1970 w31 rear gears
#1
1970 w31 rear gears
I have a 1970 cutlass W-31, It has a 3.91 rear end with the 3 spd auto trans. What would be a good gear to put in rear end if i'm putting 275/45/18 wheels and tires on it. It screams on the highway currently, so I want to make it alittle more highway friendly with out losing to much snap! Thanks!
#2
gears
Your only option is 3.42s if you want to reuse your existing posi carrier. Also they must be OEM 3.42s as the Richmond 3.42s are designed for the 3.08-3.23 carrier.
If you find OEM 3.42s & want to sell your 3.91s & they are in good shape with a nice pattern I would be interested in buying them. Shipping would be to Sweetgrass MT 59484 for p/u @ the border.
If you find OEM 3.42s & want to sell your 3.91s & they are in good shape with a nice pattern I would be interested in buying them. Shipping would be to Sweetgrass MT 59484 for p/u @ the border.
#3
Measure the diameter of the tires you intend to run on the rear, find your target cruise rpm, and plug the numbers into the rpm calculator. Usually anywhere between 2100-2300 rpm @65/70 mph is comfortable cruising for many folks.
http://www.csgnetwork.com/multirpmcalc.html
http://www.csgnetwork.com/multirpmcalc.html
#4
It's worth noting that in 1970, the standard rear end for a W-31 was 3.91, and the factory wouldn't even let you order anything lower (numerically) than 3.42.
Franky, if you want low RPM on the highway you shouldn't be driving a W-31.
#6
I bet funkwagon meant 3100-3300, which is pretty close to the RPM's you will see with that tire/rear end combo at ~65MPH. No big deal other than MPG unless you do a lot of highway miles at higher speeds. Enjoy it for what it is (a freakin' W31!), get an OD tranny or start looking for a SX/turnpike cruiser.
#7
Actually I did mean 2100/2300, I am spoiled with overdrives though. BlackGold's comments are merited, I just have the tendency to factor the 0.68 into my personal rpm comfort zone. Although a 3:08 would drastically help the drivability on the highway, the cost and availability of the gears and carrier would be significant financially as well as effort. Personally before I altered the gear arrangement, I think that (like dmullin) the overdrive would be the easiest solution to "have your cake and eat it too". Just store the original gearbox and driveshaft for originality's sake. I have a 3:08 in my '70 as well as a fresh 3:42 ready to install, but am waiting to have a 700R4 built before I do the rear swap. To each his own..
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