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I just purchased a new Gravely ZT HD 44 mower. The dealer told me the mower deck spindle bearings are sealed and cannot be greased.

My previous mower had zerk fittings for greasing the bearings, so I'm a little concerned about this. I will only be using this mower on my 1/2-acre yard, so it will have an easy life with no commercial applications.

Are permanently-sealed bearings really permanent, or will I have bearing replacement issues in a few years?

(When I was a teenager, my dad purchased an Ariens Fairway Four riding mower. It resembled a Snapper mower and had a 4 hp Briggs and Stratton engine. We used that little mower for at least ten years. Tough little machine!)

The maintenance free spindles usually last about 2-3 years in commercial use. It has been reported that the bearings are replaceable but I have no experience with them.

Richard-TX said:

The maintenance free spindles usually last about 2-3 years in commercial use. It has been reported that the bearings are replaceable but I have no experience with them.

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I am sure( I think) that Bearings Inc has the replacement. But then there is the labor - $60 to $120 per hour.
IMO, zerks are better, but they must be used, of course....Particularly after a deck wash down.
And the rubber boots to protect the bearing is important, no "sealed" bearing is sealed 100%.

Greasing ball bearings is tricky business. Too much grease is as bad as too little.

For those that don't get alot of exposure to the inside of spindles I will tell you that most of the newer ones I see are sealed bearings even if it has a zerk fitting on it, Trouble is for those that actually use a grease gun they over do it, if the spindle does not have a pop off relief then what happens is they blow the bearing seals right out of the bearing due to over pressureization, at that point the bearing is basically dead as everything in the world can get into it, The one or 2 commercial brands that tried actual greased bearings found they had more problems and complaints with them , By using sealed bearing with a pressure relief on the spindle everybody is happy, for those that don't grease they still get "normal" wear on thiers and the guy with a compulsive grease gun addiction he can pump grease in them all he wants and thinks he is doing good. The only good that any grease does on these is make it a little easier to get things apart should they need to be repaired.

Double sealed ball bearings are not meant to be greased....ever. The problem is that the grease pack is not supposed to be no greater than about 30% by volume, less if the bearing is operating near it's maximum rated RPM, slightly more if low speed. Since this is a mower spindle, the operating RPMs fall into a medium speed so a 30% pack is called for.

By virtue that there is no way to determine what the bearing grease pack is, it will get over greased. Overgreasing causes the bearing to overheat which results in all manner of bad things occurring. The reason for the overheating is that the balls have to plow through the grease instead of rolling in the race.

A one side sealed bearing would be a reasonable choice for a mower spindle but the necessary relief port is required but that also leads to problems in keeping the upper bearing lubricated properly. Grease will run down to the lowest point over time.

For those contemplating replacing the bearings in a spindle, there is more to it than just replacing bearings. The necessary axial free play/preload can be a challenge to set correctly and it does change from bearing manufacturer to manufacturer. Without several hundred dollars of precision measuring tools, the best advice I can give is to use the same manufacturer of bearing that the spindle was originally equipped with. At least there is a reasonable chance that the axial freeplay/preload will be set correctly. Using a different makers bearings will be very risky at best.

Richard - Who makes and repairs High Speed Spindles

One of the most common cause of bearing failures ------- Hitting objects with the blades. After hitting things and ever so slightly bending the jackshaft, it will cause it to ruin the bearings as well as the rest of the spindle assembly. Solution ----- DO NOT HIT OBJECTS WITH YOUR BLADES.

Sounds simple, I know sometimes you don't see stuff int he grass but you should make an attempt when you do see stuff, or walk the yard and make sure there is nothing. We have sold Gravelys for 10 years and has been the least replaced spindle out of any of them. The spindles will last if you do not abuse them.

What I have found regarding bearing and striking stationary objects isn't so much bending of the shaft, but actual damage to the bearing. In extreme cases brinelling is very obvious as in the picture below. In less severe cases a magnifying glass may be required.

Brinelling is a fairly common type of damage. I have pulled brand new bearings out of the box to find them brinelled due to rough handling by UPS or improper packaging.

I see a fair amount of bearings in a year. My bearing bill last year alone totaled over $2500.00 There were no special bearings in that. Most were common 6200 series ball bearings. I would say that about 10% of the bearings I replace failed due to brinelling. The #1 cause that I see for premature bearing failure in mowing equipment is corrosion due to the ingress of water.

