What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Differential question

Chevk587

Chevk587

Whiskey bent & Hell bound
 Premium
GMOTM Winner
Joined
Feb 8, 2015
Posts
1,068
Reaction score
1,032
Location
California
What's up guys new to the forum have some questions about gearing I just got my hands on a sweet twelve bolt what's a good gear to run??? It's an 87 blazer so it has od I won't be doing a lot of off roading but some moderate stuff I drive it every day any suggestions ??? Also what front gears should I run to coinside with the rear thanks for the replys in advance!
 
Front and rear gears need to be the same.

All depends on tire size.

A standard size is 33" tires and 3.73 gears if you are just using it for dd/weekend wheeler IMO.
 
4.56's for street or trail on 35's. It's always better to be a little low in case you decide to do some towing or put a sleeping deck or something in the back. It's a vehicle designed in the early 70's with the aerodynamics of a brick wall, so a few extra RPM on the interstate isn't going to hurt anything and the extra gearing will be nice when you're creeping around in the woods so you don't have to ride the brakes as much while going down hills. It will also be easier on your transmission since it won't be as likely to hunt between 3rd and 4th as much. :waytogo:
 
So, as someone who recently installed 4.56 gears running 35's, I do like them. However... I will say that with my 700R4, I could have easily gone with 4.88's instead. I do have a 12-bolt rear as well, with the 10-bolt front in my Suburban.

Just make sure that you can get the same ratio for the front and rear when you decide to change.

Oh and I am getting better fuel mileage since switching from the 3.73's to 4.56's. Food for thought!

Clay
 
This is awesome feed back and great advice thanks guys !
 
ccarley said:
Oh and I am getting better fuel mileage since switching from the 3.73's to 4.56's. Food for thought!

Clay
Click to expand...

Interesting. More city mileage friendly, or highway too?

I've always wondered. Does a vehicle get the best mileage right when it shifts into OD and is kinda chuggin along there at that speed.... Or if it having a few more rpms and taking the strain off the engine will actually help.
 
Deuling said:
Interesting. More city mileage friendly, or highway too?

I've always wondered. Does a vehicle get the best mileage right when it shifts into OD and is kinda chuggin along there at that speed.... Or if it having a few more rpms and taking the strain off the engine will actually help.
Click to expand...

Seems that my improvement has come from taking the strain off the engine. I'm at higher RPM's all around compared to where I was cruising, and it really likes it. I've heard that you should get best mileage if you are at or near the torque peak of the engine while at cruising speed. I've not seen any evidence, it may be out there, but it's just what I've heard.

I don't have any highway miles yet... still working on the rear driveshaft angles. Max speed right now is right about 50 mph. I'll be filling up this weekend though and can actually report the difference in mileage then.

Clay
 
For the OP, different engines also are happy with different gear selections. The answers so far are fine for a typical 350, but with a 454 or a 6.2 diesel the answer may be different.

Usage patterns also make a difference. If you're mostly driving on-road, you may want higher gears than the offroading answers you're finding here.

Whatever you decide to run, you will need the axles to match. So you could gear the new rear axle to match what's already in the front or pick something new and regear them both.
 
6.2Blazer said:
Did you correct the speedo/odo after performing the gear change?
Click to expand...

Excellent question!

The speedometer/odometer was actually incorrect before the change. It is reading correctly now (tested with GPS). How can I tell I'm getting better fuel mileage?

This is my daily driver :eek1: I have noticed the gauge has gone down less these past couple of weeks than it normally would so far. No concrete, actual proof yet, but being the daily driver, and primarily using it to go back & forth to work... it's pretty easy to tell.

Clay
 
You must log in or register to reply here.

Latest Posts

Top Bottom