Differential changes

[Stephen W.]

'66 327-350 'Vert #1241-- Can gearsets in the rear end be changed (say, from 3.08 to 4.11) maintaining the same casing parts (i.e., a "stealth swap"), with no point deductions? Could positraction be added without evidence, or would O.E. diff. cases be coded posi/ no posi?






Thanks

[Wayne M.]

Re: Differential changes

Yes, the external carrier is the same; the internal posi case is different for 3-series versus 4-series gearsets. Flight judging does not look at the stamped ratio and assembly date codes on the bottom of the carrier. Nor are the casting numbers on the carrier or the rear cover judged. They are mentioned in the judging guides for reference only. The posi ratio codes are different from the non-posi ratio codes.

[Gary R.]

Re: Differential changes

Stephen,If you have a 66 open 308 diff then you can do both of what you want. Yes you can replace the open case with a posi, I just posted yesterday about the status of the good GM/Eaton posi cases becoming obsolete but you may still find some, I stocked up.If you go that route then you will have to buy spiders, cross shaft & bolt, steel thrust washed and I highly recommend prepping the case before you install it, new, used, or NOS.You can go to 411's and keep your open or new 3 series case if you use Tom's 411 gears, made for the 3 series case. I have done this many times. I have even seen NOS first design posi cases for sale but I would not use them, again unless you prep them.Once the diff is assembled you won't know what is inside. The only time that happens is if you use Tom's HD axles that are flanged.If you have any questions I can help you with just let me know.

[Martin M.]

Re: Differential changes

If you plan on doing a PV the testerwill note the discrepancy between what the car should have, and the 3:08. And... my fuelie with the 3:08 and close-ratio tranny is a dog until 3500rpm, then hold on!