Got around to my installation yesterday. The gasket listed for the rear axles is not correct even though it cross references through the Felpro catalog. The two gaskets for the differential are correct.
Several posts have inquired about actual performance increases when looking to increase top end. For those interested in my field test results...
Testing was done using a GPS and calibrating MPH on the GPS to the reading on my speedo.
Switching my '57 3600 from STA Super Transport 8x17.5 bias plies to Bridgestone 8R19.5 12 ply radials gave me a pick up of 10% MPH. (Good luck finding the 19.5" rims!) I anticipated an increase of 7.5% when I did the calculations based on published tire specs by both manufacturers (based on the difference in circumference), but actual increase was 10%.
Changing my 4.56 rear end to a 4.10 gave me another 10%, exactly as the math indicated that it would.
Independently, either of these alterations would pick up 10%. Doing both gives a compounding effect and actually picks up 21%.
Before the change, my comfortable highway cruising speed was 52 MPH. I can now run 63 at the same tachometer reading.
Thank you to Denny Graham for his postings on the pumpkin conversion. He gave me the courage to give it a try. (If the pumpkins weighed about 20 pounds instead of over 100, this would be a piece of cake!) And thank you to Steve Reid for selling me his extra 4.10 and the fifth 19.5" rim so that I could mount a spare under the truck.
By the way, if you convert to 19.5's and your spare is currently a 17.5 with the factory under-bed mount, anticipate having to adapt mount. (I discovered this when my new spare wouldn't fit.) The adjustable smaller cleat will need to be pushed out one set of holes and the non-adjustable larger cleat will need to be nipped 1" on each side (a 45 degree cut worked fine). This will keep the spare centered and the 19.5 will just barely fit between the spring shackles.
Peace,
Maybellene
