Two questions regarding gear ratio's

[wallew]

OK, I'm considering gear ratio's.

First question is this.
What is the gear ratio for the NP205 (low gear ratio). Is it 1.96:1 or is it the 3.00:1?

Second question is this.
All things being equal, in an M1028a3 (or the M1031), what would net me the best overall setup for running gears?

The stock gearing is 4.56 and I'm considering either the 4.10 ring and pinion swap OR the 3.73 gear swap, which requires a swap of the carrier as well (per axle, of course).

This website allows you to do a side by side comparison of gear ratios between two setups. I've put in the 4.56 stock and then compared it against the 4.10's and then against the 3.73 gears. It does not appear to be a large gain in top speed between the 4.10's vs the 3.73's. And in truth not a LOT difference between the 4.56 vs the 4.10/3.73 gear ratios. Call it 5/11 mph difference in the setup's at 2500 rpm and 6/13 mph at 3000 rpm (do I REALLY want to push the 6.2L to 3000 rpm all day long? - mpg will suck at best at 3k rpm).

Gear Ratio Calculator

Given that to swap into the 3.73's you have to change the carrier (which is more $$$) instead of JUST the ring and pinion gears for the 4.10, it seems to me that the overall gain is not that much for the over all money spent.

This is with the transmission listed as the TH400 and the transfer case listed as the NP205 (1.96:1) and the tire size as 235/85/16, which is what appears to be 'stock'.

So, what am I missing?

 

[Westech]

the Np205 no way has a 3-1 low. A good thing to do to the M1008 type is a over drive swap (cost about the same as gears and housings all around) and installing a larger tire. If you do not wnat to swap tranys I would go with a 3.73 gears. Unless towing you coule even go lower. With a 3.73 gear you could hold 65 mph all day and not hurt or over rev the 6.2. If it were me.. I would do the 700 swap and install a larger tire.The hummer rims and tires seam to work well, that is what I had on my 1008.

 

[CUCVHMMWV]

You CAN get a 205 with a 3:1 ratio if you buy the Lomax kit or assembly. It replaces the stock case and internals but it will run you $1100 to $2200. It also eliminates the PTO function. LoMax 205 Complete Transfer Case

 

[NDT]

A "c" option is the Gearvendors overdrive. More money but a lot less work than ratio changes.

 

[wallew]

I'M not saying the NP205 does or does not have the 3.00:1 low gears.

The link I posted said it.

That's why I asked AND posted the link.

------

It's like the 'reversed' roll bar I saw in a Civvy mid eighties Blazer last weekend. I talked to the owner. He got it from his dad, who ORDERED it that way from Chevy. At least according to the guy who go into and drove it away.

Given it was sporting the obvious (rusted in a few places) original blue paint, and the roll bar was painted to match, I gotta believe the kid.

And when I say 'backwards', I mean it was mounted at the rear of the bed, with the down angled legs facing towards the front. You know, backwards of EVERY roll bar I've seen ever mounted in any Blazer.

Sorry, I didn't have my camera, cause if I had, I would be posting pix right now.

--------

So, stranger things have occured than 3.00:1 NP205 gears. Did the military ever order any? NO idea. That's why I asked.

 

[AJMBLAZER]

All OEM 205's had the 1.96:1 ratio. 3.0:1 is an aftermarket conversion.

The roll bar you mention you saw was the correct orientation. That's the way every one I've ever seen was installed...including some fairly pristine trucks with tops that had never been off.

I say put larger tires on and consider an OD transmission. You loose a bit of your performance with the higher gears. Not to mention it's expensive.


Skip the GV unit. Look into a Ranger unit if you go with a bolt on box.

 

[m38inmaine]

You will have to change the carrier with 4:10 as well, 4:56 up/4:10 down is the carrier cutoff. 3:73 will be the best overall gear.

 

[dieselpony]

You will have to change the carrier with 4:10 as well, 4:56 up/4:10 down is the carrier cutoff. 3:73 will be the best overall gear.

Yepp.
Besides, iirc there's no lower (faster) gearing than 3.73 for the D60/14bFF combo. Maybe for a D70 . . .

Walter

 

[AJMBLAZER]

3.42 and others are out there but rather rare.

 

[wallew]

A buddy of mine suggested 3.55's as a swap. But he did admit it would indeed mean a carrier swap.

I'm a shade confused. Everyone I've spoken with has told me that if I use gears lower than 4.10's I will have to change the carrier. But if I install 4.10's I can use the carrier that the 4.56's use.

So, which is it? Sorry, I am confused over this one.

Also, I'm having the TH400 tranny rebuilt in Scranton, Pa. It broke in half while it was being delivered to me by a buddy of mine (for expenses only - another long tale).

Aamco guy told me that he has seen a few TH400's break in half, but not many. So it will be rebuilt to his HD specs. Plus a tranny cooler added. Hopefully it will make a difference. It did when I had a 700R4 rebuilt to HD specs and added a tranny cooler.

I have a guy that will do the gear swap so I won't do that swap myself (long story). But if I can do a swap to 4.10's without a carrier swap, that's the way I'm going. That way everything 'looks' correct, but it will run at a more 'reasonable' speed and hopefully get better MPG.

So, where am I going wrong?

 

[m38inmaine]

You have to swap carriers as stated above, 4:56 uses a different carrier than the 3:73/4:10.

With stock tires:
4.56 @ 55mph 2806 rpm
4.10 @ 55mph 2523 rpm
3.73 @ 55mph 2295 rpm

In my opinion a swap to 4.10 doesn't gain enough to justify the expense, I would go with 3.73.

 

[wallew]

OK, thx for all the input.

I've spoken with four independent sources.

My buddy Stacey David.

My Aamco tranny guy.

My local differential guy.

A local Chevy dealer.

They all pretty much said the same thing.

"It depends. We would have to look at YOUR differential. There are supposedly two types. The first one is where the spider gears (is this correct nomenclature?) do match the ring and pinion gear set (or match the NEW ring and pinion gear set I want to have installed). The second one is where they don't match. If they do match, then it's simply a ring and pinion swap, $200 for parts and $200 for labor - per differential. The other one is you HAVE to swap out the carrier."

They all said until they LOOK at it they won't know.

YEAH, I agree with youse guys. MINE is probably the one where I have to swap out the carrier. But until I go get the truck, I won't know.

Once I get it home, I'll take it over and find out and put this issue to rest once and for all.

Also, there is 'supposedly' a 3.54 gear ration that should fit as well. I don't know if this is or is not true. Once I get to see my differential guy, I'll let you all know.

Again, THX for all the input. It's given me a lot to think about. Plus it shows the cost variable is either $400 per axle or $800 per axle. Given how many problems I've had so far, mine is probably going to be the higher cost one.