Hot Topics: Transmission Belt Slipping Pulley

transmission belt with pulleys

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Original Thread: Transmission belt keeps coming off pulleys

ukrbyk - Member

I have a Hustler Raptor SD 60 inch deck. A ZTR with hydro something transmissions, one per each drive wheel.

Saturday, it did pop and stopped moving. I called the dealer—it's under warranty for two more years—and they pointed towards maybe belt issue.

Looked under and indeed, the transmission ribbed belt was off.

Decided it stretched, who knows, went to the dealer and put a new one on.

Ran fine.

Started mowing yesterday—the same happened after about 20 minutes. Pop, the belt comes off.

Put it back on again, ran for 30 min or so - popped off again.

It's a very simple system - two pulleys above each transmission, main drive belt pulley, and roller tensioner. The belt wraps around both transmission pulleys, half wraps around the main drive belt pulley and back, flat belt side wraps around the pulley. Spring connects to tensioner bracket.

The tensioner is installed on a long crescent-shaped steel arm.

Being a mower, it is rather not easy to see how it's all aligned but, by hand, after all, assembled, the belt sort of feels loose.

The way it's made, spring pulls idler towards the main pulley. If "hand torqued" to better belt tension, it starts rubbing blet on the belt. Yes, I tried.

On the schematic attached, if you check where it says "transaxle drive belt", it flops loose. I've seen belts that flop loose but tighten "in action" but this one apparently does not.

Mower has only 78 hrs, spring does not look stretched. Besides, again, as I was thinking about shortening that spring for better tension, the way it's installed, it forces roller with a belt on it, into the main pulley.

Any ideas? Dealer is 20 miles away and I have no trailer to tow it. Plus, I can do this only Saturdays, due to work restrictions. So I have to rent a trailer twice for what seems to be a piddly problem.

I don't know if pulleys and idlers are on the same plane. Just can't tell, but I can remove the rear engine guard to check on this.

engine diagram

joecaption - Member

With the belt off make sure the idlers arm can move easily, mine from the factory was too tight, I backed off the bolt just a tiny amount and it worked.

Also check inside the pulleys, I once had a gumball from a gum tree get jammed in the pulley and it kept throwing off the belt.

In your manual, there should be a picture showing how long that spring should be, mine from the factory was too tight and I kept breaking the belt.

ukrbyk - Thread Starter

I was reading through the manual.

Says transaxle oil MUST be changed at first 70 hrs. I have 78.

You think it could cause some extra tension on the belt and its slippage off pulleys?

I'll change oil, no big deal.

beelzebob - Member

Not sure about transaxle as you have 2 hydraulic transmissions on your mower. Changing the hydraulic transmission fluid won't hurt the belt problem but probably won't fix it either. I would do the following.

Verify the engine and transmissions securing bolts are tight. Remove idler tension spring and verify idler arm pivots without interference. Verify the engine and 2 transmission pulleys are at the same level. Verify the length of the belt. Good luck.

cheese - Forum Topic Moderator

I agree with the advice of both members above.

ukrbyk - Thread Starter

Idler arm moves fine.

I see no loose bolts.

as is there is no way to tell if all pulleys are level but - it's all pretty much one assey so I doubt pulleys are not.

idler appears to be in line with main and trannie pulleys, I had both rear guards removed so it's a bit better view.

did oil change. Don't ask.

ukrbyk - Thread Starter

Got to take it back. Transaxles are not connected. So sure, if the frame is bent, they might be out of alignment. Nothing I can do about it.

beelzebob - Member

It's not possible to see the difference between a nut tightened to 1foot pound or 100 foot pounds. Put a wrench on the nuts of the engine and transmissions mounting bolts/studs and make sure they are tight.

ukrbyk - Thread Starter

OK, just talked to a tech at the dealer. He was almost sure that there is at least one of the transmission bolts missing, which causes it to go out of alignment to the opposite transmission and tensioner.

Figure I'll have to get it up on my lift as you can't see squat from the top. The man was positive that's what it is.

ukrbyk - Thread Starter

The Rear left hydro mount bolt is gone completely. The rear right one is loose and half threads are rubbed off it. The front right hydro mount bolt snapped in a half and was just sitting there not doing anything and the front left was loose.

porknz - Member

Having the same issue...

I know this is an old thread. Wondering if anyone can help. I have a 52" Hustler Raptor, so maybe not even the same parts, but two mows ago, my drive belt came off the first time. Suddenly no go. Deck fine. Engine fine, but no movement. Now every time I mow, the belt comes off. I'm in here looking for the correct way to put it back on again right now. If I have the bolts referenced, where am I looking for them on the mower?


ukrbyk - Thread Starter

See posts 9 and 10. That's the answer to your question.

