Is it possible to transform a pre-1926 transmission into a broad brake drum one by just changing to: 3311B broad brake drum
3321B drive plate
3323B six drive plate bolts
3337D three clutch fingers+screws
and place it under the 26/27 transmission cover?
On most 3 dip pans the drum will clear the pan, but then fitting the band will usually give clearance problems. The fellow who built the motor in my 24 tourer spent quite a bit of time heating the pan and beating a relief in it to accommodate the band. Check out a 4 dip pan for the change in shape at that point.
Hope this helps.
Allan from down under.
I think you need a four dip pan too to get enough clearance for the wide brake band.
You can have the wide drum with a three dip pan, but then you have to use the narrow brake band and the pre improved hogshead. (only advantage would be the drum saving lug shoes for the clutch)
To take advantage of having the wider brake drum you will need the 26/27 hogs head. The center line of the brake pedal is moved back. There may or may not be fitting issues with the lugs that are used to bolt the later cover to the block. You can use the later brake drum with no fitting issues by doing some trimming. Cut the back part off just where it goes over the 26/27 drive plate. The early brake drum used the drive plate as part of the brake drum surface. With a trimmed 26/27 you now have the lug caps and a full surface for the band.
If you do use the later drum in any case you will need a set of the 26/27 large clutch disk. While the later large clutch disk can be back used, the older stile will not fit. The small disk are the same.
Thanks much for responses - I have succeeded in finding a 3311B broad brake drum and also a drive plate marked with the factory no. T-710.
Now I am uncertain if this is the right drive plate, as the encyclopedia tells me, that for 1926/27: "3321B (T-749B) is a redesign to accommodate the wider brake drum, clutch finger(T-732C) and pins (T-735B) are new."
Should the one I need be marked with the factory no. T-749B?
You can check if the drive plate fits into the brake drum. If it does, it's the 26/27 style. The earlier drive plates has a larger outer diameter so the wrong style won't fit right inside the drum where it's supposed to be fastened. The fastening screws is also a special style - see the vendors catalogs.
A common modification is to turn down the 26-27 brake drum so it will fit inside a pre 26 pan and transmission cover. By that I mean make the drum narrower, not turn down the thickness. You get the benefit of a captured driving plate and better lug geometry ie, the lugs that engage the discs are separate from the bosses that have the bolt holes for the driving plate, and the lugs are fitted with steel shoes. I've done it on one or two cars.
Below is an NOS drive plate that my dad picked up 60+ years ago from a Ford dealer - note the number on the plate casting is T730B. Perhaps T749B refers to the shaft? (Each piece has a factory number but the assembled component has a part number 3321B.)
Another photo of the drive plate and an NOS 26/27 brake drum can be seen in this thread:
When you take a closer look (through magnifyingglass) at fig.549 on page 274 in the Model T Ford Service Book, you will find, that
3323B Drive Plate Bolt is not a the bolt that is referred to in parts lists and other places, but a screw to which I have not found reference anywhere. Is there any explanation to this occurrence? - I have four of these screws (missing two).
What you see is not a screw, it is a shouldered bolt drilled for safety wire. Reason you need these bolts is that the thickness of the brake drum coupled with the recessed driving plate requires the extended shoulder to be able to get a wrench on it and to secure with safety wire. If you turn down the drum as suggested above you don't use these bolts. Here are a couple photos. One of bolt, one of the modification I refer to.
Actually there were "screws" used in the Improved Model driven plate. I'm not sure which came first - bolt or screw but it appears the "screw" would have used less material to waste in manufacturing thus a later modification but that is speculation on my part. I have several sets of the screw type (slotted) and will take some pics. after coffee and head into the shop.
Could it be, that the Chapter XLII - Servicing the Improved Car - was added to the Service Manual shortly after the introduction of the car itself, so that fig.549 on page 274 is imaging an early transmission, hence the "screw" would have come prior to the "bolt"?
You might just have a point there, Niels - perhaps the "screw" type was determined to be an unsatisfactory fastener and re-designed to a "bolt". Here's photos of both.
Steve - unless someone comes up with a different documented explanation I think that's the way it went: "Screw" was initially meant to fasten the plate to the drum, but was very soon replaced by 3323B "Bolt", and did not live long enough to get its own part number, but long enough to get into the earliest batch of cars produced.
That is right, the Part# 3323B is Factory#742 for the Improved Car. Previous screw is the 3323 for the earlier drum.
So maybe the 3323B is the 'hex bolt' and there may have been a 3323A which would have been the slotted screw.
That slotted version is shown in the intro pic used in the Service Bulletin of the Improved Car transmission.
All good info. Here's another thought. Look at the photo above of the modified brake drum. See how the hex heads of the bolts would not have cleared the ID of the brake drum had the drum not been narrowed? While the bolts used in this modification are not the same shouldered bolts used later, they have the same size head. On this brake drum and driving plate, it appears only the screws would have cleared the brake drum.
If this is true the bolt diameter of the drum and driving plate must have changed to account for the hex head fasteners.
Perhaps spoke too soon. If the heads of the shouldered bolts extend beyond the edge of the brake drum there would be no need to change the bolt hole diameter. This then would be the reason for the step, ie to extend the head of the bolt out past the edge of the brake drum.