04-16-2018, 10:41 AM | #1 |
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Join Date: Nov 2011
Location: Port St. Joe Fl.
Posts: 491
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Posi Rear End
I want to switch my 10 bolt stock rear gear to a slip posi. and was wondering how many teeth are on the rear axles so I get the correct Differential (30 or 33)? The one that's in the truck is a 2.73. and with my motor I get no traction so I'm hoping the posi will help.
Should I go for the Posi 2.73? I only get 8 mpg as it is. 1985 Silverado 383 Stroker 425HP+ TH 350 B&M shift 12" wide rear tires |
04-16-2018, 11:09 AM | #2 |
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Join Date: Dec 2014
Location: Northern California
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Re: Posi Rear End
Factory rear I believe is 28 spline. Only way to know for sure will be to pull an axle and count, as who knows what’s been changed in 30+ years.
As for gearing, you may want to actually consider stepping to a lower gear. Depending on cam and engine specs, you could be below the engines power band. You could actually see an increase in mileage with lower gears. |
04-16-2018, 11:17 PM | #3 |
60-66 Nut
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,246
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Re: Posi Rear End
If your 383 is a true 425hp, you definitely need a lower gear than 2.73. You're never going to get good mpg's with 425hp pushing a brick down the road, but you should be able to get over 10 mpg.
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Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE |
04-17-2018, 04:20 PM | #4 |
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Location: Port St. Joe Fl.
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Re: Posi Rear End
maybe a 3.73?
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04-18-2018, 12:33 AM | #5 |
60-66 Nut
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
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Re: Posi Rear End
Possibly. It depends on how your engine is built. What cam is in it? Do you have a stall converter? What size are your rear tires?
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Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE |
04-18-2018, 09:18 PM | #6 |
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Join Date: Nov 2011
Location: Port St. Joe Fl.
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Re: Posi Rear End
Rear Rims 18x9.5"
Tires 235/50R18 2500 stall converter on a new TH 350 B&M shift kit tranny. |
04-19-2018, 12:18 AM | #7 |
60-66 Nut
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,246
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Re: Posi Rear End
OK, your tires are only 27.3" in diameter and that cam is somewhat mild for a 383. I would probably go with a 3.07 gear. That will keep your rpm's reasonable at highway speeds plus it should help with the mpg's and possibly help a little with the traction issue. Of course a posi will also help with the traction issue. That would be my recommendation. You could go with 3.42 gears, but that is going to raise your highway rpm's a bit.
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Power Steering Box Adapter Plates For Sale HERE Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE Hydroboost Mounting Plates HERE |
04-19-2018, 12:16 PM | #8 |
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Join Date: Nov 2011
Location: Port St. Joe Fl.
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Re: Posi Rear End
Thanks Cap.
I loved your town when I lived in Spokane. Used to go down under the freeway bridge and jump off the cliffs. Fun days in 80 to 84. |
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