[AT] Farmall M transmission locked up

[Dudley Rupert]

Another failure mode that can cause transmission lockup - and one that I
experienced a couple of years ago - is a worn shift fork -

Moving the gear shift lever from the Neutral position into any of the gear
positions should cause one - and only one - of the three shift rail fork
combinations in the M transmission to move forward or backward which in turn
causes one of the sliding gears to move forward or backward on the sliding
shaft and engage a fixed gear on the counter-rotating shaft.

Conversely, moving the gear shift lever from any gear position back into the
Neutral position should move the same rail fork combination in the opposite
direction which in turn should move the sliding gear back off of the fixed
gear.  However, if enough wear has occurred on the fork it may no longer
engage the grove on the sliding gear sufficiently to pull it back off of the
fixed gear.

In this case when you move the gear shift lever into the Neutral position
you may think you are taking the transmission out of the gear it was in but
the sliding gear remains engaged with its' mating fixed gear.  Then when you
move the gear shift lever into another gear position the appropriate shift
rail fork combination will move another sliding gear onto its' mating fixed
gear and you are then in lockup.

Hopefully the problem with the M Bill is addressing is the problem Mike has
addressed.  The fix to the problem I've outlined is painful - you've got to
change out or repair the forks and that means you've got to get inside the
transmission.

Dudley
Snohomish, Washington



-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com]On Behalf Of Mike Sloane
Sent: Saturday, July 28, 2007 3:37 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Farmall M transmission locked up

This is actually a pretty normal situation. What happens is that the end
of the shift lever gets worn and permits it to slip between two of the
shift "forks". what you need to do is remove the three bolts holding the
shifter in place on top of the transmission. It comes straight out. Then
you need to use a large screwdriver or small crow bar to force the three
forks to be lined up in a row (that is the neutral position). then you
just stick the shifter back in and bolt it up. '

The problem is that you need to restore the proper profile to the end of
the shifter -  a flat taper that is wider at the bottom than the top.
Unless you have another tractor's good shifter for a pattern, it is hard
to guess at the shape. So what I have done in a similar situation is to
use the welder to build up the end some and then test fit the shifter. I
use a bench grinder to remove and shape any excess material. It is only
the very end of the taper that gets worn, so you don't need a lot of
material. Unfortunately, the new material won't be all that hard (unless
you heat it up with a torch and quench it in oil), so it will wear down
again.

Mike

Bill Boyd wrote:
> I posted this on the Farmall board but it hasn't come thru yet.
> So I will try here.
>
>
>
> My neighbor has gotten their Farmall M transmission locked up.
> Any hints or tricks to fixing it?
> I haven't looked at it yet. Probably will tomorrow.
> Thanks for any help.
>
> BillinNETX
>
>
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