T-20 plunger/band functions

[brushcutter]

This may come as a shock to some of you but, although I am not exactly new to this amphib stuff, I will be the first to admit, that there are a lot of things that I still don't know about them. While tinkering around with the Hustler recently, I realized that I have no idea what the exact function of the plungers and their respective bands is. I know that they work as brakes on the internal drums, but can some of you explain to us(me especially) what each band does as the sticks are worked while driving forward/backwards. Having this knowledge would help those of us less experienced folks (dummies like me) as we try to fine tune our machines. My 950's left side has never pulled as hard in reverse as the right side. I have always had to pull back really hard on the left to make a turn in reverse. Forward seems to work fine although it seems to drift to the left, I figured this was a tire thing but it still does it even after going to completely different tires. This has me thinking tranny, so can any of you great and wise ones help by explaining this to we the less informed.

[Don]

Well, I'm not one of the great and wise, but maybe I can shed a little light on the grey mystery pumpkin anyway.

It's easier to think of the T20 as two transmissions on a common input shaft, which is how it acts in service. There are two drums on each side with a set of planetary gears between the inner and outer on each side. In forward, the inner drum is the "drive" drum and outer is the "brake" drum, so when the sticks are pushed forward the band on the inner drum relaxes and the the outer band tightens, forcing the power from the input shaft to turn the inner drum and the drive sprocket on that side. When you pull the stick back on that side, the band on the outer drum relaxes and the inner band tightens on the drum to stop the drum, sprocket, and wheels on that side.

When it's shifted into reverse, the drums change roles and the inner becomes the "brake" and the outer; the "drive". When you pull the stick back, the band on the inner drum tightens and the band on the outer relaxes so that the power from the sun gear on the input shaft is directed through the planetary gears and drives the sprocket backwards.

This may not be 100% accurate, but it's the way things look to me.

[brushcutter]

Thanks Don, so I guess it could be said that the outer drum/band works as the forward drive and the inner drum/band works as the reverse drive, so to speak. Therefore for my reverse problem, I would have to either tighten the inner or loosen the outer or maybe a little of both. Then drive it and see how it acts, then adjust and repeat until it acts "right". I have tried to fix this while up on blocks but I can't tell any difference without the load of the vehicle resisting the tranny. Does this all sound right to you.

[Don]

Yes, as far as I understand it.

Unless the plungers are severely out of adjustment, you may find that the problem is internal (or even in the linkage). It's always best to exhaust all possibilities outside the transmission before you pull it apart, though!

Good luck, let us know how it acts.

[brushcutter]

It doesn't seem to be really bad but I think it could be better. I bought it re-built from R.C. and called him about it after a few hours riding; he said to please,please, please don,t do anything for fifty hrs or so.Then call and he will walk me through the process, so I guess I will call him on Monday and see what he says. BTW just looking at the plungers,(I have the old eyebolt type)none of them extend out of the tranny housing the same distance when the sticks are moved. Seems to me that on a tranny with good bands/drums all adjustments would be even and all plungers would extend the same distance from the housing. Or at least the top 2 and bottom 2 would be close enough that you wouldn't notice, but on mine you can see it easily without any help. Has anyone encountered this problem before?
The adjustment section on t-20's says to adjust so that the center of the eyelet is 1 1/4" from the transmition face when pulled with your fingers. As they are now they would have to be backed OUT 1/16" to 3/16" depending on which one you were working on I don't think this would be the thing to do at this point.

I will let y'all know what comes of this. Thanks for your help.

Gregg

[brushcutter]

Don, I spoke with Mike at Richards today and he pretty much verified what you said. He also told me that the bands are not always perfectly uniform in thickness due to manufacturing processes (liner) and adhesive layer thickness after it's dry. And so, since the bands are wrapped several times, there doesn't have to be a big difference in the bands to cause a noticeable plunger protrusion difference. Also, he said that they adjust the t-20s that they build to 1 1/8" (instead of 1 1/4" as the adjustment section says), that the adjustment will work across this range, they do 1 1/8 to prevent excessive travel in the sticks. Next he said that the pulling harder thing is probably that I am actually putting no more force on the plungers in reverse than I am in forward but that it just seems so. I guess I could get a scale and see exactly how much force it takes, just for curiosity's sake. My main concern is that I don't want to trash out a $1295 transmission. Ya Know!

[boncrshr]

I am having the exact same problem...mine seems to be getting worse though. I have checked linkages and adjustment....as far as internally, what could it be??

[6X6]

Loosing Grip

Hmm. My first thought, after checking the U-Channel and linkage between sticks/plungers for binding (Requiring more force) or excess travel (Needing to come back farther) would be that the band/drum are either glazed from excessive slipping, (NOT sure best way to correct, DON?) or the band is wearing down or some of the liner is peeling. If it's the latter drum damage can result from continued use. This isn't a problem I've had yet, although Mogman felt he had to do this but a tranny (Plunger bolts) and linkage adjustment seems to have been the answer, but we did open'er up, and found the bands well within specs, did the O-Rings and sealed'er up again.

[brushcutter]

Yeah, I think I will try to come up with a way to quickly disconnect the sticks, without having to constantly remove the snap rings. Then loosen the locknuts and drive it, that way I can make adjustments as needed to get it to a sweet spot. Anyone ever tried this?If so how did it go?

[Don]

I don't imagine the bands or drums have a problem already- Richard has a very good reputation on the rebuilds, and I've used lots or his relined bands with no problems at all so far. As long as you've only used ATF in it, I doubt there's a problem inside.

I've seen people use bolts in place of the pins on the older T20s, but you need to use locking nuts or double-nut them to allow the levers to move. Can you hold the pins in by hand and check the travel with the sticks to adjust them before you install the snap rings?

Good luck.

[brushcutter]

I was thinking bolts Don, just temporarily while I check things out. I think I will drive it in forward for a little while to kinda get the "weight" of the pressure that it takes to drive. Then sit on the front, facing the rear of the machine while driving in reverse, to see if there actually IS a noticeable difference in pressure. I'm thinkin that what Mike said makes sense to me. He also said that nothing that I told him sounded like something that was going to destroy the tranny, that made me feel a lot better! He said that normally when there is a problem with reverse, that you will have a problem steering in forward also. Since mine seems to steer fine then I think this may just be a "head" thing.

[jerseybigfoot]

I had a band failure about 5 years ago at the Humphrey NY ride and the first thing you will notice a significant increase in distance you have to push or pull the lateral. In my case I lost a forward right side band and every 1/4 mile or so I had to adjust the bolt on the plunger to bring the laterals back even. Very soon after about 2 miles I had no adjustment left. Had to go up hills in reverse and down normally. Fortunately It happened in a Hustler with a reasonable comfortable nose to sit on. I drove that way for about 7 miles. This was with a RC relined band. He made good on the claim and gave me new bands and a drum. He did say that he changed the company that was relining the bands after my failure.