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Old 03-31-2006, 09:34 PM
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what is my rearend?

Can anyone tell me exactly what I have here as I am not a big rear end expert?

I know it is a chevy 10 bolt w/ 8.5" ring gear. The numbers on the ring gear states 3.83 gearing but I thought that the other two numbers are the teeth on the gears. If you look at the pic you can read GM 'part number' followed by 12 and 41 and finally 3.83 wouldn't 41/12 be more like 3.42 gears?

Also, what type of posi or locker is this I am dealing with? Any links or data would be much appreciated.

see attachment below for pic.
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Old 04-01-2006, 05:38 AM
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Differential

I only got to see 1 picture. I t looks in decent shape. What year is it. 60-70 had clutches toward the tube, I dont remember what the catch looked like. but not this. Age is signifigant just from looking at it, Every scheme in the world has been tried by somebody. are you having a problen. If it's a replaciment it's any bodys guess. GM should you only use a b oc,etc axles.. I could be aftermarket center section. Count the teeth 3.4 is likely GM number for a automatic transmission., but so is the other Does the ring gear have 41 teeth., and if you can tell does the pinion have 12. If 12 divided into 41 gives you what you got thats it. Otherwise someone has changed them. You cannot change one gear without changing the other. Next the thing to do is check the diff housing ID. for that axle the numbers will be stamped into the tube on the passenger side, probably on top. How ever it could be stamped on the front or the back. What year vehicle and model will help, but not neccessary. Get a steel brush and clean up the tube, get the numbers and call a dealer maintenance supervisor. The dealer manuals will identify everything. If the teeth numbers don't match up then some one has changed it. You can change the internal parts, or change the entire unit from one vehicle to another. I have done both many times. By the way I could not bring up but one picture or I might have been able to tell you more. good luck. mark
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Old 04-01-2006, 06:05 AM
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I say you got 3.42 gears and that differential is what they call a Gov-Lok. It ok for street but not made for abuse. They have been known to explode taking out the ring and pinion in the process. Here whats 4 Wheel and Off Road says: http://www.4wheeloffroad.com/techart...43/index5.html
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Old 04-01-2006, 08:49 AM
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The ring gear is stamped as so: (I'm sure I didn't completely read the part number right)

GM (General Motors)
1235128 (GM ring gear part number)
12-41 (12 pinion gear teeth and 41 ring gear teeth) 41 divided by 12 = 3.42 gear ratio.
3-83 (gears were manufactured in March of 1983)

And yes that is a Eaton Gov-Loc locking differential also known as the "exploding locker"

Is this in a Chevy/Gmc C/K-10/15 series truck?
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Old 04-01-2006, 10:24 AM
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ok, thanx guys....guess I shoulda left more data...first of all, it is in my 1983 K5 Blazer and it is all custom. Nothing stock anymore I don't think. I know it originally was the diesel model so it has the upgraded suspension and such. Now is has a 350 SBC in it and is running the 700R4 Tranny. There is nothing wrong with this rearend (as of yet) but I couldn't remove the fill plug from the housing so I opted for a differential cover with a fill plug and I just wanted to know what I had. The whole truck cost me $500 last summer course I have probably put close to $2000 in it since then.
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Old 04-01-2006, 12:57 PM
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gov lock and oil

Any of the LS diff's need to be kept in fluid which is usually different from regular fluid, which you probably know.With the change in the back coverwatchyour oil level, and axle seal,you can see the spots on the brake drum back up plates. You will be needing new brake shoesif you leak much. Don't forget to keep your tires the same size, run your spare or some other different tire very long and you will burn up the clutches mark
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Old 04-01-2006, 01:00 PM
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judging by the data being provided, I would assume that the 6" lift and 35's this summer probably won't be a good idea for this rearend?
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Old 04-02-2006, 10:56 AM
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With 35's I would move up to a set of 4.10 gears.
Anything over 36 inch I would personally move up to a set of or 1-ton axles and they usually have 3.73 gears or higher, most of the axles I have scavenged out of -tons have had 4.10 gears, with only a couple trucks yielding a set of 3.73's.
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Old 04-02-2006, 05:16 PM
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373-4.10

I would have thought 3.73 to be in a auto trans. Also the front axle in 4x4 3/4 ton pickup I would have bet a dana-spicer, fo that matter the rear axle a spicer. 25 years ago GMC would most likely all spicer. If you liked them check out Mopar's mark
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Old 04-04-2006, 12:38 AM
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Quote:
Originally Posted by madamstn
Any of the LS diff's need to be kept in fluid which is usually different from regular fluid, which you probably know.With the change in the back coverwatchyour oil level, and axle seal,you can see the spots on the brake drum back up plates. You will be needing new brake shoesif you leak much. Don't forget to keep your tires the same size, run your spare or some other different tire very long and you will burn up the clutches mark
The Gov-lock is not a limited slip diff. Because of that you don't really need the friction modifier additive.

35" is about as large a tire as you can use and have it not brake on you every time you drive it in the dirt. I however have had many friends break their 10-bolts with 33-35" tires and it isn't fun getting them home if you don't have a trailer or spare parts.

I think you would be better off with a 2.5" lift and some 33" tires. If you don't want to trim the fenders you could go with 4". When you go up to 6" you will need to put a whole bunch more parts and money into it. You will need things like a raised steering arm, extended brake lines, longer driveshafts, etc...

I am running 36's with 3" of lift on my '71 K5
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Old 04-04-2006, 02:09 AM
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My black stepside is running a 3 inch suspension and 3 inch body lift, and I had to hammer back the rear of the front wheel well opening.

And I'm running 4.10's as I was going to eventually move up in tire size, until I broke the truck.
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