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 > General Truck Forums > Engine & Drivetrain

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 06-18-2018, 02:26 PM   #1
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
posi rear end gears

My 87 Silverado is finished except for the posi rear end. I have the 350 engine with the 4 speed (overdrive) transmission that came in it. The right rear tire will light up but the drivers side doesn't. Some tech lines say 373 is best all round.I'm not racing it. Just a cruiser but would like both tires to spin and get reasonable mileage. What are other 350 guys installing that fits the bill.
Thanks,
Eric
my project can be viewed at :
https://www.fuelcurve.com/1987-chevy-c10-pickup/
Erix is offline   Reply With Quote
Old 06-18-2018, 02:47 PM   #2
YoungPup1977
Registered User
 
YoungPup1977's Avatar
 
Join Date: Jun 2015
Location: LAME ASS FORUM !!!!!!!!
Posts: 550
Re: posi rear end gears

If you have a true posi differential than I would think both tires should lay down the rubber....if you dont, you can add the posi carrier without replacing the gears...Good luck on smokin both tires !!!!!
YoungPup1977 is offline   Reply With Quote
Old 06-18-2018, 11:38 PM   #3
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 21,545
Re: posi rear end gears

Beautiful truck!

What gears will partly depend on what the diameter is of your rear tires and what you want out of a gear change. Are you looking for better performance or lower RPM's at highway speeds? Lower rpm's don't always mean better MPG's. The engine needs to run in it's 'sweet spot' for best efficiency.
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 06-19-2018, 02:11 PM   #4
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

I have 20Ē Mickey Thompson tires ! All I want to do is spin both tires. I can live with current gears. Thanks !!!
Erix is offline   Reply With Quote
Old 06-19-2018, 11:33 PM   #5
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 21,545
Re: posi rear end gears

20" diameter tires..........what are those on 13" wheels?

Quote:
Originally Posted by Erix View Post
I have 20” Mickey Thompson tires ! All I want to do is spin both tires. I can live with current gears. Thanks !!!
If you want a posi, then you will have to either install one or have it installed.
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 06-20-2018, 03:06 AM   #6
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Quote:
Originally Posted by Captainfab View Post
20" diameter tires..........what are those on 13" wheels?



If you want a posi, then you will have to either install one or have it installed.
Sorry !!! My wheels are 20ís on rear and 18ís on front!
Erix is offline   Reply With Quote
Old 06-20-2018, 03:11 AM   #7
toolboxchev
Registered User
 
Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 1,535
Re: posi rear end gears

Get a Detroit True Track...Eaton brand.
toolboxchev is offline   Reply With Quote
Old 06-20-2018, 03:46 AM   #8
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Quote:
Originally Posted by toolboxchev View Post
Get a Detroit True Track...Eaton brand.
Thank you very much !!
Erix is offline   Reply With Quote
Old 06-20-2018, 11:40 PM   #9
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 21,545
Re: posi rear end gears

The OUTSIDE diameter of the rear tires is what is needed to determine the optimum gear ratio for the desired usage, not the wheel diameter. Your original post sounded like you were wanting a gear change also.


Quote:
Originally Posted by Erix View Post
Sorry !!! My wheels are 20’s on rear and 18’s on front!
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 06-21-2018, 03:26 AM   #10
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Quote:
Originally Posted by Captainfab View Post
The OUTSIDE diameter of the rear tires is what is needed to determine the optimum gear ratio for the desired usage, not the wheel diameter. Your original post sounded like you were wanting a gear change also.
Iím open to change gear size if it would help but if I can posi what I have, thatís fine too. Iím trying to determine whats the best approach at this point.
Thank you for helping !
Erix is offline   Reply With Quote
Old 06-21-2018, 09:58 AM   #11
b454rat
Senior Member
 
Join Date: May 2004
Location: Binghamton, NY
Posts: 3,004
Re: posi rear end gears

I’d say 3.73s maybe 4.10s. With either gear the drivetrain won’t be working as hard, so tho seems backwards but would get better mileage, while having fun at the same time lol...
b454rat is offline   Reply With Quote
Old 06-21-2018, 10:21 AM   #12
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Quote:
Originally Posted by b454rat View Post
Iíd say 3.73s maybe 4.10s. With either gear the drivetrain wonít be working as hard, so tho seems backwards but would get better mileage, while having fun at the same time lol...
Thank you !!
Erix is offline   Reply With Quote
Old 06-21-2018, 10:50 PM   #13
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 21,545
Re: posi rear end gears

What gear ratio do you currently have?

Quote:
Originally Posted by Erix View Post
Iím open to change gear size if it would help but if I can posi what I have, thatís fine too. Iím trying to determine whats the best approach at this point.
Thank you for helping !
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 06-22-2018, 12:48 AM   #14
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Quote:
Originally Posted by Captainfab View Post
What gear ratio do you currently have?
Iím not sure. The label in the glove compartment door indicates GU2
Erix is offline   Reply With Quote
Old 06-22-2018, 09:45 AM   #15
b454rat
Senior Member
 
Join Date: May 2004
Location: Binghamton, NY
Posts: 3,004
Re: posi rear end gears

Believe that is 3.23.....
b454rat is offline   Reply With Quote
Old 06-22-2018, 09:46 AM   #16
b454rat
Senior Member
 
Join Date: May 2004
Location: Binghamton, NY
Posts: 3,004
Re: posi rear end gears

Wow, it’s 2.73s.....
b454rat is offline   Reply With Quote
Old 06-22-2018, 12:20 PM   #17
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

Thank you b454rat ! Should I just do the locker on those gears or change. If change to what & why ?
Erix is offline   Reply With Quote
Old 06-22-2018, 08:23 PM   #18
b454rat
Senior Member
 
Join Date: May 2004
Location: Binghamton, NY
Posts: 3,004
Re: posi rear end gears

Change the gears for sure!!!! At least 3.73s. Any posi that isn't the grenade lock.
b454rat is offline   Reply With Quote
Old 07-01-2018, 01:18 PM   #19
toolboxchev
Registered User
 
Join Date: Jul 2015
Location: 2nd left past the stump on a dirt road.
Posts: 1,535
Re: posi rear end gears

If you go from 2.73 to 3.73 gears your going to kill any mileage you got from that thing. It would dramatically change they way they whole drivetrain responds to the engine. I would bet that thing is a dog right now with those gears.
toolboxchev is offline   Reply With Quote
Old 07-01-2018, 03:21 PM   #20
weq92f
Registered User
 
Join Date: Oct 2016
Location: Dallas Texas
Posts: 1,131
Re: posi rear end gears

That is a very nice looking square body right there! If you really do have 2.73 out back and a standard 700r, 1st gear off the line is probably OK, but 2nd gear must be a let down ( I'm thinking WOT here ).

If you don't want to change your current mileage/driving characteristics, don't change the gear ratio.

If you want to change the way your truck gets down the road and/or increase the fun factor stop light to stop light, change the gear ratio.

I would first make sure you know what you have currently. Determine that for certain then decide what you want to do with respect to the ratio.

-klb
__________________
67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi
07 335 sport turbo 6sp
94 Trans Am GT LT1 6sp posi -- sold after 22yrs
99 540 sport V8 6sp -- sold
73 240z L24 4sp -- given to friend
68 C10 step 350/350 3.73 open -- sold
weq92f is offline   Reply With Quote
Old 07-01-2018, 03:53 PM   #21
Erix
Registered User
 
Join Date: Jun 2018
Location: Charlotte
Posts: 14
Re: posi rear end gears

The glove compartment sticker is:
Attached Images
 
Erix 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 12:29 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013 67-72chevytrucks.com