I have a 1982 Whel Horse C175--Original (greasable bearings)
I have worked on MANY lawnmowers and will give my personal opinion.
Quality machines of yesterday, had greasable bearings with the right engineering in mind.
W H Gravely and others had bearings that were sealed on ONE SIDE. Bearings were installed with Seal up on the top bearing and installed DOWN on the lower bearing. The seal --on bottom-- was installed (backwards) to allow escape of grease below the deck. Had the lower bearing been installed to prevent grease escape, over greasing would blow either the top or bottom seal. If the seals are not installed in this fashon there should be a way for the grease to escape:thumbsup: I have seen some machines that had an open bearing on the bottom with a rubber washer, or felt, with a thin metal plate covering them.
My old WH and Gravely evidently have this seal configuration because grease escapes below the deck, not on top that would contaminate belt:thumbdown:
Some machines that I worked on Years Ago were designed this way but I have not seen this in modern machines.
I think it would be wise to use a hand grease gun with only Two or Three pumps unless you are sure of grease escape.
To not discredit some of you that have "permanently sealed" ????? they are cheaper to manufacture and most people would never grease them anyway
I am a retired Tool&Die Maker and I would much rather have greasable spindles:thumbsup:

Since you are a tool and die sort of fellow, I think you will appreciate the following.

The later 40" and 50" Gravely mower decks used no-contact, labyrinth seals with tapered roller bearing in their spindles. This eliminated all of the issues regarding seals and greasing.

Excess grease contaminating the belt is not an issue as the pulleys sling any grease away from the belt.

The only problem with the labyrinth seal is that most shade tree mechanics has never seen or even heard of it let alone know what it is and how it works.

Richard-TX said:

Since you are a tool and die sort of fellow, I think you will appreciate the following.

The later 40" and 50" Gravely mower decks used no-contact, labyrinth seals with tapered roller bearing in their spindles. This eliminated all of the issues regarding seals and greasing.

Excess grease contaminating the belt is not an issue as the pulleys sling any grease away from the belt.

The only problem with the labyrinth seal is that most shade tree mechanics has never seen or even heard of it let alone know what it is and how it works.

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I have worked with "labyrinth" seals in many industrial applications but I am sure you are correct that they were used in some mower decks but I can't remember working on any.
Can you explain your remark "This eliminated all of the issues regarding seals and greasing" because in all applications I have encountered, their purpose is served by having expelled grease to discourage contaminating entry of debris. Although not revalent to deck applications, their use cannot be used for submerged components.
I, personally, do not want ANY grease close to a belt application.

I knew that you were familiar with labyrinth seals which is why I mentioned it. These type of seals were used on all of the Gravely 40 and 50" decks equipped with tapered roller bearings.


What I mean it eliminated the issues with regular seals was the tendency of the average tech installing the traditional seals the wrong way resulting in seals that were pushed out of the housing the first time it was greased.

I have seen some very overgreased Gravely decks. I have never seen a belt on a Gravely deck that had been contaminated with grease.

On the 72" Gravely decks the spindle has a grease relief port on the side. That simple addition really solved the grease near the belt issue.

You---evidently---share my knowledge concerning seals.:wink: On a similar note, I have seen a lot of people install grease fittings on the dust cap or on the spindle housing of a boat trailer. All these seals are designed to contain the grease. On many occasions the seal, or dust cap, would be pushed out:frown: On my many boat trailers, I would remove the hub and install the seal "backwards" (seal lip to outside). Installed in this fashon, grease could expell but water could not enter.
After many years, I never had a water contaminated hub:thumbsup:

Have you seen the tapered roller bearings with the integral seal? I have one in the shop as a sample but have not used it yet.

Putting trailer wheel seals on backwards can make installation of the hub a bit tricky.

lakeviewpe said:

One of the most common cause of bearing failures ------- Hitting objects with the blades. After hitting things and ever so slightly bending the jackshaft, it will cause it to ruin the bearings as well as the rest of the spindle assembly. Solution ----- DO NOT HIT OBJECTS WITH YOUR BLADES.

Sounds simple, I know sometimes you don't see stuff int he grass but you should make an attempt when you do see stuff, or walk the yard and make sure there is nothing. We have sold Gravelys for 10 years and has been the least replaced spindle out of any of them. The spindles will last if you do not abuse them.

