Anyone running 3.07 gears & 33" tires, with a 4L60?

[East Tex]

I'm building a '72 K5 with a 6.0 LQ9 and a 4L60. Tires are currently 32", but I plan on replacing them with 33"s after the project is complete. I pulled the diff covers off to find out the axle ratio, because Speartech needs to know the ratio in order to program my computer. Well I was surprised to find out that I had 3.07s. I figured that it had 3.73s but it didn't. This won't be a highway truck when its done, it may go to a local car show or take the grandkids to get an ice cream. So, my question is, has anyone on here ran 3.07s and 33"s with a LS? Does it lug bad when you're putting around town? I really don't want to invest in two new sets of gears, but I will if this isn't a good combination.
The front ring gear has some rust on the ring gear teeth, but I think it will clean up. See pics on my build thread.

[jamesjones]

While not ideal, I don't think it will be that bad. I think it would be ok until you can afford to make the change.

I have 3.73s on my 35" but I have a non-OD transmission.

When you do change, I'd go 4.11 or 4.56 over 3.73 though.

[Clyde65]

Even though my swap is different than yours, I had 3.07's with the 4l60e and 29" tires and it lugged more than I could stand. I swapped my rear out for 3.73's. I still get 19MPG on the hwy but it is much more responsive in town. foo for thought.

[East Tex]

Wouldn't I have to buy 4 series carriers to run a 4.11 ratio?

[East Tex]

Clyde, if yours was lugging with 29"s, mine will be a dog with 33"s.
19mpg is great, what size motor?

[jamesjones]

Originally Posted by East Tex

Clyde, if yours was lugging with 29"s, mine will be a dog with 33"s.
19mpg is great, what size motor?

He has a 4.8 and you plan on going with a 6.0, which has a bit more torque.

[East Tex]

That's true

[ivorton74]

I got 3.08s in my 74... Im waiting to see how it runs....truck has stock 235/75/15s...how many inches is that?

[East Tex]

I'm not sure how tall your tires would be.

[ERASER5]

33" tire with 3.08:1 about 1355 rpm at 60mph in OD. That is low.

[East Tex]

I guess that I need to start pricing gears. Any suggestions? Richmond?

[wgeyer88]

I recently regeared my 2004 Silverado running on 35" tires that came with 3.73 from the factory (tow package). The truck has the 4.8 engine and was completely under powered, granted it's much heavier than a C10. I went to 4.56 and it is much better now.

I would highly suggest regearing, it will make the truck much more drivable/fun.

I went with Motive gears after doing a bunch of research. They seem to be high quality gears at a decent price. I had them installed by a reputable driveline shop in the area. They run just as quiet as OEM, I can't tell any difference.

[East Tex]

Originally Posted by wgeyer88

I recently regeared my 2004 Silverado running on 35" tires that came with 3.73 from the factory (tow package). The truck has the 4.8 engine and was completely under powered, granted it's much heavier than a C10. I went to 4.56 and it is much better now.

I would highly suggest regearing, it will make the truck much more drivable/fun.

I went with Motive gears after doing a bunch of research. They seem to be high quality gears at a decent price. I had them installed by a reputable driveline shop in the area. They run just as quiet as OEM, I can't tell any difference.

When you went from the 3.73s to the 4.56s, did you have to buy a 4 series carrier for it to work?

[Clyde65]

Originally Posted by East Tex

Clyde, if yours was lugging with 29"s, mine will be a dog with 33"s.
19mpg is great, what size motor?

Sorry East Tex I missed your response.

I have a 4.8/4l60e with 3.73's and 275/60/15 rear tires.

I have gotten 20.5 a couple times but with all the south wind at 25MPH, and our trucks being bricks, it seems to average 19 on the highway. I think I get 14.5 city, IIRC.

[68c10airstream]

Hi East Tex, i've used parts from reider racing in taylor michigan. Very helpful, and great prices, plus a good supply of inventory on hand. It's been years since i've used them, but worth a call. Good luck, Brian Fuller

[East Tex]

Thanks guys. I've set up tons of gears, but not in quite a while. I will check into Motive gears. Now I need to check and see if I can find all those pinion shims and carrier shims that I rat holed over the years.