Gear Confusion (need to make Decision ASAP)

[GalDemSuga]

I have been under the impression (never actually checked) that my 89 Blazer had 3.73 gears. I average about 9-12 mpg with stock 350/700r4 and 33 inch bfgs and was hoping to change to 4.56s.

I took the truck to a driveline shop to have it regeared and was blown away when the shop called to say that it currently has 2.73 not 3.73.

How can this be 2.73 and such crappy fuel economy. Now I'm worried about going to 4.56. Maybe I should put some 3.73 in there.

 

[4xcrazy]

lugging the motor, it's straining to keep up to speed.

 

[4X4HIGH]

When I bought my 89 blazer it was 100% bone stock and came with a 350/700R4/NP241 with 3.73's and 31" tires and I got 14 mpg on the freeway. With a 2.73 gear and a 33" tire I would suspect worse mileage (like you're getting) because it takes more effort to move the vehicle and especially with a larger tire as well.

 

[GalDemSuga]

What do I do here Scott? I think 3.73 would be the best bet knowing the facts now. Its my daily driver/work rig and I now tow a 4200lbs camper. I have been making assumptions based on the 3.73 as for its performance so I've been putting alot on the motor and trans in the past two years.

When I bought my 89 blazer it was 100% bone stock and came with a 350/700R4/NP241 with 3.73's and 31" tires and I got 14 mpg on the freeway. With a 2.73 gear and a 33" tire I would suspect worse mileage (like you're getting) because it takes more effort to move the vehicle and especially with a larger tire as well.

 

[4X4HIGH]

If it were me I would run 4.10's with a 33" tire. With the 10 bolt axles going to 4.56 gears makes the pinion gear pretty small and they have been known to shear the teeth off the pinion.

 

[GalDemSuga]

That was the recommended choice of many boardees when I was considering the change initially based on the flawed 3.73 deal. I already bought the 4.56 now I have to get rid of them and have the driveline shop provide me with gears.
Thanks for the feedbeack

If it were me I would run 4.10's with a 33" tire. With the 10 bolt axles going to 4.56 gears makes the pinion gear pretty small and they have been known to shear the teeth off the pinion.

 

[4X4HIGH]

That was the recommended choice of many boardees when I was considering the change initially based on the flawed 3.73 deal. I already bought the 4.56 now I have to get rid of them and have the driveline shop provide me with gears.
Thanks for the feedbeack

Can't you return/exchange the gears for 4.10's?

 

[GalDemSuga]

Well I got her back today with 4.10's. I felt the difference in acceleration as I drove her home and the Speedo now pegs at 85 MPH. Gonna redo the brakes and front wheel bearings to be sure its A ok. Dont trust anyone with that stuff.

I will post any notice in MPG's soon.

 

[RootBreaker]

Well I got her back today with 4.10's. I felt the difference in acceleration as I drove her home and the Speedo now pegs at 85 MPH. Gonna redo the brakes and front wheel bearings to be sure its A ok. Dont trust anyone with that stuff.

I will post any notice in MPG's soon.

well you got your 4.10's cool.. so im a bit late...

i was gonna say if you dont expect to go over 33's... 3.73's are not bad...

i had a 350/turbo 400/3.73's and could tow, fly up the highway at 110 (yeah i was 17 once too)... but the 4.10's will do nicely too!!!! since you have a 700r4

 

[Fordum]

Man, 2.73s. No wonder you were having trouble hauling stuff.
Yeah, your engine was so far out of its power/efficiency band that it was sucking the gas trying to keep your speed up.
With normal sized tires, not towing, you would have gotten good gas mileage, but with the larger tires the engine just could not get up to speed.

I guess its lucky you did not go with the 4.56s. If you tried to drive it the way you were used to, you might have burned all the tread off the back tires by the time you got home.

I think you are going to like the new gears. Plus you have taken a big load off the rest of the drive train. If you are under the back end, stop and listen real close. The U-joints are going to be whispering "Thank You"......

 

[4X4HIGH]

Well I got her back today with 4.10's. I felt the difference in acceleration as I drove her home and the Speedo now pegs at 85 MPH. Gonna redo the brakes and front wheel bearings to be sure its A ok. Dont trust anyone with that stuff.

I will post any notice in MPG's soon.

You'll need to have the speedo recalibrated first if you plan to use it to calculate your mileage. Not only does the speedo read faster but the odometer will also add more mileage than you're actually traveling.

 

[GalDemSuga]

I plan on getting an adapter at the transfer case to help solve the speedo issue.

You'll need to have the speedo recalibrated first if you plan to use it to calculate your mileage. Not only does the speedo read faster but the odometer will also add more mileage than you're actually traveling.

 

[GalDemSuga]

LOL @ Ujoint comment

Man, 2.73s. No wonder you were having trouble hauling stuff.
Yeah, your engine was so far out of its power/efficiency band that it was sucking the gas trying to keep your speed up.
With normal sized tires, not towing, you would have gotten good gas mileage, but with the larger tires the engine just could not get up to speed.

I guess its lucky you did not go with the 4.56s. If you tried to drive it the way you were used to, you might have burned all the tread off the back tires by the time you got home.

I think you are going to like the new gears. Plus you have taken a big load off the rest of the drive train. If you are under the back end, stop and listen real close. The U-joints are going to be whispering "Thank You"......

 

[folkenheath]

Actually, the transmission is probably the one saying, "thank you". The d-shaft u-joints are probably saying, "whoa whoa whoa, slow the heck down, what is going on here?"

 

[6.2Blazer]

You'll need to have the speedo recalibrated first if you plan to use it to calculate your mileage. Not only does the speedo read faster but the odometer will also add more mileage than you're actually traveling.

To go along with this, if you had never recalibrated your speedo after installing the 33" tires with the stock gears you were actually getting better mpg than you were calculating. This is because your speedo and odo were reading low and thus were your driving more miles between tanks of fuel.