Author Topic: Differential ID  (Read 7566 times)

Offline Ronno6

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Differential ID
« on: April 16, 2018, 04:33:21 PM »
I sure wish something,ANYTHING on this truck would make sense.
1984 C10 Stepside
Differential is 8.5", 2.73 ratio near as I can figure.
Code stamped into the axle tube on front of passenger side about 3" from center casting:
  BR3  G299  1

I have searched the web for info, but I have not found anything which directly relates to this code.

Anyone decipher it??

I am not certain how this ratio would perform with a Muncie M20 with 2.52 first gear.

What information will I need to get 3.43 posi setup for this critter??
« Last Edit: April 16, 2018, 04:48:59 PM by Ronno6 »
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Offline 75gmck25

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Re: Differential ID
« Reply #1 on: April 16, 2018, 06:36:57 PM »
The 2.73 would have been a common rear end ratio with a 350/4 speed in '84, but the truck transmissions had a 6.55 super low, and 3.58 1st gear.  It sounds like you want to swap in a car transmission, so you have lost the low end ratios.

The 6 cylinder trucks had 3.42 and 3.73 as common axle ratios, and it was optional on the automatics.  It should not be that hard to find an entire axle to swap in.   Its probably better to buy an open differential axle, and then add in a locking differential from Summit or Jegs.  Most of the aftermarket limited slip or locking differentials I've looked at are designed to swap into an open axle.

The trucks with factory limited slip differentials probably had the GM gov-lok, which is not a great axle if abused with burnouts.  Its designed to help get traction in a work truck, so they never expected someone to be trying to burn rubber with it.

Bruce

Offline blazer74

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Differential ID
« Reply #2 on: April 16, 2018, 07:09:17 PM »
BR3 2.73 Non Locking, G Framingham plant, 299 day of the year, 1 shift.
« Last Edit: April 16, 2018, 07:32:14 PM by blazer74 »

Offline blazer74

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Re: Differential ID
« Reply #3 on: April 16, 2018, 07:12:14 PM »
Assuming the original gears are  in there.

Best way is to remove the cover, the ring gear should be stamped with the ratio.  Or count the ring teeth and divide by the pinion teeth.

Offline Ronno6

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Re: Differential ID
« Reply #4 on: April 16, 2018, 07:39:04 PM »
I am indeed desiring to swap in an car Muncie M20 with a 2.52 first gear.
I have done the spin the wheel and count driveshaft revs and determined that mine in a 2.73.
I think the 3.42 diff would be a good ratio, but I do want posi.

Now that blazer74 has given me the info, I can move forward when I get to that point.

I have seen references to "series 2" and "Seriies4" in relation to differentials.
What is that all about, and what is mine?

 
« Last Edit: April 16, 2018, 09:03:23 PM by Ronno6 »
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Offline VileZambonie

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Re: Differential ID
« Reply #5 on: April 16, 2018, 07:44:49 PM »
What manufacturer are you looking into?
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Offline Ronno6

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Re: Differential ID
« Reply #6 on: April 16, 2018, 09:02:28 PM »
What manufacturer are you looking into?

Don't know as of yet.
Any recommendations?

Is mine most likely 28 or 30 spline axles?
« Last Edit: April 16, 2018, 09:28:08 PM by Ronno6 »
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Offline VileZambonie

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Re: Differential ID
« Reply #7 on: April 17, 2018, 06:35:41 PM »
Most likely 28 spline. I do not like lockers and prefer LSD. Auburn Gear makes nice cone style differentials. Strong and smooth, some guys say they don't like them because they aren't rebuildable. My argument to that would be that if you trash one the whole thing is probably trashed anyway and if yours needs rebuilding it was probably weak to begin with. I have an auburn pro behind my big block and it has held up nicely. Hopefully I didn't just jinx myself :) I would say shop around and see who has good deals going on inclusive of all of the components and installation material.
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Offline Ronno6

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Re: Differential ID
« Reply #8 on: April 17, 2018, 06:40:06 PM »
Most likely 28 spline. I do not like lockers and prefer LSD. Auburn Gear makes nice cone style differentials. Strong and smooth, some guys say they don't like them because they aren't rebuildable. My argument to that would be that if you trash one the whole thing is probably trashed anyway and if yours needs rebuilding it was probably weak to begin with. I have an auburn pro behind my big block and it has held up nicely. Hopefully I didn't just jinx myself :) I would say shop around and see who has good deals going on inclusive of all of the components and installation material.

I have looked into them, and seem to be solidly built units.
Only problem is, being a 'BAMA fan, I could never tell anybody what posi unit I have............
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Offline Ronno6

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Re: Differential ID
« Reply #9 on: May 12, 2018, 08:05:53 PM »
2 things are extremely evident after a short tool around the yard:

1. 2.73 way too high....3.42 definitely in the offing
2.LS or posi for sure......I kept 1 wheel spinning quite a bit of the time ( of course, the 2.73 didn't help...)
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Offline VileZambonie

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Re: Differential ID
« Reply #10 on: May 13, 2018, 07:07:15 AM »
Yeah ditch the 2.73:1, LSD is Posi, one in the same. Just remember to factor in your tire size and transmission ratios before you buy a gear set. There are many calculators online you can use to help you better pick the perfect final drive ratio.
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Offline Ronno6

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Re: Differential ID
« Reply #11 on: May 14, 2018, 06:39:25 PM »
I have found a differential from a 1987 C10 for sale, supposedly with a 3.42 ratio.
I hope to look at it on Wednesday.

What will the stamped codes will be stamped on the passenger side axle tube if it is posi and 3.42??
Is posi indicated by a letter at the end of the sequence?

I search for this stuff online but never seem to find what I am looking for........

Hmm, I had been thinking 3.42 because I had a 79 Z28 w/4 speed and 3.73.
I had thought my tranny was a 2.20 1st gear, and the 3.42 in the C10 with the 2.52 M20 1st gear woulda been lower overall.
BUT ...the Z-28 had a 2.64 1st gear..............
I just really didn't like the 3K  rpms @60mph......... 
« Last Edit: May 14, 2018, 07:06:35 PM by Ronno6 »
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Offline Ronno6

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Re: Differential ID
« Reply #12 on: May 15, 2018, 06:37:01 PM »
Where can I find a list of stamped rear axle codes for the 84 to 87 vintage??
It gotta be out there, but all I find are RPO codes and diagrams of the
stamped codes indicating the first 2 or 3 letters indicate the ratio..............
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Offline VileZambonie

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Re: Differential ID
« Reply #13 on: May 15, 2018, 08:28:29 PM »
Do not rely on any markings on the axle housing. You need to remove the cover to determine the gear ratio accurately.
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              ⌠ŻŻŻŻŻ'   [☼===☼]
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline Ronno6

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Re: Differential ID
« Reply #14 on: May 15, 2018, 09:35:26 PM »
The current owner may not approve.....
You can lead a man to water, but yoiu can't keep him from pissing in it.