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Another recent acquisition for me. And some more high-res macro shots for you all!

This lock has a mechanism that I hadn't encountered before, in the centre of the dial there's a knob with 'S&G' labelled vertically. While dialing the combination, it needs to be 'locked' with the tabs grouped together to form a wheel (as seen in the photos below). Once the correct combination is entered you can turn the small S&G knob in the middle of the dial and 'unlock' the cam (it is otherwise shielded) and then continue turning the dial right to stop.
It's a cool feature and it would (in my not at all expert opinion) make manipulation very difficult.

Take a close look at the photos of the wheels as well and the deliberately raised sections of varied sizes

One known flaw was that apparently, by watching the chrome pointer while someone is dialing the combination, it was possible to reduce the keyspace required to carry out a successful attack. I would guess that this is why we don't see this type of dial commonly anymore?

If anyone knows any history about these or what years they were in service it would be most appreciated!

Cheers!

WOW plastic wheels... no radiologic attack on your model.
Mine looks older. And before someone asks, I haven't been able to assemble it yet.

Cheers

Interesting your's has switches inside of it, haven't seen that before in a safe lock, only on time-locks...

And you can see the missing ball bearing there in the pictures I hope Did you ever get it sorted?

You can see the date code inside the lock between the wheels and the bolt stamped in the case. September 1979.

There was an earlier version that used a true 8400 change key. The recess that you see in your back cover was an upgrade so that the 6720 change key could be used.

The bolt on your lock was made to go on an S&G 8470 extension which was used as a door lock to secure classified spaces after hours.

As you said they were disallowed in DOD use probably mid 1980's since someone could look over your shoulder and not see the actual numbers, but see the centispline pointer and guess the combination. These were replaced by the S&G 8500 series.

Flip the dial over and take a look at the back side. Some of the earlier version dials had a wall of brass BB's expoxied in the dial as a radiological attack deterrent.

Oh that's all heaps useful information! Thanks so much!
No brass ball bearings, I'll have to take photos another evening of the dial from the reverse, I was unaware this was a thing.

The centrespline pointer as you called it, is that the 'technical term' any idea for the correct name of the mechanism that it interacts with?

In theory it would be possible to find a 8430 rear casing for this type of lock then with a 8400 change key hole? Is there a reason that one type of change key is advantageous over the other? Seems a bit unnecessary...

Cheers!!

You are welcome.

The centerspline dial name I think was a trademark that dial from S&G. The inner part would be the 8400 cam and spindle.

The old style rear cover would probably take some searching to find a used one and most people wouldnt know what it was. There is no advantage to one over the other. It was simply a design change to simply things.

Yes I can barely see the ball bearings.
No I never managed to put the lock back together. I suspect something is wrong. Either me or the lock.

Cheers

God I love these locks, the 8400 / 8500 / Manifoil IV / Manifoil VIII are endlessly fascinating things.

I've only ever heard the cam mechanism on these (and the Manifoil, which is a broadly similar idea) referred to as a "split cam".

S&G's own installation instructions refer to the "inner spindle" and the "tip of the inner spindle" on the 8400 series - see step 9 on p 3 of the PDF below.

https://cdn2.hubspot.net/hubfs/5825267/ ... nstall.pdf

The original patent for the 8400 series (from 1949, wow)...

https://patents.google.com/patent/US2575674A/en

...may show some more and better nomenclature but as a result of the hilariously bad OCR applied when this thing was digitized and me not really giving two shits, I decided I had better things to do and gave up. More interested parties with less demands on their time may wish to decode the following small sample, believe me there is an awful lot more where this came from:

-snip-

The construction described so far is conventional. The present inventional resides in the modification of the driver wheel I2 and certain other parts and the provision of a slide 43 Vwhich can be selectively controlled for closing the gate I2a in the driver wheel I2 so that a person not familiarwth the combination cannot manipuisqto'fthefcombination l ofthe lock. ":Io this end,

theoutside of .the 'driver'wheel--has Jaiiiired` thereto spaced Aguides I411 and 42. These :guides are undercut fas fait I'a and 42o-to Aprovide .mar- .inal edges Which-overlapfaslide M3. lThe-slide 43 comprises Jan-'arcuate portion 33a which has exactlythefsame radius as the 'remaining Lperipheral 'surface of fthe Ydriver 'wheel t2, 'itwo legs b and #13e Eand-asecon'd transverse portion 43d Jlziihg'ithe opposite vrends -of the legs. The inner Side if rleg 45431) provided Iv'ritlri :gear teeth M which are adapted to :mesh with 4`a -sxnall pinion 16 itc lconstitute a rackand -pini'on movement, -the rotation fof the pim'on 146 icontrollin'g the 'radial movement of the slide 4-3. The pinion 66 is xed tofa #shaft i41 "which -ex'tends through -a bore in tionalrconStruction-rotatablyimounted inthe hub 6T 'the fdial |33-, is -i'xed :to fthe outer end of xthe lraftlu. As -clearly shown in Figure Tl, thebarrel d! the Llock I8 -is provided with a series l"of pins 5I of dfEerent lengths 'which are adapted to be aligned with a Isecond -pluralitylof pins S2-which are mounted in the radial recesses o'fthe hub of the jdial 13. The pins 52 -arespring loaded so that `they fare normally 'urged Ytoward the 'barrel o'fithe lock-'inthe usual fmanner. When the key 53 "is 'Jncitdnfthelbarrelpsomefof the pins152'will extend A#across -the -dividing line between the barrel and the inside of the v-hub 'to provide 'an nterlockbetweenthe 'barreland the hub-whereby th'eshaft 41 wllfbelccke'd with thevdial I3. -Ac cordingly, 1rotation fof the vldial vIl3 'will rotate the driver Wheel I 2 vvhlhih `turndrives' the 'tumbler's in the Pm'anner already described. Asfin rconventiona'l `cylimirical pin "tumbler 'ltype locks, 'the key2canfonly'he removed and inserted when the tunibler in-one position. lIn the immediate instance'lthe zero -positionfefithe -lock'is such that the pinion 416 will 4have unoved 'the slide 43 to rits radially outermost 'position where l`its outer arcuate -surface '43a -coincides 'with the outer periphery fof the driver'vvheel I2.

-snip-

As an aside, I'd never heard about the brass ballbearing thing either and since mine is a factory mounted demo sample, I've never taken it off the plastic stand to find out if it's got this addition and am unlikely to ever do so. The wheels are conventional metal though sadly.

The worthless dial lock on "spy-proof" dials can be used in the same way.

The replacement lock for the 8400 series was the 8500 series with the push in dial.
The original D54 dial used still had the S&G logo on it for awhile. That was removed for the same reason and the center knob on the dial is just blank.

I always wondered why those were so plain Jane. Now it all makes perfect sense. Thank you!

Some of the 8500 dials have concentric circles in the face of the knob, and some are smooth, I've also noticed.

You are welcome.

I think that is also one of the reason why on the X07 they required the dialing to start at random positions relative to the LCD.