Gear ratio for M1008.

[AJMBLAZER]

Newbie question here- How would you change the M1008 gears so you get better highway speeds..?

Adding taller tires is the easier way.

Other way is to have the axles regeared. Not cheap or easy but you might find someone to trade you axles if this is your wish as there's lots of offroaders out there who would give a kidney for a set of 4.56 geared 1 ton axles with a Detroit in the rear.

Would you have to change both the rear and the front differential gears ?

Yes unless you pull the front driveshaft. Front and rear axle ratios must match in a 4x4 if the tires are the same size.

So what kind of spline does a M1008 gear 4.56 ratio have? Been thinking going with a smaller ratio to get better fuel milage but dont know what tyoe of spline it has.

Spline...huh? Axleshaft spline?

 

[hobie237]

Newbie question here- How would you change the M1008 gears so you get better highway speeds..? Would you have to change both the rear and the front differential gears ?

You could change the gears, but it'd slow down the truck and really hurt it's pulling power. The TH400 has a really high first gear (2.4 and it really needs the lower gears for any sort of torque to the wheels. And yes, you'd have to change the front and rear gears, or forget about using 4WD. I have been told that the next ratio that the Dana 60 and 14-bolt have in common is 3.73 (at least commonly available) and I sure wouldn't want that.

For an easier "gear swap" you could try larger diameter tires, but that has all the negatives of the gear swap (except cost/time) with the added issues of reduced range of motion for the suspension (and/or need for a lift to get more clearance).

That said, a better idea would be a 700R4 swap- you'd win on both ends, getting a lower (3.something) first gear on the low end for more stump/trailer pulling and load hauling ability and an overdrive on the top end.

As I see it, the flaw is the TH400's gear ratios. It's a rock solid transmission, don't get me wrong, but it's really not the best choice for the job, especially with the 700R4 available.

Is the rear with the 4.56 gears the reason it feels like my M1008 is always still in 2nd gear?
Seems like it never upshifts to a higher gear?

I don't know, does it shift to third? Pretty easy to tell, but yes, third comes pretty early 20mph if everything is working good, I'm up around 38 because of a minor vacuum leak) so sometimes it'll feel like it should shift again (and, if it were a more modern truck with an overdrive it WOULD shift again), but to answer your question, yes, the fact that you run out of gear below 70mph will sure make it feel like it's in a lower gear than it should be, and yes, that's because of the 4.56.

 

[CCATLETT1984]

if you can go over 40mph you are in third gear.

as for changing the gears out, you also have to purchase new carriers. Its cheaper to put larger tires on it.

 

[aboonski]

CCATLETT1984, did you get in on the STE/ICE kits that Fred was selling by chance? Mine is due to arrive on Monday and I am hoping it has the capability to show engine RPM via the large connector under the dash. Also, if I wanted to cruise at 70 mph all day long with the 456 gears, what size tires would I need to do that? I have the H1 rims but need to start thinking about the tires that I want.

Alan

 

[CCATLETT1984]

Yes it will show the rpm's there is a tach signal on that connector.

You can run the engine at the governor all day long and not hurt it one bit. I would suggest 36" or 37" tire. if you stick to a skinny set then you can get away with not much trimming and not need to do a suspension lift. I recommend getting the front spring packs pack to what they were when new though. You can probably have them add a leaf or two to get them back to being flat. The easiest way to make more room in the front withough trimming the fenders back, is to use 1" zero-rate springs to move the axle forward. http://www.offroaddesign.com/catalog/Zero Rates.htm

For the rear you have plenty of room leaving it stock, but you could add a short block to level the truck if needed.

With my tires i can run 75mph all day long, but the engine is happier closer to 70. You will be able to do 70mph with 37's but the engine will get better mileage doing 65mph.

 

[aboonski]

Awesome reply! Thanks for the info! Really looking forward to the STE/ICE test set now! I am working with the guy who sells Hummer stuff for all of my H1 rim needs. I am trying to better my fuel economy first of all and top speed second so the tires will mean everything at that point. I love the appearance of the H1 12 bolt rims but if I can get by with the purchase of different 16" tires in the 36-37 range I may just give up on all the work required for the fancy rims. I have five of them by the way so just imagine how much it will cost for the tires and rim locks!

 

[CCATLETT1984]

check on his prices for the valve stems, dont be shocked though.

Work required, you just need two 2" spacers for the front axle, thats it.

