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My S21ZSN would not pull itself, but was kinda hard to push or pull backwards. When I lifted the rear the wheels would turn, but as soon as I set it down they would stop. I read the other thread about this, which gave me the right start on the problem. I took the bottom of the drive case off. Contrary to a previous post, it can be done without removing the shaft, wheels, etc. but the rear-most bolts are very difficult to get a wrench on (7/16"). I found the inside of the case filled with caked, hardened, 27-year-old grease. I scraped it all out and cleaned up the 'innerds'. The question now is: What lubricant should I use?

- The stuff I got out reminds me of wheel bearing grease
- The dealer I bought it from this week (new) did not know. After talking it over with him, he suggested 90W gear lube.
- There's a tiny drain plug on the bottom of the case. Clearly, grease would never drain from this plug. EVER.
- If you remove the engagement arm you can also remove the O-ring and adapter for the arm. At that point, you can squirt in lubricant around the shaft.
- Looking at the worm drive, drive return spring, etc. I don't see any reason why they would need a heavy grease for lubrication.
- The plug looks to be the same threads as a zerk. If the gunk inside is indeed grease, maybe the factory used a temporary zerk to fill it and then replaced it with the plug (just a guess).

So what do you guys think? I am tempted to use maybe a heavier motor oil like 40 Wt, or the suggested 90 W gear lube - something that can be drained out in the future. I do not want to mess around taking this thing apart again if I can possibly help it. Thanks in advance for your advice!

I ended up using Mobile1 Synthetic gear lube. At first, this worked great. After about 5 minutes, it stopped pulling again, but the mower pushes and pulls backwards fairly easily. I suspect the wavy washers that are supposed to grab the shaft are too well lubricated to do so. I dunno. Very disappointing Saturday. At this point I'm ready to take off all of the self-propelled stuff and turn it into a straight push mower. :frown:

I tried synthetic gear lube in the rear end of my Toyota Tundra (limited slip differential) and it acted WAY weird, making noises and slipping. Ended up replacing with conventional rear end fluid and the problem went away.

Snapper uses 00 grease in their transmissions available at Tractor Supply Company.

Jeff

jp1961 said:

I tried synthetic gear lube in the rear end of my Toyota Tundra (limited slip differential) and it acted WAY weird, making noises and slipping. Ended up replacing with conventional rear end fluid and the problem went away.

Snapper uses 00 grease in their transmissions available at Tractor Supply Company.

Jeff

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They make a limited slip additive that you must put in. If you don't it will destroy the rear end.

Yep...old grease out....new grease in. Use 2.5 ounces of 00
Lee

I have read on here that you can drill a hole in the bottom of the trans case and flush it out with you know that stuff in the red can then thread the hole to install a grease zerk and pump it with 00 grease

BlazNT: Didn't find anything on Google for this additive. What do I use to find this additive?

unclelee: So you'd say dump the gear lube out and refill with something like Stens 770-123 "00" Grease? I found something on Amazon that looks promising:

Stens-770-123-00-Grease

Or just add the kind of friction additive like they put in limited-slip differentials? If so, any particular's on this?

I'll give you guy's advice a try before I yank off drive parts, but fact is I'd probably be happier with a straight up push mower. I have a '92 680529 (looks just like the S21ZSN, but not self-propelled) which I've been happy with for years, other than issues with junk aftermarket wheels. Pushed it around about 3 hours this week with a smile..but I tell you what, that NOS S21ZSN has a LOT more power, even though the engine is the same. I guess that's the difference between a tired, 24 year-old F engine and a brand new 27 year-old F engine.

beg: I read that thread, too. There is a plug near the bottom of the case which may be the same threads as a zerk. How do you put 00 in with a zerk? The 00 I've seen pictures of are squeeze-looking bottles.

Some zerks may be self threading. I ran across this with auto steering rod ends. Although I could not ID the threads with a gauge they looked like small pipe thread, tapered. The hole, as I remember it, admitted the end of the threaded zerk and from there you carefully keep vertical alignment while screwing in, hopefully with a tiny hex socket (only with straight zerk?).

This is what I did my google search with "limited slip rear end additive" Any automotive store will have it in stock. Maby not this brand.
amsoil.com/shop/by-product/gear-lube/slip-lock-gear-oil-additive/

I found that stuff. I thought you were referring to an additive specific to LawnBoy drives.

By the way, today it wouldn't move on its own at all when cold, but it did drag some. So I used my old, trusty S21ZPM to mow (not self-propelled). If I didn't have that one to fall back on while I fuss with the S21ZSN, the ZSN would already be "de-propelled".

Too lazy to reread everything. Did you change the belt?

Mower is new; belt is fine. There is no slippage on pully. I did run it a little with the cover off.

The mower was NOS when you got it....it had dried up grease that you removed.
If it where to use gear lube with or without limited slip additives, that is what the factory would have put in it.
I would suggest you drain the oil out...then flush it with diesel to get the residue out.....then put grease back in like it should have.
If you haven't damaged it....it should work.

jp1961 said:

I tried synthetic gear lube in the rear end of my Toyota Tundra (limited slip differential) and it acted WAY weird, making noises and slipping. Ended up replacing with conventional rear end fluid and the problem went away.

