Comparison of Transfer Cases

[David_Hayward (RIP)]

This manual is a post-war one for civvy garages that handled ex-military 4 x 4 Chevrolets. Can anyone please compare the transfer cases, and perhaps axles, with CMPs?

http://chevy.tocmp.com/military/1945_46/4x4cmt0801.htm
http://chevy.tocmp.com/military/1945_46/4x4cmt0802.htm
http://chevy.tocmp.com/military/1945_46/4x4cmt0803.htm
http://chevy.tocmp.com/military/1945_46/4x4cmt0804.htm
http://chevy.tocmp.com/military/1945_46/4x4cmt0805.htm
etc

[Grant Bowker]

The case housing is completely different, the pages you have referenced show a 4 shaft case with the shafts arranged almost on the corners of a square layout while the CMP is set up with 3 shafts that are more or less in line. Even though the cases are different, some of the internal parts might be interchangable.

[Tony Smith]

Funny set-up that Chev 1 1/2 ton case. It appears that the front and rear output shafts would rotate in opposite directions!!!

The appearance of the Transfer case is, as Grant says, quite different to the CMP Transfer cases. There are photos of the cases in this thread. Pictured below is the Early 2-Speed case:

[Tony Smith]

And the later 2-Speed case with the larger Oil Sump:

[David_Hayward (RIP)]

I know that Fords had the facility at some point to produce their own transfer cases in the Windsor axle plant, but those illustrations look very similar to the McKinnon case design...have we got a GM oC illustration please to compare?

[David_Hayward (RIP)]

This is the only shot I have on my PC of a McKinnon case, on a C15A? There is a "GM" and an "M" stamped in a part and also a part number.

[David_Hayward (RIP)]

I has a quick peek at the US GMC parts book and it is clear that the Chevrolet (Axle Plant) case and the Timken-Detroit case owe nothing at all to the McKinnon Industries design. I just have to say that I find it remarkable that the company produced a transfer case design in 1940 from nothing in an incredibly short time.

[cliff]

Originally posted by David_Hayward
I just have to say that I find it remarkable that the company produced a transfer case design in 1940 from nothing in an incredibly short time.

David you will probably find that the motor companys design departments may have been working on one for a while and when the need arrived they produced it.

[David_Hayward (RIP)]

There is no documentary evidence yet that this was the case (pun unintended) whereas McKinnon's own papers do reveal that they were asked by "the Government" in 1940 to produce 4-wheel drive arrangements.

However there is ample evidence [see below] that Ford's men in the DND and in Windsor in the Department tasked were calling for Marmon-Herrington drive, by say November 1939. Fords therefore either envisaged using M-H compinentry, which they did of course to a certain extent, or as with using McKinnon/Chevrolet axles in some multi-drive chassis, anticipated using McKinnon multi-drive components. This clearly was not sufficient in wartime. It was only in a discussion with Sandra Notarianni, Ford of Canada's historian, that I established that Ford had the facilities to manufacture transfer case components in Windsor. I have yet to see any DND papers relating to this although Clive or others may have seen them! However I have quoted some extracts below of DND papers which might answer some points.

On 30 September 1939, Stan Ellis cabled in code from the High Commission in London to W.R. Campbell who was by then the Chairman of the War Supply Board, referring to Carr’s enquiry to Canada House regarding the Guy Quad Ant. This vehicle had been designed throughout as a 4-wheel drive [4 x 4] 25-Pounder gun tractor and was also equipped with a Winch. Could Campbell explore the possibility of using the Marmon-Herrington front end drive on the Ford of Canada 101 [-inch] chassis with an off-centre to the left rear axle differential and a rear drive shaft from the rear side Marmon-Herrington front drive shaft takeoff position on the transfer case? It would be necessary to have an offset drive shaft to provide clearance for the Guy Winch which apparently could be mounted in the [Ford chassis] frame with offset Hotchkiss drive shaft as close as practicable to the left side spring. The Guy Winch was from a conventional drive shaft universal joint position: this was desirable unless a transmission power takeoff of 20 h.p. capacity was available to use with an Air Compressor [to use for tyre inflation]. The Guy Winch was the best type for their [Ford] design providing an off-centre drive shaft feasible. Ellis was mailing Blueprints of the Guy chassis and Winch and anticipated body details later. A photograph of the body had been mailed to Carr, as well as the drawings of the Dunlop wheel on the 22nd

In a letter of 26th October Stan Ellis wrote to Sid Swallow and referred to:

The “Lorries 30-cwt.” was clarified by stating that the chassis supplied for this classification should be equipped with heavy-duty springs front and rear, and it would not be necessary to reinforce the frame. As a considerable number of these would be required for cross-country purposes, it would be desirable to equip up to 1/3rd with Marmon-Herrington four-wheel drive, with the balance to be equipped with Eaton two-speed axles. In all cases the lowest gear ratio available was to be used.

...The “Lorries 3-ton” in Column (t) page 1 were all load carriers and should be four-wheel drive. Reference was made in the schedules to the use of the Eaton single reduction rear axle. It was Ellis’s understanding that the Eaton 1940 design was considerably stronger than Ford Standard and if this was the case it was advisable to use the Eaton type. In this connection it would be necessary for Eaton to provide a suitable gear ratio to coincide with the Ford Standard used in the front axle

I suppose on reading this again this does hold out the suggestion of indigenous 4x4 componentry, though I think Ellis was talking about M-H components.

It would be useful to review past thread[s] on this subject in due course, as we did thrash this interchangeability issue before. This one is interesting:

TRANSFER CASE/AXLE THREAD

[Tony Smith]

I know it's been a while since this thread was last active, but there's always a good time to add new info.

From David Hayward's pics above, we have ruled out that the CMP transfer case bears no relation to to the 2 1/2 ton CCKW or 1 1/2 ton Chevrolet used by the US. However, there is another US military truck that does indeed appear to have some similarities to the CMP case; the Ford GTB 1 1/2 ton truck.

As these vehicles were built by Ford in 1943/44, it is safe to say that they followed on from the CMP design, but there a few differences. The CMP case is what is known as a Right-hand drop design, that is the input shaft is on the vehicle centreline while the output shafts are well to the right of the vehicle's centreline. The Ford GTB transfer case however is a Left-hand drop design, as the engine and gearbox are located well to the right of the vehicle centreline and so its the transfer case input shaft, but the output shafts are close to vehicle centre.

CMP transfer cases that have a handbrake have this fitted to the rear output shaft, but the GTB has the handbrake mounted on the rear side of the input shaft, where normally a PTO is fitted to the CMP.

Does anyone have an exploded parts diagram of a GTB transfer case, or better yet, do any members own one. Of all the US vehicles, the GTB is probably the closest in design to the CMP, and it is clear that Ford drew heavily from the CMP design.

Photos below are from Toadman's tank Pictures