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Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 2:13 pm
by BobShirleyAtlantaTx
Seems like I did this years ago, but let me run this by you guys. Is there any reason a 26-27 drum can’t be narrowed and used in an earlier transmission? I’m pretty sure the later clutch disk and driven plate are used. The driven plate bolts are replaced with socket screws, but past that won’t this work?

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 2:29 pm
by rgould1910
I've done a number of transmissions using a cut down 26-27 brake drum and driving plate. I like many features of the 26-27 set up. Not only the lugs without bolt holes and the lug shoes which hold up better against the pressure of the clutch discs, but the captured driving plate inside the drum. I use the cap screws same as an earlier driving plate but turn a lip on the underside of the bolt head to mate against the smaller cut out area of contact on the driving plate. I suppose you could machine a washer or spacer to achieve the same result.
BTW I was told on that the 26-27 brake drum will fit inside an earlier pan, but I haven't tried it.

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 3:44 pm
by R.V.Anderson
You could also find an original '25 drum that has all the features Richard cited and save yourself the effort to cut one. They aren't real real hard to find. Don Lang had a couple NOS '25 drums awhile back.

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 5:03 pm
by Scott_Conger
I am redoing a '23 runabout with a 26-27 brake drum in it. Very little clearance, but it cleared the 3 dip pan and showed plenty of use under a narrow band. I am building this to tour and will be replacing the pan with a reinforced 4 dip pan...am leaving it as-is as I see no payback for the effort to turn it down.

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 6:57 pm
by Wayne Sheldon
I have seen several earlier Ts with uncut '26/'27 drums in their transmissions. Ford did not need to bulge out the pan and hogshead to make room for the drum, Ford had to bulge out the pan and hogshead to make room for the band to have space to adjust and operate within.
I have heard that some really early narrow nose pans and aluminum hogsheads may barely hit the edge of the uncut drum. However, the '15 I had twenty-five years ago would have worked fine. I measured it in the car.
You cannot use the '26/'27 hogshead because it holds the band too far to the rear, and that could make even the narrow band hang up a bit. The narrow band in the narrow band's position on an uncut later drum works just fine. So, why cut it?

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 7:03 pm
by Scott_Conger
Wayne

my question exactly. I'm leaving mine for someone else to find (hopefully many years hence)

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 7:18 pm
by Mark Gregush
I cut mine down. Cut or uncut, does give full width of surface for the brake band to ride on. Most all the 25 back that I have seen and work with, there is a step from the drum to the driving plate.

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 9:18 pm
by Dan McEachern
You can certainly cut down a 26-27 brake drum and use it with the earlier style driven plate. When doing this, it is critical that you duplicate the shoulder diameter on the rear (6 bolt) side of the brake drum so that the lip on the mating surface of the driven plate is a snug fit. These diameters keep the brake drum and driven plate concentric during assembly. The bolt circle diameter of the 26-27 brake drum is slightly different than the earlier brake drum, so the bolt holes in the driven plate need to be remachined to match the later brake drum bolt circle and the area above the thru holes (now slots) counterbored to make room for the 9/16 bolt heads. If you do those two things correctly, the earlier driven plate works just fine on a 26-27 brake drum and is an exact replacement with no other changes needed.

Re: Cutting a 27 brake drum

Posted: Thu Mar 21, 2019 10:38 pm
by Scott_Conger
Dan

why not just keep the 26-27 drive plate? I'm not seeing a benefit to fitting an earlier plate to a later drum.

Re: Cutting a 27 brake drum

Posted: Fri Mar 22, 2019 9:23 am
by rgould1910
The 26-27 driving plate is an improvement over the earlier style because it is rigidly captured inside the brake drum.
The earlier style has a lip that fits inside a groove in the brake drum but there is usually wear in that area allowing movement/misalignment. I don't trust the 6 bolts that attach the earlier style driving plate to the drum to insure alignment when bolted up or to maintain alignment under torque. Thats why I prefer to use the 26-27 style in alll transmissions.

Re: Cutting a 27 brake drum

Posted: Fri Mar 22, 2019 9:31 am
by rgould1910
Just had a thought. I'll bet the reason Ford eliminated the rear busing in the brake drum in later production was because the 26-27 driving plate was rigidly captured inside the brake drum such that the bushing inside the driving plate insured the drum would be aligned.

Re: Cutting a 27 brake drum

Posted: Fri Mar 22, 2019 10:17 am
by Scott_Conger
Richard

that is my thought, too.