The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 06-02-2015, 05:41 AM   #1
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Gearing the rear end 86 Short Bed

Hey all,
I am sure this has been asked over and over.
Family project...aka The Dark Knight. An 86 Short bed 2wd.
Boys will drive it to and from school...(Yeah right)!!!!
Its geared 3:08 and I would prefer 3:42 or 3:73 for more off the line acceleration, however, it will see mostly highway. Looking to find that sweet spot betwen fuel economy and power, so which way one to lean towards?
DarkKnight is offline   Reply With Quote
Old 06-02-2015, 09:19 AM   #2
65standard
Registered User
 
65standard's Avatar
 
Join Date: Dec 2014
Location: Coal City, IL
Posts: 695
Re: Gearing the rear end 86 Short Bed

Depends on what trans you have. If you have a turbo 350/400, I would just stick with the 3.08. If you have the 200r/700r, I would go with 3.73 gears
__________________
Tony Nicholas @ Midwest Metal Masters

1953 Chevy 3100 392 Hemi w/727 & 9” Ford
1985 Chevy C/10 6.0L 4L80 373 locker
65standard is offline   Reply With Quote
Old 06-02-2015, 10:16 AM   #3
SkinnyG
Registered User
 
SkinnyG's Avatar
 
Join Date: Feb 2012
Location: Beautiful BC, Canada, eh?!
Posts: 2,265
Re: Gearing the rear end 86 Short Bed

I have 3.07 and TH350, and do mixed city/highway on a short (15 minute) commute. I ordered 3.73, and will eventually install a 700R4. Main reason is the way I built my engine and the torque converter need more gear.

The 3.07 gears are fine on the highway, but lackluster everywhere else.

Some say that 3.42 is a good compromise if all you have is a TH350.
__________________
1961 Apache: "Grabber Orange" Shortboxed, pancake, step-notch, air-ride, turbo, LS
1977 Silverado: Shortboxed & dropped, potato-potato
V8 Pontiac Firefly (Chevy Sprint): The ultimate engine swap: 5.7L in a 1.0L bag
Lotus Super 7 Replica: Scratch-built street-legal rollerskate
SkinnyG is offline   Reply With Quote
Old 06-02-2015, 11:39 AM   #4
piecesparts
Parts and more parts
 
piecesparts's Avatar
 
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
Re: Gearing the rear end 86 Short Bed

Here is my learning curve for you to evaluate:

My son bought an 86 SWB with a 3.08 rearend gear. We changed the tranny over to a 700 R4 and the resulting RPMs cost him a lot of gas mileage. We then had RPMs so low that the engine was working harder to keep the truck moving. Gas mileage went from 14 MPG to 8 MPG. We then put a 3.73 geared rear end under the truck and now the gas mileage is back to 14 MPG. If you are putting a 3.42 or 3.73 geared rear end under the truck, I would suggest a change in tranny to an OD style to get the best optimization of your fuel. If yopu are keeping the tranny as a non-OD tranny, then do not go too deep to keep your RPMs under control. My son's truck travels down the highway at 2300 to 2400 RPMs at 70 MPH, with a 28" tall tire on it.
__________________
Frank
piecesparts is offline   Reply With Quote
Old 06-02-2015, 02:15 PM   #5
greg64
Registered User
 
greg64's Avatar
 
Join Date: Dec 2007
Location: Kimberley, BC, Canada
Posts: 799
Re: Gearing the rear end 86 Short Bed

I'd like to know the engine and trans before making a recommendation, also the tire size.
__________________
Greg
64 GMC Suburban - 283, NV3500, 14 bolt
77 C10 swb - 292, SM465, 12 bolt
greg64 is offline   Reply With Quote
Old 06-02-2015, 05:57 PM   #6
Keith Seymore
Registered User
 
Keith Seymore's Avatar
 
Join Date: May 2009
Location: Motor City
Posts: 9,226
Re: Gearing the rear end 86 Short Bed

3.42 w/o overdrive ;

3.73 w/ overdrive trans.

