Hydrostatic Transaxle is "Jerky", stop and go

Hello everyone. I made another thread about this issue in a different subforum but I fear I was not clear enough in my description of the problem. The mower is an Ariens 42" hydro, model 936038.

Please view the short clip here to understand the problem:

• When the motion lever is in the middle position, the tractor will not drive consistently. Instead, it lurches forward, then stops, then lurches forward, then stops,....
• When the motion lever is in the fully forward position, the tractor lurches forward HARD but then drives smoothly.
• If the motion lever has been forward, pulling it back into the "neutral" position causes the tractor to go into reverse
• Reverse works well after a lurch

As the primary user of this mower is 91 years old, we need to eliminate the lurching and also we need the motion lever's middle position to work properly as the fully forward position can be too fast. A fine gentleman in the other thread offered:

3) the tensioning spring on the tranny pulley is probably weak so when the harsh jerk happens the belt goes loose a bit so it then slips a bit.
4) the pivot point on the tensioning arm floggs out oval over time cause they never get lubed by home owners who do their own maintenance.

The tranny might be a little low in oil or need to have it replaced.
Down side is you usually have to pull it out in order to check it.

Click to expand...

I do not know how to locate the "tensioning arm" or how to fix it. Also, according to my owner's manual, the transmission fluid should be sufficient for the lifetime of the device. I am wary of tearing the transmission apart as I think I might not be able to put it back together. Could anyone offer advice?

Normally I would make the effort to copy the images to my computer so they can be directly uploaded into the forum.
But as you decided not to do that making things difficult for me, why should I bother making things easier for you.
In the following image https://www.partstree.com/models/936038-960460002-00-ariens-42-lawn-tractor-19hp-kohler-hydro/drive-2/
You will see some pulleys , 50 & 52. there are the tensioning pulleys that may need replacing.
The plate 189 that they bolt into has a bush 186 that wears but no one ever bothers to check it.
It then allows bolt 185 to flog out the hole in the plate 189.

After that the link rod 279 flogs out the holes at either end of it cause no one ever bothers to lube them or the entire shifting mechanism , shaft 175 and all the bits that attach to it.

Then there is the brake rod . 79 .
Some where on it will be an adjusting nut to get a balance between braking and clutching as the one pedal does both.
For older people I back the brake off a bit so the mower is just rolling by the time the clutch takes up

bertsmobile1 said:

Normally I would make the effort to copy the images to my computer so they can be directly uploaded into the forum.
But as you decided not to do that making things difficult for me, why should I bother making things easier for you.
In the following image https://www.partstree.com/models/936038-960460002-00-ariens-42-lawn-tractor-19hp-kohler-hydro/drive-2/
You will see some pulleys , 50 & 52. there are the tensioning pulleys that may need replacing.
The plate 189 that they bolt into has a bush 186 that wears but no one ever bothers to check it.
It then allows bolt 185 to flog out the hole in the plate 189.

After that the link rod 279 flogs out the holes at either end of it cause no one ever bothers to lube them or the entire shifting mechanism , shaft 175 and all the bits that attach to it.

Then there is the brake rod . 79 .
Some where on it will be an adjusting nut to get a balance between braking and clutching as the one pedal does both.
For older people I back the brake off a bit so the mower is just rolling by the time the clutch takes up

Click to expand...

Thank you Mr. Bertsmobile for your assistance. I have finally found time to work on this.

If you have time, I'd like to ask you for some clarification on some points.

I plan to begin with the pulleys. Am I correct that, according to your description, I only need to address pulleys A and B?



Assuming yes: Should I replace both pulleys and both bolts and the bush # 186 you referenced? Is there anything else related to these pulleys that I should do?

