Listoff

Hello! I have an '87 automatic coupe. We originally bought the car with a 2.59 rear, but in the hunt for quickness, we bought a used 3.07 and had it installed, which dropped the gas mileage from 24.6 mpg to 18. I don't drive the car as much these days and gas is never cheap, so I'm thinking about installing the original 2.59 and replacing the U-joints in the drive shaft at the same time. The only issue is that the 2.59 is sitting up in my attic with no cover which has left the gears exposed. It's warm and dry up there, so I have no fear about rust or anything like that. I've never done a rear-end swap on my own and only asked the shop to do it for me. Does anyone have any suggestions on what I should do to clean out the inside of the old rear before I attempt to install it?

Thank you!

OleDog

I really don't think you have anything to worry about. If you like get a can of brake clean, and spray the heck out of it. get all the dust and grease out and you're go to go. I've got a shop, some parts lay on the shelf for years, no big deal.
Billy

383vett

Take a new mileage reading. There is no way the mpg would drop 25% by switching to a 3.07 rear gear. These were optional gears with some c4 automatics. I was running a 3.73 rear with a built 383 and an automatic and got better mileage at the street and strip than you are getting now with your 3.07. Leave it alone and enjoy the new performance set up. This is in a Corvette right?

WVZR-1

I believe I'd have to agree here. Take a GPS and do some checks of both the speedometer and the odometer and revisit this post and mention your findings. Do speedometer references at 45, 55, 65 and 75 MPH and post your GPS numbers. Do some measured miles on a major highway and compare the odometer to the GPS.

I'm guessing maybe the speedometer was never correctly calibrated and that can be redone. Check the VSS in your car for color, it's either white or black. Which is yours?

In your particular location I'd be surprised if maybe the 3.07 if driven rationally might produce equal to the previous 2.59 or potentially better. York PA - I'd think maybe better.