I had a Ford dealer install 3.73's on my '07 GT, and twice now they've said they calibrated the speedometer, but the tach and speedo are identical to my 3.31 gears. 2,000 rpm's is still reading 70 mph...

They swear it's accurate. I need to go about 80 mph to actually do 70 mph.

Does anyone know if I need to pull a battery cable for 15 minutes to have the PCM take the 3.73 reprogram?

I'm getting the Brenspeed reporgram later this week, so I figure I can fix it then...

Thanks.

 

Dealer is an idiot. Don't pull the cable. He hasn't changed anything.
What exactly are you getting from Brenspeed.
A SCT II can handle this problem.

 

Make sure you tell Brenspeed you have 3.73s. He'll put it in your tune. And yes, the dealer is an idiot.

 

I'm getting the SCT II, so I should be alright.

I probably should set the 3.73 first before pulling down the new tune.

Thanks.

 

would you mind if i ask how much the deal charged for install? total cost? i am thinking of 4:10's. wish another company made the 3:90's besided motive. that would be ideal i think.

 

When you plug in the SCT tuner, it will ask if you want to "change parameters" before you upload the tune. I believe thats where you can change stuff like tire height, gear ratios etc.

 

If you tell Brent, He'll include it as part of the tune and no need to change it yourself... If your an auto this is a far better option as all the transmission scaling will be properly done instead of just relying on the SCT to calibrate the speedo.

Also... If your an Automatic you are measuring your speed vs rpms at WOT and not cruising right? Converter slip can mask some of the gear changes, especially at very light throttle and low rpm conditions.

 

have you checked you speed agaist a gsp unit? Where are you located and what was the total cost?

 

Out the door, under $750. $170 for the gears, 5 hours labor, gear lube,. bearings, shims...

I'm in Avon, OH.

It's quick...

 

Had 3.73's installed by my dealer, it too ran about $700+. Nice thing it is all covered by warranty. I had to re set with my SCT when I got mine back. Told them not to re flash the computer that I would take care of that..
Mechanic who did the work said that was the first time that an automatic set him back in the seat!!

 

Huge diff over my 3.31 gears. Very happy with it. Hypermiling should keep my mpg in the upper 20's...

 

Thanks, I'll change it before uploading the 87 octane tune. PS - I also used to own an 86 SVO - Bright Red, sunroof.

 

how do you tell for sure what gears you have. i have a 06 gt manual and always thought i had 3.55's for a manual. is this correct? motives have given people problems right? 3.90's sound good cus i do alot of 70mph hwy driving.

 

I am going to go 4.10's and have an sct to change the gear ratio. thats the trick.

 

Starting in '06, I believe that a 3.31 ratio was standard in both manual and automatics. You may want to check your window sticker (if you have one) or have a dealer run the sn# to make sure they are 3.55s.

The only thing I've heard negative about Motives is that they have excessive gear whine.

I've had mine since '04. (Silver) It's been a challenge to get it to be a dependable driver, but it's getting there. Cooling system and suspension are next on the list.

 

it was 2007 that the mustang was standard 3.31's across the range. I didnt bother spending the money for 3.55's because i knew i would change them later anyway.

 

Oops, my bad. Sorry.

 

ok then i have the 3.55's. i guess 3.73's wont be that noticeable the? right?

 

Easiest way to find your ratio is to check the door jam sticker.