7840 SL PTO speed and rpm

[Nick14]

Hi all,

I have been finding my feet with hay and found out I went too slow with my drum mower and it didn’t cut that well.
One problem I have come across is what the lines on my RPM gauge mean. NH 7840 SL, I have the dual power option with 3 ranges and a shuttle lever.

I have one line in amber which says 540 pto (1100 ish) then I have another white one around 2000 that is also labelled 540. Which is which? I’ve been running at 1200 rpm but the speed regime is at 1500 and 2000 rpm?

Tha

 

[e3120]

There should be a yellow lever in the back rh corner of the cab marked 540/1000 or tortoise/hare. When in 540, you need circa 2000 engine rpm for 540 pto speed, 1100 is enough if in the higher gear. For mowing, you will need the low gear and higher rpm.

Some very early 40s had no lever and the 10 Series swappable shaft - fairly safe to assume that it's the '540' shaft in this case.

 

[Nick14]

That’s what I thought but couldn’t find a lever for the pto? I think it’s a 1996.
The haybob seemed to be running a bit slow hence the confusion.

I think it’s a 540 shaft but without knowing the difference I’m not sure

 

[Mur Huwcun]

Haybob won’t really need 540 but with drum mower you can set it by ear, when out of the crop it should sound like it’s about to take off!!! Same with disc mower it should be just under the speed where it’s screeching!!

 

[Lincsman]

Not the best video

But where you should be looking

 

[fermerboy]

Right at the back of the cab on the right side, down behind the levers for the spool valves(black handles) there will most likely be a small lever with a yellow knob that you can move crossways, away from the seat is 540 rpm speed, toward the seat is 1000rpm shaft speed.
It may be stiff and notchy to move, depending on if its been used much.

To achieve 540 rpm at the pto in 540rpm setting the engine needs 1900rpm, or to achieve it in high(1000) position the engine needs 1200rpm.
Use the 540 setting for high power items like mowers, muckspreaders, power harrows, balers etc. Haybobs, cement mixers, fert spreaders can be run at 540 in 1000rpm shaft at 1200 engine rpm which saves wear, diesel, and your ears.

As said the haybob will run on less than 540, maybe 400, but to get that on your 1000 gear the tractor will be ticking over and probably not able to run up and down the field.

The pto gear selected has nothing to do with which type of shaft is inserted at the back, a 6 spline stub or 21 spline hub will work . Though if an implement is fitted with 21spline shaft it will need 1000rpm.

 

[Nithsdale]

Hi all,

I have been finding my feet with hay and found out I went too slow with my drum mower and it didn’t cut that well.
One problem I have come across is what the lines on my RPM gauge mean. NH 7840 SL, I have the dual power option with 3 ranges and a shuttle lever.

I have one line in amber which says 540 pto (1100 ish) then I have another white one around 2000 that is also labelled 540. Which is which? I’ve been running at 1200 rpm but the speed regime is at 1500 and 2000 rpm?

Tha

'96 should have the PTO gear lever mentioned by others in the rear right hand corner of the cab to physically switch between 540 and 1000 gears.

As for the rev counter. The amber 540 at 1100rpm is Economy. Ignore it!!
For a mower to work properly you need to run the engine at the white 540 mark - up around the 2000rpm

 

[essexpete]

It would depend on the size and type of mower used by the OP. I have run a small disc mower on a 8340 using the 1000 rpm setting with engine revs shut down. It might not work on a hilly ground or very thick crops.

 

[Nick14]

So I tried the mower today at the white 540 setting and it cut perfectly! Sound was perfect like a jet engine.

iv looked in my cab and there is no yellow PTO lever, there is a small rocker switch next to the PTO selector which I could try? The hedge cutter, haybob and baler might work better at an eco setting rather than the higher engine revs?

 

[Nearly]

The rocker switch sounds like the diff lock

 

[agrimax]

If it's the pto off/on switch you mean,and the tractor has 4wd,the green rocker switch to the right of that yellow knob is for 4wd and the yellow rocker above it is for diff lock. It sounds like your tractor has non shiftable pto,which was optional and therefore it won't have a lever to change speeds. To get an eco pto you would need to change the rear pto stub to a 1000rpm one and then run the engine at 1100 rpm. Not a great idea to run the hedger like this for long periods as the engine isn't really being worked and the cylinder bores will become glazed.Keep the revs up for the baler too...

 

[ridger]

The rocker switch sounds like the diff lock

Rocker switch would be to let the pto over run would it

 

[agrimax]

Don't think the 40 series ever had that.

 

[Nick14]

Actually, 4wd and diff sounds about right. So I guess my machine doesn’t have an eco pto then. Bugger. I ran the hedger at 1200rpm engine and it worked fine but at the higher revs even in the lowest gear it will move quicker. Best learn to control the head at higher speeds .