Rear Diff I.D.

[swanthog]

Hello.
I found that the rear 14-bolt diff in the '80 Stepside I'm building has been welded (Lincoln locker ) -- including the center pin! I removed the rear end from the truck and spent more than an hour grinding and pounding the center pin so that the carrier and pinion gears could be removed.
Here it is in the truck with the !&$%#^@#^$ welded gears:




I went to the local parts yard to find replacement gears and all the 14-bolts were already removed except this style of Diff :



Can someone please tell me what type of diff this is? It seems nobody wants these. All had the diff cover removed and all were left intact.

The one I am trying to replace is different. The pinion gears are visible and there is no bearing as seen in the photo (right,middle).


Thanks!
Lawrence F.

[74CustomK20]

Hard to tell, but looks like you have a semi-float 14 bolt, and the one in the junkyard is a full float. Parts won't interchange far as I know.

[hatzie]

There's a reason there are no 14bolt 9.5" semi-floating axles. They break...
If you insist on keeping your axle look under the early 88-94 1/2 & 3/4 ton T400 chassis and 80's on up G20 vans.
You can buy a brand new open carrier for around $300 that comes with spider gears and re-use your ring and pinion.

If she's a 3/4 ton I'd upgrade to the 14bolt full floating axle. They're plentiful, darn close to indestructible, and cheap. So easy to set up a cave man could do it.
The only slight downside is you'll be moving to 8 lug 16" wheels.
The 3/4 ton 10 bolt or Dana 44 front axle isn't difficult to find with 8 lug hubs and spindles. Most folks are convinced they "Need" a Dana 60. Snag the axles off the same rig and you won't have any problems matching gear ratios.

The best people drive 3/4 and 1 ton trucks anyway....

[swanthog]

Thanks for your replies.

The original 1/2 ton drivetrain was replaced with all 3/4 ton gear by a previous owner. There are 8 lugs on all corners.

Here's what the rear hubs look like:








The front axle is 10-bolt and is a Dana 44.

If I nab the full floating rear axle, how can I verify the front and rear gear ratios are the same?

Thanks!
Lawrence F.

[hatzie]

That U-Bolt setup is scary. Previous owners do some frightening "repair" work sometimes. Get the right length U-Bolts for the axle you end up with and do away with the upside down U-Bolt plate that Bubba used for a spacer. Hopefully Bubba installed matching ratio front and rear axles...

Swap that POS 9.5" 14bolt with a 10.5" 14bolt full-floater. You need a 1973-1987 SRW (Single Rear Wheel) CK20 or CK30 axle. Cab N Chassis, G or P Van, or DRW (Dual Rear Wheel) will not drop in.

Since the U-Pullit goons thoughtfully pulled all the diff covers you can read the numbers on the ring gears of potential replacements and examine them for damage.
A SRW full floater is a drop in. You need the whole axle Drum to Drum with the E-Brake cables. U-Pullit yards are notorious for charging for every piece so get a price in writing before you even look. Compare to a regular salvage yard on price. It may not be worth pulling it yourself. Be very clear with the regular yard that you are asking for a Drum to Drum price and if they are charging extra for the brakes you expect the drums to be 100% serviceable and price refundable if they are worn or damaged beyond the service limit.

There should be numbers stamped into the outer surface of your ring gear. Those will tell you what gears you have right now.

A MF xxxxxxxx PP RR MM YY

A = Axle type???
MF = Manufacturer
xxxxxxxx = Ring and Pinion part #
PP = Pinion teeth
RR = Ring teeth
MM = Build month
YY = Build year

x GM xxxxxxxx 8 41 6 81 means 5.13:1 built June of 1981
x GM xxxxxxxx 9 41 5 78 means 4.56:1 built May of 1978
x GM xxxxxxxx 10 41 8 77 means 4.10:1 built August 1977
x GM xxxxxxxx 11 41 9 81 means 3.73:1 built September 1981
x GM xxxxxxxx 12 41 9 85 means 3.42:1 built September 1985

3.73 & 4.10 are the most common 3/4 ton axle ratios with 4.10 being the most common.

[swanthog]

Thanks for the detailed response Hatzie.
I wasn't sure what that u-bolt setup is supposed to look like and thought maybe it was all part of some kit. However, when I pulled the plates, I could see that the holes in the plates that the u-bolts go through were made by a torch. I'll need to research what the proper plate is and purchase it and new u-bolts.

What breaks on the 9.5" semi-floater? Under what conditions? This is only a Stepside with a stock 350. It won't be hauling anywhere near 3/4 ton worth of cargo nor will it pull anything larger than a 4x8 harbor freight trailer

Pick-n-Pull's website states that the axle, complete with drums is $250. That is the cheapset I've been able to find so far. I suppose I shouldn't assume the rear will have a similar price -- will need to call.

[Mattchu60]

The 9.5" 14 bolt is still a pretty solid axle, its not as heavy duty as the 10.5" 14 bolt which is a really tough axle, but still a big upgrade over the 10 bolt that came in the 1/2 tons. I swapped one into my truck a few years ago, everything is bigger than the 10 bolt by quite a bit.

For your driving habits that you described, the 9.5" will do just fine.

[hatzie]

Originally Posted by swanthog

Thanks for the detailed response Hatzie.

I wasn't sure what that u-bolt setup is supposed to look like and thought maybe it was all part of some kit. However, when I pulled the plates, I could see that the holes in the plates that the u-bolts go through were made by a torch. I'll need to research what the proper plate is and purchase it and new u-bolts.

What breaks on the 9.5" semi-floater? Under what conditions? This is only a Stepside with a stock 350. It won't be hauling anywhere near 3/4 ton worth of cargo nor will it pull anything larger than a 4x8 harbor freight trailer

Pick-n-Pull's website states that the axle, complete with drums is $250. That is the cheapset I've been able to find so far. I suppose I shouldn't assume the rear will have a similar price -- will need to call.

Take a face shield, cordless angle grinder, and several batteries in your stuff bag to the pick N pull. If the U-Bolts don't come loose with a breaker bar and cheater you can liberate the axle by cutting through the U-Bolts along side the springs. The axle you liberate should have decent U-Bolt plates.

Originally Posted by Mattchu60

The 9.5" 14 bolt is still a pretty solid axle, its not as heavy duty as the 10.5" 14 bolt which is a really tough axle, but still a big upgrade over the 10 bolt that came in the 1/2 tons. I swapped one into my truck a few years ago, everything is bigger than the 10 bolt by quite a bit.

For your driving habits that you described, the 9.5" will do just fine.

I agree it will work for his purposes. The problem is finding one that isn't fragged from towing or abuse.
The 10.5" full floater is bulletproof, easy to find, and it ain't rocket science to put it in.
NOTE: You will need GM yoke straps to bolt your driveshaft back in place and the yard goons have no doubt played floor hockey with them. Don't bother with the NAPA etc "equivalent" replacement straps they aren't worth a tinkers dam. Straps are GM p/n: 3920486 (you need two) Bolts are GM p/n: 458300 or 14018700 (you need four).
If the Yoke on the 10.5" is too big for your 9.5" Universal joint caps you can get a hybrid Universal joint from all the usual suspects for pretty close to the price of a stock piece.

I'd avoid a used G80 Gov-lock in either axle. Get an axle with an open diff or cough up the bread to buy an Auburn Limited Slip or Detroit locker for your 9.5"

[swanthog]

Using information from Hatzie (and math), for the rear I have 4.10:1 built 06/85:




... and for the front, 4.10:1 built 02/85:





Thanks for the decode Hatzie.