TanStang96

Hello guys I'm new to the Mustang forum and I have a couple of questions.
I was talking to a mechanic about an instalation of 4.10 gears in my 96GT mustang(Auto). He said this will be a big mistake," RPMS will be High, and in the freeway my spedometer will reach only up to 60-65 mph." Is this true? should I go with 3.73? My other question is; After driving, once I put the car in Park a Hissing sound comes from my transmission. Do you guys know what that might be? Mods on my car are: complete PI swap, comp Stage 2 cams, Underdrive pullies, Cold airs intake (K&N) Accufab plenum and throttle, B&M shift kit, TCI torque converter I don't remember if its 2400 or 3200 stall.
Mods to come: MM coil-overs and Blisteins schocks, cc plates, front lower control arms, rear lower control arms, bump steers, SLP Loudmouth 2, magnaflow Tru X pype and Bassani Midlength headers.

Dub9Stang

if your driving it on the freeway use 3.73 gears, wayyy better

0949er

what kind of numbers are you putting down?

your RPMS will not be THAT high. If you want 4.10s get them. I promise you wont regret it.

PS you might get 2 mpg more with 3.73s on the highway then 4.10's

boduke0220

I had 4.10's in My GT. I have them in My Mach 1. Best gear IMO. im at 2300rpms at 65-70. still get 25+mpg we have a .62 over drive 5th gear.

devongarver

Welcome!

First off, it will not be a mistake, it will definitely improve the acceleration of your ride. The speedometer thing...he's kind of retarded for saying it like that...Here's the skinny. Your speedometer is calibrated to your stock gear ratio. When you change the gear ratio, the calibration won't match. There are two ways to fix this. You can change it with a tuner, or with a different speedo gear on the transmission. The problem is, I am not as familiar with the SN-95's, and I do not remember if your's has a OBD2 port or not, or if it uses the speedo gears or not. I am not sure about the hissing, maybe fluid pressure bleeding off or something. Also, I would not go with 3.73's with the automatic transmission. I would definitely go with 4.10s. The final drive ratio from the auto's is different from the 5sp guys, and 4.10s will do you better IMO.

Good luck!

smythge

I've had both 3.73 and 4.10s in my auto you will be fine with either. You will need a to change your shift points with the automatic, especially the 1-2 shift

Eagle2000GT

A 1996 GT. I am not sure but I think you have a .67:1 4th gear ratio instead of the .70:1 on later models. That means your rpms will be about 5% lower than the newer cars. I don't think you can adjust the speedometer with a tuner. I think you are going to have to change the speedometer drive gear in the transmission.

The overdrive gear ratio makes a difference. I have a T-45 with 3.73 gears. I run approximately the same rpms at 70 mph as a T-3650 with 4.10s. My overdrive gear ratio is .67:1 (about the same as yours).

devongarver

Here is the gear you will need.

Eagle2000GT

I don't have an automatic but even with the new speedometer gear I think you will still need a tuner to change your shift points.

A lot of people forget that our transmissions have different gear ratios. A 2001 auto's over drive is .70:1 while a T-3650 is .62:1. The auto going down the highway with 4.10s will actually be running slightly higher rpms than the T-3650 with 4.56 gears (equivalent to 4.63 gears). The older autos and T-45s would be running slightly lower rpms than the T-3650 with 4.56 gears (equivalent to 4.43 gears). I don't think the guys with t-3650s would recommend 4.56 gears for the highway.

teej281

I guess you gotta make sacrifices somewhere. Would you rather feel like the gears were a worthy mod and get a little worse mpg or feel like gears werent as good as you thought but have gas mileage change only a little bit? I'd rather feel like my moneys were well spent. Thats just me though.