I have grooved drums on my 13 and I want to turn them to smooth the surface..
My question: What's the minimum OD that a transmission drum can be?
This way I will know if I can repair or replace.
Thanks and Happy New Year!
Make sure they are not rough or sharp, or cracked, and run them like they are. Grooves wont hurt as long as they are smooth.
I agree with Hal. Do not remove any material from the drums. Making them shiny and weaker is not helping. The factory OD is the minimum. Any number smaller than that is worse.
Justin,I would ask several of the engine builders that post here from time to time.If you do a search of past forums it might find the min od but the min od off the print and what we use 100 years later will vary widely! What is your od and how deep are your groves?? What we do not know is how close the Ford print was followed?? Back in the day when Ford was building as many Model T's as they could i doubt if any train loads were held up by .020 under drum's?? Bud.
Let me ask a similar question. What is the transmission drum diameter?
It doesn't matter if there was a minimum spec - less material is bad. More material is good.
Removing material makes the drum easier to crack. With all the work it takes to assemble a transmission and engine and then put it in the car I won't do anything that will make a drum crack, destroying all that hard work and all the parts around the drum.
Here's what Ford says:
Isn't that really talking about the clearance between the bushings and the drum shafts, not the overall size of the drums themselves. Remember, the three drums are on concentric shafts so that the triple gear can get to all three drums easily. The inside shaft is the driven shaft and has the outer most gear and the brake drum on it. The smallest gear, in the middle of the pack, is the low speed gear and connects to the middle or low speed drum. The largest gear is directly connected to the reverse drum. Each of these shafts is supported by a bushing inside the next shaft out.
Let me ask a similar question. What is the transmission drum diameter?"Quote"
The finished drum diameter as provided by Ford is 7.5" plus/minus .005" .
The question regarding machining of the drums is How much material is left?
Warpage is another problem.
Some of the early slow speeds don't have much iron on them to begin with. "core shift"
Before contemplating doing anything with a 100 year old drum I would recommend highly getting them magnafluxed.
Shown below is a reverse drum cracked across the spoke.
second picture is an early brake drum with cracks on edge of lug.
I am in agreement. I have a spare reverse and low drum but not a brake drum.
At the costs when converted, they are very expensive, but also not worth the risk.
Thank you J and M Machine Co. I have several spare bands that are not quite "round" and wanted to make some kind of tool to get the shape correct as I do not have a spare drum laying around to use and my transmission is still in the car.
An old drum does make for a good tool to round up or to straighten twisted bands.
The band needs to also be a tight circle, with a gap of about 4" between the ears of the band.
...and using a mandrel to shape the bands is important to the operation of the transmission.
Note the typical wide distorted spread of the band in the foreground before re-work, and the set of bands now ready to be re-lined.
Justin, turning the drums is not the way to go, even if you remove the minimum material. You can only get the correct finish by grinding them. Otherwise they will chew up the band linings.
Hope this helps.
Allan from down under.
That's Not true Allan!
We true all drums.
How do you "true" drums?
Wouldn't it be easier to go to your local Ford dealer and just trade the old set in and pick up a new set of bands for 60 cents like it states in the article?
Where do you find all these reference articles at? I need to try to build up my Ford library.
I have a brake drum that was turned down to 1/8" thick and it bothered me to install it. But it has held up OK for about 5 years in my 10. I wouldn't risk running Kevlar lining because of the heat generated, so I use Scandanavia. Problem is the brake band lining wears out fast, I suspect due to the new geometry of the drum. A possible remedy, if that is the case, is to use the old cotton bands, eg Sears, Wards, etc that are much thicker than the Scandanavia. That just might restore the proper fit.
I don't see anything wrong with turning the drums down a little to true things up, but I think 1/8" thickness is risky. I typically turn them down on a lathe and finish with files and successive finer sand paper. Although you can still see chatter marks, the surface is smooth. One time, I tried grinding the surface on a tool post grinder after turning, but it chewed up the stone, so I gave up on that. May try it again with a larger diameter stone. I like transmission work.
Here is a photo of my 1910 after three days of cleaning preparing for the HME.
Here is one issue that can occur with drums that are too small in diameter, and one workaround, please pardon the poor copy:
How do you "true" drums? "END QUOTE"
Mike, in 2013 I posted on here, how I rebuild a Transmission with pictures, take a look.
We have never lost a drum, or anything else out of the 350 plus transmissions rebuilt. But we don't use wore out or cracked parts, and we turn all drums.
If you don't, that is where all the unevenest, chatter, and slippage, ect. comes from, an uneven, and out of round surface, with Hi and low spots and makes the bands slip and grab.
This can be proven by the way the transmission bands worked before and after truing.
If you are worried about not getting the drums smooth enough, take it to a machinist that knows how.
Never have had to grind a drum ever, and to say you have to is just not true!
When some on here, think of truing drums they think in terms of removing a 1/4 inch from the O.D.. The normal amount is .010 to .025 thousandths. If you have a rivet groove, you don't have to take them out, as they should do more good then harm.
The last and a big reason for turning a drum in to get the out side of the drum dead center with it's bushing, so it does not stick out, off center and wobble.
You have to make sure to ream the bushings at a right angle to the drums. If you don't where ever the hole in the bushing comes out will dictate where the O.D. of the drum comes out, and also the gear teeth.
Most Guys don't know when you ream a drum bushing with out a Jig to ream the bushing hole, the reamer will follow the bushing hole. But if you use a Jig, such as Wilson or other brands, they bore a straight hole no matter where the bushing hole is.
So if the bushing hole in not bored right, the drum will be off.
We check ours with an expanding mandrel between centers on a lathe, after boring, and before truing the O.D. of the drum.
A drum that is off center, always has a band that is off center, and it's performance is off center with band movement.
Here is one issue that can occur with drums that are too small in diameter, and one workaround, please pardon the poor copy: "END QUOTE"
I have never seen a drum wore that small to give that problem, and the worst one I have ever seen was about .010 thousandths.
I think your diagram was made to show what problems you could have by running with wore out lining, and or using lining that was to thick, or to thin, and not having lining sticking out far enough out under the band ends.
You're right, the title above the diagram talks about worn transmission linings. BTW, it isn't my diagram, it came from "The Model T Ford Owner", by Murray Fahnestock.