low speed drum on trans rebuild

[dhosh]

I am going through my trans, rebuilding what I can afford, on the way. The low speed drum isn't cracked but is worn a bit in the middle. Should I attempt to have it leveled out? Not sure how, economically... Mechanics that then brake drums are few and far between... But those are in the inside of the drum surface, not the outside. I am putting on wood bands. I attached a photo... If left, will the wood wear in, eventually ?

My reverse drum rocks just slightly on the low speed drum bushing surface... But the bushing and the smooth portion of the low speed shaft next to the drum, only seem to measure .002" -.003" difference, which sounds about perfect from what I've read.

[jsaylor]

The transmission drums need to be ground not turned to get the proper finish. But you will have under size drums. May be harder to get a good pedal adjustment.

[Allan]

Once the drums are ground, they will be undersized, but that can be compensated for. First I check if there is any need, by clamping a band and lining around the drum to see just how close the ears on the band are. I have kept on the shelves some rolled sheetmetal strips which were cut to the width of the band and rolled to fit inside the band. These are in a couple of different thicknesses in material. If compensation is needed, I clamp a lining and one of the strips under the band and again check the space at the ears. The strip is clamped around an old drum and the rivet holes drilled to suit the band. Then you are ready to fit new linings and the steel spacer band using the rivets supplied with the linings.
Hope this helps, Allan from down under

[J and M Machine]

I am going through my trans, rebuilding what I can afford, on the way. The low speed drum isn't cracked but is worn a bit in the middle. Should I attempt to have it leveled out? Not sure how, economically... Mechanics that then brake drums are few and far between... But those are in the inside of the drum surface, not the outside. I am putting on wood bands. I attached a photo... If left, will the wood wear in, eventually ?

20200904_201600.jpg

My reverse drum rocks just slightly on the low speed drum bushing surface... But the bushing and the smooth portion of the low speed shaft next to the drum, only seem to measure .002" -.003" difference, which sounds about perfect from what I've read.

It's correct what the other posters have said about the drums being ground not turned. However the low speed is the thinnest of the three drums.
We make new transmission drums and gears and ours are ground but the others aren't so you can get away with it.

If you have a lathe and can secure it to turn off just enough to get it flat then polish it with sandpaper to get a smooth finish you'll be OK>
Main thing is to check all drums for cracks as the reverse is usually first to blow and check drive plate too.
You can adjust your brake bands so removing .010" is not going to be an issue.

[RGould1910]

You can turn them down if followed by ever finer filing then ever finer grades of sandpaper. Each step is done on a lathe.

[dhosh]

Dang... I sold my lathe a year ago. It was a wood lathe, buthad the ability to slow way down. I'll see if I can find someone local with an appropriate lathe.

Thanks, all!

[GrandpaFord]

The other people who responded are all correct. But here is my take on it which may or may not be correct and I will probably get some people who disagree.

The bands are going to wear in to fit the drums. So unless the drums are really rough or cracked or deeply grooved, I would just leave them alone. That is if you are using cotton or wood, as you mentioned. Kevlar is not going to wear in, at least not for a very long time.

[John kuehn]

That’s true I think and as posters have said in previous threads in the past if the drums aren’t cracked and not deeply grooved by the rivets it’s probably best to rebush the drums and let it go.
A rivet groove is most always in the center and usually run that way for years before. But that’s if the rebuilder wants to clean things up if he wants.
The drums that are made nowadays probably are made of a little better material than the originals and will probably last longer in normal usage than an original would.

[Jerry VanOoteghem]

Dennis,

Your drum looks just fine. That's not very much wear at all. Not worth removing any material from it.

[Walter Higgins]

It's always fascinating to me how removing a few thou from the high spots on a drum is supposed to be detrimental to the life of the casting, yet leaving high spots that can cause inconsistent heat input on something that is no longer concentric is preferable.

[dhosh]

Yes... Certainly seems as though it should at least be round, centered, and balance.

Jerry.... Thanks!

[Stephen_heatherly]

I personally wouldn't be worried that the drum is worn more in the middle because the band will wear in to the drum. I'd be more concerned if the surface of the drum still runs concentric to the shaft. If not the band will jerk and jar the car when you take off which can be unpleasant at the least and eventually damage other parts of the car. I would put the drum in the lathe and skim off just enough material to get the surface to run concentric to the gear again and you should be fine.

Stephen