Every day Project Grandma gets a little closer. This week, we finished up 90% of the mini-tubs which were supplied by Chassis Engineering. In our ’78 Malibu, we’ve already done segments on the narrowing of the frame rails, cutting out the stock wheel tubs, and boxing the frame rails back in. Now it was time to make sure we can fit the tire and wheel combination with our mini-tubs.

Chassis Engineering offers four different kinds of wheel tubs that work with virtually any tire size. They offer standard tubs that are 23-inch wide and 40-inches long, Pro tubs which are 28-inches wide and 45-inches long, and an intermediate tub which is 28-inches wide and 40-inches long. The smallest Sportsman wheel tubs are available either in .040-inch aluminum or .024-inch steel.

Since we were doing a mini-tub and not a full back-half, we chose the smallest steel tub from Chassis. We also knew that even that tub would need to be trimmed down width size as we didn’t need to take up our entire trunk since we would be limited by the stock narrowed frame rails. Our wheel wells are shipped unassembled, and like all C/E wheel tubs, incorporate a “Pittsburgh” seam that allows for easy assembly.

Before we could install the kit, we had to clean up the wheel well area before we could measure to fit the mini-tubs in. Mike started by cleaning up the cuts he had made before when removing the original wheel wells and removing a little more metal to give him a nice clean surface to weld the new tubs into. This was more about finishing off the “rough” grinding and cuts from the plasma cutter we showed you earlier.

From there, Ryan made a cardboard mock-up of the tubs to test fit the kit in. After a few quick slashes with a marker, he trimmed the mock-up down to the correct size needed to fit the finished tub in. This is a step that you want to spend a little bit of time on. Cardboard is a cheaper to throw away than metal so Mike made sure that the fitment was right before transferring the dimensions to Chassis Engineering supplied steel tubs. Not all chassis shops do this, and some trial fit using the actual tubs.

Here is an inner shot of the cardboard tub in the wheel well with a “rough cut. You can see there are some challenging areas inside the tub where the factory upper control arm mounting area is located. Logically here we are probably going to have to supplement the Chassis Engineering tub with some additional sheet metal here for a good seal and a clean look.

A shot from inside the car so you can see the approximate location and fitment of the cardboard tub. Because the C/E tubs are so nicely sized in terms of length, we will never have a problem getting our Malibu slammed down to the ground like we are planning.

To make building the tubs a little easier, Mike brought a tub-jig he had built out of wood from his shop. To make it work for this job, he had to modify it a little bit because of the tire size we chose for our project. This made it easy when crimping the ‘Pittsburgh’ seam of the tub to hold the two pieces of metal together.

While Chassis Engineering doesn’t require it, Mike went ahead and riveted the end of the kit together before crimping down the edge. That way, there is no way for the two parts to slip or slide apart changing how it would fit up into the car while he was test fitting it in the car. After that he used a hammer and pounded down the Pittsburgh seam to secure the tub together.

The C/E wheel-tubs are capable of really fitting up to a 32-inch tall tire and one at least 14-15-inches wide. Obviously we won’t need that much room due to our tire size, so from there he simply cut down the blank tub to the size needed to fit into the car. Not wanting to have to go back and add metal in later, he cut them out a little big and trimmed them to a perfect fit. The same process was repeated for the passenger side tub.

Once the mini-tub was properly cut and then fine-trimmed, it was time to install it into the car. Since we cut out the inner wheel tub, we would have some work to do here that could be called trickery. We tack welded the tub to the front and rear inner sheetmetal that was cut away, as well as to the rear trunk hinges.

Mike also took the chance to cut out the trunk and weld in a new panel that covers the hole where the spare tire well was located in the trunk of the car. Then all that was needed to do was weld the now trimmed tubs in. He started off tack welding everything in place. Later Mike will go back and lay down a real nice bead to cap off this part of the build. While normally you would weld the tub into the inner fender as well, our car will be retaining her 70’s appliance-white paint job so we didn’t want to risk bubbling its unique surface. We’ll just fill in the gap with some seam sealer later when we weld the rest of the floor back in. For now check out some finished shots below.

The rain might be coming down finally in Southern California, but that doesn’t mean this car is down off the lift for good. We still got lots more to do before we can mock up the engine and transmission as well as a few other surprises. Check back next week as Mike Ryan will be getting to what some say he does best – putting in a Chassis Engineering roll cage, along with a full upgrade to the SFI 25.5 spec.