M1009 axle swap with H1 37's...Oh my what gear ratio to run...?

[Asmoday]

Hello All,

So I've been reading and reading as many posts as I can on swaps to the H1 37's on here and I'm at a crossroads now. Actually my head hurts.

I'll be swapping in a D60 and 14 bolt axle set into my M1009 in the near future and I'm trying to decide what gear ratio would be the best. I have looked at many conversion charts available on the web seeing different RPM's based on the rear axle ratio/trans set-up.

I was going to drop in the 700R4 but many hard core off-roading buddies of mine, some of which I really respect knowledge wise keep steering me away from the 700R4 urging me to stay with the TH400 that's in there now. I have the 700R4 but it will definitely need a good rebuild before install. A gear vendors OD unit later on would not be out of the question either but it would be a while until I can swing that buy.... I believe that the recommended highway RPM on the 6.2 at desired cruise speed should be around 2200-2300....correct?

So...if I'm looking to do 65-75mph on the highway and not stress the 6.2 what would be the best gear ratio to run but not be a toad around town or off-roading?

Using the formulas provided in the link below running 37's with a 3.73 gears would be very close to the current stock 31's / 3.08 set-up but it seems most of the info I have read say to go with 4.10's or even 4.56's. I am leaning towards keeping the TH400 though.

http://www.4x4offroads.com/gear-ratio-chart.html

This is a great online chart as well...

http://www.grimmjeeper.com/gears.html

I'm lucky to be able to pick what rear ratio I want from the gentleman I'm getting the 14 bolt from but understandably I would prefer to only do this gear set-up once. The D60 has no gears right now.

All advice is appreciated...!

 

[HillbillyWizard]

It sounds like you are going about the choice the right way!
My first thought... 4.56, keep the TH400 and get the OD.

4.10 might be the way to go, but 3.73 is too high IMHO.

A couple questions though: Are you planning to do any towing? What percentage of off-road / highway and around town do you drive?

 

[gringeltaube]

Suggest 4.10:1 for cruise & light duty, only; 4.56:1 for serious business and if towing trailers, often.

G.

 

[twomorestrokes]

Personally I'd go with the 4.56 with the low hp 6.2 if you want to keep any of the low end drivability and performance, especially with the H1 wheels. Each one of the wheel/ tire units with bead locks weigh close to 200 pounds! That's a lot of unsprung weight to get rolling. You will still be able to cruise 65-70 comfortably and it will feel like the typical 350 equipped civy unit at low speed in town driving. In 4wd low in the woods with a good load of wood it still has more than enough umpf.

My TH400 works way too well to think about getting rid of it but if I was changing anything I would stick with the 4.56s and swap in a 4L60. I like those much more than the 700s.

My mileage stayed the same after the switch to 37s because I basically stay at the same cruising RPM as before but it is 25-20 mph faster which is much more enjoyable. An overdrive would be nice though.

 

[1ton cucv k5 turbo]

I think your on the right path... but..... Speaking from experience, running H1's, 37's and 4.56 gears, you will not want to run long term down the highway at those speeds.. It really begs for another gear... IMHO... Adding a gear vendor OD or swapping to a 4L80 will get you where you want to be. 1st 3 gear ratios of a 4L80 is the same as the 400. Im about to do the 4L80 install myself for this very reason, as i cant fit the GV unit on mine... ( 203/205 doubler takes up too much room...)

 

[twomorestrokes]

I think your on the right path... but..... Speaking from experience, running H1's, 37's and 4.56 gears, you will not want to run long term down the highway at those speeds.. It really begs for another gear... IMHO... Adding a gear vendor OD or swapping to a 4L80 will get you where you want to be. 1st 3 gear ratios of a 4L80 is the same as the 400. Im about to do the 4L80 install myself for this very reason, as i cant fit the GV unit on mine... ( 203/205 doubler takes up too much room...)

Good information. True, it would be nice to have another gear up there above 60 but as far as driving long distances with the TH400, I do it almost every weekend heading up north to the lake. 100 miles each way at 65. It feels better than 50 did before the wheel swap. I'll wait till my 400 needs attention before I'll take it out.

 

[Asmoday]

Really good points made...Thanks!
As far as towing...I may tow something like a 101A at some point but as a rule I don't tow much. I do use the truck as a daily driver with moderate off-road adventures on the weekends and for getaways.
What engine RPM are you guys getting at highway speeds with the 4.56'S? Say...55, 65 and 75?

