ZT52HD DECK VIBRATION FIX

Kit was installed and I’ll have an update tomorrow after I get it delivered and test it out!

Awesome. Please let us know.

Do you have a part number for this kit?

cpurvis said:

Do you have a part number for this kit?

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According to my dealer it is still in the process of testing so there’s no part number.

So first impressions are good and bad. I have the same parts replaced as the person that posted the youtube video with the kit installed. The good news is that there is less belt slop/whip and it seems to dampen vibration in general with the pto engaged. The bad news is that it doesn't seem to make much difference in that rattle noise that whirs in and out. That still seems to be more related to that front left deck arm. I think its still worth having installed to calm down the belt whip but imo Gravely needs to create a fix for that deck arm. I think if they could keep the arm from making contact with the bracket it sits in, that would help a lot. When I have time im going to try and create 2 shims to slide in there and zip tie them around the arm so they stay put and that will keep the arm from sitting against either bracket which seems to be a large part of the noise.

There is something about that deck design which causes it to have a resonant frequency close to its operating rpm. When I first saw it, I thought it was unusual in that you could take off a belt and still have the center and left spindles working. Seems like one too many belts to me and the deck drive belt flops around far too much.

I tried to change the resonant frequency by adding magnetic weights to the idler pulley brackets but either I didn't have enough weights or was putting them in the wrong places.

I've never seen a mower deck with a damper on the idler pulleys but, short of redesigning the deck, (which I think it needs) that may be a good enough band-aid fix.

edit: I don't own one; a friend does. That's how I got mixed up in this.

cpurvis, I just joined the forum today, and was reading about this vibration problem. I have a ZT HD 60, and this thread caught my attention. After reading your post, I am pretty sure that you are on the right track. I worked in the vibration field for 21 years, and learned a few rules of thumb about causes of vibration.. As you pointed out, the deck has its own unique resonant frequency. For whatever reason, the 52" deck has that resonance, and it is inside the machine operating range. That is to say. as the mower ramps up from idle to full speed, at some machine speed the resonance is excited and the vibration starts.

The decks on other machines have a unique resonant frequency as well. Those frequencies are well above the operating range of the mower. Therefore, the deck does not vibrate. I make an assumption here that the operating speed for the 52" mowers is roughly 3600 RPM. This would mean that the deck vibrates because the resonance is right on top of the 3600 RPM (max speed).

A detail that must be respected about vibration is that it can get complex. If you take the 52" deck (alone) and set it on a work bench, the resonance will be unique for that part. As you add components (spindles, pulleys, etc), the resonance moves around because the resonance of each component adds to or subtracts from the original resonance of that deck system. What I am saying here is that the composition of all of the parts attached to the deck affects the resonance. I know I am using the word resonance a lot, but please bear with me.

cpurvis, your idea is on the correct course, but I see two possible "gotchas". 1) As you pointed out, the magnets attached to your weights may not be strong enough. When dampening a system the dampening weight needs to be rigidly attached to have the maximum impact, and 2) You may not have enough weight to resolve the vibration.

I know that I have babbled long enough, so let me cut to the chase. Please remember that I have no data from these components so I am just sharing information in a limited fashion based on my life experiences. If I was trying to solve this, the first thing that I would think about is how to stiffen the deck system.

How do you do that? There are a couple of ways. The first is to make the metal in the deck thicker. This would add rigidity to the structure, and, therefore, suppress the vibration. This is not likely going to be what Gravely does because metal costs money, and they are in the business to keep as much of that as they can.

Another way to raise the resonant frequency is to add rigidity by using a method that can be field implemented. This is the solution I would try to follow first because it can be done in a practical fashion. I would take a length of strap metal like you can buy at building supply stores. For a 52" deck I would suggest maybe 30 to 40 inches in length. I do not know how the deck is constructed on top so you may have to alter the length. Longer is better. You can also add rigidity by using thicker metal. For example, instead of a 1/4" strap maybe try a 1/2" strap. Along the length of the strap drill a hole for a 1/4" bolt every six to eight inches. Drill the holes through the deck and the strap. In each hole place a 1'4" bolt. This will bond the strap to the deck very tightly. Place the bolt heads on the bottom side of the deck to minimize intrusion into the blade area. The strap needs to be on a top flat surface of the deck. Preferably toward the center.

You will have to decide if you want the holes in your deck. The strap will be on top. If you wish to remove it you can do so, and leave the bolts in place.

This is a theoretical solution. The philosophy is the same for any lawn mower. It is just physics. You may have to get creative in your own way. If anyone implements this, please let us know the results. If it does not work, I may have to change my user name.

Thanks, Bullgoose! I'm glad you joined the forum.

I wish Gravely had you working on the problem!

@Bullgoose - there are several existing holes/bolts that go through the top of the deck (I think they hold the baffles....I'd have to look again). Would I be wasting my time with 3 10" sections of strapping (in order to use existing holes), instead of 1 30" or 40" section?

my87, as I stated in my post, there is no right or wrong way. What you suggest is worth a try. I know I would prefer to drill my deck as little as possible. If the bolts you wish to use retains the baffles underneath, then by using those existing holes with longer bolts you would save some drilling. Be sure the strap.is flat against the deck. That is to say, leave no gaps between the two parts.

If you use two straps, make them as long as will fit. Reuse the existing holes that you refer to as much as practical. If you go with 10"-12" lengths, place a bolt on each end, and one in the middle. You do not have to use a ruler to space the holes. Just place the holes toward each end, and close to the middle. The most important objective is to have the two parts as tight as possible. Make the straps as thick as you can. I would guess 3/8" thick would do the trick. I believe Home Depot or Lowe's would have what you need. Let us know of your success..