Centramatics didn't fit my 1980 Airstream with aluminum wheels
Let me start off by saying I have no complaint against Centramatic. Their customer service has been above reproach.
A few weeks ago I decided to put Centramatic balancers on our 1980 Caravelle. It is equipped with the original 1980 style aluminum wheels, as shown in the first photo.
From Centramatic’s web site it looked like it would take the model 300-356 balancer, but to be sure I phoned Centramatic to confirm this. The first person I talked to said that model number had been changed to 300-556, but she thought I needed the 200-221 Special. She referred me to a second person who said the model for my Airstream was 330-556A, so I ordered a set, which were promptly shipped.
The 300-556A balancers arrived. They are about 12-1/2 inches in diameter. I held one up to the inside of a spare wheel and found it wouldn’t fit in the wheel.
I called Centramatic back and this time was referred to Jerry in Tech Support. He confirmed that the 300-556 was too big for my wheel and I did in fact need the 200-221 Special. He immediately shipped a set of those and issued a UPS pickup order for the first set of balancers, all at no extra charge.
A few days later the 200-221 Special balancers arrived. They looked like they were going to fit fine. The mounting surface of the wheel is essentially a plane surface 12” in diameter, so the ring has to face inwards toward the brake drum.
The wheel mounting surface on the brake drum stands out from the drum (second photo) and it looked like the balancer would fit with the ring facing the brake drum. I put on the first balancer and mounted the wheel. It was immediately apparent that the wheel didn’t seat properly; when lightly tightened with a wrench the lug nuts were flush with the ends of the studs. Normally about 3/8 inch of stud sticks out past the lug nuts.
When I took the wheel off and looked more closely I realized that the balancer wasn’t really seating on the brake drum. The ring was contacting the brake drum with the Centramatic web still more than ¼” from the mounting surface, as shown in the third photo. When the wheel is mounted the ring is clamped between the cast surface of the wheel and the cast surface of the brake drum, which is clearly not the way it's supposed to go together.
Our axles were replaced with new Henschen Dura Torques at the factory a few years ago, which might be the problem. I don’t know if the brake drums on the late model replacement axles are different from the ones on the original 1980 axles, but in any case, neither the 300-556A or 220‑221 Special balancer fit the present combination.
At that point I was out of both time and inspiration as we were about to go on the road, so I again contacted Jerry at Centramatic and he gave me an RMA number to return the second set of balancers for a refund.