A few things. Did you manipulate the belt over the peg (between the 2 frame pans) ahead of the idlers? Does the variable speed pulley roll and change speeds freely? When you do a front belt, you also need to replace the rear- unless you have just done it. If you need further help, post the proper model # from below the seat. Should be the long number near the serial.

Thanks for the reply.

Re-"Did you manipulate the belt over the peg (between the 2 frame pans) ahead of the idlers?"

I did a helluva lot of "manipulating" of the belt. This is the most difficult thing I've ever done on a piece of outdoor power equipment. I hope my neighbors didn't hear all the verbal firepower fired at this problem.

The mower won't move at all. It's presently shut off in front of my shop, so I can't answer your question about changing speeds.

I'll check on the proper model number; what I entered was what I had written in the operators manual.

Well, you would know if you snuck the belt over the peg or not. There is a hole in the lower pan ~ 3/4" diameter or so- with a peg above it. It is located ahead of the double idler assy. You need to lay the belt on its side to sneak it through. Most of these are like that.

Thanks, Tomplum. Yes, I did that. It took me at least an hour to get the belt slid under the keeper pin. Now the pin is "inside" the belt.

Here's what is underneath the seat regarding model number:

188392
13AP609G063

Ser. # 1D243H20064

I found the problem with the belt. It was outside one of the belt retainers on the engine pulley. That's fixed and the mower will drive--however it is still running in a jerking manner in forward, but runs smoothly in reverse.

Is this a transmission issue, or something else?

Later in the day, I decided to try to mow the lawn with the mower. It was doing the jerking and hesitating at first, but it did run for about 15 minutes before the next set of problems arose.

The machine jumps and jerks forward, and in just a few minutes afterward, the machine is very hesitant to move at all. But it will run smoothly and flawlessly in reverse.

SO, I managed to get the thing turned around and drove in reverse back to the tool shed. Trying to go forward resulted in a myriad of noises and sensations.

First, the mower made a different sound, higher in pitch than it usually emits. There were the sounds of something "flapping" against something hard. It was coming from directly beneath the seat I was sitting on, and that's where the rear end of this machine is, where I was sitting.

I could feel the vibration from whatever it was that was causing it, because it was in time with the sounds.

I think something bad has happened to my mower, and I'd appreciate any comments from those of you who have been there before. This machine has over 1550 hours on it (according to the clock) and I'm wondering whether or not to repair or replace it.

I've already contacted the repair shop.

Looking further into this issue, it seems to be a problem with the differential. The MTD website lists a part called "differential" and the price is $200.32. Could someone tell me if that's the price of the entire assembly or are more parts involved in replacing this assembly?

I hate to be the one to break the news......but,
the part you have been looking at is the "true differential", which is but one sub-assembly of the TRANSAXLE assembly.
People often refer to the transaxle as a transmission, or a differential (though it is technically inaccurate).
Most small tractors of this genre use a single unit that has all the functions of both components and is called a transaxle.
Now for the news of prices:
The part you can buy for $200.32 is the core differential.
To get the complete transaxle assembly you need part number 918-0424 @ $489.74 each (it's on a different page).

Ouch. That's what I was afraid of. In your experience is it usually the case that whenever problems like this start coming up the machine is nearing the end of its useful life?

I've started looking at some other mowers. I have a feeling that this mower is past the point of diminishing returns.

Thanks for the reply mownie.

So, does it make sense to you that the machine has 1550 hours actually on it - time it takes to mow X a good guess at how many times it was used? Are you getting a jerk like sensation through the drive pedal/ clutch? A jerking sensation can be from a burnt belt - which could have easily happened as the belt was installed over a guide. Plus, remember what i said about needing the rear belt when the front was replaced. That will mainly affect the ground speed- giving a lower or non working low speed however. The rear idler is always suspect on these so you want to roll the pulley w/ o a belt on it. The center two not so much -but it happens. I've personally not seen a differential in one of these cause a jerking- usually a clatter or a complete failure. It is possible however.

