Any guesses on the ratio?

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

mr4454

Full Access Member
Joined
Oct 18, 2018
Posts
56
Reaction score
17
Location
Las Vegas
First Name
Alan
Truck Year
1978
Truck Model
K10
Engine Size
350
Hello all,
I have a 12 bolt rear end I took the cover off and counted 40 teeth on the ring but was unable to count the pinon. any ideas what my gear ratio would be? Hope the photos will help. its 1978 k10 4x4
Thank you all, and have a great weekend

You must be registered for see images attach


You must be registered for see images attach


You must be registered for see images attach
 

Arkansas_V8

Proud Redneck
Joined
Jul 1, 2019
Posts
3,022
Reaction score
3,961
Location
Springdale, Arkansas
First Name
Brent
Truck Year
88
Truck Model
V20 Suburban
Engine Size
5.7
Just a guess. 3.08

Arent they usually marked somewhere with the gearing?

Check the outer part of the ring gear for the numbers. Some are marked.

Sorry been a while since I have done it.
 
Last edited:

Arkansas_V8

Proud Redneck
Joined
Jul 1, 2019
Posts
3,022
Reaction score
3,961
Location
Springdale, Arkansas
First Name
Brent
Truck Year
88
Truck Model
V20 Suburban
Engine Size
5.7
If its marked it will be to the left of that yellow line on the ring.
You must be registered for see images attach
 

legopnuematic

Licensed Junk Dealer
Supporting Member
Joined
Oct 27, 2016
Posts
1,710
Reaction score
3,662
Location
MO
First Name
Spencer
Truck Year
1971, 1̶9̶7̶4, 1976, 1979,1̶9̶8̶5, 2002
Truck Model
Dart Swinger, Sierra 10, C10 Cheyenne, C10 Big Ten, Silverado 10, Ram 2500
Engine Size
225/6, 350 c.i., 350 c.i., 5.9l Cummins
3.07 is 14:43
You must be registered for see images attach


Sent from my Moto Z (2) using Tapatalk
 

mr4454

Full Access Member
Joined
Oct 18, 2018
Posts
56
Reaction score
17
Location
Las Vegas
First Name
Alan
Truck Year
1978
Truck Model
K10
Engine Size
350
awsome thanks for the info, if it's not marked then what do I do?
 

CSFJ

-----------------
Supporting Member
Joined
Jul 1, 2014
Posts
6,160
Reaction score
5,162
Location
------
First Name
-------------
Truck Year
-------
Truck Model
-------
Engine Size
-------
The picture you posted shows 14:43. Divide the 43 by 14 and you get 3.07xxxx.
 

Arkansas_V8

Proud Redneck
Joined
Jul 1, 2019
Posts
3,022
Reaction score
3,961
Location
Springdale, Arkansas
First Name
Brent
Truck Year
88
Truck Model
V20 Suburban
Engine Size
5.7
The picture you posted shows 14:43. Divide the 43 by 14 and you get 3.07xxxx.

Legopnuematic posted that to show mr4454 where the numbers may be. If he saw a picture I didn't with numbers, then I apologize.
 

CSFJ

-----------------
Supporting Member
Joined
Jul 1, 2014
Posts
6,160
Reaction score
5,162
Location
------
First Name
-------------
Truck Year
-------
Truck Model
-------
Engine Size
-------
Legopnuematic posted that to show mr4454 where the numbers may be. If he saw a picture I didn't with numbers, then I apologize.
Lol. I wasn't paying attention. Though that was the OP's pic.
 

C10MixMaster

Full Access Member
Joined
Dec 6, 2016
Posts
756
Reaction score
1,420
Location
Kingman AZ
First Name
Ben
Truck Year
1977
Truck Model
C10 BIG10
Engine Size
ZZ4 350
awsome thanks for the info, if it's not marked then what do I do?

its an open rear end so

1 chalk front wheels
2 jack up 1 rear wheel
3 pick a reference point on the wheel you jacked up such as a wheel weight or letter on the tire
4 spin the wheel until the reference point is down
5 mark the drive line on the bottom
6 spin the drive line counting the revolutions of the drive line until the TIRE has gone around TWICE and is in its original starting place
7 if ithe drive line spun
3 plus a smidge = 3.08
3 plus 1/4 = 3.23
3 plus almost 1/2 = 3.42
3 plus 3/4 = 3.73
4 plus a smidge = 4.11
 

Keith Seymore

Full Access Member
Joined
Jul 13, 2015
Posts
2,609
Reaction score
8,018
Location
Motor City
First Name
Keith Seymore
Truck Year
1987
Truck Model
R10
Engine Size
4.3L
Hello all,
I have a 12 bolt rear end I took the cover off and counted 40 teeth on the ring but was unable to count the pinon. any ideas what my gear ratio would be? Hope the photos will help. its 1978 k10 4x4

The only axle I see available with 40 teeth on the ring gear is a 3.08 (40/13= 3.08)

https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1978-Chevrolet-Truck.pdf (page 128)

You should be able to see at least one tooth on the pinion. The trick is to mark it with crayon/paint and rotate the pinion slowly, counting until that tooth comes back into view. (You won't be able to see all the pinion teeth at the same time).

K
 
Last edited:

Keith Seymore

Full Access Member
Joined
Jul 13, 2015
Posts
2,609
Reaction score
8,018
Location
Motor City
First Name
Keith Seymore
Truck Year
1987
Truck Model
R10
Engine Size
4.3L
If you have a 305 motor,3.08s.Look in the glove box,should be a code build sheet in there.

305 cu in engine not available in a '78 K10, per the link I attached.

While checking the SPID label is an excellent idea, if it is the base ratio then it won't help much. It will show as "GQ1 - Base axle" but not define what ratio that is (because it changes, based on the powertrain charts).

If it is an optional ratio then it will go ahead and give the RPO and the corresponding ratio (ie, "GT4" - 3.73 axle").

K
You must be registered for see images attach


You must be registered for see images attach
 
Last edited:

4WDKC

Full Access Member
Joined
Jan 27, 2016
Posts
2,366
Reaction score
1,090
Location
Southern Florida
First Name
Kacy
Truck Year
1987
Truck Model
V10
Engine Size
350
305 cu in engine not available in a '78 K10, per the link I attached.

While checking the SPID label is an excellent idea, if it is the base ratio then it won't help much. It will show as "GQ1 - Base axle" but not define what ratio that is (because it changes, based on the powertrain charts).

If it is an optional ratio then it will go ahead and give the RPO and the corresponding ratio (ie, "GT4" - 3.73 axle").

K
You must be registered for see images attach


You must be registered for see images attach


these also assume the axle hasnt been swapped.. getting the numbers off the ring gear is the best option.
 

Forum statistics

Threads
41,859
Posts
903,686
Members
33,372
Latest member
83elcowes
Top