Hi, what kind of results will I get if I make this swap, my rear has alot slack right now 172,000 miles. will I burn more gas, do I have to change out the gear sensor on tranny and whats involve in replacing these gears. I have a 88 5.0 TPI.

yeah when i first got my car i had to change a blown rear end... i went from i think 2.80 limited slip was the stock?..to a 3.23 posi..the take off is much better performance is a lot better...gas sucks but that i don't think has anyhtign to do wiht the rear end

As far as replacement of the gears go, i would leave hat up to a pro. There are some very strict tolerances involved and if done wrong can ruin a set of gears in a hurry. If you change gear ratios you will have to change your speedo gears as you mentioned. I am going to assume that you have the 10 bolt rear which means you can't have 3.27 gears, a comparable set would be 3.23s or 3.42s. The 3.27s were for the Borg Warner 9 bolts. Go to the tech articles section and go into the f-body FAQ. Scroll down until you get to the section about speedo gears. It will tell you how to calculate the speedo gears you will need to work with your chosen rear end. There are two speedo gears on the tranny. The drive gear and the driven gear. The driven gear is located at the rear of the tranny on the drivers side. Unbolt the bracket that holds it on, pull the old one out and put the new one in. The drive gear is much more difficult. It requires removing the tailshaft of the tranny to get to it. I can't remeber but you may be able to get away with only replacing the driven gear. As far as gas mileage goes, you will see a slight decrease going from 2.73s to 3.23 or 3.42s. I dropped a couple MPG on the highway when I went from 2.73s to 3.42s. As for e.t.'s. The norm is usually 2-3 tenths but it depends on you engine, tranny, wear, etc... You may just want to get a low mileage rear end from a yard and put it in yourself. Its not hard at all. That is what I did, I'm very pleased, only set me back about $400. Hope this helps.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson

'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Comp Cam, Comp 1.6 Rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter