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I have a third season Gravely ZT 50 and about 4 acres a week to mow--lots of new trees and a pond to slow stuff down. The mower will leave strips of unmowed grass, behind front wheels. This occurs more frequently when grass is strong and growing quickly--we have had a lot of rain in our little corner of SD recently. This happens with new blades, sharpened blades. I have releveled and whatever Gravely customer assistance recommends--nothing helps. Is this a problem with machine design or is there something else that can be done about it. It's really aggravating to see those strips pop up. It gets a little better if I drive very slowly--but then I might as well be on my old MTD mower for getting the work done.

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We moved your thread to the Mower & Equipment Operation forum.

Seems like one or more blade may be too short. Yes, crazy as it seems. Deck design takes blade match and complete coverage into consideration. Possibly the "strip" may only be on the left or right side of your deck to give you a clue.

I would stop and fully shut down your machine as you cut and see strips right behind you. While on hands and knees, follow the strips back to your deck to see the exact location source of them.

Good luck on your close up inspection!

mqs said:

I have a third season Gravely ZT 50 and about 4 acres a week to mow--lots of new trees and a pond to slow stuff down. The mower will leave strips of unmowed grass, behind front wheels. This occurs more frequently when grass is strong and growing quickly--we have had a lot of rain in our little corner of SD recently. This happens with new blades, sharpened blades. I have releveled and whatever Gravely customer assistance recommends--nothing helps. Is this a problem with machine design or is there something else that can be done about it. It's really aggravating to see those strips pop up. It gets a little better if I drive very slowly--but then I might as well be on my old MTD mower for getting the work done.

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Trick question here....how did the Gravely perform the first season(and maybe second season) you mowed with it. If the answer indicates that there wasn't a problem with the uncut strips my guess is that you did not purchase a ZTR that was designed to mow 4 acres/week(the Gravely ZT is the entry level Residential ZTR Gravely offers and is designed....like ALL entry-level residentials...for homeowners with < 1-2 acre lawns). I know everyone tries to find the best mower that they can afford, but IMHO you cannot really expect that Gravely ZT to hold up(performance-wise) with a 4 acre/week requirement. You say that it happens more when you let the grass get too tall. My advice would be to try mowing more frequently where you are not cutting more than 1/3 of the total height(if the grass is 6" tall, set the deck at 4" which cuts 2/6 of the total height). Unfortunately if you want your grass cut at 2" high you would have to cut twice(at least) if you let it grow to 6" high. Realistically, if you want your grass maintained at 2" high you need to mow it when it is 3" high. If you are trying to mow 5"-6" grass at 2" any residential ZTR would have a major problem cutting 4 acres cleanly. I apologize if I have offended you in any way, but I think you have too high of expectations for an entry-level Residential ZTR:0(

P.S.
I guess the shorter answer would have been "yes, there is a problem with the machine design for what you are tasking it to do".

Here are some general reasons a mower can miss a strip of grass on each pass. One reason just pertains to 2-blade mowers, but maybe one of these will help.

• The blade tips are worn.
• Your overlapping may be insufficient: The tires push down grass during each pass. If you line up your tires with tire marks from the previous pass, the grass does not get a chance to stand back up during either pass. Overlap more than the width of your tires on subsequent passes. This will allow the blades to draw up the trampled grass from each previous pass and should produce a nicer looking cut.
• Right hand turns: Twin-blade mower decks are designed with the discharge on the right side. The left blade is positioned slightly forward and in front of the right blade. During left turns this cutting overlap is maintained. This provides cutting overlap when traveling in a straight line. The tractor operator should therefore make mostly left-hand turns when cutting grass.
• Improper cutting deck adjustment: This can produce a vacuum imbalance that, under certain circumstances, causes airflow to push outwards from the front of the cutting deck. Consult your tractor Operator's Manual for specific Deck Leveling and Deck Engagement adjustments pertaining to your specific model tractor.

(Uncut Strip - Riding Mower)

lawn mower fanatic said:

Here are some general reasons a mower can miss a strip of grass on each pass. One reason just pertains to 2-blade mowers, but maybe one of these will help.

• The blade tips are worn.
• Your overlapping may be insufficient: The tires push down grass during each pass. If you line up your tires with tire marks from the previous pass, the grass does not get a chance to stand back up during either pass. Overlap more than the width of your tires on subsequent passes. This will allow the blades to draw up the trampled grass from each previous pass and should produce a nicer looking cut.
• Right hand turns: Twin-blade mower decks are designed with the discharge on the right side. The left blade is positioned slightly forward and in front of the right blade. During left turns this cutting overlap is maintained. This provides cutting overlap when traveling in a straight line. The tractor operator should therefore make mostly left-hand turns when cutting grass.
• Improper cutting deck adjustment: This can produce a vacuum imbalance that, under certain circumstances, causes airflow to push outwards from the front of the cutting deck. Consult your tractor Operator's Manual for specific Deck Leveling and Deck Engagement adjustments pertaining to your specific model tractor.

