GMC Sierra

How can you tell if you have a low speed rear end with out the tag for gear ratio ?

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Joyce Davis

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How can you tell if you have a low speed rear end with out the tag for gear ratio in a 1985 GMC High Sieria 3500
--
Joyce Davis

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.
u15231@uwe (GMCGalviaCarKB.com) asked:
How can you tell if you have a low speed rear end with out the tag for gear ratio in a 1985 GMC High Sieria 3500
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Joyce Davis
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I took a look at that calculator. Didn't dig into the website to far but on the 1st calculator that pops up there is nothing about transmission ratio. For a test I entered my known road speed, tire size and RPM, that calculator came up with 3.4 something. I run 4.56gears. There are some calculators on the web where he could enter known RPM known tire size and known tranny ratio and get a accurate rear ratio. Check some gear mfg sites maybe.
(GMC Gal via CarKB.com) asked:
How can you tell if you have a low speed rear end with out the tag for gear ratio in a 1985 GMC High Sieria 3500
--
Joyce Davis
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If you have a open differential jack one rear wheel up, chock wheels and support vehicle with a jack stand. Put vehicle in neutral and climb under vehicle. Watch lifted wheel and count how many times you turn the driveshaft to get one turn of the wheel. Use chalk to mark the wheel and driveshaft so its easier to count. Exe. you turn the drivshaft 3.5 turns to get one wheel turn you probably have a 3.55 rear, 3.75 turns 3.73 rear. If you have a posi rear both rear wheels will have to be off the ground. Also you can pull the cover off the rear and count teeth and do the math. 41 on the ring and and 12 on the pinion will be a 3.42

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This is incorrect. Jack up 1 wheel, mark it and the driveshaft. Turn the driveshaft until the wheel has turned exactly 2 revs. The number of turns of the shaft equals the axle ratio. This only works for open differentials. If it's posi, jack up both wheels and turn the drive shaft to make the tires make one revolution.
Al
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jack one wheel up and turn it around and count the turns versus the turns on the drive shaft. example 10 turns of the drive shaft and 5 turns of the wheel = 2 to 1 ratio. old john

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i have a problem with 4.3 and code p1345
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