Brake Drums

[Crash]

I have brake drums from a 65 SIIA and a 73 SIII. They were removed and put on the shelf in two piles. Apparently there is a difference but I can’t see it. Our host’s list one part number for the IIA and for anything after 1971 a different number.

What is the difference or are they interchangeable?

C

[jac04]

Check the diameter of the lug stud holes. IIRC, the older ones used smaller diameter lug studs.

[Les Parker]

Hello there, the early (pre 1969) have 5/8" diameter holes, the later (post 1970) have 9/16" stud diameter holes.

[Andrew IIA]

Hello there, the early (pre 1969) have 5/8" diameter holes, the later (post 1970) have 9/16" stud diameter holes.

I'm no math wiz.... but... 5/8" would be 10/16" (thus bigger than 9/16"), yes?

are these numbers reversed ?

[Les Parker]

Very astute, just checking to see who was paying attention !!

Yes:-

9/16" = Series IIa
5/8" = Series III

[Crash]

That worked! I had looked at the two piles many times and for the life of me could not see a difference.

Once I put them side by side and used my trusted caliper it was obvious which was which!

A few more thingsto look at and I will be ready for my winter parts order.

Thanks

C

[Mountain132]

Where do late SIIAs fall?

I have a 1970 which I believe uses the SIII studs, is this correct? I've always ordered the SIII drums? There is a little play around the stud but I'm not sure if they would fit through a 9/16th opening. It is much warmer typing than it would be to break out the calipers in the barn/garage.

[SafeAirOne]

Where do late SIIAs fall?

I have a 1970 which I believe uses the SIII studs, is this correct? I've always ordered the SIII drums? There is a little play around the stud but I'm not sure if they would fit through a 9/16th opening. It is much warmer typing than it would be to break out the calipers in the barn/garage.

If your lug nuts require a 1 1/16" socket to remove, you've got the fatter studs and therefore the drums with the larger hole, presumably.

[Crash]

The RN site suggests the Drum changed for models after Oct 1971. And the SIIA drum up to Suffix G.