I bought my 2002 (five-speed manual with Tow Package) Blazer last month, and the gearing seems *WAY* too low. It's easy to move out from a stop in second gear. On the freeway I buzz along over 2000 RPM, and people are still passing me like I'm standing still.

I looked at the RPO code in the glovebox today, and it shows "GU6" (3.42 rear ratio) but I have LT235/75R15 tyres and the numbers don't add up : in fifth gear, it's running 1500 RPM @ 45 MPH and 2000 RPM @ 60 MPH. I'm thinking it has the 3.73 (GT4) rear axle -- how can I check??

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The easiest way is to pull the rear diff cover and count the teeth or look for the numbers stamped into the ring gear. 2000RPM at 60MPH seems about right for 3.73:1 gears.

 

Mine's the same way, Tachs out at 2500 rpm's running 70mph.

2 door, 5 speed, GU6, 235/75/15's.

 

Thanx swartlkk, I'm gonna pull the diff'l cover off Sunday and have a look.

I put the tyre size (235/75R15) and GU6 ratio (3.42) and five transmission gear-ratios for the M50 into the "Speed/RPM Calculator" at car-videos.net and it shows speeds over 10% greater than what my speedo shows for each gear and RPM. I'm thinking either the speedo is off, or else I have the GT4 diff'l gears, or maybe both.

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First bought a differential cover gasket, sealant, and gear lube; then pulled the cover to look at the gears. Found the tiny little hard-to-spot stamp "41/12" on the ring gear, then counted ring teeth to be certain -- yes, 41 of them. So my Blazer does indeed have the 3.42 "GU6" gearset. Now I'm thinking the speedo is off, next step is to check against some mile-markers.

Out of curiosity, I have to ask : does anybody reading this have the 3.08 "GU4" rear gears? If so, is that coupled with the wide-ratio "MG5" transmission?

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I've checked mine with a GPS, both speeds matched.

I think it's the trans gearing, I know what you mean about the low gears though, on the interstate in 5th gear I find myself hitting the clutch trying to find a higher gear, only to realize I'm already in 5th.

 

Checked my vehicle VIN against the "RPO Decoder" (thanx, Kyle! See link below) to make sure my Blazer has the M50 transmission (not the MG5) yes it does. Now I definitely want to get the 3.08 "GU4" rear gears. Seriously, with the torque of this motor and the depleted-uranium manhole-cover flywheel, I can start in first gear at idle; or in second gear with just a *tiny* bit of clutch feathering.

RPO Decoder by VIN