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/
Keith Seymore is offline   Reply With Quote
Old 06-02-2015, 07:59 PM   #7
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Thank you.
Plans are to stick the 400 we have in it, engine 350 ci.
As for tires, 15 s...but not sure yet on actual tire sizes...yet.
Truck is stripped to the frame and everything is being looked at.
Posted via Mobile Device
DarkKnight is offline   Reply With Quote
Old 06-02-2015, 10:22 PM   #8
greg64
Registered User
 
greg64's Avatar
 
Join Date: Dec 2007
Location: Kimberley, BC, Canada
Posts: 799
Re: Gearing the rear end 86 Short Bed

I've got 3.42s and a non o/d transmission (sm465). With stock tires, the combo works well. 60 mph is about 2600 rpm, and that's about as fast as I go. I'd like to have Keith's o/d transmission.
__________________
Greg
64 GMC Suburban - 283, NV3500, 14 bolt
77 C10 swb - 292, SM465, 12 bolt
greg64 is offline   Reply With Quote
Old 06-02-2015, 10:35 PM   #9
franken
Registered User
 
Join Date: Jun 2013
Location: Somewhere
Posts: 3,123
Re: Gearing the rear end 86 Short Bed

The 1:1 trans and ~3:1 rear gives you a compromise at both around town and freeway driving.
If you go to a lower rear, you'll be sad on the freeway.
Get an OD trans and a low 3.73/4.10 rear and you're happy but can't buy food.
A TH400 is a great trans but ~30% power loss in a 350 truck is asking to be disappointed w/ power.
franken is online now   Reply With Quote
Old 06-03-2015, 12:44 AM   #10
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Thanks again all!
Posted via Mobile Device
DarkKnight is offline   Reply With Quote
Old 06-03-2015, 06:32 AM   #11
D13
Registered User
 
D13's Avatar
 
Join Date: Feb 2007
Location: Memphis MI
Posts: 1,851
Re: Gearing the rear end 86 Short Bed

wait... you want your teenager to have more acceleration and tire spinning capability?
GM built millions of 3.08 geared trucks (like almost all V-6 and 6.2 diesels).
Think of your motor's cam range, aim for the bottom end of the torque curve at normal driving (so on my motors it's 1650 at 55, ~2000 at 70), then run the gear / tire calculators to find the optimum gear for MPG. Then decide how much you want to trade off for performance.
As a point of reference my 77 has manual trans and 2.73's, my 87 has 700R4 and 3.08's, my 3/4 ton has really tall tires and 3.43's and even with the 250/3OTT will pull anything but is not happy over 60mph.
__________________
1987 2 ton
1982 250/TH350 beater in progress
Dad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrapping
Plus a mess o' tractors
D13 is offline   Reply With Quote
Old 06-03-2015, 07:19 AM   #12
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Re: Gearing the rear end 86 Short Bed

Posted via Mobile Device
DarkKnight is offline   Reply With Quote
Old 06-03-2015, 07:21 AM   #13
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Re: Gearing the rear end 86 Short Bed

Well...that's what the other half is saying....until she sees the bill to put this truck back together..haha...my bet is they drive my current 2012...
Appreciate everyone's input.
If I remember...didn't GM make a 3:23 gear as well?
Posted via Mobile Device
DarkKnight is offline   Reply With Quote
Old 06-03-2015, 11:44 AM   #14
wilkin250r
Registered User
 
wilkin250r's Avatar
 
Join Date: Sep 2010
Location: Lake Tahoe, Nevada
Posts: 755
Re: Gearing the rear end 86 Short Bed

Quote:
Originally Posted by DarkKnight View Post
Thank you.
Plans are to stick the 400 we have in it, engine 350 ci.
As for tires, 15 s...but not sure yet on actual tire sizes...yet.
You don't have an exact tire size, but you have an IDEA, correct? Is your truck essentially stock suspension and tire size, around 31 inches tall? Or is it lifted, maybe 33~35" or bigger? Is it lowered? (which could either be bigger, or smaller tires, depending on the look you're going for)

I believe most of the replies in this thread are based on the assumption of stock tire size around 31 inches tall. You might not know your exact tire size, but if you're lifted or lowered, let us know so we can answer you accordingly.
__________________
I know a little about cars, but if you have a question about electricity or sport quads, I'm your man!!!
wilkin250r is offline   Reply With Quote
Old 06-03-2015, 08:50 PM   #15
DarkKnight
Registered User
 
Join Date: May 2015
Location: Wittmann, AZ
Posts: 18
Re: Gearing the rear end 86 Short Bed

For now it will be mostly stock height, so yes, around 31 in tires...Thank you all again
Posted via Mobile Device
DarkKnight is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 09:06 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com