Location/picture where to change spedo gear?? 66 mustang

Assuming you have a C4, the speedometer gear goes into the transmission at the driver's side of the trans, on the outside its attached by a nut a and a retaining plate wich also holds it in the right position, and on the inside, the gear is locked onto the spedometer cable with a retaining clip. I hope this helps, i don't have a picture of it on hand but it's a very simple procedure.

:bigthumbsup

Here be my picture. I got '66 289 with C4. This is on drivers side. On left side of pic. you will see where it goes into tranny. Pretty easy job. Takes some patience trying to get it out. A 3/8' or 7/16" wrench i think ya need. There are right hand & left hand driven gears. Make sure you get the right one, with the correct amount of teeth. Mine had 16 teeth and was Right hand.

SD... just leave the gear out who cares how fast your going haha jk jk

You need a right hand gear if the hole is on the driver side (which yours should be) and a left hand gear if the hole is on the passenger side.

heres the difference:

The reason why I asked was because I bought this off of Ebay and didn't indicate what side gear I needed: 19 TOOTH FORD SPEEDOMETER GEAR C4,C5,C6,AOD,AODE,4R70W | eBay

It just indicated for a C4 Auto

@SD - nope not yet I'm still waiting on the engine to come back from the machine shop lol but by the end of july it should be all back together

@66Sprint - the calculation is:

(drive gear teeth)x(rear axle ratio)x(tire revolution per mile)
1000

2.80-3.50 gears have a 7 tooth drive gear and 3.55+ gears have a 6 tooth. the tire revolutions per mile can be calculated here:

U.S And Metric Tire Size Information Calculator

whatever the number comes out to, round it up/down to a whole number. for example, mine was 18.4 so i needed an 18 tooth speedo gear

6T6Coupe said:

Here be my picture. I got '66 289 with C4. This is on drivers side. On left side of pic. you will see where it goes into tranny. Pretty easy job. Takes some patience trying to get it out. A 3/8' or 7/16" wrench i think ya need. There are right hand & left hand driven gears. Make sure you get the right one, with the correct amount of teeth. Mine had 16 teeth and was Right hand.

Click to expand...

Are you talking about that FAR left side where there's a hose going in> Looks like a brass part?

Alright! I'm back again. Gotta it in, and I can actually see a real speed now. It was easy, although I had to pry it out a bit just because it was in there for millions of years. It works, and you guys helped out lots. Now I can hit the freeway and see how fast I really am going with my rpm's at 3K. I'm assuming 65-70. Thanks!

Ok, so if I did the math right, I was right when I bought this https://www.mustangsunlimited.com/itemdy00.asp?T1=F1116 01 .

Tire size 185/75/R14 (809.15 rotations per mile)
Rear axle ratio 3.20:1
Drive gear teeth 7

Than does anybody know where I can get the drive gear for inside the transmission? When I looked at mine it was really beat up. C4 automatic transmission.

Speedo gear - LH rotation is typically used in 4 speeds MT's & RH rotation is used in all others AT, T-5 TK and 3 speeds MT's.

Trans with the cable speedo hole on drivers side typically use RH gears. Trans with the Pass side holes typically use LH gears.

That info from NPD pg 154. They also have a RH & LH pic to compare yours with, if needed.

Glad you got it installed finally SDRider!