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Crash
12-06-2010, 11:56 AM
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
12-06-2010, 12:07 PM
Check the diameter of the lug stud holes. IIRC, the older ones used smaller diameter lug studs.
Les Parker
12-06-2010, 12:08 PM
Hello there, the early (pre 1969) have 5/8" diameter holes, the later (post 1970) have 9/16" stud diameter holes.

:)
Andrew IIA
12-06-2010, 01:59 PM
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
12-06-2010, 03:42 PM
Very astute, just checking to see who was paying attention !!

Yes:-

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


;)
Crash
12-06-2010, 08:51 PM
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
12-06-2010, 09:04 PM
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
12-06-2010, 10:19 PM
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
12-07-2010, 12:53 PM
The RN site suggests the Drum changed for models after Oct 1971. And the SIIA drum up to Suffix G.