WTF ! wrong gears ?

[pjaneiro]

Ok, i'm at about 70k now, and from what i've read so far it would be a wise choice to replace the fluids in the diff, anyhow, my rpo codes say gt4, so i should have the 3.73 gears right ? after doing the "trick" of having one of the rear wheels to the ground and lift one and making it spin two times ( i don't have a locker) i should get my gear set, well it stop a bit shy of 3 and half rotations on the shaft, so i beleive this is a 3.42, now is there a similar trick for the front ?, i need to know if both are geared the same, i never had any issue on snow, but on dry pavement it's hectic, hmm back to my original question, when i asked the dealer for the transfert case oil, he smirked and told me that the blue oil in the transfert case should NEVER be changed, it's a synthetic blend specially made and that once changed can screw with the gears and clutch inside, he told i should do the front and rear diff, but never touch the transfert case....


so my three questions are,

how can i check my font diff gear ratio

should i or should i not change the transfert case oil

and, did gm screw up on my rear diff ? or whole 4x4 assembly ?

[AlekG]

You would know if your front diff had different gears because your transfer case would be in pieces in your driveway, or somewhere out in the road.

The front and rear MUST be the same for 4WD to be viable.

GT4 should be 3.73 gear ratio, however, did you buy the vehicle used? The gears may have been swapped before you bought it. If not, then the sticker may be incorrect.

If you want to be 100% sure you could download the PCM programming with HPTuners or similar. It will say what the gear ratio the PCM is programmed for. I am assuming that when the speedometer is saying 100 km/hr you are actually going 100 km/hr.

A decent auto shop could also get that info for you using their scan tools.


As for the oil, the first place to look is the owner's manual. I don't have mine handy but I believe it does recommend when changes should be done for the diffs and the transfer case.

AG

[91RS]

To be honest, that trick isn't very accurate. I'm not sure I could tell the difference between 3.42 and 3.73 like that. You probably have the 3.73 like the RPO says you do. If you've got 70k on it, you should definately change both front and rear diffs and the transfer case. Differentials are supposed to be changed every 30k and transfer cases every 50k. The differentials use 75w-90 gear oil (I like Royal Purple, only $12 a quart at O-Reillys and has the limited slip additive already in it) and the transfer case needs Auto Trak II (which you can get from the dealer). The front axle takes 1.7 pints, the rear axle takes 2 quarts (or 4.8 pints with an 8.6" ring gear), and the transfer case takes 2 quarts.

[pjaneiro]

You would know if your front diff had different gears because your transfer case would be in pieces in your driveway, or somewhere out in the road.

The front and rear MUST be the same for 4WD to be viable.

GT4 should be 3.73 gear ratio, however, did you buy the vehicle used? The gears may have been swapped before you bought it. If not, then the sticker may be incorrect.

If you want to be 100% sure you could download the PCM programming with HPTuners or similar. It will say what the gear ratio the PCM is programmed for. I am assuming that when the speedometer is saying 100 km/hr you are actually going 100 km/hr.

A decent auto shop could also get that info for you using their scan tools.


As for the oil, the first place to look is the owner's manual. I don't have mine handy but I believe it does recommend when changes should be done for the diffs and the transfer case.

AG


Thanks for the reply , indeed my speed is not correct ever since i had my pcm tuned it's always been >>gaga<<, i know for a fact that it was accurate before, our pcm has little support in the tuning community and the speed calculator is innacurate from what i've been told, i have bigger tires 30.5" and i had them compensate for that, but even then, it's still too slow, when the speedometer says i'm going 60 i'm actually going 65.5, I also have the speeding ticket(S) to proove it ;-)),but then again i did tell them i had 3.73 gears, but now i am not sure, my rpo code does say gt4

[pjaneiro]

To be honest, that trick isn't very accurate. I'm not sure I could tell the difference between 3.42 and 3.73 like that. You probably have the 3.73 like the RPO says you do. If you've got 70k on it, you should definately change both front and rear diffs and the transfer case. Differentials are supposed to be changed every 30k and transfer cases every 50k. The differentials use 75w-90 gear oil (I like Royal Purple, only $12 a quart at O-Reillys and has the limited slip additive already in it) and the transfer case needs Auto Trak II (which you can get from the dealer). The front axle takes 1.7 pints, the rear axle takes 2 quarts (or 4.8 pints with an 8.6" ring gear), and the transfer case takes 2 quarts.

