Trying to get gear ratio

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by renchr01, Jan 19, 2011.

  1. renchr01

    renchr01 New Member

    I have an 88 GMC Sierra. I looked at the RPO codes for the rear and even checked RPO then called GM dealer. Low and behold they could not help me. The only 2 G codes I have are : G60 and GQ1.. The G60 means it is a spring axle.. Got that much. The GQ1 tell me it is a standard ratio rear... What the heck does that mean.
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I would search for the VIN decoder here on the site that will tell you more info as well. Since i find it odd that there is a GQ1 but no GT symbol.
  3. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    It might just be faster to go count rotations:

    1) Jack up both rear wheels
    2) Mark the tire and driveshaft
    3) Rotate the wheels through one turn while counting the number of rotations of the driveshaft. How many times the driveshaft rotates for one wheel rotation is the gear ratio (so, if the driveshaft goes through about 3 3/4 rotations, you have a 3.73 axle)
  4. renchr01

    renchr01 New Member

    Ok MrShorty I took your advice n jacked the wheels... Results are... 4.75 rev for driveshaft to 1 rev tire...
    Last edited: Jan 19, 2011
  5. stephan

    stephan Rockstar 4 Years 5000 Posts

    4.75 or 3.75? That's incredibly low. Could you be off by 1 revolution?
  6. 99Chevy

    99Chevy New Member

  7. stephan

    stephan Rockstar 4 Years 5000 Posts

    That's a great idea 99Chev, but the posters vehicle is an '88 like mine & compnine wouldn't take my '88 Silverado vin#. I've tried it several times & it keeps giving me the message "check back later, we update new vehicle info regularly" which makes me think it might only go back 20 years. It never tells me my truck is too old, the site just doesn't seem to recognize the vin # as being in it's base & judging from their answer maybe the computer thinks it's too new to be in there yet lol
    The other prob with him using comp nine is that with a 23 year old rig, some previous owner could have put a different gear set in it.
  8. Patman

    Patman Rockstar

    go see a transmission shop. usually the also deal with rear ends and transfer cases. they will probably know off hand.
  9. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Sounds like a 4.88 rear end, then. Not a stock ratio, though. Do you have any reason to suspect that someone has rebuilt the rear end at any time?
  10. renchr01

    renchr01 New Member

    Well I tried it again and still came up with 4.75. After looking at the possibilities it sounds like it is a 4.75 rear. I tried plugging my vin into the link and it tells me the same try back later. Then I plugged it into a different vin decoder and it gave me everything but the gear ratio. The reason I was doing all the inquiring was because someone brought the truck to me and said the transmission sounded like it was slipping and giving high RPMs. I took the truck out and test drove it and while testing I did notice that it sounded like the revs were going up but no slippage. I then hooked a tach up and tested and everything tested fine but the RPMs were running at about 3000 @ 55 MPH. So I figured I'd check the ratio and with this 4.75 ratio it would explain the high RPMs

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