Has anyone here done a DIY gear swap (10R80)?

[Crow]

I am debating whether to swap gears on my 3.15 10R80 car. The plan would be to buy the whole pumpkin from Ford Performance and install it myself, or possibly find a shop to build a Wavetrac or Torsen for me. I've swapped a diff out before but I'm no expert and until now I've mostly owned German cars. I'm pretty comfortable with the idea of swapping the whole pumpkin, but rebuilding the diff isn't something I've done before. That said, I don't know of any shops in my area that would do it.

Has anyone here gone the DIY route on a gear swap on the 10R80? If so (or even if not) I have a few questions before taking this on.

1. Do I need to change the pinion flange if I buy the whole pumpkin from Ford? It reads to me like it is only required for the 15-17, but I wasn't sure here.

2. Does anyone have a link to the Forscan settings necessary to set the gear ratio so the transmission shift points, etc are correct? Or is a tune necessary here?

3. For anyone who has driven the 3.15 and 3.55, is it worth swapping to 3.55, or is going straight to forced induction the better path? My concern here is melting the cats with a supercharger - no cats = my wife probably won't ride in the car, and I can't say I care for the smell either.

Any advice or experiences would be appreciated!

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[ZXMustang]

Yes I own two S650s with each gear and the 3.55 gears are superior by far. Unless you are going to do a blower, then you might want the taller gear to help with 1st/2nd gear. But for NA cars, the 3.55s are magic compared to the 3.15s.

 

[Dark Sprite]

See first page here for some useful info, covers some of what you’re asking about: https://www.mustang7g.com/forums/threads/changing-diff-ratios.165888/

 

[LouG]

Rebuilding diffs is not hard, but does need engineers blue, dial gauge, and having been taught by someone who knows.

 

[Neggytive]

Normally I'd say look on car-part.com and see what was out there for a whole used 3.55 differential, but there are not a lot of them listed and they seem to want stupid money for them.

Dropping a whole pumpkin in there is probably about the same price as getting a set of gears, the shim/install kit, and finding someone that knows what they are doing to set it up.

It is generally accepted the automatics do not NEED the 3.55 because the first 6 gears move so fast and the ratios work to keep the car moving

A stick does not have the advantage of the intermediate gears, and somewhere on this forum I posted a reply showing how the final gear ratios work out with the various transmission and rear end options, you can do the math if you know the transmission ratios for each gear and the rear end ratio

Now the question is what are you trying to accomplish and what are you willing to give up to get it?

You can also use any one of a dozen online calculators and work backwards from 70 MPH, knowing the tire diameter, rear ratio and say the 10th gear ratio which IIRC is something like .636 to 1 and figure out if you can live with it, and you can approximate it probably by driving the car in 7th or 8th gear with the 3.15's in it, again just calculate out the rpm using the tire diamater ( easily found online) the gear ratio ( 3.15. 3.55, or even 3.73) and the transmission ratio and see where the RPM's come out

There is more to this than what I am willing to get into, such as having the right gear to keep the engine spinning where it makes the most power, if the engine can't spin the gears for lack of power or you are way out of the power band you are just wasting money.

Gear Ratio

1st 4.696

2nd 2.985

3rd 2.146

4th 1.769

5th 1.520

6th 1.275

7th 1.000

8th 0.854

9th 0.689

10th 0.636


A 255-40R19 tire has a diameter of 27"

So using this lets try the math

RPM=70 * (3.15*.636)*336/27

RPM= (70*2.0034*336)/27

RPM= 47,120/27

3.15 gears RPM to do 70 is 1745 rpm's

Now do 3.55 10th gear 70 MPH

57845/27 now you are at 1966 RPM's doing 70

In 8th gear, 3.55, almost 2900 rpm @70

Now if you want to go deep, say 3.73 and I think there is a ford center section for that, remember 2018 to current fits, just got to change the flange....


RPM= (70*(3.73*.636)*336)/27 =2066 RPM's cruising at 70 with 3.73's in 10th

OK so you want to do 120, and never go into an OD gear, the math gets simple

Lets do 3.55's

(120*3.55*366)/27 , 5300 RPM's and that is a sweet spot for that engine

3.73's

(120*3.73*366)/27 comes out to 6067 RPM's in 10th

in 8th

(120*(3.73*.854)*336)/27

120*3.18*336/27

128473/27 = 4756 rpms, but you are in an OD and the engine is not going to be thrilled trying to make speed without the benefit of torque multiplication.


But now that you know how it works, and if you look at a stock dyno curve and figure out where the sweet spot is, and shift right above it so the power drops back into the sweet spot, you can figure out if you can get the benefit of a lower gear by manually shifting and keeping the engine in the sweet spot or of you want to drop 1200+ install labor and a flange kit to swap the center section.

If you do swap out the center to a 3..55 or 3.73 ( go big or go home!) look to see what hardware is single use/torque to yeild and make sure you have it on hand when you start.

And the Forscan stuff isn't hard as far as telling the modules the correct value for the speedo to read right, but you might want to force the transmission into relearn mode to adjust for the new gears.

It requires going in and clearing some data with a bi-directional scanner then driving in a specific way to get the transmission to start learning again

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