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I've been hitting things (stumps, logs, occasionally a rock) with my Kubota ZD21 for the past eleven years. The original spindles continue to be trouble free. My old Gilson garden tractor uses 3/4 inch diameter spindles for a smaller deck. It came with tapered roller bearings that had a short life despite regreasing. I replaced the bearings with same-dimensioned sealed ball bearings, which have lasted for many years. The difference may have been that the small spindle diameter flexed enough in our high-work conditions to edge-load the roller bearings. Ball bearings have no such vulnerability. An additional important factor is the quality of bearing seals that are installed. Many mower companies add additional metal debris shields for spindle bearings and these can materially reduce the amount of dirt reaching the vulnerable bearing area.

The major bearing companies all offer extensive online information regarding their research and product capabilities. A major factor is how much money and engineering talent a company devotes to its spindle assemblies. None of the bearing companies known to me have published research material that I can find on the difficult situation of mowing deck spindles, their bearings, and their lubrication needs. Any better knowledge sources would be appreciated, since I have an abiding interest in lubrication and bearing technology.

TX, Giles and Marvin, I am always impressed with the latent knowledge residing in this forum. As a tinkerer here are some comments for your review.

Do big box riders have the fancier spindle bearings?

What is a labyrinth seal and how does it work?

You are telling us that some spindles have cartridge bearings like FWD cars-two rows of rollers , back to back? In cars no adjustment, just press them home.

A member of this forum also confirmed that mower decks with zerks are "placebos" placed by the mfgr to make uptight owners feel good ( My craftsman manual says grease 'em)

I have greased the 3 spindles for 10 years and never seen any displacement or overflow. Such greasing cannot penetrate shields and seals on bearings?

Over the years I have successfully restored lube to bearings in alternators, vacuum rollers , etc by gently prying off the plastic seals, cleaning, packing and re-

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seating the seals.

There are small grease gun "needle" attachments that allow sneaking by some seals and lubricating them.

marvinlee said:

I've been hitting things (stumps, logs, occasionally a rock) with my Kubota ZD21 for the past eleven years. The original spindles continue to be trouble free. My old Gilson garden tractor uses 3/4 inch diameter spindles for a smaller deck. It came with tapered roller bearings that had a short life despite regreasing. I replaced the bearings with same-dimensioned sealed ball bearings, which have lasted for many years. The difference may have been that the small spindle diameter flexed enough in our high-work conditions to edge-load the roller bearings. Ball bearings have no such vulnerability. An additional important factor is the quality of bearing seals that are installed. Many mower companies add additional metal debris shields for spindle bearings and these can materially reduce the amount of dirt reaching the vulnerable bearing area.

The major bearing companies all offer extensive online information regarding their research and product capabilities. A major factor is how much money and engineering talent a company devotes to its spindle assemblies. None of the bearing companies known to me have published research material that I can find on the difficult situation of mowing deck spindles, their bearings, and their lubrication needs. Any better knowledge sources would be appreciated, since I have an abiding interest in lubrication and bearing technology.

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Years ago, I owned a Gilson with spindles and bearings like you stated. Bearings would last about two seasons and I would replace them. I was discussing this issue with a lubrication specialist (oiler) that I worked with. He asked me what kind of grease I was using and I stated the same kind I use on my automotive applications. He suggested that I use a quality EP2 grease. I did as he suggested and ran the mower for approximately twelve more years without a problem:thumbsup:

Cherokee Mike said:

I just purchased a new Gravely ZT HD 44 mower. The dealer told me the mower deck spindle bearings are sealed and cannot be greased.

My previous mower had zerk fittings for greasing the bearings, so I'm a little concerned about this. I will only be using this mower on my 1/2-acre yard, so it will have an easy life with no commercial applications.

Are permanently-sealed bearings really permanent, or will I have bearing replacement issues in a few years?

(When I was a teenager, my dad purchased an Ariens Fairway Four riding mower. It resembled a Snapper mower and had a 4 hp Briggs and Stratton engine. We used that little mower for at least ten years. Tough little machine!)

