83 C10 axle identification

[dunyet]

I just picked up a 1985 c10 SWB stepside near Memphis. Trailered it home to Mobile last weekend. Got home and had a vibration above 50mph. traced it down to the axle, took the cover off and found the issue. the PO welded the pin thru the spool piece, I had to cut it to remove the C Clips. it was a 10bolt.

i went to the local pull a part yesterday and got a 12 bolt rearend out of a 1983 C10. I was wondering if any of you could identify it as being an 83 truck axle?

stamping on the housing is GM72 the passenger side axle tube has a stamping of KAA 234W72

thanks in advance

[kwmech]

Picture would help a lot

[dunyet]

Here's a couple the KAA and the 234W72 are on the axle tube

[hatzie]

According to the 1979-1984 parts books;

KAA is an 8.875 (Truck 12bolt) axle with 3.07 gears and JB1-JB3 Brakes used in 1979.

[dunyet]

One more pic
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[dunyet]

I did confirm the 3.08 gears on the ring gear it’s stamped 14:43

Got it installed this evening, now I have to a different u joint for the driveshaft. Existing one for the 10 bolt will not fit this axle everything else bolted up in place.
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[hatzie]

3896839 is the raw Truck 12 bolt casting number. All that tells us is it's an 8.875 axle.
The stamped three digit letter codes are what tells us what it came from and how it was optioned.

[N2TRUX]

Originally Posted by dunyet

...Got it installed this evening, now I have to a different u joint for the driveshaft. Existing one for the 10 bolt will not fit this axle everything else bolted up in place.

You will need a conversion U joint. I recently did the opposite on my 77 Cheyenne. I swapped a 12 bolt 3.08 to A 10 bolt 3.42 Take a look here- "Elwood" the 77_remix in post #247 it lists the U joint I used.

[dunyet]

Thx guys, I got it on the road yesterday. I did pick up a conversion U joint it was at advance auto parts. Moog #372.
I need to check my ring gear in my old axle I believe my truck is running less RPMs now at 60mph. I must have had lower gears in the 85's 10 bolt, again thx for the help

[hatzie]

You can look up the original axle ratio in the parts books using the three letter 10 bolt axle code off the axle tube or just get the gear ratio off the gears.

If the old axle isn't the same ratio as the new one you'll need to swap the speedo gear(s). If you're lucky you'll only need to swap the driven gear. If you need to remove the driven gear you'll have to pull the tail housing. Get new seals and maybe even the driven gear housing if it's the least bit loose. I'd be sorely tempted to replace the output bushing in the tailshaft housing as long as it's off.

The speedometer gear usage charts are in the parts books. You can download the 85-91 parts books and look em up. They're in my manuals post.

Type "1985 SPEEDO GEAR USAGE CHART" in the search box and it should take you to the first page of the charts. If you leave out the year you'll get several hits before you eventually get to the charts.

To read the speedo gear chart You'll need your tire size, RPO for the transmission you're running and the already known new axle ratio... 3.08... Not sure why GM lists 3.07 some places and 3.08 others. Meh close enough.