Tremec 3650 gear ratios need help
 

I read that the 03+ TR3650 5th gear has a lower ratio of .62 then the .68 that late 01-02 have. Is this true? can anyone confirm this?

Doing the math it seems like that may be true since I know my car (03) does around 2,000 rpm at 75 mph and the math says it should be at 76 mph at those rpms w/ the .62 overdrive. For the .68 overdrive, at 2,000 rpms, it should be at 69 mph. However, I know the 05+ has the .68 so I'm more incline to think that the 01-04 TR3650 had the .62.

Mine is dead on 70mph at 2k with stock gearing.

With the .62 5th gear at 70mph would put you at 1858rpms.
With the .68 5th gear at 70mph would put you at 2038rpms.

So I wonder what the deal is. This means my car for sure has a .68 5th gear ratio in the tranny. What does your car do at 70mph?

I wonder if they changed it to get better highway mpg out of our cars? makes me wish I had a 03-04 tranny with the better 5th gear.

I don't know much about how to do that math, but since you are comapring your two cars, tire size differences are being taken into account.

Tire height should be almost the same with a 275 vs 245 or 315. They are all very close in total tire height.

What does yours do at 70mph?

Mine is around 2000-2100 @ 70

Mine is right at around 2K rpm @ 70 mph also, don't know the exact rpm.

3.55 gears and 2000 rpm @ 70.

Since mine does 2,000 at around 75, it's below that at 70. But I'm w/ you, sounds like a push for better mileage by dropping 5th down. Seems strange that Ford would use the lower ratio for 2 years only though...

As for tire height, I'm assuming 26" (stock height) in my calculations as well as a 3.27 rear gear.

Ok so I had to drive to Melbourne,FL yesterday and I did some tests for it. I got 2k flat at 75mph and at 70mph I am just over 1800rpms. So looks like this can not be true cause that means my 2002 GT has a .062 5th gear ratio.

wish my POS cruised 70 at 2k...i think im turning 2300 at 70 and 2500 at 75

mine has a T-45 transmission, but it cruises at 70@2100 RPM (ish)

i found aftermarket axleshafts, so i dunno if the diff is stock or not, need to take a gander at it.