Sheared PTO shaft again on Flail Mower

[DennisH]

Hey guys looking for some advice here.

I have a older 5' Alamo Flail Mower that appears to be in good working order that I installed a new PTO shaft on last year along with new blades and bearings for the roller (the one that rolls on the ground). I have greased all fittings / drained and re-filled the gearbox. The blade drum truns freelyly by hand with no binding.

Last year I was cutting some grass about 12" high and hit a few hard items here and there and a few laps later the PTO shaft sheared. I repaired this by cutting about 2" off the shaft and it worked fine after that for the rest of the year.

My nephew was mowing today on the second use of the year and sheared a PTO shaft again (says he didn't anything). Both times it sheared at the mower side and when checked for binding it turns smoothly.

The shaft is from TSC and says it fits "PTO series finish mower; size: 5 ft. cut".

Any ideas why this mower keeps shearing PTO shafts? There is a belt between the mower gearbox and the blade drum so I can't see this thing locking up under use, the belt would slip first.


Also, I just went out to the Montage Enterprises website and the PTO it shows for this mower has a slip clutch on it, should I be running a slip clutch?

 

[DennisH]

I have looked at Caroni, Land Pride and Phoenix mowers and they don't have a slip clutch.

 

[JasG]

A slip clutch won't hurt anything that is for sure.

You said the shaft is a "TCS is for a 5' finish mower". The flail mowers I have seen took more HP to run than a 5' finish mower. Very possible the shaft you have isn't up to the needs of the mower. A landpride 6' finish mower is listed at 15 Hp min. The smaller flail mowers I know have a mininum of 25Hp and some 40 HP. It is very possible the shaft isn't rated for the HP needed to run the flail.

What you need is the HP of the mower and or the tractor and make sure the shaft is rated for that HP.

I came across this listing below on another forum a long time ago. Maybe this can help, it is suppose to be the size of the PTO based on N numbers. I think the N number referes to the yoke strength, but they increase the shaft also, or maybe both. It's been a long time since I have had to remember this.
6N Series Upto15HP(540RPM)&22HP(1000RPM) ADS-8,9
12N Scries Up to 17 HP (540 RPM) & 26 HP (1000 RPM) ADS-10,11
14N Scries Up to 22HP (540RPM) & 33 HP (1000RPM) ADS-12,13
35N Series Up to 40 HP (540 RPM) & 60 HP (1000 RPM) .... ADS-14 thru 17
44N Series Up to 70 HP (540 RPM) & 105 HP (1000 RPM) ADS-18,19
55N Series Up to 100 HP (540 RPM) & 130 HP (1000 RPM) ADS-20,21

Personally I would oversize the PTO a little and use a slip clutch with a flail mower depending on the application. If you were to pick up a post or hit something that could lift into the mower it would save damage.

 

[greg_g]

Assuming your flail is belt-driven, there's no need for a slip clutch. The fact that the PTO shaft failed before the belts slipped is a strong indicator that you bought the wrong PTO shaft. Just because it's long enough, doesn't mean it's strong enough. You need one designed to handle no less than the mower transmission rated horsepower. My guess is that you need at least a Series 4 shaft.

//greg//

 

[leonz]

About your mower,

You need a "complete" Eurocardan 24 inch PTO shaft, you should be able to obtain one or its equivalent at TSC, Menards, Farm and Fleet, Agrisupply and the Belarus USA folks.


_________________________________________________________________
Once you go flail you never go back:thumbsup::licking::drool:
Pronovost or not at all!!!:thumbsup::licking::drool:

 

[aczlan]

About your mower,

You need a "complete" Eurocardan 24 inch PTO shaft, you should be able to obtain one or its equivalent at TSC, Menards, Farm and Fleet, Agrisupply and the Belarus USA folks.

He needs a heavier shaft by the sound of it, not just a different brand... Buying a Eurocardan PTO shaft in the same size as he currently has will do him no good.

Aaron Z

 

[greg_g]

He needs a heavier shaft by the sound of it, not just a different brand... Buying a Eurocardan PTO shaft in the same size as he currently has will do him no good.

That was my point. I don't think either previous shaft was a (minimum) Series 4 or equivalent shaft, regardless of brand. Just because it's long enough - doesn't mean it's strong enough. I'm not in a position to go measure the Eurocardan on my flail right now. But odds are it's this one,

//greg//

 

[DennisH]

My tractor is a JD 870 28hp, I'm headed to go look at where it sheared and will post some pictures.

 

[RickB]

Assuming your flail is belt-driven, there's no need for a slip clutch. The fact that the PTO shaft failed before the belts slipped is a strong indicator that you bought the wrong PTO shaft. Just because it's long enough, doesn't mean it's strong enough. You need one designed to handle no less than the mower transmission rated horsepower. My guess is that you need at least a Series 4 shaft.

//greg//

At least. I'm not sure I wouldn't put a series 5 on it, no more than ONE costs. And make certain the belt isn't over-tight.

 

[greg_g]

My tractor is a JD 870 28hp, I'm headed to go look at where it sheared and will post some pictures.

Speaking from experience, anything lighter than a Ser.4 will
(a) twist the shaft into an unusable fixed length,
(b) break the weld between shaft and one of the flex joints, or
(c) the coupler itself will snap in two in the middle of the flex joint
not necessarily in that order.

It's good that the tractor PTO was protected. But the idea is to get a shaft that's stout enough to smoke the belts, rather than committing suicide first.

//greg//