Replacement transmission for the T-20

[kunzmm137]

I have been in the design stages for a transmission that would be a bolt in, economical replacement for the T-20 trans. Most of us love the t-20, but lets face it, they can be expensive to rebuild, and if your machine is missing the trans, they can be difficult and expensive to find.

I am using this poll to get a feel for the amount of interest there would be, to see if it is worth building a prototype for testing purposes.

In designing, I had to stick with a few rules, 1. it must be built with easy to obtain parts, 2. maintenance must easy and not expensive, 3. it should have a reasonable purchase price.

I think I have met the goals that I set with my design. A total rebuild of "friction items" would only cost about $70, compared to $450 for a set of bands in the t-20. Purchase price for a new tranny would be between $400-$450.

I would not be able to determine a good service life for the design until the first one was put into service, and monitored for hours and wear. I do not feel that it will be for high horsepower machines, but more for general use.

After the prototype is tested, I would also be interested in having a few more made for durability testing, where a couple of our interested members would receive a transmission (at a discounted price) to put in their machine and keep track of hours and what type of driving they did, and if it had a failure, it would be sent back to me for necessary design flaw changes.

[6X6]

I'd be interested as I too have been kicking around Ideas. However I do not have the CNC equipment I'd really need. My thoughts started after I started the racer and was more for use with high HP. However, even with a mild 20sHP 2-stroke I couldn't be an "average use" tester, I don't take it easy on my machines, I don't think I'm even capable of doing so if I wanted to. Of course just the act of Skid steering is quite a strain on any tranny, but if you are able to go through with it and I have some extra money, I'm sure I'll have something I can put it through hell in.

Edit:
My thoughts on this would be (adding to your points)
1) Should mount with same stud pattern as T-20 so Fabrication isn't needed. (no issue with additional mounts so long as it doesn't interfere in mounting where a T-20 would go.)
2) I'd personally go for dry brakes since they are more progressive and not as grabby.
3)It would be great to see output sprockets that can be replaced without opening up the tranny, for gear changing or just replacement (Although ratio changes probably aren't a concern for most. Thats just my ever-competitive side coming out again.)
4) Probably not possible but if so, the ability to counter rotate would be great.

[kunzmm137]

My thoughts on this would be (adding to your points)
1) Should mount with same stud pattern as T-20 so Fabrication isn't needed. (no issue with additional mounts so long as it doesn't interfere in mounting where a T-20 would go.)
2) I'd personally go for dry brakes since they are more progressive and not as grabby.
3)It would be great to see output sprockets that can be replaced without opening up the tranny, for gear changing or just replacement (Although ratio changes probably aren't a concern for most. Thats just my ever-competitive side coming out again.)
4) Probably not possible but if so, the ability to counter rotate would be great.

My answers to your thoughts:
1) The trans would have the same mounting points, same sprocket location, same clutch location, and same forward/reverse lever location as the t-20. A "bolt in" replacement.
2) My design does use dry disc brakes
3) Output sprockets would be able to be changed by pulling the clutch off, no need to open the trans. Also, ratio changes would be possible.
4) My design could permit counter rotating, but I probably won't incorporate that. It puts extreme stress on the trans.

[nightowl]

I would be interested in doing some testing for this. I have a large machine. A Super Swamp Fox.
I think it would be Great if you was to have an alternative for the Tried and Proven T-20.

[hydromike]

4) My design could permit counter rotating, but I probably won't incorporate that. It puts extreme stress on the trans.

I don't know that counter-rotating puts additional stress on a T-20, if that's what you mean. The input shaft of the transmission is spinning in the same direction, and it probably sees a comparable load. You're just utilizing the planetary gear set to get that particular output shaft going in the opposite direction. I think "extreme stress" is a misnomer here. I've been in several machines that utilize split shifters, and the T-20 responds quite well to the modification.

The only time I've ever really experience "grabbiness" in a T-20 is when that particular machine used the lateral springs, and I just wasn't used to using them. Actually "pulling back" vs. "not pushing forward" to disengage the brakes was a new concept to me. I think that a lot of folks use the lateral springs, and to each his own. I just think the level of control you get over the T-20 is significantly higher without the springs. Even with the racers, and when the T-20 is adjusted properly, they don't ever feel "grabby" to me. The Baker Hill dry brakes are more forgiving in this environment, since the level of effort you put into steering is substantially higher, and if you goof up and move your arm wrong at 45 mph, you're not as likely to end up in the rhubarb.

Brake surface area is something that you'd really need to take into account. The three wraps of a band on the each T-20 drum is quite a bit of surface area. I haven't measured a band, but I think it's something that a spot-caliper (Baker Hill), or a Scrambler brake setup would be hard pressed to duplicate. I've never driven a Scrambler, but how easy is it to "feather" the hydraulic brake setup on such a design? Also remember that the Argo brake setup gets wicked hot, and at least some models (all? I don't know...) actually need to be cooled with a fan. Brake fade is not a good thing.....

I know the T-20 suffers from a lot of things, but overall it's a great setup. I hate leaky plungers, and the lack of a low range. Of course with the evolution of the hobby, something better is bound to come along, and this may be it!

Just my thoughts on the subject....
~m

[6X6]

and if you goof up and move your arm wrong at 45 mph, you're not as likely to end up in the rhubarb.

.........
~m

Mike, I think you grow too much rhubarb, seems you end up in it a lot

[lewis]

Is your thought process a completely new style trans or a remake of the t-20? Do you have foundry capabilities for a new style case? Just thinking out-loud, i wish you the best in this endeavor.

[Stonewall]

This sounds like a great idea, a new, drop-in, easy to maintain, alternative for the expensive t-20 would be great. Would the internal design be simpler as well? I spent over $800 to rebuild my t-20 and I really don't think that I got everything right. (Although I think someone had it apart before I aquired it...) I would be up for testing your design under normal use and circumstances, I am not hard on my machine at all.

[rustyazalie]

Solid shaft going completely through. (I want to add a power take off on the other side for powering a prop). Am looking at doing same with a T-20 presently. 2 speeds would be nice yet would complicate construction and reliability.
Rusty

[jpswift1]

Solid shaft going completely through. (I want to add a power take off on the other side for powering a prop). Am looking at doing same with a T-20 presently. 2 speeds would be nice yet would complicate construction and reliability.
Rusty

That's a great idea, and it probably wouldn't be all that difficult to do.

[hydromike]

If you had a solid shaft going all the way through the T-20, i think it could be a great place to have a PTO. You could keep the T-20 in neutral and still utilize the PTO. I like this idea....

[jpswift1]

It probably wouldn't be very difficult to do at all. The only custom parts you would need to machine would be a longer main input shaft with a key way or splines cut in it. You could use the output shaft (that comes on the clutch side of the T-20) on the other side of the transmission equipped with the PTO so that the main input shaft would be able to go through and out the other side. And this way you could have your driven pulley mounted on either side of the transmission.