Help I.D.ing Drums/Backing Plates
- Thread starter Steve Ciccalone
- Start date
DICK SPADARO
Well-known member
basic answer 39-42 style backing plates, 40-46 style drums
JM 35 Sedan
Well-known member
One drum has the inner style hub and the other has the outer style hub. Some say drums with inner style hubs were '40-'42 and drums with outer style hubs were '46-'48. Sometimes attached balance weights on '46-'48 drums will interfere with '32-'35 wire wheel mounting. Spindles are '46-'48. Backing plates are definitely '39-'42 because they have both upper and lower adjustments.
Steve Ciccalone
Well-known member
JM, appreciate the comment about the balance weights. I thought they might be that. Dick and hotcoupe thank you too. I always figured '39 was all to itself because of the bolt pattern.
Richard (EV8G)
Senior Member
Spindles are actually Model A with probably X-2000 (cheapo) adaptor used to mount the brakes and space the inner bearing.
They are "square" so could confuse with 42-48 BUT the kingpins
with the sockets and provision for bolt-on arms are the giveaway...
DICK SPADARO
Well-known member
Whoa correction time, Jm35 got me to re look again at the drums, I only looked at the outside picture and thought the shine was from the paint. But the inner picture of the drum identifies one with the inner hub as 40-46 and the one with the outer hub 47-48.
Richard (EV8G)
Senior Member
Hey Dick! For MANY years I had always heard that the drums with the hub inside the drum are 40-42 (the 40's have a smooth cone area without the pressed-in stuff to add strength - per assembly line photos)... and that the drums with the hub flange on the outside are 46-48. HOWEVER I once had a "46-48' drum with an outside hub that had an 01A part number on the hub... so I have taken the position of "who knows for sure?" and always qualify my answer to the question "what year is what?"... The big parts book lists them with 51A prefix (45/46), but as replacement for 40-48 and does not indicate if the hub is inside the drum or outside. I had never heard 40-46 and 47-48. Where did you get that??? R.
DICK SPADARO
Well-known member
Richard, The chassis parts books dont identify parts other than a designated part number for the installation. The backing plates are pretty specific but the brake drums are just grouped under o1a,21a or 51a prefixes. The judging standards book outlines the backing plate difference but doesnt address the brake drum difference. Probably you are correct in the assumption that "who knows for sure is the answer" but after trashing enough parts it seems that the flange style hubs show up around here more on later 47-48 vehicles than the earlier style. This is also may be the reason that the flanged hubs are some what harder to find. As they were a later production item and as the brake system changed in 49, turned out to be a short run part. So around here the innie hubs are categorized as 40-46 and the outtie hubs are 47-48. I'm not going to loose any sleep over it, it might just be a regional thing. Maybe one of the readers of this thread will chirp in and set us on the straight and narrow.
JM 35 Sedan
Well-known member
Richard, thanks for the correction on the spindles. I thought they were '46-'48 for sure. Never worked on a Model A so I'm just not familiar with those parts.