Re: AUTOMATIC strength, or Everything you wanted to know about Lockomatics, but........

[n9ads@domain.elided (Howard R Pletcher)]

On Sun, 4 Jan 1998 01:01:22 -0700 (MST) Tom Mandera <tsm1@domain.elided>
writes:
>I seem to recall hearing of some issues about the AUTOMATIC and 
>LOCK-O-MATIC hub strength.
>
>Is there a strength issue to be concerned about vs. "standard" manual 
>hubs?  I recall reading the LOCK-O-Matic (I have the earlier 
>AUTOMATIC) hubs got a design change mid-run to a stronger assembly.
>
>Any differences in strength between the AUTO mode and the LOCK mode?
>
>
Yes, there is a big difference in strength between the auto mode and the
manual mode of the Lockomatic Hubs.  Essentially, you have two completely
different and totally separate hub mechanisms in one package.  The manual
mode hubs are functionally the same as the manual hubs--you turn the knob
and a splined collar is moved in to engage a splined body attached to the
end of the axle shaft.  With this the whole front hub is mechanically
locked together for forward, reverse, engine braking, everything. 

The automatic mode is a separate mechanism in the inner part of the hub. 
It is what is called a Sprague Clutch that is used in various mechanical
drive systems.  It works by having about 10 5/16" diameter rollers riding
between the inner surface of the round outer hub body  and a 10-sided
"nut" that is attached to the end of the axle shaft.  When the wheel
turns without the axle turning, the rollers lie down on the flats of the
"nut" and there is no connection between the nut/axle shaft and the outer
body/wheel.  When the axle shaft turns, the nut forces the rollers out
against the hub body and this locks the hub parts together until the
wheel is driven faster than the axle and the nuts go back down onto the
flats of the nut.

To make all this work, there is a slotted cage that holds the rollers in
the correct postilion, a spring around the outside to pull the rollers
down onto the flats, and a set of nylon friction shoes that provide some
drag for the cage for the rollers so that the rollers don't just rotate
on the flats of the nut, but rather climb toward the points of the nut
and are forced against the outer body when the axle shaft is turned.  The
surface these shoes ride on is the lock nut for the wheel bearing
adjusting nut, which is the reason with Lockomatics, there are not 2
standard wheel bearing nuts--the outer one is perfectly round with set
screws to lock it in place.  Now is the time to get your service manual
out--the pictures won't explain how it works, but you'll be able to see
what the parts described are.  I had access to a cut-away hub that I
played with for quite a while until I really understood what was
happening.

The way the hubs are built, I think you could actually remove the outer
section with the knob which is the manual part, put a flat plate on the
end to seal it up, and still have the complete automatic part--not that I
would recommend this, but it does show how separate the two modes are.

The difference in the way the modes work explains the strength
differences.  In manual mode you are trying to shear the splines off of a
metal collar--doesn't happen very often.  In the auto mode, you are
forcing the rollers out against the outer body (in a situation that can
produce some impact loads besides) and you can split this body.  It's a
steel ring 1/2" to 3/4" thick, but the holes for the hub mounting bolts
(5/16") don't leave a whole lot of metal at those points.  Tom, I'll
predict that if you don't blow one the first time you try front wheel
drive low mode to power out of a bad situation, you will the second time
(in auto mode).


There were no changes in the Lockomatics that would significantly affect
their strength from the first in the early 60's through 1980.  There were
some differences in the manual mode over the years.  The first hubs, both
manual and automatic, were not spring loaded.  To lock them in, you had
to get the splines on the inner and outer parts aligned so the hub could
lock in.  The ends of the splines were tapered to help them slide
together, but sometimes it took repeated rocking of the Scout to do so. 
By about 1966 or 67, the MANUAL hub was redesigned so that the collar was
connected to the knob by spring-loaded pins so that the knob could be
turned to the engaged position even if the splines did not engage and the
collar would snap into position when the vehicle moved and the splines
finally aligned.  The first manual hubs had a straight, tubular hub body
while the spring-loaded ones received the tapered body most of you are
familiar with.

The Lockomatics did not receive a spring-loaded feature until about 10
years later--the parts book shows a difference in Lockomatic hubs built
12/2/76 and later.  It is not possible to tell the difference externally.
 The early spring-loaded Lockomatics suffered from a weakness in the
spring-load mechanism that caused them to fail into the manually locked
mode--the hub itself did not fail.  This was due to a collar that carried
the springs that was made of a fiber material.  It was replaced with a
metal part and I doubt if there are any still running with the fiber
part.

Some folks swear by their Lockomatics and others only swear at them.  I
have been running them since 1971 and wouldn't have anything else.  BUT,
I consider the automatic part suitable only for on-road and mild off-road
running.  They are great for pulling out of an icy parking lot onto a dry
street in 4WD, shifting into 2WD and driving 15 miles down the street.  I
will run them in auto mode in light snow situations, but when the road
becomes covered, I lock them in.   I've had the experience of having the
rear end lock up and start to come around just from engine braking on icy
roads in auto mode.  I'll use them in auto if I just happen to come upon
a mud hole or loose-surface hill that I could probably dig my way through
in 2WD anyway, but when I head out on a trail, or hook onto someone to
pull them out, I lock the hubs.  I figure that's the reason I've only
blown one in 27 years.  Actually, they're perfect for the type of use the
average yuppie-mobile SUV gets, but for serious off-road use I would
expect to eventually break them.  On the other hand, I've also talked to
people who plow snow in the auto mode and this seems to be one of the
most hazardous applications--get a wheel spinning, hit pavement, and buy
a new hub!

I hope this helps you understand some of the differences between the two
modes.  Just keep in mind that the two modes are really two different
mechanisms.

Howard Pletcher
Howteron Products Scout Parts