Changing M1009 Rear Ratio from 3.08 to 2.73

Just curious, I was looking through my LMC catalog and saw where there may be a 2.73 ring and pinion for the GM 10 bolt and ran the numbers through grimmjeeper and saw that I could do almost 70 and 65 for sure at the same rpm's as I do 55. Would 2.73 be to high and make the Blazer too slow off the line, or slow me down more when going up a hill. I know there's good mileage had at 3.08, but I wonder if I could get better with 2.73.
Thanks for your help.

The low power 6.2 isn't going to be particulary happy having to work that hard. That swap would not be on my radar. The truck would suffer everywhere else. You coukd achieve similar results with a 700R4 and even gain a deeper 1st gear. Overdive would likely only be a downhill or with the wind gear.

Having never owned a CUCV diesel blazer but knowing the anemic nature of the gasser of the same era, I owned a 85 K5 blazer 305, auto, 3.08‘s, I would say you would be very disappointed in the snail pace starts and the crawling up the slightest hill holding it to the floor in 2nd gear. You will most likely loose mileage because you will now have your foot deeper in the throttle all the time just to keep it rolling. Don’t forget these things are as aerodynamic as a brick so even a good headwind will slow you down. If it were myself I would consider doing a 700R4 swap instead which will give you a lower 1st gear for slightly better off the line and a .7 overdrive for highway cruise when the conditions are right.

Well first off you would have to change both the front and rear ring and pinions, drive-line bind can happen with different ratios.

You would probably be better off getting a set of 33" tires, you shouldn't need a lift to fit 33's.
It'll be about $500 for two sets of ring and pinions, and install kits, and that's if you have the mechanical know-how, experience, and patience needed to swap and properly setup differentials. If you have a shop do it, then it'll be around $1000. Vs $700-ish for new tires mounted on your stock wheels (or you can probably find good used tires already mounted on craigslist for $3-500).

It would run at similar RPM's with 33's. They would drop the RPM's at 65mph to about 2040, down from 2250 stock (vs 1990 with 2.73 gears).

I had 35's on my 1009 and it was a dog off the line and didn't like hills much. It still did 19.8 mpg @ 60mph on a trip I took last summer. It is much happier with 33's on it now.

33's would be way cheaper and more worth it compared to a gear swap or 700r4.

What kind of mileage are you trying to achieve?

I had 33x10.50's on the first Blazer I owned and mileage went down slightly. But I was usually able to maintain 20mpg's 22 on a good tank. Just thinking out loud and was curious. I also have a 12V Cummins that I keep wrestling with, whether or not to put it in my Blazer or if it would make it too front heavy.

I don't know how much better mpg you will get with a 1009. I've heard guys claim high 20's with a 6.2L w/ 2wd 2.73 gears, and 5 speed manual.

A Cummins in a K5 would be pretty awesome. Everyone says it would be too heavy, but they work in C/K pickups just fine. It would just need heavier-duty springs.

Forget it. The slippage in the torque converter at highway speed would offset any potential gains. All that lost torque manifests as heat too so it would be harder on the transmission. For the money to properly install two ring and pinion gears you would be far ahead to slip in a 700R4 that has a lockup torque converter, eliminating slippage and waste heat issue.

I ran 2.56 on my i got off a 68 nova for a year or so also had 2.73 for about 6 month that came of a 74 camaro , but when back to 3.08 with the 33" tires . did about the same fuel MPG, it ran good, however it had a turbo kit on it, also for the 2.56 had to play with the carrier unless you use the one that came with the gears, with the 2.73 was nothing especial as far as the carrier...

od trans.. might be cheeper and easier.. although depending on your driving it might not help.. 700r4 in 1009 was useless too many hills not enough highways to exploit the the od..I considered 354 and 373 od tranny..

Recovry4x4 said:

The low power 6.2 isn't going to be particulary happy having to work that hard. That swap would not be on my radar. The truck would suffer everywhere else. You coukd achieve similar results with a 700R4 and even gain a deeper 1st gear. Overdive would likely only be a downhill or with the wind gear.

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Rebelpride said:

Just curious, I was looking through my LMC catalog and saw where there may be a 2.73 ring and pinion for the GM 10 bolt and ran the numbers through grimmjeeper and saw that I could do almost 70 and 65 for sure at the same rpm's as I do 55. Would 2.73 be to high and make the Blazer too slow off the line, or slow me down more when going up a hill. I know there's good mileage had at 3.08, but I wonder if I could get better with 2.73.
Thanks for your help.

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I suggest a no on that. A 6.2 diesel is not exactly a power house engine and 2:73 gears would be too tall. Especially on a long hill. 3:73 gears with a 32x11x15 or 33x10x15 tire is a good combo.

I ran 33x10.5x15 tires on a 74 K10 with 3:73 gears. 70mph was not an issue..

My current 79 K20 has 3:73's with a true 33in tall tire. 65mph is easy and I can do 70mph as well. I just cap it at 65mph because the 406 small block has a drinking problem...

Best overall combo I have driven is 700r4, 33" tires, 3.40 ish gear. Have had almost every normal setup. Get well built 700r4 first then the others if you want to dial it in.