It is prudent to test the parts , work out what is faulty and replace these parts.
Having said that Jerkiness can be caused by pulleys A & B.
Pulley C does little as it is on the slack side of the belt and is just there to stop the belt flapping around when the brake is applied.
I would be looking closely at the bush, the plate and everything that moves the plate.
Also have a good look at the brake adjustment
A brake that stays on too long after the slack in the belt is taken up will cause the mower to lurch violently

Two things I would also check. First is the condition of the belt, worn, cracked, or pieces missing will cause this problem. Second, does the tensioner arm which moves pulley B and possibly A must move very freely and smoothly.

bertsmobile1 said:

It is prudent to test the parts , work out what is faulty and replace these parts.
Having said that Jerkiness can be caused by pulleys A & B.
Pulley C does little as it is on the slack side of the belt and is just there to stop the belt flapping around when the brake is applied.
I would be looking closely at the bush, the plate and everything that moves the plate.
Also have a good look at the brake adjustment
A brake that stays on too long after the slack in the belt is taken up will cause the mower to lurch violently

Click to expand...

Original (inferior) view:




Pulley B was extremely difficult to remove, partly because the nut was extremely stiff and partly because the plates 189 and 190 move as torque is applied to the nut. Pushing down the brake pedal helped a little bit, but now the brake is stuck/locked down! How can we re-loosen the brake?


Here is the view after the pulley B has been removed:



Here is the superior side of pulley B:



Here is the inferior face of pulley B:




Here are two shots of plate 190.




Here is the bolt 49:




We could not remove pulley A and, by extension, plate 189. The nut loosened, but I guess the bolt is turning with the nut. What can we do to remove it?


Here is a shot of the link rod #279, still attached and unmodified:




In case it's interesting, here is the other side of the transmission:




Finally, here are two shots of the brake shaft #64. Please note that I took these photos before the brake got stuck. Is this the shaft where we would find the "adjusting nut" you referenced? You wrote that it was on ".79" but I couldn't find that number anywhere in the parts diagram.

Rivets said:

Two things I would also check. First is the condition of the belt, worn, cracked, or pieces missing will cause this problem. Second, does the tensioner arm which moves pulley B and possibly A must move very freely and smoothly.

Click to expand...

Thanks for your comment. The owner says the drive belt was changed within the past two years. I believe him as the belt looks clean and new.

As for the tensioner arm, could you specify which item you mean on the following parts diagram?

https://www.partstree.com/models/936038-960460002-00-ariens-42-lawn-tractor-19hp-kohler-hydro/drive-2/

Firstly that belt is toast judging by the crack in one of the photos.
Secondly it is either the wrong belt or is severely worn.
The proper belt , which is expensive is a wrapped kevlar fibre belt.
That belt appears to be a plain unwrapped el cheapo ( cause I know better than all those thieving rat bags who force me to buy those overpriced funny colour belts when a regular one at 1/4 the price will work fine ) belt.
If it is a plain unwrapped belt then you problem , or a large part of it, lies there.
Unwrapped belts are designed NOT TO SLIP .
They quickly get hot & sticky just like your car tyres.
Wrapped belts are designed to slip for the purpose of clutching.
Your belt should be # 21546076 which is an A 90.375" belt.
Plain belts are made in whole inch sizes only so pretty sure you will find it is a plain A90 belt.
If Mr Half Witt had bought a wrapped Kevlar A 90 he may have gotten away with it
But using a plain belt that is also 3/8" too short is asking for trouble.

bertsmobile1 said:

Firstly that belt is toast judging by the crack in one of the photos.
Secondly it is either the wrong belt or is severely worn.
The proper belt , which is expensive is a wrapped kevlar fibre belt.
That belt appears to be a plain unwrapped el cheapo ( cause I know better than all those thieving rat bags who force me to buy those overpriced funny colour belts when a regular one at 1/4 the price will work fine ) belt.
If it is a plain unwrapped belt then you problem , or a large part of it, lies there.
Unwrapped belts are designed NOT TO SLIP .
They quickly get hot & sticky just like your car tyres.
Wrapped belts are designed to slip for the purpose of clutching.
Your belt should be # 21546076 which is an A 90.375" belt.
Plain belts are made in whole inch sizes only so pretty sure you will find it is a plain A90 belt.
If Mr Half Witt had bought a wrapped Kevlar A 90 he may have gotten away with it
But using a plain belt that is also 3/8" too short is asking for trouble.

Click to expand...

Hello Mr. Bertsmobile1. Thank you for your advice. I have ordered the new kevlar belt.

Part number 189, where the two idler pulleys are mounted.