What is my rearend?

[66fleetsidewarrior]

I've got numbers 8856525 and nothing comes up when I try and research them. I have a '66 c10 with a 327, which we just built and sounds amazing. According to chevy they only put posi 4.11's but I can't find anything about it. Any info is appreciated as always! thanks guys.

[Captainfab]

Other that telling you your truck has a 12 bolt, I can't tell you what geat ratio you have. There are 2 ways to determine that. One is to find the build code stamped on top side of the passenger side axle tube. This method will only be accurate if no one has changed anything inside in the past 47 years. The best and what I always recommend, is to simply pull the cover and have a look. The tooth count is stamped on the edge of the ring gear. IE: 11 41 is 3.73 gears.....41 divided by 11. The differential is one of the most neglected parts of a vehicle. Yours could most likely use an oil change. It'll only cost you a couple quarts 80W90 gear oil and a cover gasket......and if you're lucky a bottle of posi additive.

[66fleetsidewarrior]

Originally Posted by Captainfab

Other that telling you your truck has a 12 bolt, I can't tell you what geat ratio you have. There are 2 ways to determine that. One is to find the build code stamped on top side of the passenger side axle tube. This method will only be accurate if no one has changed anything inside in the past 47 years. The best and what I always recommend, is to simply pull the cover and have a look. The tooth count is stamped on the edge of the ring gear. IE: 11 41 is 3.73 gears.....41 divided by 11. The differential is one of the most neglected parts of a vehicle. Yours could most likely use an oil change. It'll only cost you a couple quarts 80W90 gear oil and a cover gasket......and if you're lucky a bottle of posi additive.

I'm definitely going to be swapping fluid. It has been sitting for about three years and since I have owned it over the last year and a half it hasn't moved except when we have pushed it out of my driveway. I'll check those numbers tonight to see what it is. Thanks for the info!

[NEWFISHER]

Why did I think this was a horrible garage build accident?

[66fleetsidewarrior]

Originally Posted by NEWFISHER

Why did I think this was a horrible garage build accident?

No horrible accident here. The previous owner didn't give me much info on the truck when I bought it and this is my first classic truck that eventually be completely restored. So far we rebuilt the motor, bored it out to a 331, threw some bigger valves in a different set of heads, put a little bit of a cam in it, put some chrome on it simply because it was cheaper than OEM, new gas tank. Disc brakes are next, new driveshaft, headers, completely rebuilt transmission, air suspension, vintage air, new steering column new glass and seals all the way around, new wood for the bed, replace sheet metal where needed and then paint it. There are no numbers on the passenger axle housing that I can see but I will put the cover and see what ratio I come up with.

[boucher racing]

After reading this post, I got to thinking what rear gear I was running and changing the gear oil was not a bad idea anyways.

I am loading up for a T5 to 700R4 swap and gearing is important with the O/D tranny.

So I pulled the cover and had a look. Help me out... this is a 3.54 rear gear??? am I reading this right?

-

[66fleetsidewarrior]

Originally Posted by boucher racing

After reading this post, I got to thinking what rear gear I was running and changing the gear oil was not a bad idea anyways.

I am loading up for a T5 to 700R4 swap and gearing is important with the O/D tranny.

So I pulled the cover and had a look. Help me out... this is a 3.54 rear gear??? am I reading this right?

-

That should actually be 2.55 gears if i did my math right. According to the way they explained it, 46 divided by 18 equals 2.55.

[boucher racing]

I double checked, it reads 46 - 13.

Is this a stock option? Dana 60 - 35 spline, 3.54 gear ratio....

Thanks all

[61K10]

I had a 72/3/4 dully with 3.54 gears

[Captainfab]

Yes those are 3.54 gears.

If this is a Dana 60 with the 6 lug, that is a rare differential

If it is a Dana 60 with 8 lug, not as rare.

If it is a Dana 44 with the 6 lug, that is quite common in the GMC's

[boucher racing]

Originally Posted by Captainfab

Yes those are 3.54 gears.

If this is a Dana 60 with the 6 lug, that is a rare differential

If it is a Dana 60 with 8 lug, not as rare.

If it is a Dana 44 with the 6 lug, that is quite common in the GMC's

Good info. It is in a 66 GMC swb w/ factory 250.

How do I tell the difference between a Dana 44 and 60?

[Captainfab]

This pic is for a front differential, but the rear differential center section is the same. The covers are very similar but there will be either a 44 or a 60 in the #3 position.

A shortbed 1/2 ton will likely have a Dana 44.