Tractor / mower clutch bodge

[Harry Bloomfield]

Lawnflite 703 Autodrive. PTO clutch for deck drive was slipping, so I decided to have a go at it. I have looked at it before, a mechanically operated clutch (rather than electrical) and then I found it was simply metal face, to metal face - no sign of any friction material, but it worked, so maybe that was how it was designed to work?

I have been unable to find a proper manual for it or any sort of diagram of the tractor or the clutch, nor even a replacement clutch, though I have not looked too hard for the latter.

It uses three balls, in deepening slots to engage disengage, with a strong spring to engage and a light concentric spring to push the plates apart.

Lacking any better idea, I thought to try a bit of thin card to act as friction material between the two metal plates, but couldn't find any suitable. What I did find was some material marked Novus Econostus

1.5mm which has been laying about in my workshop for decades, probably intended as gasket material of some sort (light browny orange colour), so I cut some of that into a disk and super glued it to the clutch plate.

Drive to cutting deck now seems to work fine, but for how long? I cannot see the clutch being under much stress, because it has sort of worked metal to metal for the past few years.

[Harry Bloomfield]

Harry Bloomfield presented the following explanation :

Bump, someone must know?

Is a clutch ever designed to operate without any friction material just steel against steel. There were no obvious signs of any friction material ever having been there..

[The Natural Philosopher]

yes. Conical style clutches and IIRC centrifugal cluthes often used metal... ...ooi is this yours?

[newshound]

Your description of 3 balls in deepening slots made it sound more like some designs of freewheel to me (rather than a clutch). It's certainly true that freewheels are usually metal to metal. As TNP points out there are also various types of metal to metal clutch. Some use sintered bronze on hardened steel multiplates (later Norton Commandos, I believe). You don't want steel on steel to see too much slipping, unless it is in an oil bath.

[newshound]

Lawnflite manuals seem to be available to download. The Laser ride-on mower that I used to have simply slackened off a V belt to disengage the drive.

[Harry Bloomfield]

The Natural Philosopher brought next idea :

That looks like it, but its neither conical or centrifugal. The clutch is engaged by a level by the steering wheel, that spring then forms the force to push the two clutch plates tightly together.

[Harry Bloomfield]

newshound laid this down on his screen :

This is/was just steel on steel. The three balls in the slots, are just the means to force the clutch plates tightly together, via a coil spring and bearing.

[Harry Bloomfield]

newshound expressed precisely :

That is what this one uses for the propulsion system V-belt, tightening it to provide the drive, but the PTO for the deck uses this weird clutch system.

[newshound]

Interesting. I guess it is just meant to be on-off. Provided the load is high enough it probably never really slips. I wonder if it is hardened steel, or just mild steel? Ordinary grey cast iron would probably work OK as the graphite might help to prevent the metal picking up or scoring.

[Harry Bloomfield]

There has to be some initial slippage and wear, when it engages with the engine running at full speed, so not quite on off.

The metal plates seem to be just pressed mild steel and both are quite scored. I have had a long term issue with my grass being quite tough and moist, jamming up the cutter deck - probably causing a lot of clutch slippage.

I earlier ran a full test of my 'gasket material' modified clutch and it seems to be holding up.

[Brian Gaff]

Does seem a little on the crude side. Some materials can make it snatch and if it gets at all hot during running it might melt or go sticky. Brian

[Harry Bloomfield]

Brian Gaff brought next idea :

Seems to be working fine, better than it has ever done in my ownership

- now I have run a more thorough test. It shouldn't get hot, unless due to the friction of the clutch slipping.

[newshound]

It might well be good. Quite simple heavy woven cotton used to be used for clutches and brakes on things like cranes.

[John Rumm]

I have the same mower - mine is probably the 2007 model.

The clutch still works ok on mine, but its definitely a progressive action. You can engage the blade gradually... usually wise if you are not sure if the deck is clogged or not - saves stalling it.

[Harry Bloomfield]

John Rumm pretended :

Yes, it is very progressive and a clogged deck I find is a very regular problem. It is never obvious that the deck is clogged up jamming the blade rotation, which probably explains my clutch issues.

Because it clogged so often, I stopped using the grass collector on it to make the deck and duct a bit easier to clear out. I'm thinking to remove the duct entirely, to knock up a bit tin to convert it to side discharge duct. If I just remove the rear discharge duct, it blows the cuttings onto the pulleys and drive belts, causing them to slip.

[John Rumm]

The standard deck is not really configured to allow cut'n'drop, since it blows all the clippings out of the central top opening. So you can cut and collect, or block the outlet altogether with the mulch plug, and then cut and mulch. I have tried defeating the grass collector interlock, and just allowing the rear duct to discharge into free space

- but it has quite significant airflow, and you get plume of blown grass that tails probably more than 10' behind you! Perhaps adding a baffle there to redirect the stream at the ground would work.

(A side discharge chute could work - although because of the counter rotating blades, the grass is being swept forward at the outsides of the deck)

To minimise clogging on damp grass, I adopt a number of procedures... I don't take off much at a time - start on the longest grass setting. If worse comes to worst, then mowing twice without clogs is less hassle than having to unblock it every 5 mins). Don't allow the collection bin to get too full. Keep the glass collector interlock disabled, and have a

5 or 6' long bit of scrap timber handy. When it clogs I then take off the collection bin, engage the brake lock, hold the seat down by hand and engage the blades. Now with one hand holding the seat to keep that interlock engaged, you can poke the duct with the wood. A quick stir will normally loosen it enough to then blow out. (perhaps one of these days I will wire up an interlock disable switch to knock out the grass box, and seat interlocks)

I have toyed with the idea of taking an angle grinder to the back of the deck and cutting away the back wall, so that it can be reattached with a hinge mechanism, and some kind of two position lock. That way you could close it and lock it shut to get the current mode of operation, fit the mulch plug, then lock the flap open to allow grass to fall out of the back.

Armed with a tow behind sweeper, that would be quite handy for the tricky first cut of the year when everything is a bit damp.

(once its got to this time of the year, clogging is pretty rare I find)