i want to build my 8inch diff in my 75 mav. it is totally stock. I have a 302 roller that comes to life at 2000 rpm I am about 300 horse. (ish) my tires are 17s on the back. the car is driven on the street but I would like to take it on the track someday. c4 with a shift kit. I want to run a mini spool. my question is this. what all do I need to buy to do a mini spool conversion? what gears would you run to make the car accelerate very hard but still be able to do a little highway driving. this is my fun car so it wont need to be all that sensible but i dont want a car that cant maintain 65 with out spinning itself to death. I have never done any diff work at all. I need to know exactly what to look for. This car has been a great learning experience for me and this forum has helped in so many ways. so now for the next learning experience!!
the only thing you need to install a mini spool is a mini spool, oil, and sealant. its not very hard to install a mini spool. its much harder to install a gear set. to install the mini spool you will have remove the axles then the drive shaft then the third member from the housing. use a dial indicator to measure the back lash of the ring gear to the pinion shaft. remember or write down this measurement. or you can mark the spanners so you can adjust them back to the exact location that they are at. mark each cap so you know which side they go back onto. remove the spanner locks. remove the cap bolts remove the caps and spanners. remove the carrier remove the ring gear bolts remove the ring gear. its pressed on and will need some force to to come off. i use a centering drift in the bolt holes and work it off by hitting the ring gear in the bolt holes with the drift and a hammer. go back and forth on two opposing bolt holes to walk the ring gear off mark the two case halves then use a chisel to split the carrier case in half right behind the flange that the ring gear bolted to. knock out the roll pin that holds the cross shaft in to the carrier case. remove the cross shaft remove the spider and side gears insert the mini spool insert the cross shaft and its roll pin put case have back together. this may require some force. make sure the bolt holes are properly lined up. install the ring gear. this is a press fit and the proper way is to use a press. use a drop of red lock tite on each ring gear bolt and install it torqued to 60 ftlbs. put carrier back in the third member. put the spanners and caps back on the third member. use a drop of red lock tite on the cap bolts and make sure the bolts and there holes are oil free. torque to 40 ftlbs adjust the spanners back to the marked location and double check that the back lash is the same as before you disassembled it. clean the mating surfaces of the housing and third member thoroughly. apply a bead of silicone sealant to the housing surface and insert the third member into the housing and tighten the nuts to 25 ftlbs. install the axles, then fill the rear with gear oil. it will take about 2-3 quarts. put the drive shaft back on. do not over tighten the u joint bolts. they only need to be torqued to 15 ftlbs. use blue lock tite on the nuts to keep them from backing off. as for gear ratio. it depends on how much freeway driving your going to do. if you do allot then i would put 3.25s in. if your are only occasionally going on the freeway then 3.55s will be good. if you will hardly go on the freeway and want to be the king of stop light drags then 380s will be the way to go. as for installing them i would recommend taking it to somebody that does it regularly to do it or guide you as you do it.
How tall are your 17" tires? 3.25 might not be enough gear. On my Falcon I have 25.20" (205 60's x 15) tires with a 3.25 gear and I rev about 3300 at 75 mph. This is where I get the best mpg (19.75).
Id do the 3.50s if I was you. With an AOD myabe 3.89s but with the C$ the 3.50s will be a happy medium. Not too high on the freeway and still a noticeable different off the line.
