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difference between ZA and ZB

J

jaycoop

Member
Dumb question of the day: I purchased a derelict tractor which I was told was a ZAU. (no ID tag). However, I wonder if it is a ZB, as it has what looks like a torque amplifier and I didn't think the ZA's had such. What are the main differences between the two models? Thanks!
 
ZB did not have a torque. Torque came out with 335/445. ZB has raised platform and high steering column as well as 12v system. Picture or motor serial would help.
 
ZA has a hand clutch lever, whereas the ZB has a foot clutch.
And, as mentioned ZB has a raised platform, and seat and steering wheel are both centered. Steering wheel on ZA is slightly offset, and steering column runs down the left side.
 
Thanks for all the good feedback. It must be a ZA based on its basic features. What frustrates me is that the 'assembly' I'm referring to is not illustrated or described in either of my original ZA manuals (operator's and repair). It is in the same housing as the left side brakes and is in the way of accessing the brakes, which I'm trying to repair. I need some tech on how to remove it and would gladly follow printed directions, but it isn't included in the ZA manuals. I did remove the first snap ring, then the second, but the assembly will not slide off of the shaft, and I don't want to force it. Thanks for all the help so far and any additional!
 
If on left brake it is the kinda live pto setup. Many were removed as clutch pack slipped under load. All it did was slip bull pinion.
 
If you go to the Agco parts books on line and look in the ZB book[ same unit as ZA] and look at the power release controls for live pto page, you can see how all those pieces in there stack together, it has been a long time since I've had one apart, usually the splines on the drive disk are rusted on the shaft splines, they're a handy unit when they're working.
 
Thanks - I will look at the Agco manuals. I would assume that this feature was only on the late ZA's, since most of the MM manuals from the period do not include it.
 
M/W pto clutch setup became an option in late 52. It could be added to a U with disc brakes. On older models the bull pinion shaft had to be changed. Also used on GB, Massey 95 Super and later models until true live pto came out. Had a 1954 U diesel with one as well as a 1955 UB diesel.
 
Thanks for the additional info....that explains why it is on this tractor but not in most of the company literature for a ZA. The Agco parts diagram seems to show disc brakes (?) on the left side in connection with the live PTO assembly....and shoe brakes on the right side of the tractor. Might be the only time in history where both types were used on the same axle/shaft (?). ?.or is the disc setup just for the PTO and there is a separate shoe brake setup (to stop the tractor) behind the live PTO assembly? I'll find out when I dig into it, now that I see how to disassemble it. Thanks everyone....great responses!
 
The PTO clutch for MM was made by Ausco-Lambert not M&W. M&W did make one for after market for several tractors.

MMDEL
 
I & T Manual MM-6 for GB UB ZB has some information on this "live power take-off" clutch

Also Manual MM-201 which has several models included in one manual

Dad had one on a 52 UTU. Problem was when they were adjusted for smooth operation they would slip. When adjusted so they did not slip the operation would be have a lot of jerk and chatter.

Many of them have been disconnected by disconnecting the lever mechanism and bolting the clutch plates together
 
You are correct, left side is disk brake behind the clutch unit and the right is a drum brake, I've got a ZA set up that way
 
Thanks to all of you for your help and all the info! I got into it today....reminds me of disassembling a manual transmission, only you're sitting on the ground, instead of standing at a workbench, because the bolts holding the assembly to the casting are the last thing you get to. A painful process...lots of snap rings, clips, prying and skinned knuckles. I put all the PTO related parts in a box....retained only the disc brake parts; cleaned everything up and put it back together (there is still sufficient pad material left, and not oil soaked). Some future owner of this tractor can re-install the PTO parts, but I'm not going to fool with them. Now I can take a test drive and find out whether the disc or drum side stops better. :)
 
Was at a sale today if western Wisconsin. There?s was a ZA that was restored, new tires all the way around and it was announced that the owner bought it new.

Sold for 2600...
 
ZB has the steering wheel in the center in front of the operator and the operator sits on a platform above the transmission. The ZB also had a foot pedal on the left for the main clutch. ZA had the (Main clutch for the engine) hand clutch on the right side.

The pto clutch (with the lever on the left) could be retrofitted into the ZA even if it did not come with one. Usually they kept the drum brake on the right side if they were retrofitted.

It basically disconnected the left bull pinion from the differential which stopped forward travel, so it was not a 'live pto' in the strictest meaning of the term. The transmission was still turning so you could not shift gears. But if the Combine or other implement was plugging up, stopping the forward travel stopped feeding more in and allowed it to clear iself.
 
Thank you, that's a clear explanation. Mine is a ZA for sure, but may or may not have come from the factory with the 'live PTO'. In disassembling it, I can see where a lot of engineering thought went into it. I can also see where it might become problematic if it wasn't correctly adjusted or if it became worn out or oil soaked.
 
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