Just picked up my 06 GT two days ago. I was underneath the car this morning installing my Flowmasters & I looked at the rear diff. cover. There’s a white sticker on the diff. cover that has a bar code, a part number and the numbers “3.31”.

WTF????

Everything I’ve seen about the rear end ratio for a 5 speed 06 says it should be 3.55.

Automatics get a 3.31.

I haven’t had a chance yet to put the rear end on jackstands and rotate the driveshaft & count the number of times it takes for the rear wheels to make one revolution. I’ll be really p.o.ed of Ford gave me a 3.31 rear end.

I have noticed that I have to rev the engine a bit when starting out in 1st gear. Plus, I have stalled it a few times. I thought it was me getting used to the car and the lame drive-by-wire gas pedal. P.S., I know how to drive a 5 speed.

Do anyone have this same sticker on their 5 speed GT’s rear end?????

Although, if I did get a 3.31, I should be able to get Ford to pick up the install of a 3.55 ring and pinion at no charge (or maybe 3.73 or 4.10).

 

Go see what your rpms are at at 70mph in 5th for us.

 

Mine has the same sticker, says 3.55 though. That'd be a huge mistake on their part, I don't see why they wouldn't do the work for free to fix or put in the gears you want.

 

One more thing to think about if they did install a 3:31...What gearing does your processor/speedometer think is back there? Your speed could be off too.

 

Check the tag on the driver's door for the Axle code, on a Gt with 3:55's it should read CD but if it says BG or CG then it is a 3.31 from the factory and that's just it.

What does your window sticker say? If you need me to PM me your Vin number and I'll run it on Ford's Oasis report and that will tell you what ford says it has in it.

Thanks, Doug.

 

Thanks for the advice on checking the driver's door for the axle code. It says "CD", so it should be the 3.55, but the sticker on the axle still says "3.31".

In a day or so, I'll jack up the rear and count the driveshaft rev's for 1 tire rotation. I'll check the posi, too, while I'm at it.

Thanks.

 

if they did screw it up, put 4.10s in

 

ahh.. those monday cars

The dealer should have to correct the gear ratio to the proper one. If they are swapping ring & pinion you should be able to get them to upgrade to a higher numeric gear ratio. You may have to pay for any supplemental work (recalibrating speedo, any additional cost between the 3.55 and the 4.10's)

 

Wouldn't it be easy enough to document the RPM's at 70 like requested and let someone compare?

 

If the wrong gearset is installed for the speedo calibration, would this even work? (could you be sure Where does the speedo get it's input from, rear axles back, or forward of the diff? (don't know, myself).

 

I don't know for sure, but it seems like the RPM's in the tach should be right regardless of the speedo calibration.

 

There are a few ways to see if something is wrong.

To see if the speedo is incorrect, drive on the interstate at 60MPH. You should go exactly one minute between mile markers, any more or less and the speedo is off.

At 60 MPH the engine speed should be around 2200 RPM. I don't have the tire data infornt of me to do an exact calculation, but I can look it up when I get home.

 

One other weird thing, I don't have a hyrocarbon trap. I checked yesterday (planning on removing it) and to my surprise, there is no trap.

I'm not too upset about that...

I'll do some driving in a day or so (and jack up the rear & count the driveshaft rev's) and report back on Tues / Wed..

 

Ford has been leaving the HC trap out for a while now. I cant remember exactly when you stopped using them but I think it was towards the begining of this year.

 

Are you sure about those RPM's?
I think mine is 2000-2100 RPM @ 70 MPH.

 

Nope. The signal for vehicle speed is taken off the output shaft on the transmission. The speedometer can either be calibrated with different gear ratios between the output shaft and the speed signal (old style mechanical speedometers) or by changing the electronic calibration in the speedometer (or computer. Like these cars).

If they have the "standard" 3.55 calibration programmed in at the factory for a 5 speed manual GT but accidentally install 3.31 gears, the calibration WILL be off for the vehicle.

For example: Let's say you are cruising down the highway at an "indicated" 70 mph with the wrong 3.31 gears installed. The computer "thinks" you have 3.55 gears installed (like you should have) so it is sending out a speed signal correct for 70 mph at the transmission output shaft speed. But you really have 3.31 gears installed. So your car is actually going FASTER than what the speedometer is saying. How much faster, well, in this case you are actually going (almost) 76 mph.

If you were in a 65 mph zone and thought you had nice 5 mph buffer left (out of the normal 10 mph over before pulling them over), you would be sadly mistaken. And probably argueing with the cop to no end because you KNOW you were not going that fast!

 

StangNut,

I haven't driven my car in a few weeks so my numbers could be off.

Since the car is brand new, best to take it back to the dealer and ask.

 

I don't disagree with that, but ...

If you read what I wrote, I didn't say the Speedo would be right, I said the *TACH* should be right regardless of if the speedo is right or wrong ...

Carry on...

 

Update... I finally got my GT up on rear jacks. A little more than 7 revolutions of the rear drive shaft gave met 2 rev's of the rear wheels. That tells me that I've got the 3.55 rear end although the sticker says "3.31".

Wrong sticker :angry:

w/3.55 rear end .....

I'm a little disappointed because it "felt" like I didn't have the low end torque that I thought I'd have. I thought I had the 3.31 rear end.

Reason for 3.73's or 4.10's...

Thanks for all of your help!!!

 

You probably convinced yourself it was 3.31 based on the sticker, thus the lack of TQ in your mind.

Glad they got it right for you.