Transmission Question Ford 640

Stupid question since I don't know the first thingt about what I'm asking about. Can one purchase the, I believe Ferguson overdrive or tranny attachment, that adds the lower gears to a stock Ford 640 transmission? What is it called? Somewhat readily availble used? Costly?

Thanks
 
If you have a true 640 as in it has a 4 speed transmission yes you can find a Sherman for it but there are more then just one type. There is the over drive which is the most common and speeds the PTO up. And there is the under-drive which slows things down including the PTO. And then there is the combo which gives you over under and standard gear so you would have 12 froward seeds which if the prefer one and yes probably around $500-100 for one
 
Besides the Sherman auxiliary transmissions that old mentioned there were a few other brands as well. One that does not change the PTO speed is the Howard, which sits between the transmission output and the differential, and was originally designed for use with the Howard rotovator, which was an early roto-tiller.
 
Thanks for the feedback. That's great since mine is a true 640 with a 4 speed. What would be the best option of those you mentioned. One thing I noticed is that with the Brush Hog Mower, the tractor has to speed up the rpm's and speed to make it operate correctly. Would be nice to creep and mow if necessary.
 

you'd have to have the howard to change the speed of the wheels in relation to the speed of the PTO. Any of the Sherman's, as has been stated, are not going to change the ratio of the PTO speed to the transmission speed. In other words, a Sherman may speed up or slow down the propulsion, but it will also slow or speed the PTO respectively.
 
The problem with the Sherman is it effects PTO speed so to have say a combo and running it in under drive yes you would go real slow but the PTO speed would also be cut by about 1/3 so that would not help. There is also the Howard aux transmission but they are harder to find and when and if you do they cost 3 times more and are some what fragile. Me I would not install any of the Sherman's unless it was the combo that way you have 12 speeds
 
Should you decide to put a sherman in you want to look for one with a 10 spline input shaft, like the one in the photo. I'm pulling this one out of a 640. It is the same that will fit your tractor. Later model had a fine 15 spline shaft and will not fit your tractor without changing the input shaft and nose cone. As others have said the sherman will also effect the pto speeds but with a wider section of gears you might be able to find a happy medium.
As far as the the howard goes it's easier to find one for an earlier N model tractor than to find for your 640 and If you did find one you will paid big bucks for it. The few that I have seen over the last 20 years or so have only been for sale with the tractor. Earlier model howard will not fit your tractor.

Kirk
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