What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Real-life gearing input

swettysblazer

swettysblazer

Swetty The Yeti
Vendor
GMOTM Winner
Joined
Jul 20, 2009
Posts
5,919
Reaction score
2,617
Location
North Jersey
I'm looking to regear my 3/4 tons that are going to be going in my Blazer. Specs are 350/700r4/NP241. I am planning on running a set of 37" Hummer takeoffs. Basically, what I want to know is if you were me, what gears would you choose?
I have talked to a few guys and they seem to think I should go with 4.88's, and this is what I initially thought I should go with. I know there are calculators out there and I have used them, but I want to know some real world experience in driveability with this setup or anyone who has something close to this. Thanks in advance.
 
I'm running 350/700R4/NP241 with 35" tires and 4.56 gearing and wished I had went with 4.88 or 5.13's. I think with you going with a 37" tire you would definately want 5.13's. The issue with 5.13's though in a 10 bolt front axle is that the pinion gear becomes very small and are known to break easily.
 
4.88s or 5.13s for sure. OD will make up for them and you will get an even better low range out of it.

And sadly, my 10bolt with a locker and 5.13s have never gave me a single problem with my 40in Boggers, but I just stripped the ring gear and broke the housing on my 14 bolt. So, the world of trucks and tires works in mysterious ways.

I run a 454/400/205 with 5.13s and it would be beautiful on the road with an OD, but around town its perfect with my 40s. And them 37s your using are heavy as hell, so the 4.88s would probably be good, but the 5.13s would probably give it more of a "race car" type take off and such while still having the ability to cruise at 55/70 comfortably.
 
454Sub said:
4.88s or 5.13s for sure. OD will make up for them and you will get an even better low range out of it.

And sadly, my 10bolt with a locker and 5.13s have never gave me a single problem with my 40in Boggers, but I just stripped the ring gear and broke the housing on my 14 bolt. So, the world of trucks and tires works in mysterious ways.

I run a 454/400/205 with 5.13s and it would be beautiful on the road with an OD, but around town its perfect with my 40s. And them 37s your using are heavy as hell, so the 4.88s would probably be good, but the 5.13s would probably give it more of a "race car" type take off and such while still having the ability to cruise at 55/70 comfortably.
Click to expand...

I agree, i think you would be totally fine with 5.13s but it just depends on how peppy you want it low end and possibly slightly more fuel consumption top end. Either way, 4.88 or 5.13 are your two best choices.
 
I ran 37" Hummer takeoffs on my last K5. I went to 4.88's and loved it. Was a 350/465/205 combo. It was ideal for a daily driver with no OD. Made many road trips in it. Most of them pulling a loaded snowmobile trailer on the highway.

Having OD would make me really consider 5.13's. It'd help the 700 live longer too...less load in the lower gears.
 
You WANT 5.13's, inside of a 14b.... For the reasons stated earlier.

I speak from experience, having owned the same setup as you.
With the exception of mine being on 10b/14bff.

4.10's brought the suck!!!
As in, NEVER USED OVERDRIVE, and ALWAYS hunted gears anyways.

5.13's woulda been NICE.
Ask NorCal_Chris about being under-geared... :haha: :haha:
 
I'd go 4.88 or 5.13 with 37s and overdrive. That would get you close to stock power and cruising rpm. I have heard anything over 4.88 the pinion gets weak as was said. But if you are using a good quality set like Yukon or Randy's r an p. I dont think you have as much to worry about. Also have to worry about the shafts and hub locks being weak with the 37s. Good thing is they are not a super agressive tire.
 
Looks like right about 1800 for Install kits, gears, and lockers front and rear from Summit. Definitely gonna have to sit and think about it.
 
Thats why I chose to go with the deeper gears, incase I stepped up tire size. And now that I blew the 14bolt up and a 60 is in the works, Im going with 5.38s instead of the 5.13s for the extra umph.
 
I ran 4.88s for years with a 12 bolt rear and a 10 front, 38" tires, 350/TH350/203 and it was a great combo all round...Felt like a stock truck running 4.10 with 33" tires. With that being said....I would go with 5.13s...Just in case you want to run 40" tires in the future.
 
I have 5.13s in my 1-ton axles with the 350TBI/700/241 set up and I have 38" tires. Wish I had a bit more gear, or maybe I wish I had a fresh engine (I've got 205,000 miles on my engine...). It drives well, but it's not very powerful.
 
I currently have 4.88's in my crew cab running the 37" mils.

I love it. I only wish I could have tried it towing up some larger hills or the rockies one more time. Last time I did it, was with 36 mils and 4.10's and it really sucked.

With the current setup, I don't really need to use the OD gear on 55 mph roads but do if not loaded down. At interstate speeds while towing, I can hold the OD for most situations pretty easily around here. I'm sure if I got in to the rockies I would be grabbing gears. Mostly flat around here. The RPM's are right for my engine and that gearing at 70-75.

Keeping in mind, my crew cab likes a little bit lower RPM than your 350 might.
 
I have had two vehicles with 37s and 4.56 gears, and I like them as a combo!!!
My 1987 Jimmy (sm 465 so no overdrive)- 4.56s were perfect!
My 2012 Power Wagon (6 speed automatic, crazy like .625 overdrive)- 4.56s are good but it doesn't like to go into overdrive much (lower gears might be nice but are not an option for my truck, 4.56 is lowest rear axle gear made, also 4.56 is what came stock)

With both rigs (granted apples to oranges comparison, lol!), I have liked my 37s and 4.56s setups! The only thing I don't like right now is my high high overdrive but, yours is not that high. (700r4 are .75 IIRC)

Basically, doing the math, assuming 3.73 stock gears with stock tires (30") is about the same as 4.56 gears and 37s: (37/30)x3.73= 4.6003… So, 4.56 gears would keep your speedo dang close to correct with 37s. But, 4.88 might be worth some speedo error since it would give a bit more grunt.
 
Meh, it's simpler than all this blah blah blah :D

If you use it more on road ( more freeway ) = 4.88
If you use it more off road ( around town driving) = 5.13

But, as mentioned, you are treading thin ice gearing a 10b that low, 37s, and I read a locker?!?!?! Woo, you must be really soft with the gas pedal!

I have 400/700/241/60/14/4.88/38x15.5". Will go 5.13 later, but it drives great now.
 
It also depends on the environment your using your truck in. Mud for example, with its non tractionness, isnt going to break stuff as much because there is no sudden shock of wheels grabbing. Now, rock crawling or asphalt neutral drops and that style of traction shock through the drivetrain will reduce that 10 bolt to scrap quite quickly.
 
I have 5.38 gears on 38 tsls (measure 36.5) running a 700r4...been rockin that setup for 6 years...wouldnt change a thing...
 
You must log in or register to reply here.

Latest Posts

Top Bottom