Rearend gear ratios 1980-1987 most common

[DoubleDingo]

My '81 C20 has 4.10. When I had my dad's '79 GMC K15 it had either 3.73 or 4.10. I think 3.73 because it didn't rev as high at 60 mph. The lower revs were not because of bigger tires.

 

[TPISly-C10]

mine OEM Diesel 1986 C10 is GU6 3.42 that i keep for my LS 4L80E swap!

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[Rusty Nail]

I guess 3.08

 

[Curt]

1/2 tons came with 3.73 and down (numerically)with automatics.All of the 1/2 tons and higher rated pick ups with manual trans usually has 4.10s.K-30’s are the only pickups I see with 4.56 from the factory,but not often.

More people use to order their trucks back then,so it changes things up.

 

[MikeB]

My 82 C10 had a 250 six with 3-speed manual and 2.73 axle. Not at all suitable with the 250 six, but works well behind a 350/TH350 that occasionally sees 65-70 mph freeway speeds.

My 81 C10 had a 305 with TH350C and 2.56 axle. What a slug that thing was in 4th gear with the T/C locked-up!

I think both of these ratios were standard for those engine/trans/year models, because axle ratios weren't listed as an option on the glove box stickers.

 

[mlparkey]

My 1986 C10, 350/700R4 has a 3.08. My 1976 C10, 350/T350 had a 3.73.

 

[Keith Seymore]

Sorry - just now seeing this.

I always ordered a 3.42 with a non overdrive transmission. Always ordered 3.73 when I had an overdrive. They provided a nice balance between off the line pep and highway fuel economy.

The bulk of dealer stock vehicles had higher axles (lower numerically - like 3.08) than that which is why I was considered a crazy person for ordering those "more aggressive" ratios.

K

 

[78C10BigTen]

Sorry - just now seeing this.

I always ordered a 3.42 with a non overdrive transmission. Always ordered 3.73 when I had an overdrive. They provided a nice balance between off the line pep and highway fuel economy.

The bulk of dealer stock vehicles had higher axles (lower numerically - like 3.08) than that which is why I was considered a crazy person for ordering those "more aggressive" ratios.

K

My 78 c10 came with 3.08's behind a th350 and now it has a 3.42 behind the same th350.

 

[Drauka99]

My 81 C10 had a 305 with TH350C and 2.56 axle. What a slug that thing was in 4th gear with the T/C locked-up!

My 81 had a 305 with MY6.... 2.56 axel as well. Was a dog in 4/OD, lost speed in 4th unless is was a steep downhill grade.

 

[Bextreme04]

My 74 C20 had 4.56 behind a 350/TH350. My 80 K25 has 4.10 behind a 350/TH400

 

[Old60Driver]

My 83 K20 has 4.56 behind a 350/TH400

 

[Big Ray]

Dad's 87 R10 with 305, th350c had 2.73 in it.
His 86 K5, 305, 700r5 had 3.08.
He always bought the ones no one else bought. He just didn't know better didn't either at the time, I was off doing the Harley thing.

 

[Hunter79764]

1987 K20 Suburban (ok, V20...) 3.73 with TH400
73 C20 pickup (grandpa's old one) 4.10 with 3 speed +granny gear
74 K5 and 78 C10, both with TH350 I think, not a clue on either.

 

[RetroC10Sport]

Every square ive had that wasnt a 4wd after 81 had 3.08
My 82 350/350th 84 305/700r4 86's 350/350th
This leads me to think that 3.08 was super popular in 80's due to cafe regulations saying that a certain number of vehicles had to meet mpg rules. One was an hd optioned truck(stiffer front springs,7 leaf rear,bigger brakes etc.) and still had 3.08

Both my pre 80's 2wd(76-78) were 3.73 as well as my 82 4wd.

So just from that id say 3.08 or god forbid 2.7x. My brother has an 86 silverado with th350 and 2.7x and its a turd

Growing up, we had a lifted K10 on 38s that had 2.56s. That truck was ungodly slow.

 

[Hunter79764]

My 85 Monte Carlo has 2.14's. Even with short 225/70R14's, the TH350 shifts out of first at about 78 mph or so. I tell people its basically a 4 speed car that's missing 1st gear...