How to find gear ration

[fullauto4u]

Hello again, I have a '98 GMC K2500, where would I find info on the gear ratio ? on the codes on the inside of the glove box ?

[SCREAMINXL]

Look in the glove box. GU6=3.42 GT4=3.73 GT5=4.10 G80=gov lock posi:)

[fullauto4u]

Thanks for the info, lokks like I have the 3.73's (was hoping for 4.10's)

[ChevyCowboy]

will a 93 k2500 have the same codes ?

[grancito]

Pretty sure it will be the same, but if you have a different one, look at "GM option codes" on the internet there are color codes in one list and transmission codes in another.

[torque454]

With all this talk of tachometers being off and stuff like that, im betting i need to check the sticker in the glove box to verify my axle ratio. The tach tells me its got 3.42s but if its a a 3/4 ton like its labeled (and since its a non EGR engine which i understand were only 3/4 ton engines) it should be 3.73 and the tach doesnt quite show the correct rpm for 3.42 but it was closer to 3.42 than 3.73 if i remember right.

[grancito]

A problem with after market alternators is that the pulley size can be different and show incorrect revs. After many alternator failures mine was replaced with a genuine part that had to have a new regulator after one year, that bit is for those who have charging problems, the alternators don't last long.

[SCREAMINXL]

If anyone wants 4.10's mine are coming out soon. Shoot me an offer. The rearend is open, no posi.

[ChevyCowboy]

ok so i looked inside the glove box and in the g's it has GMC GT5 _80 i dont know what the missing letter is
(cant read it well its scrached off) would that be a g also and mean that i have a posi?:confused: the gt5 means its got 4.10's correct

[SCREAMINXL]

I'd say you have 4.10 with a posi:)

[DaveS]

Reading this, it made me wonder what ratio I had on my 1995 chev. 3/4 ton, 6.5. Looked in the glove box and all the codes are worn off. How else could you find out the gear ratios?

[Texaschevy]

u can go to a dealer give them your vin and theyll give an options sheet for that truck and then same thing itll have the gt codes gt3- 343 gt4- 373 gt5- 410

[grancito]

You will have 3.73 or 4.1, Mark the side of the drive shaft and the bottom of the tire, move the truck one turn of the tire and look to see if the drive shaft mark is up at the top it's 3.7 if it is to the side a little down, it is 4.1

[Husker 6.5]

Reading this, it made me wonder what ratio I had on my 1995 chev. 3/4 ton, 6.5. Looked in the glove box and all the codes are worn off. How else could you find out the gear ratios?

Check the pass. side axle about five-six inches from the diff. Although it is supposed to be visible from the rear, the three letter axle code could be rotated around to the top, front or bottom of the axle tube. For the 14 bolt 10.5" rear the codes are as follows: (1) indicates posi-trac diff

RYK, RYN(1) - 3.42
RYL, RYP(1), XYL, XZC -3.73
RYM, RYR(1), XUD, XYM, XYY, XZA, YAL - 4.10
XYN, XYR, XYZ, XZB - 4.56

Hope this helps.

Husker 6.5

[grancito]

Even easier, Tach reads 1917 rpm at 60 mph for a 3.73 diff.

[A. Bomb]

Tach reads ~2150RPM at 65 mph in a 2000 dually K3500 with 4.10 gears.

[grancito]

Should read 2282 rpm calculated for 245 75 16 tires at 65 mph, if the standard tire size is larger then the tach reads lower.

[Chevylover]

Or 1800 rpm at 60 mph with 265/75/16 OEM alloy rims and 3.42 gear ratio !
With these wheels, my speedo is absolutly exact. Checked with the Police !

If i put my 285/75/16 BFG on 8x16 Alcoa's, than my speedo will show lower than real.


Cu,
Sven


Cu,
Sven

[grancito]

Was that an expensive speedo check?

[Chevylover]

Was that an expensive speedo check?

No ! Absolutly free ! I remarked while driving with my 285/75/16 and a Navi on board that it shows much more than my speedo. I checked with the 265/75/ in winter again and now the speedo is +/- 1 km/h off. So i asked a friend at the local police station, if he could check my truck with their laser pistol. My navi was right.

245/75/16 -> speedo ahead about 100 Km/h but real 96 Km/h

265/75/16 -> speedo exact +/- 1 km/h

285/75/16 -> lower than real - 120 Km/h showing but in real 130 Km/h.

All with the 3.42 gear ratio.

Cu,
Sven