. You can buy prebuilt crossmembers at an affordable price, saving you the precious resource of time.

If you’re having trouble choosing the right style crossmember for you project be sure to read more about how to choose the right crossmber.