(Uncut Strip - Riding Mower)

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VERY GOOD info lmf!!!! I started to say something about checking the deck's leveling/pitch, but honestly I'm not as experienced with some of these problems as some of you guys. I still believe the OP undersized the machine for the job at hand, but some of the suggestions you gave may very well help his problem. At least I hope so. I don't know how long the previous MTD rider he had lasted, but my guess would be that mowing 4 acres weekly he shouldn't expect more than about 8-10 years of service out of that ZT 50 before he starts having major problems with the engine, transaxle or other components that were not designed for that kind of usage:0(

Retiredcarguy said:

Seems like one or more blade may be too short. Yes, crazy as it seems. Deck design takes blade match and complete coverage into consideration. Possibly the "strip" may only be on the left or right side of your deck to give you a clue.

I would stop and fully shut down your machine as you cut and see strips right behind you. While on hands and knees, follow the strips back to your deck to see the exact location source of them.

Good luck on your close up inspection!

Click to expand...

I will give it a try--but I will have to careful none of my farmer neighbors see me crawling up behind the mower. Might be too hard to explain.

Based on the original post it seems the deck does not have the vacuum to lift the grass so that it can be cut quickly. Reading between the lines it appears the wheels are pushing the grass down coupled with the wet conditions creating the problem.

You might try mowing a bit shorter to see if it helps. Am assuming the belts are good and the deck is operating properly. Engine speed at 3600 rpms.

Not familiar with this mower but 4 acres a week shouldn't be a big deal for it.

It does appear that lower cutting level leaves less stripping. This is OK provided we stay as wet as we are right now. Before mowing yesterday I cut side by side comparing my preferred level with a cut one step lower. The deck was scraped and clean. The lower cut did not leave a trail while my usual level did. My old MTD lawn tractor did not leave a strip at the preferred level--just takes twice as long to do the job. Darn thing just keeps chugging along at less than half the cost of the Gravely. Gravely needs to investigate--design flaw!!!

Higher lift blades might help.

This mower is very capable of handling this job.

You are cutting to high. Cut at a lower setting or don't wait do long in between cuts.

High lift blades will help but will leave bigger clippings.

Try setting the deck 1/4 inch lower then the front. This way the front if the deck does not lay the grass down.

Do a test mow a pass in reverse. I bet it cuts better.

sjessen said:

Higher lift blades might help.

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Or maybe a mulch kit.

Carscw said:

This mower is very capable of handling this job.

You are cutting to high. Cut at a lower setting or don't wait do long in between cuts.

High lift blades will help but will leave bigger clippings.

Try setting the deck 1/4 inch lower then the front. This way the front if the deck does not lay the grass down.

Do a test mow a pass in reverse. I bet it cuts better.

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I agree completely....I didn't consider heeling the deck, but that also could help!!

There could also be a couple of other problems. The pulley may be spinning on the spindle under a heavy load (unlikely but possible). The first thing I think of though is debris build up under the deck. If wet grass and dirt builds up around the blades under the deck it changes the air flow preventing the blades from lifting the grass. It doesn't take long for build up to happen. You may try cleaning under the deck every couple of times you mow.

Thanks for all the input--I mowed yesterday and what worked best was overlapping more (keeping one front wheel out of unmowed grass), means a few more rounds but the job looked a whole bunch better. This time of the year when grass is heavy, even when dry, I get a lot of build up under the deck and scrape it out after each job. I have one section, about 1 acre, of what amounts to old pasture that has a lot of bromus, in addition to overseeded blue grass, that was a real bear. Nasty clumps of chewed up grass. Yes probably should have cut it twice, but needed to beat the next round of rain!!! Thanks again for all the advice.

Glad to hear. Sometimes, the most complex problems have the simplest of solutions.

mqs said:

Thanks for all the input--I mowed yesterday and what worked best was overlapping more (keeping one front wheel out of unmowed grass), means a few more rounds but the job looked a whole bunch better. This time of the year when grass is heavy, even when dry, I get a lot of build up under the deck and scrape it out after each job. I have one section, about 1 acre, of what amounts to old pasture that has a lot of bromus, in addition to overseeded blue grass, that was a real bear. Nasty clumps of chewed up grass. Yes probably should have cut it twice, but needed to beat the next round of rain!!! Thanks again for all the advice.

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Yep, wet grass or cutting more than 1/3 the total height(my owner manual actually states never cut more than 2" at a time, in addition to the 1/3 rule) are contributors to leaving uncut grass. But as pointed out to me in another thread....buildup underneath the deck can also result in leaving uncut strips where the buildup is(the grass/dirt clumps prevent proper "lift" of the grass blades when cutting the grass under that area of the deck).

P.S.

I was just on the Gravely Support webpage asking a question about their deck heeling instructions in my Owner manual and I ran across this QUick Answer Link info:

"Why does my mower leave an uncut strip of grass?

Traveling too fast for conditions or cutting too much off at once, are common reasons why there is uncut strips of grass left behind. Therefore try slowing down and/or take less off the top of the grass.

The following are things to check, if you are confident that is not the case:

1. Make sure that the correct blades are installed on your mower and that they are installed in the right direction. It's possible to install blades upside down.

2. Check that mower blades are sharp and not overly worn.

3. Ensure that deck pitch (front-to-back) and deck level (left-to-right) is adjusted correctly, per the directions in your Owner's Manual.

4. Check that all belts are in good condition and adjusted properly.

5. Check that the deck is clean and that there is no buildup of grass clippings."

Sounds like that covers most of the advice that's been given here!!