Poor take off on Craftsman lawn tractor YS4500 (917.27660)

WillBeamesOctober 20, 2013

I have a craftsman YS4500 (917.27660) tractor and have been having some drive problems recently.
Last year the main drive belt started slipping so I replaced it with a new one. It fixed the problem for a while but then I noticed the tractor laboring up hills with (what I think is) the transmission making a kind of whirring churning sound - whir whir whir up hills. I have also noticed that I have to kind of stamp on the brake pedal to release it and engage the belt. Also, the brakes to stop the tractor seem to be failing.
I've had the tractor 7 years, I don't think I've beaten on it particularly. I've changed the engine oil and filter every 50 hours, air filter and plugs but have never touched anything else...including transmission fluid...

Anyway, I did some digging around and was able to find a YouTube video for changing transmission oil, at least on a mower that had a drain screw. My transmission has no drain screw so I drained it from the fill hole and refilled it with 2 quarts of 20W50 as advised in another thread which covered my transmission. (351-0510)
Two quarts of grey oil came out of it as well.
However, my problem persists.

I have also noticed that if I am having problems setting off and I pull my toe up the back of the brake pedal I set off at full speed. I had a look underneath and the brake return spring is rusty but other than that it seems ok.
When I release the brake normally the pedal goes about 2/3 of the way back to the top (unless I use my toe). The push rod that runs to the brake system is also not all the way back but when I push it all the way back the spring in the brake system is slack, almost like it's the wrong one (to long) or hooked in the wrong place, maybe because the metal plate is resting against the bolt head that is visible in the center of the picture. I bought the tractor with 8 hours on it so I'm pretty much the only owner and it's never been shop serviced while I've owned it. I've attached a picture of the brake area in the rear showing the spring that looks like it's wrong.

With the pedal not returning all the way I'm guessing that the pulley isn't exerting full tension on the drive belt....should I just buy a new brake return spring (the one for the pulley that is under the tractor and connects the pulley bellcrank to the chassis ?) As I said before, it's rusty but looks ok.

What is the loud whirring sound I hear ? (pulleys or tranny?)

Thanks for any suggestions anyone can give.

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Can you confirm the model number of the transaxle by finding the Hydro Gear I.D. decal on the tranny.
I have had no luck finding a Hydro Gear manual for 351-0510.
I have a manual for 310-0510 and I do believe the 351is similar to it but I'm not certain the 310 manual can sub for the 351.
From your photo and your text, I'm not sure which spring you are calling "wrong". I have edited your photo to include numbers for positive ID of the spring. Pick one of them.
Also, did you perform the purge procedure after you changed the oil?

    Bookmark   October 20, 2013 at 11:02PM
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Thanks, I have attached a picture of the sticker that is stuck to the tranny.
The spring I was talking about is #2. When I have the brake pedal all the way back (in the maximum release position) the left end of the spring is loose in the hole that the hook goes through. I'm assuming this is because the metal plate is is hooked into is pushed all the way up against the bolt (dead center of picture) so can't go any further.

Purge procedure....no. I didn't know there was one.

I've since read that in some trannys there is a splined shaft that can get ground away. I'm reasonably mechincally minded but my fear was that if I undo the bolts holding the casing together, when I separate the two pieces things will just fall out and I won't know how to put them back again. Will things fall out if I do this or is everything attached inside ?
Also, on the parts diagram I have on Sears website there is no part number covering the brake system in my picture - any ideas what those part numbers are ?


    Bookmark   October 21, 2013 at 9:06AM
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OK, let's do some basic checks before making any premature decisions to bust the case open. Because you stated that you are unaware of the need to purge air from the hydro, it is possible that your entire problem might be caused by the "FREE WHEELING LEVER" having somehow gotten partially activated.
This lever is what must be enabled when you need to move the tractor by "hand" when the engine is not running.
So, if you also are unaware of this feature, learn about it before doing anything else.
Do you have the Craftsman owner's manual for this tractor?
If so, there are 2 topics you need to read immediately.
The first topic, "TO TRANSPORT", explains the operation of the free wheeling lever (which operates the bypass valve, bypass valve lever is what spring #3 connects to in your pic).
The second topic to learn about is the purging procedure (a few pages after the free wheeling text).

