I've currently got a green 22 tooth gear in my transmission and I would like to speed up the indicated mph to be a little more accurate. I bought a red 21 tooth gear and sat the two side by side. The diameters are quite a bit different almost a tooth in height and I am wondering if the red gear will actually engage? Anybody know?

 

you dont indicate what transmission, auto TH400, manual M21, etc. so maybe this link will help you

http://www.transmissioncenter.net/sp...n_______va.htm

 

It's an M20 and I didn't find what I wanted there, but thanks for passing it on. The store I bought it from assures me that it will work as intended. I'm guessing it there is a range to the depth that the driven gear makes contact with the drive gear and that the red gear goes in a little deeper.

 

how about posting the part# or something that it can be verified before you end up with a stripped gear and pieces of plastic in your trani

 

The diameter must be the same. Imagin this, the shaft gear is the ring gear and the housing gear is the pinion. If the pinion gear is too small, tooth contact will not be available. I don't know what shaft gear you have, but I just recently installed a 17 tooth pinion housing gear. Now my speedometer is nearly perfect for acurracy. I don't have any idea of what my shaft gear tooth count is, sorry. Al

 

alswagg: I can see two possibilities. If there are different numbers of teeth around the same diameter gear, then the tooth width would have to change to allow different gear counts to work. So the mesh wouldn't be quite right. Alternatively the gear teeth could be the same size and larger diameters only partially meshed, allowing some slop in what diameters work. Somehow a range of driven gears for the same drive gear is made to work.

I was hoping to find a table that says what color gear goes with what drive gear. If my green gear and my red gear share the same drive gear it should be OK.

melwff: no identifying marks on the red gear. looks just like the green gear.

However I just found this table

http://home.comcast.net/~chevelleengineer/speedo.htm

which shows red and green sharing the same diameter drive gear, 1.76", of which there is only one, and that one is steel.

And then there is this admonishment in red

If you use incompatible gears, they will destroy themselves and possibly fill your tranny with plastic chips.

Haven't found an explanation as to why a range of tooth counts is mechanically possible. Everything is probably OK, its just that I sorta like to understand what is going on, rather than blindly trying things. I may try e-mailing the author if that is still possible.

 

I had a similar problem recently. There are two different diameters of steel drive gears - 1.84" and 1.76". If you have the small (1.76") drive gear, you must get a large diameter plastic driven gear.

I believe the 22-tooth green gear is the large diameter driven gear. If that worked in your car, you must have a small diameter driven gear. You will need to make sure the driven gear you get is a large diameter type.

Try this website for calculating the proper driven gear. All you do is plug in your tire diameter, drive gear size, and rear differential ratio.

http://www.stl-vettes.com/65vette/ge....htm?rear=3.36