Thanks Mark wasn't sure of the material. I bet if someone has the dimensions of a new drum we could probably establish limits of how much can be turned off. The drums seem beefy enough that quite a bit could be machined off. The problem I see is the band length. I would think relined bands would easily take up .040 on a machined drum.
Dang tha' bad luck!... We had a welding supplier come and demo a spray rig but I didn't get to see it in action. I would have to agree with you Mark, the drums definitely appear to be made of cast iron, the sand marks are a dead giveaway. But check this out, Lester (our chief welder in charge) said that if we can figure out all the techy stuff, and there were enough of these things to pay off, he is not against buying a rig and doing them as a sideline. We haven't talked pricing and I don't want to risk infringing on our forums commercial interest rule, but if this process could done for $80 to $100 per drum this would be a huge savings for members in need of such a service. I think R.C. gets quite a bit more for his drums, not sure what R.I. gets. If nothing else we might find a cheap process whereby we could go to a well tooled machine shop and get them done at a cheaper price. I think I am gonna take one of the really chewed up ones(p.o. ran gear oil in it bands started eating drums) and have the CWIC look it over and see what he thinks.
Also RC said that the drums could be turned down....NONE ... do I smell something?
Also RC said that the drums could be turned down....NONE
Never been in a t20, but thinking about automatic transmissions.. if there's enough meat to machine the drums smaller, what's left is where the band anchors end up in their workable travel. .040" off the OD means .120 circumference times 2? band wraps = a 1/4" difference in band adustment. If that's the issue, bands with thicker lining, or shorter bands, or longer anchors..
A more practical approach would be to Machine the drums for a shrink fit steel ring. There is not allot of heat generated in a T-20 that would cause the rings to get loose ..010 shrink would be allot of force holding the ring in place. I understand there were racing t-20 drums machined from steel so I don't think the material would be a factor. I already install steel rings on outboard drums where they fit the bronze bushings with good results
Mark M is right. The drums are ductile cast iron. Finish O.D. is 6.210. Write it down somewhere so you don't have to hunt for it if you ever need to know.
I talked with Matt @ R.I. about the specs on the T-20 drums. He said that you can safely turn the drums .030 undersize. That's only .015 per side. In a lot of cases that isn't enough to clean up any grooves or pitting. Anthing smaller than .030 may still work, but your bands would have to have a lot of material on them & in good shape. The more you turn the bands down, the farther the plungers will come out of the T-20. What you have to watch for is that the plungers don't come out so far as to expose the O-ring.
In my opinion, welding is not a good option. The heat will distort the ring gear & you'll lose the burnell hardness of the drum. Joe M. just sent me 4 drums, (2) that had been welded to see if any of them could be saved. The ones that were welded were all ready .050 undersize & still probably needed another .050 just to clean up the terrible weld job. Maybe Joe can post a pic of one of his welded drums. The (2) that I was able to clean up, he posted in his gallery. In my opinion the metal spray is a quick fix. It may look good, but in the end, you won't have the right burnell hardness & possibly ruin a good set of bands. Just something to think about since pulling a T-20 out is not much fun, especially if you have to do it again down the road, because you tried to cut corners. It's the brain of the machine. It's too important not to fix it the right way. Sometimes that means spending a few bucks. Fix it right, the first time, while you've got it apart.
Whipper
OK I read the t20 write up, so now I have an idea of how it works. The thing has no band adjustment other than the plunger travel, with the fixed anchor rod. Great idea, if you're a mfg selling replacement parts.
Unless you can get creative and move the band anchor, I don't see a way to take any OD off the drums.
Last edited by Roger S; 08-15-2009 at 05:22 PM.
You can always cut the loop off the band and reweld it.
Thats what RC and I talked about and I guess I should have clarified ("do i smell burning bands?") If you took any off the drums several things could go wrong really quick, such as plungers pulling out causing fliud loss, burnt trans parts due to lack of fluid. I guess you could say that a little bit off the diameter of the drums means a lot to the bands.
But now you've got me thinking,... I'm liking Jerseys steel ring idea... so what do you think about this, test drums for hardness... order sleeves that are the same... turn drum down to necessary size... freeze drum to shrink...press ring onto drum...then turn drum to spec.
Whipper, how did the useable drums work out or is the jury still out on it?
Joe just got the drums back on Friday. He'll have to let us know if they work. The pics of what they drums looked like when he took them out are posted in the Max forum RI thread that he started.
Whipper
hey brushcutter, did you ever get a chance to rockwell a shift pin? i bought a set a few weeks back and measured them before i put them in. they are the same diameter as the shank on a bowman 1/4-20 bolt... just wondering how they compare from a hardness standpoint. if they are similar, it would be easy to cut a bolt and round the ends a little bit to make a few spare pins. i don't have access to a rockwell tester right now so i can't look into it myself.
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