Lawn Boy Model S21 ZSN

grasscutter(5b Ont Canada)April 30, 2010

This is a 1989 self-propelled model and runs great. But when it starts cold, the transmission is in gear regardless of the handle control. After spinning the rear wheels on the sidewalk till it grabs, it finally behaves properly, and I can control it with the handle. I have done all the adjustments in the manual but it makes no difference. Lawn Boy specs "A" greese, but I can't find any called that. So I used axle greese. When it's cold, it won't freewheel when I pull it backwards, so something won't disengage, or seizes up. The mower is almost uncontrollable when cold and is dangerous. Can someone please suggest how I might solve this one? Thanks.

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Ffor the hard to pull backwords start out with general service. Grease the zerk fittings on both rear wheel levers. Remove the rear wheels, clean debris from inside wheel area. Remove the gears that drive the wheels making sure not to loose the key and spring under each gear. remove rust and excess grease from gears and apply thin layer grease on drive gears so turn freely.

For the drive away when handle released first verify cable is fully disenguaging drive arm at transmisson area. Kink in cable or grass build up between transmisson enguagment arm and deck could create your issue. Otherwise you may have to drop the transmission and replace old grease with new. Also run mower with belt cover off to see full operation of drive to look for obvious issues

    Bookmark   April 30, 2010 at 11:17PM
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grasscutter(5b Ont Canada)

Thanks Eric ... I did have the belt cover off, and did all the adjustments ... cable is free and works when it's warmed up. But I have never had the wheels apart, and didn't think anything could go wrong in there. I'll do as you suggest and report back !! Can you suggest the kind of grease I should use ... the Lawn Boy 'A' is no longer available. Thanks.

    Bookmark   May 1, 2010 at 10:27PM
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I like #00 grease inside the gear box and #1.5 white lithium grease for the clutch housings, axle end gears/ratchets, wheel gears and axles.

    Bookmark   May 1, 2010 at 11:16PM
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grasscutter(5b Ont Canada)

I tooke the wheels off today, and they were pristine. No grass or dirt inside, and the gears were clean, no rust, and they turned freely. The spring and pawl were clicking and working great. There was some dried grease around the edges, which I removed. I re-lubed them with lithium grease as recommended by saxman (thanks) and now I see how those things work. Which tells me why they freewheel when pushed forward, but when pulled back, the check pawl engages and tries to turn the transmission. Which doesn't turn. So maybe that means the lube is dried up in there and the clutches are not slipping ... or perhaps the differential isn't turning freely. Before I take the transmission apart, what should I be looking for or the most likely problem?? Any advice much appreciated. Thanks.

    Bookmark   May 2, 2010 at 6:22PM
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htimsdj(Zone 6)

Hey - I had this same problem on the same mower - I know exactly what it is ...

That transmission is gunked up inside, and this is preventing it from ever disengaging. Take it apart, clean it, repace worn parts, and add new grease. Should be like new.

If I remember correctly, as soon as you start it, the rear wheels start spinning. After running a while, it slows or stops (the grease gets moving).

The only grease I would use in the zerks or in the transmission is Mobil 1 fully synthetic grease.

    Bookmark   May 2, 2010 at 9:43PM
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grasscutter(5b Ont Canada)

Brilliant htimsdj!! Thank you. That's it exactly. So now I have the confidence to tackle the job, expecting likely success. Could you tell me if you needed any special tools to do it ?? I presume you removed the whole transmission, shaft etc ... did you replace the seals and the packing ?? Many thanks.

    Bookmark   May 2, 2010 at 10:54PM
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lawnmowerdan(ne fla)

mine does this too

    Bookmark   May 3, 2010 at 7:41AM
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The mowers i worked with this set up have a plastic acces cover on the lower side of the deck however its held in place by bolts that go though and locknuts on the top side. The locknuts are absolutly imposible to reach with a wrench so you need to take off the wheels, handle bracekts and all the other linkages. I never tackled the project personally and the mechanic manuals lawnboy printed do not describle how to service this transmission internally. By the way according to diagrams theres a gasket between the access cover and trasnmission casting so if it tears you will need a new gasket or a liquid form a gasket if that works

    Bookmark   May 4, 2010 at 12:04PM
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grasscutter(5b Ont Canada)

Thanks to all for advice and direction on this. I'll give it a go. Bought the synthetic grease yesterday. For the benefit of others with this problem, I'll post an update when its done. Cheers.

    Bookmark   May 4, 2010 at 11:28PM
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htimsdj(Zone 6)

I did not replace any parts - just cleaned it up really well. I tried to disrupt as little as possible. I don't have the mower anymore, but I believe I dropped the case off the bottom of the transmission and cleaned what I could in place. I didn't want to remove the drive shaft and deal with all of the reassembly. I cleaned out what I could with scrapers and rags, then cleaned the parts with a solvent. Then I added the grease.

I had no problem removing the plastic cover on the top of the deck. With this removed, access was easy.

One last point - I believe the transmission on your mower is the "5 speed" variety. This means you can select one speed from among 5 based upon how many washers you put between the top and bottom of the pulley. You might experiment to see which arrangement you like.

Finally, I use the Mobil 1 synthetic grease (in the can) in the transmissions on the 3 speed units and the easy stride units, and (in the tube) in the grease zerks.

    Bookmark   May 11, 2010 at 12:30PM
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grasscutter(5b Ont Canada)

Thanks htimsdj. It's been so cold I haven't started the repair yet, so it's great to know that as long as nothing is damaged, I can try doing it without complete disassembly. I will surely try that first. Much appreciated.

    Bookmark   May 16, 2010 at 10:24AM
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