Gear Ratio

[ksquare84]

I know there’s a ton of posts about this but I’m having some trouble figuring out the gear ratio. This is what I see on the ring gear on my 1984 GMC k2500 Base

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[nvrenuf]

Looks like 41/9 which is 4.56.

Btw, that gear oil looks NASTY.

 

[ksquare84]

It was horrible hasn’t been changed in 30 years and hasn’t been on the road in 22 years.

 

[bucket]

Looks like 41/9 which is 4.56.

Btw, that gear oil looks NASTY.

Yep, looks like moisture got to it.

It's worth paying attention to where the diff vent is placed. On one of my trucks, rain water would run from the bed and onto the frame. The water would then run under the top flange of the frame (much like a roof without a drip edge) and run right into the diff vent that was wedged up against the inside of the top frame flange. A minor repositioning of the diff vent took care of that issue.

 

[ksquare84]

Yep, looks like moisture got to it.

It's worth paying attention to where the diff vent is placed. On one of my trucks, rain water would run from the bed and onto the frame. The water would then run under the top flange of the frame (much like a roof without a drip edge) and run right into the diff vent that was wedged up against the inside of the top frame flange. A minor repositioning of the diff vent took care of that issue.

Thanks again for the info after taking another look I found that the breather was completely broken off and covered in several layers of sediment.

 

[K5 Blazer]

You are stoked you have 4.56 gears. I am spending $4100 to have my gear ratio changed from 3.07 to 4.56. It's for both the front and rear axles.

 

[Camar068]

You are stoked you have 4.56 gears. I am spending $4100 to have my gear ratio changed from 3.07 to 4.56. It's for both the front and rear axles.

wow.....why so high?

 

[K5 Blazer]

wow.....why so high?

We did the calculations on it 4L60E transmission with 33" tires. My options were 4.10 or 4.56. 4.10 would have been a little better for the freeway driving. I figured this vehicle is more around town driving and I wanted to have the torque when I put my foot into it. Cruising speed at 70mph should be around 2300 rpms. Do you think I went to low and should have gone with the 4.10 gears?

 

[bucket]

We did the calculations on it 4L60E transmission with 33" tires. My options were 4.10 or 4.56. 4.10 would have been a little better for the freeway driving. I figured this vehicle is more around town driving and I wanted to have the torque when I put my foot into it. Cruising speed at 70mph should be around 2300 rpms. Do you think I went to low and should have gone with the 4.10 gears?

I definitely would have chosen 4.56 gears. There's really no efficiency gained by trying to lug down an engine that's pushing a brick through the wind.

 

[Camar068]

We did the calculations on it 4L60E transmission with 33" tires. My options were 4.10 or 4.56. 4.10 would have been a little better for the freeway driving. I figured this vehicle is more around town driving and I wanted to have the torque when I put my foot into it. Cruising speed at 70mph should be around 2300 rpms. Do you think I went to low and should have gone with the 4.10 gears?

Sorry for being vague, why is the price so high? I had mine changed (front/rear) for about $1,200 and that included new front wheel hubs and installation kits. I know I got a deal compared to other shops locally, but $4,100?

I went with Richmond Gear so the front/rear kits were total about $500.

 

[K5 Blazer]

I live in the San Francisco Bay Area, everything is very expensive here. That was not the highest estimate I received. One quoted was $2500 per axle. As part of that estimate, I was told the drive axles in the rear end were bad and needed to be replaced as well. This also includes an Eaton limited slip differential installed as well.