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I know your original post is kinda old, but just in case you are keeping up with this thread and the additional posts(very knowledgable I might add) have not put your mind at ease, please allow me to do that. I did some considerable research last fall on this very topic because I, like some others, had been the owner of two lawn tractors and I had looked for/insisted on greasable mandrels. Even though your ZT HD doesn't come with the Gravely XL spindles like mine(with a 3Year Warranty) yours also are in a cast-iron housing with a 1" steel shaft and will be VERY durable. I concur with the post that states 99.9% of today's mowers that have aluminum spindle housings with grease zerks....the grease NEVER touches the bearings!!" I had several mechanics tell me that(my Gravely dealer's mechanic actually showed me a mandrel he was replacing on an older, but fairly recent model, Ariens that had grease zerks and the sealed bearings that were inside it). He told me the reason the service was needed was that the owner hit a culvert, bent that blade badly and compromised the bearings in that spindle. He told me that the XL spindles on my Gravely Pro-Turn 100XDZ were warrantied for 3Years of "Commercial usage"(no "hours limitation") and that under normal "Commercial usage" they would most likely last a "minimum" of 5 years. He said that with my "residential" use of that Commercial ZTR, the sealed bearings would most likey last me 3 times that long. I was finally convinced that it was not a "high risk" to purchase a quality ZTR that has sealed bearings(especially if they are in a commercial grade cast-iron housing). Soooooo....I don't expect to need to replace my spindle bearings during my lifetime(I am getting ready to retire, which is the reason for this "investment"). I don't think you have anything to worry about for a long, long, long time on that ZT HD:0)

I have a 2004 Gravely PM 44Z. It has 1015 hours on it. Residential use only. I was wondering how long the spindles should last as well? Just put new belts and blades on and spun the spindle manually to check for grinding or noise. All seemed ok. I guess if it's not broke, don't fix it. 20th year residential mowing. I've read that it's possible to get up to 3000 hours on the 17HP Kawasaki engine. This could be the first and last mower for our one acre lot. Gravely is a solid zero turn mower.

OK well I will weight into this one
1) the first consideration is the size and quality of the bearings .
the bigger the bearing the faster the balls roll over the races and the faster they roll the lower the wear till they end up sliding rather than rolling
The quality of bearings varies drastically from what I like to call shopping trolly wheel bearings through to high precision lathe bearings .
2) the amount , type & operating temperature of the grease packed into the bearings
Too much will cause the rolling elements to slide rather than roll as will to thin a grease
Too thick and it will generate a lot of heat
Thin grease promotes sliding on the inner while thick promotes sliding on the outer .
3) materials & hardness
Lots of cheap bearings are flame hardened to a depth thinner than electroplating and once that wears the rollers / balls will gouge the race
4) number of rolling elements.
Cheap bearings will often have 1 , some times 2 less balls than a quality bearing and these will never provide good service in a mower spindle .
5) cage , people overlook the cage all the time and a lot of cheap bearings fail because the cage falls apart
Using the wrong type of bearing and this is the biggie for mowers .
A deep grove ball bearing is in engineering terms the wrong type of bearing to use on a mower spindle where axial loads can be quite high.
A long while ago , quality mowers had the correct bearings which are angular ball bearings or tapered roller bearings .
However both of these are expensive and mowers are just about all built to a price .

The landlord runs 4 2000 series cub cadets on his 1000 acre farm .
20 acres are orchard & the rest is pasture so these mowers do around 1,000 to 2,000 hours / year depending upon seasonal variations & stocking levels .
These cubs have tapered rollers and in 12 years we have replaced 1 set of spindle bearings over the 4 decks .
Mind you he is a farmer so the spindles get 1 stroke from his grease gun every week .
I have 3 Great Danes they use 6400 series bearings and the GD service manual says to replace them annually .
I have 8 Time Masters and Toro recommends new bearings every 2 years or 500 hours whichever comes first .
However most need replacing the right ( discharge ) bearings twice a year and these are open bearings with external grease seals & overfill ports .

So it is one of those "how long is a piece of string questions? "
Checking bearings regularly by grabbing the edges of the blades & attempting a See Saw movement will usually detect a failing bearing well before it does any great damage and often you can get away with replacing just 1 bearing and on most mowers the longest part is removing the deck .

FWIW I use marine grade Lithium grease

I'll just leave this here.

Don’t trust the “Experts” Grease your mower deck sealed spindle bearings Common sense maintenance.