04-22-2007, 06:04 PM | #1 |
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Join Date: Mar 2007
Location: Ft. Worth, TX
Posts: 20
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Rear End Ratio ID
Hi Folks,
I have a 79 GMC Heavy Half and I am trying to ID the rear end ratio and if it is a limited slip or not. The options list is not in the glovebox and I cannot seem to find the ratio etc anywhere on the truck. Is there someplace I can find the ratio and if it is limited slip or did a certain ratio combo come on this truck? The axle is a 12 bolt 8 3/4 unit, that I know for sure. I need to change the fluid and I need to see if I need the aditive or not. Please advise and thank you. |
04-22-2007, 06:30 PM | #2 |
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Join Date: Jul 2006
Location: Central PA
Posts: 12,201
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Re: Rear End Ratio ID
well you have a few options...
1. pop the cover and read the numbers on the ring gear... 41/11 = 3.73 and so on... If it has springs in the carrier then you have limited slip, if not then it's open. You will see the spings that i'm talking about... 2. Jack up one wheel (rear preferred), if you can roll it then it's open. Mark the drive shaft and see how many times the driveshaft turns to roll the wheel twice, (i.e 3 times = [3.08's? 3 3/4 then 3/73?) If the wheel doesnt turn then it's limited slip... 3. In that case jack up both wheels and do the same as above but only count how many times the driveshaft spins vs. one wheel revolution? 4. Hold the brake and do a burnout, 1 black mark = open 2 marks = limited slip If you have another vehicle to run to Autozone then just pull the cover and drain it... Make since? I'm lost now...
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The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer" Last edited by msgross; 04-22-2007 at 06:34 PM. |
04-22-2007, 06:35 PM | #3 |
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Join Date: Mar 2007
Location: Ft. Worth, TX
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Re: Rear End Ratio ID
Thank you for the info, since I have to remove the cover anyway I will go that route.
Thanks. |
04-22-2007, 06:36 PM | #4 |
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Location: Central PA
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Re: Rear End Ratio ID
Just be sure that you have a way to travel and get more.... Wouldn't be the first time someone stranded themselves (I did it with the wrong oil filter once!)
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The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer" |
04-22-2007, 06:54 PM | #5 |
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Join Date: Mar 2007
Location: Ft. Worth, TX
Posts: 20
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Re: Rear End Ratio ID
Thanks but no worries, I have a spare vehicle just incase.
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05-01-2007, 03:46 AM | #6 |
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Join Date: May 2003
Location: Shreveport LA
Posts: 3,170
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Re: Rear End Ratio ID
You may have 4 sets of numbers on the edge of the ring gear. One pair is the tooth counts, and one pair is the date of manufacture.
I don't know which pair comes first, but the date code should be obvious. |
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