differance between d7 3t and d7 4t

No difference from what I can tell in the War Department Technical Manual.
Maybe gearing...I didn't compare that.

OM, the 4T was made for the army weren,t they. We used to get one in once in awhile to work on after the war so the Govt. sold them I guess.I think some of them were assembled here near me at a plant that made tanks too in Berwick Pa.

Yes, SJ...4T was Army version, 6T was Navy.....all the same stuff as far as I know....course now someone will correct me 😊

Hi, Sandcreek and Old Magnet.
In some cases, there was very little if any difference between the 3T and 4T D7's. How-wevver, as I understand it, the U.S. Army did require some of the 4T's to have different gearing from the standard 3T arrangement. I think the same applied to the 6T series that was made for the U.S. Navy and I'd hate to bet that the army and navy collaborated on this and made the variations the same.

Old Magnet,

I think you know your s**t, Yes I think you are correct, so I guess you have been correct-ed😉 -glen

The 4T and 6T tractors were built for specific Army and Navy contract orders .. using the basic 3T tractor .. and adding the specific requirements (which were mostly attachments) listed in those contract orders.

I have never specifically seen one of those orders, but I understand that the biggest change between the 3T, 4T and 6T was in the specific attachments, that were requested to meet the conditions, that the tractors had to perform under. The attachments involved, included winches (front or rear) .. starting, lighting and generating systems .. specific Military attachments such as tie-downs, brackets for military tools and jerrycans .. and possibly, gearing variations.

The 1949 military manual description on the cover, states .. "Tractor, Crawler type, Diesel driven - 17,100 to 22,500 drawbar lbs pull - Standard Caterpillar D7, 74 in gage - Tractor S/No's 7M1-up, 3T1-up and 4T1-up" .. thus indicating that there are no serious changes in specifications between all these tractors.
The variation in drawbar pulls, indicate gearing changes to me. I do not recall any HP variations between these tractors, so gearing is the only possible reason for the variations in drawbar pull.

The manual does not list transmission or final drive specifications, but it lists every other single specification.
Interestingly, the listing under "accessories" shows 3 different generators (Bosch & 2 Delco Remy's) .. a battery, lighting & starting system .. head lamp bulbs .. dash & tail lamp bulbs .. and a starting engine starter .. that are all noted, as "Special Attachments". These areas would be the main areas of difference between the different S/No's.

Thank you for all the information. I can not believe the wealth of knowledge and the friendly help on this board. I think I will buy the old girl. Thanks again.

Hi, OzDozer.
Thanks for the additional information on the variations. I had heard of the gearing variations but didn't know that all the other bits and pieces were also specified varaitions.

Thanks again.

Thank you for all the information. I can not believe the wealth of knowledge and the friendly help on this board. I think I will buy the old girl. Thanks again.