You dont have to run the beadlock inserts, but a guy on www.pirate4x4.com "cj66Dean" (something like that) makes metal inserts that function as a beadlock only, not run-flat. They are ~$50 a rim. I have pics of them in my photo album that is linked in my signature. I love the beadlocks. I had a front tire blow while going 65mph on the freeway on the way home from aberdeen last year, I felt no jerking just a sloppy feeling from the steering. the tire wasnt able to spin on the rim at all and that let me pull over safely. Plus if you HAVE to, you can swap a tire on the side of the road without any special tools.

 

[aboonski]

I'll check out your photo album and that's probably how I will go. Three of the rims & tires that I got had runflats inside plus they had the stock valve stems so all I wound up buying was the fitting with the inflator valve inside which was quite reasonable. I was really happy to borrow that penta-socket to remove those bummer nuts from around the rim. Any value in those penta nuts at all or am I stuck with them to use as sinkers?

 

[CCATLETT1984]

the new nuts are regular six-sided, the penta's are fine to use if you have the socket for them.

 

[AJMBLAZER]

You could change the gears, but it'd slow down the truck and really hurt it's pulling power. The TH400 has a really high first gear (2.4 and it really needs the lower gears for any sort of torque to the wheels. And yes, you'd have to change the front and rear gears, or forget about using 4WD. I have been told that the next ratio that the Dana 60 and 14-bolt have in common is 3.73 (at least commonly available) and I sure wouldn't want that.

4.11's are available as well.

For an easier "gear swap" you could try larger diameter tires, but that has all the negatives of the gear swap (except cost/time) with the added issues of reduced range of motion for the suspension (and/or need for a lift to get more clearance).

There are other options to fit taller tires without resorting to a tall lift. Mine has 38's and 1" of front lift.

 

[11Echo]

A half dozen of my cilvilian 1 ton 4x4's have had T 400 trans/3.73 gearsets/33" tires and plenty of power and speed. No problems.

 

[ARMYMAN30YearsPlus]

Now that is a tow is it a C12 but it looks bigger. On my 1031 what is the biggest tire I can put on it without cutting it?

 

[11Echo]

Now that is a tow is it a C12 but it looks bigger. On my 1031 what is the biggest tire I can put on it without cutting it?

I would think you could run the 33.3" tall 255/85-16's like I have on my M1008. I have no problems with clearance. The shop body on your 1031 should have enough room for them also. Others here might have other tire option choices. The aircraft is a C45.

 

[hobie237]

I guess I just use my truck in a more atypical manner. I guess I could throw on 33" tires, but I doubt I'd notice much of a difference, because they're only about an inch and a half taller than stock. I don't know if they'd allow for enough suspension movement for me to be happy. While I'm sure it could still pull, sometimes- but I could use a bit more power and/or gear- that's why I'm going with the 700R4- it just seems silly not to have an overdrive and the better 1,2,3 ratios- especially when reman 700R4s can be had for under $1000, and the swap could be done in an afternoon.

That said, I wasn't aware that 4.11 was commonly available, but that's good to know.

I'm not really interested in cutting the fenders on my truck. Got nothing against those who do it, just not interested myself.

 

[AJMBLAZER]

You could fit the 255/85R16's like he mentioned without cutting anything. They wouldn't rub anywhere even if you flexed the wee out of it.

 

[hobie237]

Yeah, but they also wouldn't be that much taller than stock, and therefore wouldn't be all that helpful for me. The 700R4, on the other hand, will give me BETTER low end pulling and an actual overdrive- hard to beat that for my needs.

 

[AJMBLAZER]

Talk to Croatan about that. He's got the same tires as me and feels that even with the 700R4 feels he's low geared.

4.56's in a diesel truck like ours with stock tires is like buying a stock tired gas truck with 5.13's.

 

[11Echo]

For tire comparison I will use a BFG Mud-Terrain for example.
LT 245/75R16 30.7" - 677 revolutions per mile at 45mph.
LT 235/85R16 32.0" - 650
LT 255/85R16 33.3" - 625
LT 285/75R16 33.1" - 628
LT 315/75R16 34.8" - 598, requires some extra clearance.

Next time I tire up this dually, I will put 255's on it.

 

[CCATLETT1984]

before i lifted my truck i had 285/75R16's on it

 

[beaubeau]

Well guys I got my M1008 home yesterday. took it out on the road today and I thought it did not shift out of 2nd gear!!!???. 55mph and it does SCREAM!!! The people who specked these vehicles out for the US of A must have stock in GM, engine division, and the oil Cos. Way geared too lo, even for off road. Why such a Low gear ratio in M 1008 and Hi gears in M1009??? I am going to find a doner truck and change to 3:73. I had a 2500 6.2 in 84 and it was perfect gears for all around use. 25 -30 mpg. Next week I pick up my m1028.