Quick Speedo Gear Question
04-30-2007, 10:49 PM
#1
4th Gear Member
Thread Starter
Join Date: Mar 2005
Location:
Posts: 1,198
Quick Speedo Gear Question
hey guys im a little confused about what speedo gear to purchase cause I just ordered a set of Motive 4:10's for my 89 AOD.
Which speedo gear do i get for my car? Since my car is an 1989, it should be a 7 Tooth drive gear correct? So is this the correct one? Automatic 7-Tooth 4.10 Ratio / Black 23 Speedo Gear.
Much help appreciated. Thanks
AND I did look at the tech thread. It didnt really clarify it.
Which speedo gear do i get for my car? Since my car is an 1989, it should be a 7 Tooth drive gear correct? So is this the correct one? Automatic 7-Tooth 4.10 Ratio / Black 23 Speedo Gear.
Much help appreciated. Thanks
AND I did look at the tech thread. It didnt really clarify it.
04-30-2007, 11:17 PM
#4
Join Date: Apr 2007
Location:
Posts: 37
RE: Quick Speedo Gear Question
Well, I'm not sure about what your AOD came with, I had to count teeth on my T5 to get the right stuff. Looking at the FRPP catalog they do not list a combination for 4.10's and 7 tooth drive gear, however 23 teeth seems to be correct. Here's the formula for figuring out best scenerio from the catalog:
Driven gear teeth= Drivegear teeth x Axle Ratio x Tire Rev Per mile/1000
So for instance I use Avon Tech 225/55/16 tires, and according to TireRack they have 806 revs per mile. I have a 6 tooth drive gear, and a 3.55 ratio.
6x 3.55 x 806/1000 = 20029.1/1000 = 17167.8/1000 = 17.1678driven gear teeth required for accurate speedo. So I would choose the closest gear, which would be a 17 tooth gear.
On a side note, I trusted a vendor once to know what I needed in order to make it right and man did they mess up. I had no idea what was in the car when I bought it and told them what rear end gearing I had and which way my speedo was off and they sent me a gear that made it worse. Moral of the story is be sure of what you have and order the right part yourself.
Also, the gear they sent me was a 23 tooth unit, which is actually a GM part since Ford doesn't make one, and my trans tore that thing up. I hear this is common for those gears. I did find a vendor on Ebay that sells them and I bought one from them and it seems to be better quality then the other junk I had.
Hope this helps.
Since there's no
Driven gear teeth= Drivegear teeth x Axle Ratio x Tire Rev Per mile/1000
So for instance I use Avon Tech 225/55/16 tires, and according to TireRack they have 806 revs per mile. I have a 6 tooth drive gear, and a 3.55 ratio.
6x 3.55 x 806/1000 = 20029.1/1000 = 17167.8/1000 = 17.1678driven gear teeth required for accurate speedo. So I would choose the closest gear, which would be a 17 tooth gear.
On a side note, I trusted a vendor once to know what I needed in order to make it right and man did they mess up. I had no idea what was in the car when I bought it and told them what rear end gearing I had and which way my speedo was off and they sent me a gear that made it worse. Moral of the story is be sure of what you have and order the right part yourself.
Also, the gear they sent me was a 23 tooth unit, which is actually a GM part since Ford doesn't make one, and my trans tore that thing up. I hear this is common for those gears. I did find a vendor on Ebay that sells them and I bought one from them and it seems to be better quality then the other junk I had.
Hope this helps.
Since there's no
05-01-2007, 12:12 AM
#6
4th Gear Member
Join Date: Sep 2006
Location:
Posts: 1,138
Thread
Thread Starter
Forum
Replies
Last Post
Luke9222
4.6L General Discussion
19
10-22-2015 11:55 PM
