Can anyone tell me what gear is in the 1965 Mustang I6? Also would there be any benefit from putting in a different gear?

 

2.79 probably. It will have a lot more pep with a better gear, but you also limit your top speed and mileage on the highway. More gear is better with cars that have overdrives.

 

So what kind of gear would be good to put in just to get a little more snap out of it without taking away too much from the top end?

 

What kind of transmission and what size tires you got

 

It's just a stock I6 auto transmission, I have 15" tires but looking at upgrading to 17".

 

Is it hard to change gears yourself? I thought it might just be removing the axle cover and taking the gear out and putting the new one in, but think it might be harder then that.

 

Yes, there is much more to it than that. If you dont know what you're doing you better have a shop do it, or you'll have a very noisy, annoying problem. The gears need to be aligned correctly using some sort of magnetic tool, i dont know the whole process, only watched a video on it. Also, your axles will probably need new bearings pressed on, which requires a shop press. The gears alone cost around 200, and the shop will probably charge you 300+ for labor. So you're looking at around 500-600 to have gears swapped.

 

If you have to ask how to do gears, don't do them. It will end up being a very expensive mistake. I have set up rears, but still prefer having shops do it since it's a pia.

 

Get the axle code from the door tag, It will tell you what gears you have. I dont know if anyone even makes different gear ratios for the 7 1/4 rear.

 

They have to the ranger uses it and the mustang still does.But to get 17s cheaply you might want to look in to a 5 lug swap which is the rear end and front spindles.