Also, as I had 52 inch Hustler, I'd suggest getting rid of it asap. It will be falling apart on you. Like mine did on me. Literally, falling apart. Just wait till deck bolts will break or get lost during mow, with deck plowing into the ground on a move. Bends blades and plows through the grass.

If you go LAawn Mower Forum, you'll see plenty of gripe about them 52-inch Hustlers.

porknz - Member

I'll see if I can find where they are in the manual somewhere and see what I can do about tightening them.

I hear you on a new mower, it's just not in the cards for me. I have stuff rattle off all of the time. I need to try to order the parts that hold the mower deck up on the left side as that's held together with what I could find in the garage after having the deck drop etc. as you mentioned. Not in the cards for a few years at least though.

ukrbyk - Thread Starter

I had so much trouble with mine, it didn't make it in my hands for even a year. Blades pulleys WILL grind off the shafts and you will have to replace entire hubs, as they will ruin shallow gears at the top too. Along with a new pulley. That's a very cheaply made mower.

Bolts, you just match and buy them at chain stores, like Home Depot or Ace. Ace has much more options. You also want grade 10 bolts, nothing less. They have grade 8, I believe, on the mower, and threads strip. Go through it and add locking washers to every deck attachment you can find. There are horizontal bolts on deck height adjustment system, those break first.

You need to go through every bolt you can find about every 2 months, to re-tighten them. I double nutted and locking washered everything I could. Then transmission started coming down in the back.

Transmission bolts are roughly where I marked them on the schematic, looking from the bottom up. Takes the slightest tilt in transmission for the belt to come off.

Also, watch the oil level in hydros and make sure you do replace it on regular basis. That's another pain, as they made it very hard to get to.

engine diagram

porknz - Member

This if fantastic help. Does the raptor 52" have hydros? I keep seeing that term and I don't know what it is. I change the engine oil, but I haven't changed any 'hydro' oil. Thanks for the amazing help here.

ukrbyk - Thread Starter

You have hydrostatic transmission, commonly referred to as hydro. This is what allows you to use dem handles and turn or change direction on a dime.

I'd strongly suggest obtaining a User Guide, they are free on the Hustler site, and do your maintenance. I know, on 60-inch Raptor SD, hydros have to be serviced at 80 hrs. I do not remember, what it was on 52 inches, something less.

porknz - Member

Thanks. I'll look that up too and see what my hours are at.

porknz - Member

Didn't find anything in the manual about hydros in the maintenance, so I'm thinking I have a different model possibly, but I'll double check.

Did find the...

fuel filter

air filter

oil filter


Bought all of these in a package deal recently so I'll get on them right away.

Bonus, found the missing parts from the deck, so maybe I can get those ordered and the deck will be a little more even? That and new blades might make the cut more tolerable.

porknz - Member

And looking where you marked, I think I had one of them drop before, so maybe one is getting ready to again and that's pulling the belt off, as you said.

Thanks again.

porknz - Member

Well what do you know...bolt and washer missing under one of the transaxle pulleys and there's about a half-inch gap where it has dropped. That ought to help. Now to take the other one off so that I can see what I need to go buy to replace it I guess.

ukrbyk - Thread Starter

That made me feel good.

Also, mind what I say - dedicate half-day and go through EVERY bolt you can find, and secure them. Especially the deck bolts and nuts, hidden behind any metal pieces. Hustler used real cheap hardware on those, that's why you got what you paid for.

No worries, my then 60 inches $5K Sd was not much better.

Those are cheaply made mowers.

PamSanders - Member

Nice information and detail.

Jeff Hamm - Member

Hydro fan knocks drive belt off

I keep reading these forums and people are finding that bolts are missing, or somethings bent... but what if the fan just knocks off the belt and everything else is fine? I took some photos, this looks like a manufacturing problem. Any suggestions?

cheese - Forum Topic Moderator

The fan is not supposed to be able to contact the belt. If the fan is touching the belt then either the fan is bent or the transmission is tilting because of a loose/missing mounting bolt and allowing it to tilt and throw the belt.

buck53pnt - Member

have had the same issue with my Raptor, I finally fixed the problem, like many others I noticed bolt broken and sheet metal mounts cracked etc. I replaced the mounts with heavier mounts and better bolts, the cracked tabs I re-welded, and added gussets. still had issues popping the belts.

Finally looked at the fan tips, the left hydrostat had a few tips that had curled up and would pop the drive belt off, so I trimmed all of the fan tips back probably 1/4-1/2" and that has solved the issue completely. hope this helps someone else.