Do I need different gears with 33” tires and 4” lift

[sqhead]

I have a 85 Chevy k10 with gm-10 bolt with 2.73 gears and 4-speed Muncie. I’m putting 4” suspension lift with 33” tires and 383 stroked. Should I change the gears to something like 3.73 or will it be ok. I was reading about tearing up tranny in overdrive but I assume they are automatics? It’s a daily driver no off-roading.

 

[Shorty81]

You are going to be a little on the tall side. You need at least 3:73. Your truck will feel a bit sluggish.

 

[sqhead]

3.73 is what I was thinking. Wonder what others were referring to when I read about destroying the gears with big tires and high gears. I didn’t understand that one. It was on a forum I was reading thru elsewhere.

 

[Redfish]

What 4 speed Muncie do you have?

I am running 33s with 3.42 gears with an SM465 4 speed. I am fairly happy with it but it was never a dragster before the mud grips. If I were going from the ridiculously tall gears you have I would suggest going to 3.73s.

 

[Shorty81]

What 4 speed Muncie do you have?

I am running 33s with 3.42 gears with an SM465 4 speed. I am fairly happy with it but it was never a dragster before the mud grips. If I were going from the ridiculously tall gears you have I would suggest going to 3.73s.

I'm running 31s with SM465 with 3.73. This feels like the sweet spot, truck very happy. 2000 rpm at 55. 496BBC, 208 transfer.

 

[sqhead]

Thanks for the good info. Sounds like 3.73 is leading the way. Does anyone have any recommendations on brands I’ve seen Yukons pretty pricey but Amazon has them for couple hundred cheaper so I’m assuming something is different. Also, I’m assuming I need to change my posi carrier that is being used on my 2.73 now right? Gonna have to replace it all?

 

[gmbellew]

I'd get a truetrac to replace your factory G80 and don't forget you also have to regear the front on a 4x4.

 

[sqhead]

Who makes the tru trac and why do you recommend them?
Thanks for heads up on front also

 

[gmbellew]

detroit/eaton makes the truetrac. it is a gear driven posi and doesn't require additives. very good street manners and very good offroad. just not a true locker, so if you are crawling over rocks and hitting difficult trails and putting tires in the air, you may want something different. quickperformance.com has good prices on packages.

 

[Camar068]

Thanks for the good info. Sounds like 3.73 is leading the way. Does anyone have any recommendations on brands I’ve seen Yukons pretty pricey but Amazon has them for couple hundred cheaper so I’m assuming something is different. Also, I’m assuming I need to change my posi carrier that is being used on my 2.73 now right? Gonna have to replace it all?

look at Richmond Gear as well.

 

[sqhead]

Does Richmond gear have a specific kind you like?

 

[Bextreme04]

Thanks for the good info. Sounds like 3.73 is leading the way. Does anyone have any recommendations on brands I’ve seen Yukons pretty pricey but Amazon has them for couple hundred cheaper so I’m assuming something is different. Also, I’m assuming I need to change my posi carrier that is being used on my 2.73 now right? Gonna have to replace it all?

The carrier split for a 10 bolt is above 4.11, so you should be fine with the same carrier. If you currently have a stock G80, you might consider going to the tru-trac or a Yukon Duragrip unit. They are both less prone to self destruction than the stock Eaton unit and are well regarded as strong units. Richmond, dana, or spicer gears are good quality and decent prices. Yukon gears are also pretty good, but more pricy.

 

[justhorns]

You should remember, bigger heavier tires weigh more, and take more power to spin up. yes, you need lower gears, but just weigh the tires and wheels. I bet you add 50 lbs at each corner. The diameter of the bigger tire is directly affecting gearing, but weight is the enemy to acceleration. I had bigger tires on my white truck, Ralph, and when I got a deal on these smaller tires, the truck rode better, accelerated faster, and handled better. I know many may want to choke me for this, but, you can't beat physics.. So you must join em.

 

[Grit dog]

3.73 is what I was thinking. Wonder what others were referring to when I read about destroying the gears with big tires and high gears. I didn’t understand that one. It was on a forum I was reading thru elsewhere.

Even though gears would be easier with the axles out, personally I’d do some rpm/gear ratio calcs, and keep in mind you (presumably) are going to have some good horsepower.
Presuming you have a granny/1:1 4 speed and not an 833 or whatever that one OD model trans was, you might not like 3.73s if you’re planning on driving it at real freeway speeds for any length of time.

 

[Grit dog]

3.73s are about right though unless you plan on real freeway driving in the 75-90mph range. Then you’re at 3krpms + on the highway.