Project Spec E30 Part III: Removing the Sunroof Cassette

I read the rules — twice — so it was time to get to work transforming this into a Spec E30. Lots of cars are built at home in the garage, and that’s where we’re going to build this one.

One item that many builders leave in place on a Spec E30 is the sunroof cassette. Reasons vary as to why, but it’s a component that legally can be removed and it carries mass high up in the roof, so it’s well worth the time to remove to help maximize the car’s on-track potential.

The sunroof assembly itself comes out of the car easily with simple hand tools. It’s quite heavy, and taking into account its location up on the roof, it is something you want to remove from your car. On the other hand, the stamped-steel cassette that houses the sunroof is rather difficult to remove. It requires a few special tools to remove it from the car and leave the roof intact. The cassette is mounted to the roof with factory spot welds and adhesive.

One special tool you will find useful is a spot weld cutting tool. I found one for $8. If you can’t source one, you can get away with using a quarter-inch drill bit, because we are not reinstalling the cassette like you would do with a repair or a restoration. The other tools you will need to remove the cassette are an electric drill, die grinder with a cut-off wheel, center punch, small hammer, putty knife, pry bar and a heat gun.

The first step is to locate the spot welds on the front of the cassette. You will notice the roof panel is folded down in three places to form the roof opening. This is where the cassette is spot-welded and glued to the roof. The factory claims there are five spot welds in the front, five more on the inside above the B pillars, and two more on the inside left and right edges of the sunroof panel. I’m here to tell you, on this car I’m confident the factory worker was drunk because I found multiple spot weld strikes that far exceeded the number given by BMW! Finding them can be difficult, so you need to look for either the dimple imprint of the spot weld or the flat circles in the paint.

To get a feel for how the spot weld cutting tool works, first center-punch all the spot welds you can find. Then on the five spot welds in the front of the cassette, drill them out. Try to cut through only the first layer of sheet metal if you can. You just need a good feel for what it takes to cut through the sheet metal around the spot weld. Cut those first five, then find each spot weld on the driver and passenger sides in the same area and cut those. If you are using a drill bit, go to town and drill the entire way through, being careful not to get into the roof panels behind it. Next, move inside the car for some overhead drilling! This will be a good workout, not to mention the pleasant feeling of hot metal shavings raining down on your arms. Don’t sit directly underneath your drilling area!

Now you can break out the heat gun and putty knife. Looking at the cassette from inside the car, the rear section is simply glued in at the factory. Heating the cassette will help soften the adhesive and allow you to get the putty knife in a corner for a good starting point. Use the small hammer to work the putty knife around the entire rear portion of the cassette. Next, I use the prybar to gently pry on the cassette, to test how loose it is. On the folded sections of the roof, I had to gently pry back the folded portion to help break free the adhesive. It’s OK to deform the metal there a little because you can return it to its original shape after the cassette is out. If there is resistance, then you too might have had a drunken factory worker, like we did, and locate all the extra spot welds. Just be careful to not deform the roof panel because it’s not as easy to repair or hide when you are finished.

On the B pillar sections that you already drilled, the cassette metal should move and show that it’s been completely separated. Next, it’s time to cut through the four brackets welded to the roof frame using the die grinder. Once all the spot welds and the welded in brackets are dealt with, the last thing that will be holding up the cassette are the four drain hoses on each corner of the cassette. You can either remove the hoses or cut them. I choose to cut them simply because it was easier. Be ready when you cut the hoses because that’s the only thing holding the cassette in place! Once free, the cassette will come out in one solid piece. These could be a desirable part to a diehard BMW enthusiast who is restoring a car, so remove it with care to reap the sales rewards.

The total weight of the cassette, sunroof and its related hardware is about 60 pounds. The best part is now you will be able to fit the main hoop of the cage up flush with the roofline! That’s easily a 3- to 4-inch gain in headroom and it will make all the difference in the world for the cage.

Now that the stripping of the interior is complete, the cage will be the very first thing going in the car. We will talk more about the cage design we chose for this build on the next installment.

This is one of the spot weld dimples. Others can be a flatter dimple or look like nothing at all if the paint filled in the hole. They can be difficult to spot, so check the cassette carefully.

This is a spot weld bit. The center holds the bit in place while the teeth machine out the material around the spot weld. It’s very similar to a larger hole saw. I got this one for $8.

There are five spot welds on the right side of the cassette and five more on the other side. Notice how the spot welds are harder to see than the previous example.

This is the smaller bracket that is welded to the frame. Use a die grinder to cut the welds to separate the bracket from the roof frame.

Victory! The cassette is out! You can see where the rear of the cassette was glued in. It doesn’t take much effort to separate the cassette from the roof, but it’s well worth the effort because it removes weight from high up in the chassis, which lowers the car’s center of gravity.

The cassette assembly in its entirety. If you’re careful not to damage the part, and it’s still a rust-free example, you might be able to sell it to someone restoring a street car.

Image courtesy of Shawn Meze

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