Is there any way to determine the number of teeth on the drive gear without taking the transmission apart? I've got a 27 tooth driven gear but don't have any info on what the drive gear could be.

try pulling driven gear out and use a mirror to see if you can see what color the drive gear is looks like they use 3 different colors then go to bowtieoverdrives web site to match color to size hope this will help you

I'm assuming you're really asking "What gear ratio do I have?"

Aside from physical counting, a cleaner and approximate method is on a flat parking place somewhere put a white chalk mark on the driveshaft and on a rear tire at the 6:00 position where it touches the road. With a buddy, VERY SLOWLY roll the car (while the tranny's in neutral) forward exactly one rear tire revolution. And without getting under the car (need I repeat this last statement?) use a bright flashlight to count the full and partial driveshaft revolutions.

Your count should end up somewhere close to one of the following possible ratios:

2.55? (2-1/2)
2.73 (2-3/4)
3.08 (3-1/10)
3.23 (3-1/4)
3.55 (3-1/2)
3.73 (3-3/4)
4.10 (4-1/10)

However, if you already know the ratio and really are asking for the number of pinion teeth, take the number of ring gear teeth (e.g. 41) and divide it by the R&P ratio (e.g. 2.73) and you should get a number of pinion teeth (15 in this example).

Hope it helps.

mnunn you gave him some good info but I think he is looking at the speedometer drive

elmpala, can you give us a little more info on what you are dealing with?

I could be wrong here, but if rearend ratio is known, rear tire diameter is known and driven gear is known then this should be as simple as looking it up in a chart or one of the calculator programs out there...

Thanks for all the info guys. I took a flashlight and found I have a white drive gear which from one of the many sites I visited told me it has 13 teeth. According to the same site I need a 35 tooth driven gear for my 3.42 rear end. I don't think they're available so I'll probably need a new driven gear, I currently have a 27 tooth gear, and an adaptor similiar but not the same as I had with my TH350. Finding out the proper combination has been the final problem I am dealing with. Any info would be appreciated.