T-20 problems (teach and coach me please)

[Rusty-Gunn]

Hi. After a test ride of our Max IV the machine wouldn't turn left in reverse.
Then it wouldn't turn going forward. Then it wouldn't go at all. Then it ran fine.
I adjusted the bottom plunger bolts inward about one to two turns.
At first it seemed to run fine forward, but wouldn't turn rear left, then it wouldn't do anything.
What I suspect is the bands need replacing. Could this be the case?
I also considered that the woodruff key on the secondary is broken. I lost the original on the ground but could not find it, so I installed a new one thst is a tiny bit thinner. Could this be causing the issue?
In either case the engine and trans will need to be pulled out.
Also, how does the T20 actually work? I pull the right lateral, what goes on inside it? Pull both laterals, what goes on in there? How does it work?
Thank you for the help.

[Mike]

If the woodruff key was out, I would expect it to affect both sides the same way. If you are saying that only the left side didn't work in both reverse and forward, I'd start by checking the diamond shifter on the left side. If you're saying it won't do anything on either side, I'd think the woodruff key could be the likely suspect.

[dirtdobber]

Rusty you say test ride....what is the history of this machine? Is it new to you? Or have you rebuilt it or something?

[Rusty-Gunn]

Thank you Mike. We will be pulling out the trans asap. I gotta get this fixed.

[Rusty-Gunn]

I looked at max6x6.com. They have woodruff keys 3/16x3/4 size. Our local hardware store only had 1/8" thickness. I suppose its on the weak side and sheared.
Assuming they have key stock 3/16" thick I can cut a new one.
If not, what can I use? Are these steel or aluminum? Thank you.

[Rusty-Gunn]

Dirtrobber... we've owned this one about four years. It had a broken "ear" bracket, of which we fixed. This test ride was to check if all was okay, as we also replaced the axle bearings on the miiddle left side. The first ride of about five miles was fine, but I hadn't put the machine in reverse on that trip, so if it had a reverse issue at the time I didn't know about it. My bad for assuming it ran fine.
After that test ride we noticed the left rear bearings seemed loose so we changed out those (they seemed tight on our initial inspection). Then this short test ride today, and nò steeing. Personally I suspect the woodruff key, with tons of hope the bands/shifters are fine.

[Rusty-Gunn]

I made a woodruff key out of 1095 high carbon steel. It is 3/16 x 3/4 with a "bump" the curve of a nickel.
I hope it fits, and hope its strong enough to use. Any suggestions on this?

[Rusty-Gunn]

I didn't think we'd get to our Max IV this evening (our youngest daughter came home for a 5 day visit today) but we did.
We got the engine out easy enough. Next we checked the diamond shifters. Both look normal.
Afterwards we unbolted the secondary from the shaft, slid it over to the tub, and yanked out the Ace Hardware woodruff key. No issues here. Its intact. I devided to install my homemade kry and it fits in correctly.
I have no idea if the 1095 high carbon knife-making steel (annealed) is strong enough, but its the correct size.
This leaves me with the brake bands. Perhaps they are worn out.
The wife and I expect to remove the T20 tomorrow and crack it open.
I figure I may post my questions if I am needing advice.

[ARGOJIM]

Rusty, basically you have 4 bands and 4 drums, pushing forward on both stick pulls the 2 bands on the 2 drums enacting forward drive while pulling back the other 2 of the 4 bands enact the other 2 drums for brakes. In reverse same scenario only the shifter engages the other 2 drums and planetary to create reverse with the forward push now being the brake and rearward pull drive.

Before you pull anything apart I would check all of your shear bolts in the sprockets if so equipped as lack of drive or brake will be greatly affected with even on bolt broken. Use wrenches to be sure they are not broken.

[dirtdobber]

Your home made key is probably strong enough. Before you tear into the transmission, are you sure the laterals/plungers were properly adjusted? Also, as a clue, do the plungers stick out of the case and if so how far?

how does the T20 actually work?

Again, I'm no expert but here's what I think........The T20 is 2 transmissions in 1, that's why you can control each side independently. Each half has 2 drums, 2 bands and a set of planetary gears. The planetary gears interlock between the two drums, meaning the input shaft turns the the 3 small idler looking gears attached to one drum and in turn these 3 gears mesh with a ring gear on the second drum. The input shaft turns the planetary gears which then turns the drums. Each drum has a respective brake band. The drums free-wheel until the brake is applied to one or the other. When you apply the brake (pulling or pushing on the lateral applies the brake bands) a drum stops free-wheeling and because of the nature of planetary gears, power is then delivered to the output shaft. The two drums are counter rotating which thus produces either forward or reverse. The shift collar has to be engaged with the correct drum to receive the forward or reverse motion. The free-wheeling nature of the two drums is why you can have your machine in either forward or reverse, but not have any power until you move the laterals and apply a brake band.

So, if the lining of a band wears out (good lining is somewhere in the neighborhood of only .040" thick) then its metal-on-metal which doesn't produce the friction needed to hold the drum, but it will produce plenty of wear on the drum like driving your car with worn out brakes.

You could have worn out bands or failing bands (de-laminating), although i'm curious why the problem seems intermittent. Poorly adjusted bands/plungers or problems with the lateral linkage may also be an issue (I don't know about Max machines, I'm speaking generally). Once upon a time I found some good instructions for adjusting the bands. If I can find it again I'll edit this post.

Let us know what you find.