    Bookmark   October 21, 2013 at 12:01PM
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I just got confirmation that the manual for "310-0510" covers all trans versions listed as -0510.
It is a free download if you go to the Hydro Gear website.
Beware there are 2 "options" regarding how the transaxle controls are configured (by the end user, aka Craftsman).
The tractor you have is configured with the "Friction Pack" option instead of the otherwise popular "Return To Neutral" option.
Keep that in mind when looking at the manual.
Behind the lever held on with the castellated nut is the brake caliper assembly. That lever has 2 "ramp like" cams which push in on 2 "Brake actuating pins" (items #62 in IPL).
Often in service, these pins will become gummed up or rusted in place and can cause the brake pucks to drag, sometimes dragging badly enough to keep the tractor from moving at all.
Find those pins and spray them with your favorite brand of rust bust product (aka Liquid Wrench, PB Blaster, etc.) to ensure that no dragging is happening.

    Bookmark   October 21, 2013 at 12:27PM
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Thanks. I tried earlier to reply but something went wrong and it didn't post so if you see two similar posts you'll know why.

I know what the freewheel lever is if you mean the lever I pull out that enables me to push the tractor around by hand. I will check to make sure it is all the way back in. There is a good amount of resistance when I try to set it to freewheel and it snaps back in place when I unhook it so I assume it's working properly.

As for the bypass valve being open in the purge procedure...does that mean the freewheel lever is in the "freewheel" position when I try to purge the air ?
Wheels off the ground, run in forward, then in reverse, 6 times each, then again with the valve closed ?
How is the air purged, through the expansion tank ?

    Bookmark   October 21, 2013 at 2:03PM
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Will - let me re-emphasize what Mownie mentioned earlier in this thread - you need to get your hands on an owner's manual for that machine; read and follow the maintenance advisories.
It will have detailed hydro tranny purging instructions, etc.....

    Bookmark   October 21, 2013 at 4:04PM
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Yes, the air will vent out through an atmospheric vent located in the expansion tank.
It behooves you to obtain the manuals from Sears and Hydro Gear if you have not done so, but yes, it is the free wheeling lever that operates the bypass valve when you are purging the tranny.

    Bookmark   October 22, 2013 at 12:48AM
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I have the owners manual and followed the instructions to purge the tranny. However, the tractor still makes a lot of noise when in gear and still doesn't pull very well up hills. Maybe a little better than before.
What could be causing the noise now, still air in the tranny perhaps ? Something else like a worn gear ?

    Bookmark   October 30, 2013 at 10:25AM
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Does the free wheeling (bypass) valve operate smoothly in & out when you perform the purge, or if you are doing it to roll the tractor by hand?
If the bypass valve does not move freely, and "click" into its proper detent positions.......it could be still bypassing a small volume of oil.
As to "worn gears" being the source of noise AND ALSO being related to poor performance: Highly unlikely. The gears in this unit are the few that are required for just ONE reduction ratio between the drive motor and the differential section of the unit, and the differential gears themselves.
The final reduction gearing would only be noisy during periods where the tractor ground speed was pretty fast and the pitch of the noise would change with any increase or decrease of ground speed.
The differential gears themselves DO NOT have any relative motion to each other EXCEPT when executing corners (turning tractor to left or right) or when one wheel is spinning due to a loss of traction. At all other times the differential gears may as well be welded together as they remain stationary relative to each other.

I suggest you might want to completely disassemble all the brake and friction pack parts for inspection, cleaning and lubing (where needed). Because Hydro Gear does list brake adjustment disorder as a possible cause of noise and poor performance, I am inclined to think that there may still be something about that friction pack and the brake caliper/pucks that may be at the root of the problem.
If you put the trans into free wheel mode, are you able to roll the tractor at all by hand? If not....that may be confirmation of a dragging brake.
If you undertake the disassembly of the brake and friction pack, be sure you take plenty of photos as you take it apart so you will know without question where each part came from and how it was oriented. Don't rely on the other manuals for that, they can sometimes be vague, but your own photos will be clear.

    Bookmark   October 30, 2013 at 11:11AM
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