I want to upgrade my 68 mustang 289, c4 tranny, to a better Rear End. It has a stock 8.8 rear end with stock gears idk the gear ratio. I was thinking of installing a posi locker and 3.73 gears. Im not trying to build a car for the track. Just some good muscle for the street. Would i be better off getting a 9 inch rear end or is the 8.8 good enough? What about the tranny? Is there something better i could put in it or is a c4 good? Any suggestions or ideas would be great thanx!

 

The stock rear end in your car is not an 8.8, it is an 8 inch. You can find complete center sections for the 8 inch with the gears you want and limited slip that are rebuilt on Ebay. I think the seller I got my 9 inch center section was RMustang.

Since your car is a C4, I would not go more than 3.20-3.50 gears, because you don't have OD. If you want posi, go with traction lock.

 

The 8 inch with out slicks or hard driving can handle up to 400hp.Once you go past that or break it then you need a 9 inch.The c4 is one of fords best trans made only reason id ever replace it is for a over drive like a aod.

 

if you dont drive it on the freeway much at all...you could get by with a 3.50 as tx65 suggested. You could look into the eaton tru-track LSD. I run one and am very happy with it.

-Gun

 

thanx guys i was really thinking about going with 3.73 but i guess that would not be such a good idea with my c4. If i have the chance tu upgrade to a 9 inch would i be better of with it? to handle more HP?

 

if your rear tier is 25" tall and you stuck 3.73s in there you would be spinning 3700 RPM at 75 mph...absolute murder. 3.50s would be 3500, 3.20s 3200, and 3.00 would be 3,000 rpm at 75.

Unless you plan to build an engine that puts 400 hp to the ground in the near future then you'll be okay with the 8"

-Gun

 

If its a 9 inch that bolts in the car go for it.

 

If you won't exceed the power that the 8inch can handle, then I would stick with it. Beefing up parts without a valid reason may only hurt performance. A 9ich weighs about 30 lbs more than an 8inch. That might not seem like much, but that is un-sprung weight, which can have a significant impact on the way the car handles. The rotating mass is greater in the 9inch as well, so you're robbing power that would otherwise go to the wheels.