Speedometer Gear question

[michaeloberg1980]

In my previous post I mentioned that I picked up an SN95 T5 Transmission for my 1984 mustang. I have a shortened drive shaft and am going to use the SN bell housing. I modified the crossmember to compensate for the fact the transmission will sit about 3/4 of an inch farther back. But now onto the speedometer gears.

My transmission is 1352-246 see below:



Under Speedo it says 8T which I assume means 8 tooth? Confirmation needed here.

Since this is a 94-95 mustang, I am not positive that my speedometer gear on my 1984 1/2 Mustang will mesh. Here is a picture inside of the SN Trans:



Here is a picture of my speedometer gear on the car which has 17 teeth:



LMR has a speedometer calculator to help determine the gear needed. In that calculator is the data on my car, but not sure if I select 8 tooth on the calculator. I would assume I do because the decode of the transmission says 8T under Speedo (1st Picture).



So with that, LMR notes:

• 8 Tooth
  
  • Select this if you have a:
    
    • factory 1990-1995 Mustang T5, AOD, AODE
    • 1996-1998 GT T45, AODE, 4R70W
    • 1994-1998 V6 T5, AODE, 4R70W

Since this is a 94-95 T5, I again can assume I need an 8 tooth speedo gear, part suggested is here:



Now if you look at picture 3 I have in this post, I already have a 17 tooth speedo gear, but what I don't understand is the option on the LMR calculator. When I select 7 or 8 tooth it is the same part number. Am I overthinking this, should I just plug my 18 tooth gear in and go? I don't want shredded plastic in my transmission. Under the same not section on LMR's website it says to select a 7 tooth gear for the following applications:

• 7 Tooth
  
  • Select this if you have a:
    
    • factory 1983-1989 Mustang T5 or AOD
    • Ford Racing M-7003-Z World Class T5
    • Tremec 3550, TKO, TKO 500, TKO 600
    • Tremec T56 Magnum
    • 1996-1998 Cobra T45
    
    
  • Or you are converting your 1990-1995 Mustang T5 to a 7 tooth drive gear

I am so lost on this and am looking for some help, the LAST thing I want to is tear the transmission apart to replace the speedometer drive gear. The color of the gear in the transmission is a greenish color you can see in the 2nd picture.

Thanks in advance.

Mike

[JKengineering]

By using the formula in an old ford motorsport catalog the math comes out to 17.75 so I would use a 18 tooth gear. This assumes a 8 tooth drive gear, (the catalog lists a 8 tooth gear for 90-95 T5's) 2.73 axle ratio and 813 tire rev. per mile.(245/45R17, from

Sumitomo HTR Z5 data on tire rack).

Mike

[michaeloberg1980]

Perfect - the calculator I was using put it in-between a 17 & 18 tooth gear. Either way this will mesh with the internal 8 tooth drive gear and not eat plastic, from what I can tell. Thank you!