[austinado16]

A guy on the local CL was giving away a '99 Yardman "AutoDrive" Model 604 lawn tractor. Now how could I pass that up?:dunno:

New battery, seat, and tubes in the front tires and it's running great. Still some problems with the mower deck...ie, one of the rear mounting bracket assemblies is complete ripped off and missing:banghead3, but otherwise, not to0 bad.

Anyway, it's got a nasty pulsing whirrrr from the single speed transaxle and based on the parts diagram below, I can only guess that it's coming from the weird (to me anyway) 1 piece $200 differential assembly.

Anyone played around inside one of these transaxles? I've rebuilt a few of the 5 speeds, but haven't had a single speed apart. What's the story on that diff assembly. Can it be taken apart? Or is a moot point because when they grind themselves up, it doesn't matter since seperate parts aren't available?

BTW, the variable speed pulley seems fine, and although there are a few noisey tensioner pulleys, the loud whirrrring noise is only created in forward and reverse with the tractor moving.

I'll do a bit more diagnostics before taking it apart, and post some photos of the inside of the trans as I make progress.

 

[austinado16]

Yeah, this is probably the cheaest-a$$ lawn tractor I've had my hands on, so I'm glad it was free. Hate to see stuff like this wind up in the land fill though, so I'll probably put a little effort into repairing it. Good learning experience too. Plus, I love transmission work.

What were you finding on the failed transmissions? One common thing, or just all kinds of random stuff?

It's weird that the differential is all enclosed and only sold as a complete assembly. I'm dying to know what's hidden in there......and also, how does it get greased since it's not exposed to the rest of the trans? Filled internally and then capped off?

 

[austinado16]

Got it apart, no damage. Slight wear/looseness in the bushing on the diff. gear side of the countershaft. Very little grease is used to build this transaxle. The diff has some slop, but no damage. I packed it full of Bentonite and put it back together and back in the tractor. No sense in having it all torn apart for a week or 3 while I decide if I want to spend $200 on the diff assembly.

One thing that makes a lot of noise is the really small drive gear that engages the diff gear. It makes a clack for every tooth strike against the diff. I wouldn't doubt that that is where the loud whirrrr is coming from. There's not damage to the teeth on either gear, it's just that they are straight cut, and just smacking into each other. Of course that eliminates side loads, and doesn't waste hp, but it's all traded for noise.

It's an extremely simple transmission, I don't get why they couldn't have put a decent differential in it, and then filled it full of Bentonite.

Here's what it looked like when I opened it up...

 

[austinado16]

I replaced the differential assembly and both bushings on that mainshaft, and the noise is much improved. More of a consistant gear whine, and none of the crazy noises it used to make.

I took apart the old differential and didn't find any damage inside. It was easy to take apart. Too bad you can't buy the individual parts. All I found was loose bushings that should fit snug (but don't now) in the stamped steel differential cup.