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Old 02-23-2006, 12:08 AM
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Rear end gearing

Let me first say I have looked everywhere possible for this info, but I couldn't find it anywhere else so i'm begging for some insite here.

I just found out my 81 Chevy C10 originally had a L6-250cid engine from the factory. My question is .. What was the typical rear end ratio for this engine/truck combo? It's a 10 bolt oval cover. I thought it was a 3.08, but now I have no idea.. Any info at all will be appreciated!

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Old 02-23-2006, 07:01 AM
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First off you have the standard run of the mill GM 8.5 inch ring gear equipped axle and the axleshafts have a 28 spline count.

My 1981 Dealer Order Guide and Quick-Spec contains everything the entire Chevrolet line-up came with from the factory except for dealer only options.

According to the book:
Your engine
RPO LE3 4.1 liter 250 cubic inch engine,
Came with either one of the transmissions:
RPO MM3 3-speed manual
RPO MM4 4-speed manual
RPO MX1 automatic (most likely the TH350C)
And came with the following axle ratios according to the transmission AND GVWR rating:
The 2.73 gear ratio had an RPO number of GQ1 EXCEPT for the MM3 transmission equipped C-10 truck with the 6100 GVWR, it was not available and the GQ1 code was given to the 3.08 gear ratio in this application ONLY.

The 3.08 gear ratio had an RPO number of GU4 EXCEPT for the MM3 equipped 6100 GVWR, and it was given the number GQ1

All three transmissions were offered with either the 2.73 OR 3.08 gear ratio for the 4700, 5200, 5600, and 6100 GVWR ratings EXCEPT for the above mentioned differences in the 6100 pound GVWR.

The axle COULD have been ordered with the L69 engine axle code GQ1 with a 2.56 ratio, or the LE9 engine axle codes GT4 (requires RPO Z82) or G84 (high altitude applications only) axle code for 3.73 gears.

ALL ratios were available with locking differential which carried an RPO code of G80.

Your truck would have came from the factory with ANY of the tire sizes:
FR78-15B, P205-75R15, P225-75R15, P235-75R15, or LR60-15, and 4X4 would have also came with the optional 10R-15B size tires.

IF you have the RPO code listing for your truck it MIGHT be in the glove compartment on a large decal, but most were worn out and the adhesive let loose and the decals are long gone by now.

If this is the original axle and hasn't had the gears changed over the years, there will be an axle identification code on the passenger side axle tube between the the cast iron center gear carrier section and the passenger side spring mount on the front side of the tube. I listed all of the original codes above.

If you have the original driver side door there will be a decal on the rear facing edge of it with the GVWR rating of your truck. The 1980 and older trucks listed the GVWR on the VIN tag.

All of this information can also be found by bugging the parts counter guy at your local Chevy dealer too.

You can also get a microfiche copy of the original dealer window sticker that was put in the window of your truck if you contact the GM archives and ask for it. I got one for my 1981 Malibu, and my 1982 C-10, but they are available from 1977 to 2000 from what I can remember.

Hope this helps you.
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Old 02-23-2006, 09:25 AM
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What puzzles me is he said his rear axle cover is oval. That doesn't indicate an 8.5 which is decidedly round. You can ID your axle here:

http://truckparts-specialists.com/ca...ture-guide.htm
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Old 02-23-2006, 07:49 PM
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The only thing that would indicate anything other than the 8.5 in a Chevy truck, would be a different cover bolt count (12), a Dana 60, or hopefully not if it would even come close anyway a 7.5 from something else modified to fit under the truck.

He did state a 10 bolt cover.
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Old 02-23-2006, 08:28 PM
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Agreed. A 7.5 should have never been installed from the factory, but I don't know of any oval 8.5". That website should clear some things up.
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Old 02-23-2006, 09:20 PM
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Thanks for all the info. I verified it is an "oval" 10 bolt cover. I looked all over the passenger axle for a part number or marking of any sort and nothing. I have the original truck sticker with the option codes, LE3 L6 250CID, MX1 Auto Tranny, and ZJU 205/75R15 tires, but it doesn't say anything about the rear end. I wouldn't be suprised if it's from something else, I just wish I knew what it was.

Last edited by underdog305; 02-23-2006 at 11:15 PM.
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Old 02-24-2006, 02:02 AM
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This will also help, looking at the bottom of the housing center section, there will be metal "fangs" protruding straight down just at the 7-o'clock & 5-o'clock bolt locations.
The 8.5 will have larger metal "ears", and the 8.2 won't have anything.

GM 7.5/7.625 inch axle.



GM 8.5 inch axle.



GM 8.2 inch axle.

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Old 02-26-2006, 07:54 PM
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I found a code on the passenger side RUB 112W11. I've looked for a explanation of the code, but I cant find anything. Anybody know what it means or where I can find out?
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Old 02-27-2006, 11:57 AM
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rearend ID

I put a rearend just like that under my 58 apache 1/2 ton. It is a 8.5 ring gear 28 spline Axel(Powertrax order form shows a 30 spline as well) GM 10 bolt.73 to 87 Chevrolet trucks have ether a GM12 or a GM 10 bolt (with the oval cover).Mine has a 41 tooth ring gear and 11 tooth pinion gear.I also installed a Powertrax locker in it.I ordered a clear gears cover for it and it is definitely oval in shape.It should have 11 inch brake drums.I can email you a picture of the rearend if you want.I am not good enough with this thing to attach the picture to the post
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Old 02-27-2006, 12:23 PM
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Hollander says RUB code is a :

41-15 (2.73) non-locking
10 bolt cover
8-1/2" ring gear
11x2" brakes
Chevrolet 10 pickup 78-80 conv. cab,
4x2
GMC 1500 pickup 78-80 conv. cab, 4x2
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Old 02-27-2006, 12:39 PM
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Thanks to everybody that helped me figure this one out! Now anyone know of a rear end shop in South Carolina that can make it a 3.55 posi? or is there a gear kit out there that's worth buying?
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