At 1550 hours, it is definitely into the range where some things are going to show cumulative wear.
But, if you feel you could handle a DIY transaxle replacement, you might still come out OK (compared to farming it out to a shop).
When you are dealing with a pro shop, $500 will not get near as much bang as if you are doing the work yourself.
You almost have to factor in whether you think doing the work yourself is a source of satisfaction, or if it is a dreaded tribulation.
I will offer that the condition you are seeing now might be due to wear out of the sliding clutch (aka shift collar) in the input section of the transaxle.
If that were the case, and you could replace the defective/worn parts yourself, your cost for parts could be as little as about $65 to $120 dollars (depending on whether you would also need the shaft that the collar and 2 bevel gears ride on.
If you were to have just those parts/service done at a pro shop, that alone might approach the cost of an entire transaxle assembly.

Re tomplum: I went out to the tool shed (with my glasses this time) and cleaned the window off the clock. It actually reads 155.8 hours. I didn't see the decimal point. That can't be right, though, since in the 8 years I've owned the mower I've used it for about 40 weeks a year, and it takes at least 2 hours per week to mow the lawn. (I was trying to maintain a fescue/bermuda winter/summer lawn. I've given up on the fescue and the bermuda will require more frequent mowing.) So the actual number of hours on the machine is at least 640. Probably a little more, but considerably less than 1550.

When the mower wouldn't move after I changed the belt I shut it off immediately. It wasn't on for more than 15 seconds. I may have ruined the belt, but I don't understand how it can run smoothly in reverse if that's the case, but then I don't understand a lot of things.

The upper belt looked like new, while the lower belt was cracked with sections missing. That's why I thought changing the belt would solve the problem. I bought a new upper drive belt and still have it, and if need be I'll put it on. The idler on the upper belt section turned smoothly and the spring is stout.

Re mownie: I don't feel competent enough to tear into a transaxle. I was dreading changing the upper drive belt, since doing some searching about the job it was obvious that is was not a piece of cake. While there is a good deal of satisfaction from doing things myself, there is a limit to what I'll attempt.

I've made an appointment with a local repair shop to look at the mower. I'll post a followup when I know more.

Thank you both for the responses.

UPDATE

The mower came back from the repair shop yesterday, and the mechanic confirmed my worst fears--the transaxle is beginning to go out. Exactly what part, I don't know because he didn't open the transaxle. But the symptoms all point to an imminent failure of this very expensive part.

He was able to do some kind of adjustment to the drive system so that the mower will run in forward as well as in reverse. I tried mowing with it and was able to get around the entire lawn (~30,000 sq. ft) with no problem. But it is very loud and the unusual noises are still there. It doesn't make the "flapping" sound anymore, but it is obvious that it isn't going to last much longer.

After mowing the lawn with a 22" push mower 4 times in temperatures in the 90's and a heat index over 100, I went to the local Home Depot and bought a new Ariens 46" mower with a 22 hp engine. I hope I made the right choice. As nearly as I can tell, it's supposed to be a good value.

I 'googled' a photo of an LTX 1842, and it doesn't look a whole
lot different than my Huskee 25HP/50" machine. Mine is on
its 8th season of cutting some 130,000 sq. ft., and the hour
meter reads 420. Aside from the spring on the VST belt
breaking every two years or so, I've yet to have an issue
with the transaxle per se, but I did recently experience the
bearing on the stacked VST double pulley siezing up. Had to
order the whole assembly, not just the bearing, and what shows
up off the big brown truck is a bracket requiring me to drill
new holes in the frame rail to support it. Screw that; I
just moved the new pieces to the old bracket and remounted
everything. Drilling holes would have required the removal
of the left rear wheel, which has never been pulled before,
and if my experience trying to get the engine pulley off
the driveshaft in order to change the drive belt is any
indication, it wasn't going to happen. As far as changing
the drive belt goes, I have to unbolt the engine and lift
it off the frame in order to wrap the replacement around
the engine pulley. I've done that twice now; it's pretty
easy once you know what you're doing. I think I did it in
less than 30 minutes this time !! Only other major money
spent has been 3 new deck spindles. I once estimated that
with the width of my deck, allowing for a few inches of
overlap, I 'travel' ~4 miles each time I cut my lawn. All
in all, not bad for the roughly $2400 I've spent on it.
Next machine will be a zero-turn, for sure !! Good luck with
your new ride !!