FYI FORD MustangSteve's Ford Mustang Forum / Finally got speedometer dialed in on the 69

**Posted by MS** 8/14/2024 4:53 PM

69 Mustang
3,50:1 rear gear
T5 five speed transmission, 0.67:1 overdrive
235x60R15 tires
Drive gear in the tranny has seven teeth (yellow color)
Installed 20 tooth driven gear (black color gear)

Checked with my MPH app on the phone, and it is within 1/2 MPH. I call it a success!

**Posted by Rufus68** 8/14/2024 5:30 PM

That's great. It seemed common for me to have factory speedos be at least 2mph optimistic at highway speed.

**Posted by RTM** 8/14/2024 6:22 PM

I would call it a success as well. It’s a good feeling when you get something dialed in.

**Posted by rpm** 8/14/2024 10:50 PM

That's a whole lot more success than I've had today. Can't wait for the day to be over. The only good news I had today was my car broke down at home

**Posted by BILLY WALTON from GEORGIA** 8/15/2024 12:58 AM

I will be glad to get mine to that point.

**Posted by BobE** 8/15/2024 8:14 AM

Glad you got it worked out.

**Posted by MS** 8/15/2024 8:36 AM

BILLY WALTON from GEORGIA wrote:
I will be glad to get mine to that point.

Billy, your car should use a 20t also, if you have a yellow, seven tooth drive gear.

I bought the gear on ebay for $12.95 shopped. Like everything else, they were around $4.95 pre-covid

**Posted by BILLY WALTON from GEORGIA** 8/15/2024 9:03 AM

MS wrote:
BILLY WALTON from GEORGIA wrote:
I will be glad to get mine to that point.
Billy, your car should use a 20t also, if you have a yellow, seven tooth drive gear.

I bought the gear on ebay for $12.95 shopped. Like everything else, they were around $4.95 pre-covid

I bought one a while back I need to run it over to my buddy while its on the lift.

**Posted by John Ha** 8/15/2024 9:14 AM

MS wrote:
69 Mustang
Checked with my MPH app on the phone, and it is within 1/2 MPH. I call it a success!

Not to be overly critical, but the speed difference is actually a percentage. The MPH difference will vary with speed. For example, my SUV speedo reads .5% less than my actual speed. So at 25 mph, my actual speed is 1.25 mph less than the speedometer reading. At 70 mph indicated, my actual speed is 3.5 mph less than indicated.

**Posted by Rufus68** 8/15/2024 10:26 AM

John Ha wrote:
MS wrote:
69 Mustang
Checked with my MPH app on the phone, and it is within 1/2 MPH. I call it a success!
Not to be overly critical, but the speed difference is actually a percentage. The MPH difference will vary with speed. For example, my SUV speedo reads .5% less than my actual speed. So at 25 mph, my actual speed is 1.25 mph less than the speedometer reading. At 70 mph indicated, my actual speed is 3.5 mph less than indicated.

It's pretty reasonable to assume he checked it with his phone going between 45 and 70, so if he has only 1/2mph difference it is very good. No percentage needed.

**Posted by MS** 8/15/2024 5:57 PM

I check at 60 and 70.. No other speeds will be off significantly when it reads exact at 60