resurfacing drums????

[racerone3]

i just got a t-20 that had been sitting open behind a shed. i'm getting it cleaned up and found that the drums have some light pitting. i was thinking of putting them in the lathe and taking a few thousandths off to get rid of the pits. does anyone have any first hand experience doing this? i'm not worried about killing the drums, if they are already shot, but i'd rather not turn the drums, and buy new bands only to find that i can't get it adjusted to where it will work

[jpswift1]

If you turn them down as little as possible while still trying to remove the deepest pits, you might be alright. Sometimes when drums are turned down, even just a little, they become too small for the bands to grip on......especially older bands that were made with not that thick of brake band material on them. You might be able to use some newer bands that were manufactured with slightly more brake material on them compared to the older ones. Let us know how it turns out.

[geno]

if you turn them down and the band clearance is too much reline the bands with thicker material

[Meinfield]

I turned my down ten thousandths (20 thousandths diameter) with great results. Got rid of the pitting, and I simply tightened up the bands a bit when I reinstalled them. Be sure to polish them a bit after turning, but you do not want them smooth. I think I used 280 grit wet paper.
Chris

[racerone3]

thanks meinfield. that's the kind of response i was looking for

i ran some #'s on it today and here is what i figured out.

current diameter is 6.215" multiply by pi (3.14) = 19.5151" circumfrence
minus ten thousandths is 6.205" times pi = 19.4837"
subtract and come up with a difference of 0.0314"
the bands in the T-20 wrap the drum 2 1/2 times, so multiply 0.0314 by 2.5
and the difference in the distance the band has to wrap around is 0.0785 inches. on the plunger adjustment bolts (3/8 24) that works out to about 2turns

i ran my #'s by one of the engineers at work and he said it sounded right to him.
what do you guys think???? am i missing anything??

[racerone3]

ok experts. how pitted is too pitted? i've heard everything from.. any pits will kill the bands, to.. "as long as you can't feel the pits with a finger nail it will be fine. the guy who does all my machine work that needs to be done precisely looked at these drums last night and didn't think shaving 0.010" is going to get rid of all the pits

[Swamper]

Hello Racerone3. I don't have experience with the T-20, but I do have experience with transmissions. First question I have, is the surface rough to the touch from the pits? what is the width of the bands? Is the pitting covering all of the surface of the drum or only partially?
I will give you an example of what I do to the drums in my racing transmissions. I run a Mopar 727, and on the forward drum I drill 36 1/16 dia. hole symmetrically around the surface. The bands I use have 3 ribs the full length of the band. The reason to drill the holes is to allow the fluid to be displaced quickly and to lighten the drum. Same for the grooves in the band. So as you can see there is not 100% band contact to the drum. Same as your drum. So if the drum is fairly smooth, the pits should not damage the band. Sorry for the long explanation, but I thought it would relate better. By the way my band stops the forward drum while it is spinning approx 8,000 RPM and from the readings from my data collector, I am experiencing around .016% slippage.
Cheers, Al

[racerone3]

ok... i went ahead and did it. gave my machinist friend the drums on new years eve. got them back tonight, free of charge. he took the ten thousandths off and it got rid of the pitting on all but one of the drums. the one it didn't fix was out of round by about 0.005", so it has 2 small spots that the pitting is still there. the other 3 drums were round but varried 0.008" in size from 1 drum to the next. all that being said, i don't think the removal of 0.001" should hurt me too bad. it'll be a few months before i buy bands to put it back together, but i'll post a follow up whenever i get it done and test it