I know a guy that wants to sell a Moore transmission for a model TT. But I don't know a thing about them. Can anyone fill me in on them and what one might be worth?

I have a Moore in my 1914 and would like to find another. Condition of course is important, if it is complete I would guess it could be worth $500 up. They are rare and hard to find, so you would have to take it from there as to what you want to pay. Some other transmissions have sold for a lot more than $500.
The thing you have to think about also is I don't think there is a place for replacement parts. Check linkages, inside gears, is all the linkage there and etc. Hope this helps.

If the Moore is for a TT? It will not easily work in the car chassis. Since the Moore is generally only a direct and 50 percent under-drive, and the TT is so very low geared to begin with? They are not very desirable in TT trucks. I would think they are only worth couple hundred dollars, and then only if they are in really good condition. (I have part of a truck Moore that is one of the most worn out things I have ever seen!)
The car chassis Moore is also generally only a direct and under-drive. The are desirable to brass car owners because they can be put onto the earlier rear ends that are not compatible with a Ruckstell. For those that want to remain closer to "era correct" for 1913 to '15 Ts, the Moore was one of the first after-market added gears transmissions actually marketed to model T Fords. I have never been able to fully confirm when they were first available, but it appears to have been late 1915. Ruckstell, on the other hand, was not actually marketed until after the World War, about 1920. For some of us, that detail matters.

Jason, First thing you need to do, is confirm whether it is the car version or the truck version (mostly the size of the flange where it connects to the rear end, however, almost nothing else will interchange between them either). That makes a big difference to the dollar value.
The second thing, is to check the condition inside and out. They used simple bushings inside and if the bushings get worn, the gears can wear badly. A badly worn one may be worth a few dollars for parts, but not much more.
Good ones that properly fit the car chassis do seem to sell for over $500. And I don't see many even at that.

A Moore can be re-machined to turn it into an overdrive, and most of the parts are designed to be assembled either way. But I have never seen one that was done that way.
Drive carefully, and enjoy, W2

I strongly recommend that you look at one of the best posts I have seen on the Moore transmission from Jay-In California, posted on the Forum in 2010, titled Moore Auxiliary Transmission. Great information!! Search the topic then put MTFCA behind the topic and you will find it.

It's definitely the TT version since it's still attached to a worm gear set up as part of the rear end of a truck that's in pieces. But ultimately, if it works basically as an under drive then I'm not that interested. I'm focused on getting my TT a couple mph faster, not slower. Thanks for the great information!

Wayne, the Moore in my buckboard has roller bearings on the layshaft. I was surprised I could still buy them new in 1986. I had to make a new layshaft and have it case hardened. Other than that, the rest was really good. Because the gears are in constant mesh, they were not knocked around at all.

Perhaps mine is a later model, and they made improvements.

Allan from down under.

Interesting, Allan. The two I have owned (1 TT & 1 car), both had bronze bushings there, as did a few others I have seen apart. They may have made some that way, I don't know. I did talk to a fellow once that told me he had put roller bearings into a Moore. He said it worked great!
Drive carefully, and enjoy, W2