I like the idea of the 4.56's as I have a carrier for that and I know that going to 4.10's requires a different carrier but I wont be able to do an overdrive set-up for a while if I don't go the 700R4 route and I don't really want to be stressing the poor old 6.2 too much...LOL.

As for the 4L80...I thought those required a expensive on-board appropriate computer? How difficult is the swap if I want to keep my NP208 and stock cross-member set-up? 1 Ton CUCV K5 Turbo...I'm addicted to your threads...LOL.

 

[Keith_J]

37 inch tires demand 4.56. I wouldn't recommend speeds over 60 regardless if you have an overdrive, you have a short wheelbase vehicle with solid axles and leaf springs. Nothing you can do to make it handle safely on the highway at higher speeds. You have too much unsprung mass and higher center of gravity with the lift necessary for 37s. If you were to brake heavily, the axles will deflect asymmetrically, the front half will dive and the rear will jump.

Furthermore, there isn't all that much torque from the 6.2 engine, taller gears will only further handicap it. You are putting 37s on for serious off-road work and going to taller gears will hurt performance off road.

 

[twomorestrokes]

There is a 4L60 aned a 4L60E which is the electronic one.

 

[Asmoday]

I think 1 Ton is going to use a "4L80"...not a "4L60"...? Correct?

 

[cameron8757]

The 4L60 is the later electronic version of a 700R4

 

[Asmoday]

Thanks...I'm aware of that....but....for what it's worth my understanding is that the NP208 from the M1009 will mate with the 4L80(spline count) but the 700R4 requires the appropriate NP208(which I have) with correct splines. Nonetheless I believe 1 Ton is referring to the 4L80.

I don't want to get off the thread though...

 

[1ton cucv k5 turbo]

Asmoday.. you are correct... there are 2 ways to go to install the 4L80. One would be getting a stand alone computer. It can be had for around $600 and up... however you will also have to fab up a throttle position sensor, and a speed sensor in order for it to shift/work correctly... 2nd way... ( this is the path im going...) is to get a manual valve body. Theres several different brands and types out there, and they range from 240-600... ( Im going with TCI for est. $600, after doing an exhaustive search, thats about the best one avaiable...IMHO) You will not need a computer,or deal with extra sensors, etc... Down side though, From my understanding is that you will have to drive it like a manual, just without a clutch. ( i do not know this for sure yet...) Im getting a Reverse manual valve body, as it will work better for me, as i'm more offroad than onroad... the difference is the shift pattern. Mine will be PRN1234 instead of the normal stock pattern of PRND321. Im going this route due to simplicity and how i use my rig... Going with a 4l60 will be the same as going with the 700R4, but than add the expense of adding the stand alone computer, sensors, etc... to me... that route isnt worth the extra headache and $$$... IMO...

 

[Recovry4x4]

The 6.2 is no powerhouse. With that said you would need to compensate for that with either a turbo or gears. Having owned the M1009 and M1008, there is a huge difference in their ability. The Oh-8 has gears 1-3 and the Oh-9 feels like it has gears 2-4. While I know the 400 (3L80) is brutally stong, the 700R4 can easily and affordably be built to handle much more than the 6.2 can hand out. The 3.06 first gear does wonders to help get things moving as well. The .70 overdirve really helps a bunch with the low 4.56 gears. Other than the percieved weakness, the 700R4 is a perfect match for the anemic 6.2. Just like for the 6.2, there is a cult hate group that depises the 700R4 because of problems in the early years. I've owned countless 700R4 trucks and my current one is a 6400# suburban. It has the factory 6.2, 700R4 and swapped in 3/4 ton axles with 4.10 gears. It goes faster than I need it to go and one day will have the 4.56 gears. I've towed plenty of 5000# loads with that truck with no issues from the transmission. For my uses, the 700R4 is the perfect transmission. I have one almost ready for my M1008 and a second one to rebuild for the M1010 that I'm getting. Get a quality rebuild and keep it cool and the 700R4 will last a long time. A decent rebuild will cost only slightly more than the 4L80E computer or manual valve body.

 

[twomorestrokes]

Again, there is a 4L60 transmission and the later 4L60E transmission. You do not need a stand alone computer to run the 4L60 transmission. It has a manual TV cable which is mechanically linked to the throttle. You could use a simple toggle to engage TC lockup when needed.