Thanks, i used a lazer marker on both the wheel and the drive shaft, and between 3.42 and 3.73 we are talking about a 1/4 turn, so it's still noticeable, but then again, i know what you mean, there's still a little play involved. for the the fluid change the rear diff is quite easy to spot the drain and fill plugs, but where in hell are the ones for the transfert case ? or the front diff ?

i'm more of a visual guy, so pics are always welcomed :)

Thanks everyone for your help

[WOOLUF1952]

To be honest, that trick isn't very accurate. I'm not sure I could tell the difference between 3.42 and 3.73 like that. You probably have the 3.73 like the RPO says you do. If you've got 70k on it, you should definately change both front and rear diffs and the transfer case. Differentials are supposed to be changed every 30k and transfer cases every 50k. The differentials use 75w-90 gear oil (I like Royal Purple, only $12 a quart at O-Reillys and has the limited slip additive already in it) and the transfer case needs Auto Trak II (which you can get from the dealer). The front axle takes 1.7 pints, the rear axle takes 2 quarts (or 4.8 pints with an 8.6" ring gear), and the transfer case takes 2 quarts.

Sorry if this is :offtopic: or:hijacked . But, #1) I have the G80 option. Is there a G80 in front and back diffs? And #2) Will the limited slip additive hurt if there is no G80 in the front?

[the roadie]

There is no G80 locker for the front diff, and there are none from the aftermarket either (and I pretty much guarantee there never will be). Limited slip additive shouldn't hurt the open front diff. gears.

[WOOLUF1952]

:thx & :thx

[Foosh]

ahhh it would be nice to get a front locker and yeah 3.42 and 3.73 are pretty close, how'd you mark it?

[ScarabEpic22]

Cant answer your gears question man, but Ill tell you for sure change all of the fluids. Front and rear diffs use 75W-90, Id recommend either Royal Purple or Amsoil synthetics. You're dealer is lying, get 2L of transfer case oil from a different dealer and change it. I did mine at 50K, about hit 97K now so its time again. Probably over Christmas break when I have a garage and my tools in the same place.

[91RS]

Thanks, i used a lazer marker on both the wheel and the drive shaft, and between 3.42 and 3.73 we are talking about a 1/4 turn, so it's still noticeable, but then again, i know what you mean, there's still a little play involved. for the the fluid change the rear diff is quite easy to spot the drain and fill plugs, but where in hell are the ones for the transfert case ? or the front diff ?

i'm more of a visual guy, so pics are always welcomed :)

Thanks everyone for your help

I don't have any pictures since I'm 2wd, but the transfer case plugs are on the back of the unit (i.e. facing the rear of the vehicle) and the front diff has the plugs on the driver side of the unit. It's actually nice that these trucks have drain plugs on the rear diffs, because almost all other GM vehicles don't have drain plugs.

[pjaneiro]

Damn, Just called two other dealers, THEY TOLD ME THE SAME....maybe it's a winter issue ? so far 3 dealers have told me to NOT CHANGE the transfert case oil...every fiber in my body tells me to, but now i wonder...

For the marking it's quite simple, get those laser pointers at your local dollar store, tape one to the sidewall of your wheel and the other one on the driveshaft, if you don't have lockers lift only one wheel and rotate the wheel 2 TIMES and count the the times the driveshaft rotates, if you have a 3.42 gear set the shaft will rotate 3 times and just be shy of half a rotation, if you have 3.73 it will rotate 3 times continue to a 3/4 turn extra and if you have the 4.10's well 4 complete rotation and just a bit extra more...kinda simple, so visually there is a huge difference between 3.42 and 3.73, just like when you watch the needles on a clock, beween 3:30 and 3:45 there's a good margin

[pjaneiro]

I don't have any pictures since I'm 2wd, but the transfer case plugs are on the back of the unit (i.e. facing the rear of the vehicle) and the front diff has the plugs on the driver side of the unit. It's actually nice that these trucks have drain plugs on the rear diffs, because almost all other GM vehicles don't have drain plugs.


i was looking at it last night, and i must REALLY be blind, i think i spotted the front diff ones, but teh transfert case. NADA.....maybe i have a "special one" ;-) or maybe the guy writing this text is "special"

I wonder, if i were to go to gm and tell them HEY, it says 3.73 but i got 3.42's, i want my 3.73's

If that's the case, would it mean that when i'm driving in the city in alot of my stop and go traffic i would get crappy mpg ?

[hatchet669]

i was looking at it last night, and i must REALLY be blind, i think i spotted the front diff ones, but teh transfert case. NADA.....maybe i have a "special one" ;-) or maybe the guy writing this text is "special"

on mine i saw them facing the rear.. there is one on the top to the rite and one on the bottom to the left... some people have regular bolts.. but on mine i have a inwards set hex hed... i didnt look at it to long but it is a negative screw.. but it was something that was a positive socket would be needed..

i mite have a pic but that would be at home... i'll check when i get there.. after work of course

[pjaneiro]

on mine i saw them facing the rear.. there is one on the top to the rite and one on the bottom to the left... some people have regular bolts.. but on mine i have a inwards set hex hed... i didnt look at it to long but it is a negative screw.. but it was something that was a positive socket would be needed..

i mite have a pic but that would be at home... i'll check when i get there.. after work of course

Well it's official, i am blind, i've even asked my brother to check for me, THERE ARE NO openings in the rear or in the front, I might of found the front diff ones, but for the rest, nada....Anyone has pics of the front and transfert case ?

Thanks