Low-Range; Tire Size; Locker; and Midship Tanks

AlanTDickey · April 15, 2003

I have ordered a new 2003 GMC Sierra 4x4 crew cab 1500HD with the 6.0L it should arrive in a week or two. I have read a lot lately about things I may want/need to do to this truck on this site and others. I still have several questions for you knowledgeable truck folks out there:

1. With my 4 speed 4L80-E 2.48:1 first gear, my 4.10:1 rear end; and the 2.72:1 low-range reduction - my crawl ratio is 27.7:1. This seems a little high (gear not number). My current, stock 99 Trooper’s crawl ratio is appx 32.0:1, and it is a little to high for my tastes when climbing or descending steep hills. Can I, and is it a good idea to, replace the 2.72:1 low-range differential with one that provides a greater reduction - say 3.5 or 4.0 to one? [someone told me that I could not. Someone else said I can, but that I would have to stand on the brakes to keep it from moving in low range.]

2. I want to put GY MT/R 285/75/16s on the truck on 16x8 wheels. No French BFGs for this former Marine. I’m not going to put a lift the truck right now. I would consider cranking the torsion bars, but only if it does not harm the CV joints or create too much of a toe-in. How much do I have to crank the bars (not to level it - just to fit the tires)? Would a new front-end realignment then fix the toe-in problem? Will this hurt my CV joints? How much rougher would the ride be? In the stock configuration, would the 285s rub only on the back of the front bumper/fender, or would it also rub on the back part of the wheel well? If the former, can one simply shave off the back end of the plasticky bumper that would contact the tires? How?

3. Does the Eaton rear locker really lock fully and strongly if one of my tires is off the ground? See http://www.duramax.bizhosting.com/power_la...ton_lockers.htm.

When does it lock - i.e. how much of a difference in rpms will start the locking? How does it unlock? Eaton’s website states that unlcocking occurs “When both wheels regain traction.” How does it know? Do I need a manual locker if I plan on climbing some steep hills?

4. TransferFlow’s website says that its Midship Replacement Tanks are “Available for 2500 and 3500 series GM pickups only. Will not fit on 1500 series due to low clearance.” It left me scratching my head because according to the GM info, the 1500HD actually has higher clearance (8/9”) than even the 2500s. Does anyone know if TransferFlow is goofed up or is there a valid reason why the tanks would fit on a 2500, but not a 1500HD?

5. The 1500 non-“HD” as well as the 2500 can have the snowplow option. Why is the 1500 “HD” the only version that cannot come with the snowplow package?

6. Why in the #$&*% doesn’t GM put bigger wheel wells on its full-size trucks? I have more tire room on my little Trooper.

Did I make a good purchase?

I appreciate any input on any of these questions.

Shaners · April 16, 2003

First off, Welcome to the forum!!! :thumb:

1) You will have to try out low range and see how you like it... Mine seems about perfect and I have the same setup, (4.10 and 6.0L) but my t-case is slightly beefier. Your new crewcab will be alot bigger than your Trooper and will not go places that you have been before because of the OAL (You'll high center).

2) Your 285's will fit with some T-bar cranking and an alignment and possible trimming of the lower air dam in front. I don't recommend that you bottom out the adjusting bolts. Ride will be stiffer but still OK.

3) The Eaton locker is pretty darn solid. I think it is better than a limited slip for the conditions you want to drive in... but let me warn you again you will be driving a much bigger truck that weighs about 1500-2000 lbs more than the Trooper. In 4wd these trucks climb pretty good...

4) The 1500HD is not the same as the 2500HD. I believe the frame rails are different and that may be the problem. Call TransferFlow for the correct answer...

5) The 1500 and 2500 are lighter trucks... The biggest they come is excab longbed (1500) and excab shortbed (2500). Your truck will be heavier than the 2500 because of the crewcab option, but otherwise the suspension etc. should be pretty similar to the 2500.

6) Not only does GM need bigger wheelwells but also bigger tires... I think the small 245 tires are a cost cutting way of putting a load range "E" tire on the truck.

