GST shuttle shift and tractor rpms

[dannyk]

My owner's manual for my L39 with GST says to "Reduce engine speed to low idle before shifting the shuttle shift lever." Is this really necessary? If I have to use the throttle lever to go back to idle every time I change direction (forward to reverse and vice versa) and then I have to use the throttle lever again to increase rpms before moving, this would seem to be a very cumbersome transmission!

What am I missing here? Is the preferred technique for dirt work to keep the engine at idle and use the foot throttle?

I'm confused!

Danny

 

[DK35vince]

I would think foward/reversing at higher RPM's would be addition shock on the transmission and wear /tear on the clutch's.
Simply use the foot throttle for loader work. What to forward/reverse let off on throttle peddle, want to go push down on throttle peddle.

 

[art]

I hate not having a foot throttle for loader work! They are the best even on skid steers!

 

[DUMBDOG]

I use the clutch when going from forward to reverse, sometimes at 2000 rpm without a problem.

 

[dannyk]

OK, so I get the feeling that there are two methods for using the GST when doing a lot of forward-reverse movements.

One would be to keep the engine at idle and use the foot throttle as necessary.

The second would be to run at normal working rpm but use the clutch when shifting from forward to reverse (or reverse to forward) using the shuttle shift.

I'm wondering which of the two methods most people use and which method is most productive?

Danny

 

[Soundguy]

Bottom line.. even if you keep the engine speed up and use the clutch.. you will be getting more clutch wear... IE it will slip more...

I think leaving idle speed set and using the foot throttle for the variable speed control is probably an ideal way to let the powershifting style trans work best.. ( though i don't own one nor have i read their manual.. however.. the fact that your manual specified that.. and not leaving it running full tilt and using the clutch.. well.. lets just say that i feel that their engineers probably knew what they were doing when they wrote those specs.. )

Soundguy

 

[KennyV]

Soundguy is right on…
The foot clutch (dry clutch) will wear out much faster slipping the trans input. Use the foot throttle and the shuttle shift (wet clutches). The clutch is only generating heat, with limited air to dump the heat (dry clutch), it will burn itself up a lot faster than the wet clutch pack, this system has the entire hydraulic system to shed heat. This has been discussed at length within the past 6 months. As before, I still never use my foot clutch, ever. I cut the rpm and shift using GST or the shuttle shift, letting that actuate the hydraulic clutch pack. Much more efficient. (I drive my tractors like I never want to see the inside of the drive train)…
In your car or truck, you would never set a high rpm then move your gear selector from reverse to first and back to reverse… at least not many time$... KennyV

 

[Ben3130]

All this makes sense when talking about doing FEL work, but what about when running a rear pto implement? For example, what about when you are brush cutting and need to change directions? Granted, the amount of direction change is a LOT less than when doing FEL work, but I still don't want to idle down, shuttle shift, power up, back up, idle down, shuttle shift again, power back up, then resume mowing. It seems like that is also a lot of wear on the tractor. In this case would it not be better to just shift without changing your rpms? Some of my mowing is around obstacles where manueverability is less than optimal, so I end up having to shuttle shift at least once to change directions.

I don't mean to sound antagonistic, but I've started doing a fair amount of mowing for friends and relatives, and I don't want to be running the tractor in a way that will cause unnecessary wear and lead to earlier than expected failures.

 

[KennyV]

Ben…
When I am running my RFM at pto speed, and I need to reverse, I can easily slide my selector GST down through the gears, this slows forward momentum and I can shuttle to reverse and slide back up the gears to reach a speed in reverse that is easy to control what I’m doing, then back to forward and etc… all this happens very smoothly and never do I need to slip a dry clutch…
The main point may very well be, as you stated, while mowing you don’t really need to be reversing a lot… KennyV.

 

[dannyk]

Kenny,

But when you do this, do you drop the engine rpms when shifting to reverse? If I understand you correctly, you always drop the rpms to idle using the foot throttle when shuttle shifting, even though this will also drop the pto speed?

Sorry, still a bit confused. By the way, I did find the thread entitled "Why use clutch with GST" that was started on 9/27/06. There's lot of useful information there that I have to study.

Danny

 

[KennyV]

Danny…
There is no need to drop rpm in that situation. With any attachment that is running PTO at 540 rpm, you can not shed engine rpm in the brief time you need to make a shift. By changing your forward momentum with the shuttle shift, you can maintain the engine/pto rpm, and be in a low enough gear to prevent a shock to the drive train… This is harder to write/read about than to actually do… try it on your GST… after a few attempts you’ll get it right and it will happen instinctively after that…
All this said, I know that you can ‘simply’ push in the foot clutch, make the change with the shuttle and feather the clutch out to stop forward movement and start rearward… after all it’s an independent PTO, seemingly just for this purpose. That may have been true with older tractors with larger clutches, and even then they did get eaten away by friction heat. These cuts today have smaller clutch surfaces, less robust pilot bearings, and most important for me… I’m a lot older now and I do not want nor have the energy to split a tractor to change the clutch and pressure plate, too much work and too many dollars.
I know you can beat a well made piece of equipment hard and for quite a while before there are consequences. I just don’t want to expend the time or cash to replace or rebuild…
This thread started with the question about repeated use of the shuttle during loader use with engine at a set rpm… it’s the shock to the drive train that will eventually get you there… using your dry clutch will remove the shock, but it will generate a lot of HEAT. That heat over any time will eat up your clutch parts. You can save the shock and heat build up simply by using the foot throttle with the shuttle when doing loader work. When working with a fixed pto rpm need your glide shift will easily allow you to keep rpm up and no shock to drive line, and no heat build up in wet clutches… KennyV.

 

[Soundguy]

IMHO. there is no real wear just throttling down then back up again.. on the other hand.. there IS wear leaving engine tached out and hitting the dry clutch just to change directions... If it were me.. I'd either throttle down or drop thru the gears. Anything to reduce shock load.

soundguy

All this makes sense when talking about doing FEL work, but what about when running a rear pto implement? For example, what about when you are brush cutting and need to change directions? Granted, the amount of direction change is a LOT less than when doing FEL work, but I still don't want to idle down, shuttle shift, power up, back up, idle down, shuttle shift again, power back up, then resume mowing. It seems like that is also a lot of wear on the tractor. In this case would it not be better to just shift without changing your rpms? Some of my mowing is around obstacles where manueverability is less than optimal, so I end up having to shuttle shift at least once to change directions.

I don't mean to sound antagonistic, but I've started doing a fair amount of mowing for friends and relatives, and I don't want to be running the tractor in a way that will cause unnecessary wear and lead to earlier than expected failures.

 

[dannyk]

Thanks for the detailed responses. I'm no mechanic and I won't pretend that I understand everything you guys are saying, but I will take your advice! Thanks again!

Danny

 

[dannyk]

One more thought: You guys should be writing Kubota's manuals!

The section on the shuttle shift in my L-39 owners manual is extremely brief and says only two things: When shifting the shuttle, 1) reduce rpms to idle and 2) hold the shift lever briefly in neutral. The dry clutch isn't even mentioned.

I'd be willing to bet that many folks are doing as I started out, namely using the foot clutch to switch directions without reducing rpms since there is no discernable shock to the transmission.

Danny

 

[KennyV]

namely using the foot clutch to switch directions without reducing rpms since there is no discernable shock to the transmission.

Danny

That’s because you are slipping the clutch when you ease it back out… That will work fine until the heat builds up to the point that it starts burning things up. The shuttle and the GST lever will also slip the wet clutch pack, (I still reduce rpm and or forward movement) , BUT it being a wet clutch, there is somewhere to dump the heat…
Any way you do it, it’s going to work… but using the wet clutch pack when you need to disengage the engine will reduce long term problems…
One of the best improvements made to brakes was making them wet brakes for this same reason… many people have left the brakes on and driven off on their tractors, then noticed later that they ‘oops left the brake on’… with dry brakes they will burn up quickly, wet will take a lot of abuse, somewhere to dump heat… enjoy your tractor...KennyV.