Snapper uses 00 grease in their transmissions available at Tractor Supply Company.

Jeff

Click to expand...

BlazNT said:

They make a limited slip additive that you must put in. If you don't it will destroy the rear end.

Click to expand...

Ok I want too straighten out this post. I was responding to the person with the Toyota Tundra "jp1961" That is why I quoted him in my response.

BlazNT: Now I understand. Sorry for the confusing followup question.

Unclelee: Taking it apart again this evening to clean it out again. I also took apart the wheel drive assemblies. The grease in them was more like wax. Should have figured it was more than just the transmission that needed re-greasing. Soaking in kerosene right now. I bought Sten "00" for the transmission. Is this also the right grease for the rear wheel axles and the wheel drive assemblies? If so, how do you inject it into zerk fittings when it doesn't come in a grease tube? (I'm talking about the zerk on the wheel and the zerk on the height adjuster.)

I use high temp grease that goes in one of these

Use type 00 or marine grease i torn down my single speed trans in my 10301 and pumped it full of marine grease and it works fine.

OK, just to close out the thread:

I took apart both drive gear assemblies (the ones that sit inside the wheels and drive them). The years had turned the factory grease to wax; the springs were not strong enough to push the key into the pinions. I scraped the wax out and cleaned them up with kerosene. Once they were completely clean I greased them with Stens 00 grease and reassembled. There doesn't seem to be a way to grease these assemblies other than to take them apart. I used a drill on the pully shaft (9/16" socket) to test the mechanisms, they seemed fine.

So it turned out this NOS S21ZSN had three different problems develop over the years of sitting at the dealership:

a) There was something in the drive cable at the handle end that stopped the cable return spring from disengaging the drive. I believe it was bug parts (blech!). With the help of silicon bicycle cable spray, I got little black pieces out of the top of the cable once I removed the bottom end so the cable could move its full stroke. Once the cable was cleaned up, it worked fine. Full, normal (i.e., when assembled) stroke of the actuating arm on a new S21ZSN is about 5/8".

b) The grease inside the drive transmission had turned to wax, making the transmission prone to not disengage when the handle is released. Even when the fork-shift was disengaged (by pulling the arm clockwise, toward the rear of the mower), the drive/driven plates kept gripping the driveshaft. Once released, they did not want to grip the driveshaft unless a lot of counter-clockwise force was applied to the arm - more than the spring-loaded arms could apply.

c) The grease inside the drive pinion assemblies had turned to wax (see above).

I tried the mower out Thursday and Saturday (about 3 hours) and am please to report the mower drives VERY well and has tons of power. Just like a new one, heh he. I am glad that I stuck with it and didn't remove the drive apparatus. It was worth the pain to get it working right.

Thanks again to all of you for your advice, especially Unclelee.

thanks for following up , good read

For what it's worth I went looking for 00 grease and the best deal for me was from amazon, a 9 oz. tube for a little over $10 ea.

In the search I called local Lawn Boy dealers and they said that that they now use white lithium grease. Being in a hurry to finish the job I went with the lithium grease.

In a short test everything worked well, but I'll reserve judgement until some time has passed.

If problem appear I'll try to remember to report back here.

Current project: Restoring 30 Year old S21BSN, same as S21ZSN. BSN has Blade Brake Clutch, Had the same tranny problem in addition to a broken shift fork. After much discussion with some lube engineers, it seems the semi-fluid grease (NLGSI 00) will work the best. Will fill to the top of the bottom housing. I disassembled the entire tranny, and cleaned all disc clutch components. Actually found many of the discs rusted, Polished all of them.
Enclosed is the tranny pic minus the shift fork which I have on order. My pic will not fit.

Current project: Restoring 30 Year old S21BSN, same as S21ZSN. BSN has Blade Brake Clutch, Had the same tranny problem in addition to a broken shift fork. After much discussion with some lube engineers, it seems the semi-fluid grease (NLGSI 00) will work the best. Will fill to the top of the bottom housing. I disassembled the entire tranny, and cleaned all disc clutch components. Actually found many of the discs rusted, Polished all of them.
Enclosed is the tranny pic minus the shift fork which I have on order. Pic will not fit

Do you have a question?

waynieboy said:

Current project: Restoring 30 Year old S21BSN, same as S21ZSN. BSN has Blade Brake Clutch, Had the same tranny problem in addition to a broken shift fork. After much discussion with some lube engineers, it seems the semi-fluid grease (NLGSI 00) will work the best. Will fill to the top of the bottom housing. I disassembled the entire tranny, and cleaned all disc clutch components. Actually found many of the discs rusted, Polished all of them.
Enclosed is the tranny pic minus the shift fork which I have on order. Pic will not fit

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Waynieboy: This thread of mine is old, but appears to be useful for people with self-propelled drive issues. I actually still have an issue that perhaps you are seeing, too... I can't get the wheel covers to stay against the wheel. They kind of snap-in, but come right out of their grooves as soon as you turn the wheels. I didn't think too much about it, but it has allowed lots of grass and debris inside the wheels. Do your wheel covers stay in their wheel grooves? The drive shaft seems to push the wheel cover off the wheel on the side opposite the drive shaft due to a planar difference between the height adjuster and drive bearing bracket and the slight wheel cover depression towards the center of the wheel.