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| | | | Joined: Feb 2020 Posts: 22 'Bolter | | 'Bolter Joined: Feb 2020 Posts: 22 | Would appreciate some thoughts on rear axle gears. Current rear gears are 3.55 with a Muncie 420 behind a mildly warmed over 235. Taking off in 2nd (3.57) winds out pretty quick before shifting. I just picked up a TKO600 with the 2.87 first gear and the .82 OD that's gonna run back into a Camaro 10 bolt. Should I stick with the 3.55's or would 3.42's be ok. I don't want to ask too much from the engine and clutch taking off in first gear........or am I just making a big deal out of nothing? | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | I think the 3:55 would be just right for that.
George
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | The difference between 3.55 and 3.42 is so small, one probably couldn’t tell the difference.
Stick with what is in there.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Jul 2000 Posts: 2,191 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,191 | I have a 51 3100 fully restored. The engine is a 235 and the numbers say it's a 58-62 block. I have an SM420 bolted behind it, torque tube rear with the 3.55 setup. The truck has 15 inch wheels with P225x75 tires in the rear. She runs like a dream....up to 50 mph. It would be nice to at least go 55-60 if I get on the highway to go somewhere. If I bump up to 16 inch wheels and tires is that gonna give me 5-10 mph more? Should I go with a "regular" 4 speed, open rear end with lower gears? If so, what easily swapped 4 speed and rear end would you graduates of Truckology recommend? Thanks for any and all ideas.
Bodini Do you have a Camaro rear end or are you shopping for one? Camaro rear ends came with a variety of gears including 3.55 and 3.42 depending on the year, engine and transmission. Camaro web sites have info on how to ID a rear end.
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Always tell us what year and model truck you're working on. Thanks, Mike B  | | | | | Joined: Mar 2014 Posts: 4,483 Moderator, Electrical Bay | | Moderator, Electrical Bay Joined: Mar 2014 Posts: 4,483 | The 3.55 with a 2.87 first will give you a starting line ratio of 10.18. The 3.42 and a 2.87 first is a slr of 9.81. If you're planning on using it as a pickup, I would leave the 3.55 in there. 10.18 is ok for a 235 but honestly speaking that ratio is just barely ok if you're hauling anything heavier than a sheet of plywood and a few 2 x 4s. GM wanted a starting line ratio of 12.08 for the 235 in a 1/2 ton pickup. I would not consider any ratio below 10 unless I had a strong V8 and was setting up to drag race and even then not with a standard transmission. Good luck.
~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
| | | | | Joined: Feb 2020 Posts: 22 'Bolter | | 'Bolter Joined: Feb 2020 Posts: 22 | Thank you gentlemen. The truck is a 1951 3 window 3100. I picked up the 1978 Camaro rear from a salvage yard and plan on having it rebuilt so no worries in the future. Looks like I'll stick with a 3.55 setup. I don't plan on putting anything in the bed except for a couple lawn chairs when I go to a show. | | | | | Joined: Mar 2019 Posts: 119 'Bolter | | 'Bolter Joined: Mar 2019 Posts: 119 | I agree that in your situation the difference between 3.55 and 3.42 is minimal. That is less that 4% difference in driveshaft speed at any road speed. You can get that much difference just due to the different diameters of the various brands for tires in the same nominal size. I doubt if anyone driving a vehicle could tell the difference.
So take the easier/lower cost/less risk route!
Rusty
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