990 PTO power

[TheRosenator]

The PTO lever on my 990 has two settings and I’m wondering what would work best with a bush hog. I tried putting it on but the lever would just shake and not go into the setting. Interesting enough it would on the logging winch without an issue.

[tomryall]

540 RPM is likely the correct speed, a 990 only has a 540 speed shaft , and if your brush hog fits that shaft then it was designed for 540 RPM.
unless someone has changed the yoke end and that is unlikely.

[ollek]

Is your 990 a Implematic or a Selectamatic? Do the tractor have a dual speed or a single speed PTO? A 990 Selectamatic can have either PTO version. Have you had the clutch oedal fully depressed when you move the PTO speed selection lever? The correct PTO speed is determed by the implement manufacturer, ask them. Tomryall, a David Brown 990 have only one PTO shaft, but you can select 540 or 1000 rpm if the tractor has dual speed PTO. The 6-splines shaft used is the one ment for low power output on modern tractors and was the only shaft available when the 990 was made. The 21-splines shaft is meant for higher outputs and can be found only on later tractors. David Brown started to use a dual speed PTO with a turnable shaft where one end had 6 splines and the other 21 splines. This setup was fitted to 1410, 1412 and all 6-cylinder models.

[SteveCollett]

To add a bit more confusion.
There was no standard until the early 60's on splines. When PTOs first came in manufacturers went for their own sizes to encourage customers to use their equipment. I believe some early Fergie 20's have a non standard shaft size
gradually the sizes became standard but it was realised there should be 2 sizes so small equipment was not fitted to large tractors with too much HP
In the UK the 6 spline and the 21 spline became standard but there were still American models into the 80's with a 20 spline shaft which confused all who were not aware as it looked so similar to the 21.
David Browns were pioneers in the dual speed PTO recognising quite rightly that running low power equipment such as hay turners at low revs was far more fuel efficient, and it increased the range of speeds available at 540 revs

[Gard]

Most equipment made today uses the 540 RPM PTO. If I am cutting a field with the brush hog that is not very tall I often use high PTO with low engine RPM. On tall fields I switch to low PTO and high engine RPM. I have an old Howard rototiller that can be used at either 1000 or 540 RPM depending on soil conditions. The 2 speed PTO is great.

[tomryall]

The 20 spline shaft is 1 3/4" diameter, it is really popular here now as farmers are using high HP tractors on grain carts and big augers and other machines, you see them advertised on auctions as "big shaft 1000 pto"

[TheRosenator]

Well it’s a Selectamatic from I think 1967...Depress the clutch? The previous owner wasn’t doing that and I wasn’t doing that when I used the winch. Now I’m guessing I was screwing up. Next time I try it I will depress the clutch. I’m pretty sure it’s a two speed.

[tomryall]

I have never seen a 990 that was'nt 2 speed PTO. but that does'nt mean there was one.only DB that we ever had that was single speed was 950 implematic.

[Valiant Farmer]

I have had two 850 diesels and they have both been single speed PTO's. Just my observations...

[ollek]

Lets hope that you have not damaged the PTO gears too mutch, if you have moved the PTO selector lever without depressing the clutch pedal fully down. This is once again a problem that could have been avoided by reading the Operators Manual. A 2-speed pto have 3 positions on the lever (540 rpm / Neutral / 1000 rpm). The one speed unit have 2 positions on the lever, (Neutral / 540 rpm). Please get yourself a Operators Manual as soon as possible, it can turn out to be expensive not to use and maintain the tractor in the corect manner.

[philedge]

Well it’s a Selectamatic from I think 1967...Depress the clutch? The previous owner wasn’t doing that and I wasn’t doing that when I used the winch. Now I’m guessing I was screwing up. Next time I try it I will depress the clutch. I’m pretty sure it’s a two speed.

Without using the clutch, Id be fairly sure crashing the PTO into gear will have damaged/worn the gears so Id be looking to do a gearbox oil change together with a new filter and a clean of the filters magnet.

[TheRosenator]

Lets hope that you have not damaged the PTO gears too mutch, if you have moved the PTO selector lever without depressing the clutch pedal fully down. This is once again a problem that could have been avoided by reading the Operators Manual. A 2-speed pto have 3 positions on the lever (540 rpm / Neutral / 1000 rpm). The one speed unit have 2 positions on the lever, (Neutral / 540 rpm). Please get yourself a Operators Manual as soon as possible, it can turn out to be expensive not to use and maintain the tractor in the corect manner.

Yup - I have the operators manuel and the maintenance manuel ..unfortunately was relying on the previous owner (recently deceased) who has had it for the last 20 years. Lesson learned