Finally, I think you'll love the truck unless you do "serious" off-roading... because it's too darn big in tight places!!!

Good Luck...

AlanTDickey · April 16, 2003

Thanks for the helpful response Shaners.

I’m glad to hear you like the Eaton lockers. The photos I saw on the previously-referenced website put my mind at ease a little too despite some of the lack of confidence I have heard about them.

I will definitely avoid trails with tight switchbacks or obstacles higher than acceptable for a 153” wheelbase. There are some books and websites with good information on the characteristics of many of the 4x4 trails here in CO, and they usually identify trails not suitable for full-size vehicles. I already have some trails in mind that meet my needs for adventure in a large machine. My uncle has followed me up some fairly hairy trials with his 1994 Ex-cab F-150, which I believe is only about 12” longer than my soon to be real truck. I think its turning radius is only about 3-ft shorter.

If the lockers work as hoped, however, the Sierra may outdo the LS diff Trooper on some trails I know of with steep rocky climbs without terribly high obstacles, and I can throw a lot more gear in there. It is in this environment that a low low-range would be helpful for additional power and control. I’ll try it out at after I break it in. Also, the trooper I think has about 8.5" of clearance with my 265s, and the Sierra with the the 285s will have about 10" of clearance, which hopefully will help offset the high centering problem on reasonable trails.

I'll send some photos if I make it to the top of Mt. Everest.

That leads me to another question, aside from the GM factory party line, what should I do or not do in the first 500 miles to properly break in this beast?

I’m hoping that GM will send me some photos, where I can see the little tires on a sonogram of the truck. If it doesn’t come soon, I’ll request a cesarean (ordered it on March 12).

I am hoping that I can crank the T-bars a little less if I shave off some plastic from the bumper/air dam thingy to help fit the 285s. I’m nervous about messing with the ride, CV joints, or tire wear too much. Does anyone know whether putting a Westin grille guard up front will require that I crank the t-bars a little more than otherwise to fit those tires?

I failed to mention that I had already called TransferFlow, and they could only repeat what the website said, and reaffirmed that it was a clearance issue. When I suggested that the 1500HD has the same clearance, they simply expressed suspicion on this point. For now, I've shelved the dream of a 45 gal tank. I don't want a replacement gas tank hanging down too low for a rock to puncture.

Thanks for the input.

Shotgun · April 16, 2003

You will have no problems fitting the 285's..I have 305 MTR's on mine and all is good..I cranked the t - bars a little to get the stance i was looking for.I haven't gotten mine re aligned yet but so far I have seen no reason to do so......Gun

Dihappy · April 16, 2003

Alan, Eaton has an Electronic Locker that should be available about now.

You could manually lock the rear end or unlock it from inside the cab.

Ill be going that route when they make one for my 10 bolt sometime next year.

Shotgun · April 17, 2003

ARB makes those lockers now...I'm partial to the air lockers because of the increased reliability. Click here >>ARB air lockers

AlanTDickey · April 17, 2003

Thanks all for the advice.

Shotgun, you're truck looks good, and you have the tires I think I'm getting - GY MT/Rs, though I will probably go with the 285s.

Do you like them?

How do the ride and wear?

I've read three awesome reviews. I want good on-road handling; 3-ply sidewalls; great handling on rocks, snow, water, sand, and mud; and nothing from France. It's either the MT/Rs or the E-rated Revos. I'm leaning to the MT/Rs because of the treaded sidewall structure.

Also, on the tire-sizing issue, I'm thinking about ordering tomorrow a Ranch Hand Bull Nose replacement bumper. See:

Front Bumper

It seems like this would avoid any rubbing by the 285s on the front side and would make the front end a lot stronger in case of impact with anything.

Anyone had any experience with these?

Shotgun · April 18, 2003

The MTR's are great and they are the quietest rough terrian tire made as far as I know and they pull in the mud like nothing you've ever seen.I pull a travel trailer often and a gooseneck with a John Deere 2640 and they handle the loads well.My bro in law just put BFG M/T's on his 1500HD and I had to pull him out twice the other day,he is very dissapointed but I'm not .....Gun :thumb: