3.42 ratio rearend - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**spudder** · 03-20-2019, 08:56 AM

Want to change rearend in my truck. Have 7000r4 tone know where I might find a 3.42
Rearend close to Effingham, Illinois..

**kwmech** · 03-20-2019, 11:01 AM

Soooo...what rear do we have? why not just change the gears

Keith Seymore · 03-20-2019, 01:30 PM

I would recommend a 3.73 ratio with the 700R4.

K

Ski-me · 03-20-2019, 01:38 PM

Quote:

Originally Posted by Keith Seymore

I would recommend a 3.73 ratio with the 700R4.

K

Agreed, minimum 3.73.

**mongocanfly** · 03-20-2019, 01:48 PM

i also agree with Keith...3.73s....but also ,what size tires are you running?

**jocko** · 03-20-2019, 09:03 PM

Spudder, 3.42 and 700R4 may result in too low of rpm at lower highway speeds - lugging would be possible. What diameter tire do/will you have and what’s your current rear gearing? 3.73 really is the sweet spot for an o/d trans. Even a 4.10 is probably preferable to 3.42 unless you’re trying to break a land speed record. But agree with all the above folks - there’s a reason GM put 3.73s in the vast majority of their 1/2 tons in the 90s and 2000s.

cerial · 03-20-2019, 09:52 PM

Mine 87 has a 5.7, 700, with 3.42 ratio running 235/75/r15 tires.

It depends on what you use the truck for. Most of the time I am putting along coasting a majority of the time with next to no rpms. But I can always drop the thing into direct and drive that way.

If your towing 3.42 gears come in handy by not using overdrive unless your on flat ground. Run around 2500 at 65mph in direct. Which is about as much wind as I want to push.

That being said they came with the truck and I am only running 30" tires. Bigger tires require more gear.

Greenlee · 03-20-2019, 10:31 PM

My ‘87 4x4 came with 3.42’s and 700r4 also. I ran 31” tires with that combo. I would have preferred 3.73’s, but the 3.42’s did fine.

**spudder** · 03-21-2019, 09:05 AM

Thanks guys for your replies. I have had several trucks with 3.42 gears and always liked that gear. Never ran oversized tires. I now have two later 2 door Tahoes, one with 3.42 and the other with 3.73. I like both of them!
Have a project '64 pickup with a 700R4 and want to use a square body rearend in it. Just got home from Arkansas and could not find any square body 3.42 or 3.73 rears. Can't believe how the stuff has dried up!
I think I need a rearend out of a '83 to '87 C10 or '83 to '91 in Suburban with 700R4.
Any help locating a rearend close to home would be appreciated.

03-20-2019, 08:56 AM	#1
spudder Active Member Join Date: Aug 2012 Location: Central Illinois Posts: 103	3.42 ratio rearend Want to change rearend in my truck. Have 7000r4 tone know where I might find a 3.42 Rearend close to Effingham, Illinois..

03-20-2019, 11:01 AM	#2
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,390	Re: 3.42 ratio rearend Soooo...what rear do we have? why not just change the gears

03-20-2019, 01:30 PM	#3
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,149	Re: 3.42 ratio rearend I would recommend a 3.73 ratio with the 700R4. K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/

03-20-2019, 01:48 PM	#5
mongocanfly Post Whore Join Date: May 2015 Location: Alabama Posts: 14,585	Re: 3.42 ratio rearend i also agree with Keith...3.73s....but also ,what size tires are you running? __________________ Mongo...aka Greg RIP Dad RIP Jesse 1981 C30 LQ9 NV4500..http://67-72chevytrucks.com/vboard/s...d.php?t=753598 Mongos AD- LS3 TR6060...http://67-72chevytrucks.com/vboard/s...34#post8522334 Columbus..the 1957 IH 4x4...http://67-72chevytrucks.com/vboard/s...63#post8082563 2023 Chevy Z71..daily driver

03-20-2019, 09:03 PM	#6
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,934	Re: 3.42 ratio rearend Spudder, 3.42 and 700R4 may result in too low of rpm at lower highway speeds - lugging would be possible. What diameter tire do/will you have and what’s your current rear gearing? 3.73 really is the sweet spot for an o/d trans. Even a 4.10 is probably preferable to 3.42 unless you’re trying to break a land speed record. But agree with all the above folks - there’s a reason GM put 3.73s in the vast majority of their 1/2 tons in the 90s and 2000s.

03-20-2019, 09:52 PM	#7
cerial Registered User Join Date: Mar 2014 Location: Ionia, MI Posts: 199	Re: 3.42 ratio rearend Mine 87 has a 5.7, 700, with 3.42 ratio running 235/75/r15 tires. It depends on what you use the truck for. Most of the time I am putting along coasting a majority of the time with next to no rpms. But I can always drop the thing into direct and drive that way. If your towing 3.42 gears come in handy by not using overdrive unless your on flat ground. Run around 2500 at 65mph in direct. Which is about as much wind as I want to push. That being said they came with the truck and I am only running 30" tires. Bigger tires require more gear. __________________ 1991 Metro commuter 1991 s10 future project truck 1987 V10 backup daily/junk truck 1985 K20 Winter beater 1991 R30(squarebody) c/c flatbed towrig 1994 s10 80"wb custom build

03-20-2019, 10:31 PM	#8
Greenlee Registered User Join Date: Jun 2004 Location: El Lago, TX Posts: 1,668	Re: 3.42 ratio rearend My ‘87 4x4 came with 3.42’s and 700r4 also. I ran 31” tires with that combo. I would have preferred 3.73’s, but the 3.42’s did fine.

03-21-2019, 09:05 AM	#9
spudder Active Member Join Date: Aug 2012 Location: Central Illinois Posts: 103	Re: 3.42 ratio rearend Thanks guys for your replies. I have had several trucks with 3.42 gears and always liked that gear. Never ran oversized tires. I now have two later 2 door Tahoes, one with 3.42 and the other with 3.73. I like both of them! Have a project '64 pickup with a 700R4 and want to use a square body rearend in it. Just got home from Arkansas and could not find any square body 3.42 or 3.73 rears. Can't believe how the stuff has dried up! I think I need a rearend out of a '83 to '87 C10 or '83 to '91 in Suburban with 700R4. Any help locating a rearend close to home would be appreciated.



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