The Stovebolt Site Forums The Shop Area Driveline identify this differential

I have a 1950 3100 chevy truck with this differential. It seems to have 3.55 gearing as deduced from the counting the revolutions of the tire to the yoke turning,

It might be a eaton Napco as I have found pictures where the cover looks the same. But hopefully someone can help me identify?

Rick

answering my own question as I looked on a recent stovebolt search and it appears to be a eaton. Now I need to confirm gear ratio as I have a 261 engine with a 1986 s10 T5 transmission,I hope it was changed to 3.55 otherwise it is a 3.90

If your trans has an 0.82 od then the 3.55 is good (2.91 final drive) but if it has the 0.67 od the 3.90 would be better (2.61 final drive). The 3.55 with a 0.67 is a very shallow 2.28 which might require 4th gear with hills or strong head winds.

Thanks Evan for your response. My s10 fifth gear is 0 .76 so accordingly if it is

A 3.90 x 0.76 = 2.96

B 3.55 x 0.76 = 2.69

c 3.73 x 0.76 = 2.83

According to Tom Langdon web site the gear ratio should be between 2.50 and 3.0 so looks like whatever I have is within range. I will take the differential cover off to determine exactly what I have then the question is what is the preferred ratio or should I not worry about it?

Rick

IMHO 3.55 is a little high geared to run overdrive IF you're not in the flat lands (unless you run small diameter tires).

I'm sure you will be taking off the cover. Then you can read the stamp on the ring gear to confirm ratio. That is the only way to be sure.
There was no NAPCO rear end. Same as 2WD.
That is the all time worlds record sketchy rear end swap I have ever seen. A coil that seems to do nothing, welded to the tube, on top of leaf springs with welded Ubolts to the tube. I can't look at it.

Good observation bartamos I too thought this was the strangest rear end I have seen. Now the question is it worth trying to make work or start looking for something else? Or could I simply cut off what appears to be coils going nowhere and look for a proper spring bracket kit?

Rick

Coil overloads Bart,lol
Somebody needs to hunt the guy that did that down and give him the what fer!

I cringed when I saw the pic. Looks like a lot of short cuts over the years, I hope Rick has better plans for this old truck.

I'm afraid that something like those coils were on my truck when I got it. Some big round "sockets" welded below the frame arch. Those were the first things to go. I whacked them off as soon as I had the bed removed. I'm sure they reduced the spring travel and served as "axle bumpers" providing a nice steel-on-steel contact.

I would take bed off, as Kevin says, cut the coil off, cut the welds on the leaf off. Clean up the tube. Keep the leaf intact and find the proper ubolts and plates. Move shocks and mount per original, if they are not. Somebody was carrying real heavy loads back in the day and wanted to "beef" it up.

Fortunately it appears they didn't weld on the spring leaves, just the axle housing. If they had welded on the spring leaves, I would consider them scrap. Useful only for knifemaking stock. Everything else can be salvaged. If they were carrying heavy loads, I would check the axle housing for straightness.
I had a '72 Chevy 1/2 ton that had been used to carry a monster slide-in camper and had a sagged axle. I had it straightened, but they got the center section out of line with the axle tubes, even though it was straight at the wheel ends. It had a limited slip in it and the binding of the side gears shucked the petals off of the friction plates and threw the bits into the pinion bearing. I wound up replacing the entire rear axle. Of course the guy I bought it from neglected to mention the damage. I happened to see him at a campsite a year or so later, and he looked incredulous that the truck was still on the road.

Thanks Bartamos and Kevin your feedback is appreciated.

I will do as per your recommendations and as a preventative plan, I will take the entire differential into a local place that only does differentials and make sure everything is straight and in good order /rebuild before re- installing properly with new shocks / proper Ubolts and plates

Finally was able to pull differential; cover last night.

Confirmed as a 3.90 gear ratio so with my T5 od transmission fifth gear at 0.76 my final is 2.96. I hope this will work as a daily driver but I will inquire with differential shop the cost of putting in a 3.73 and see if it would be worth it.

I would advise against changing from 3.90 to 3.73 with the .76 overdrive. I am assuming that you are running an inline six.
Your RPM will be too low in 5th gear until you hit 65-70 MPH.
It may sound quieter, but your gas mileage will actually suffer since your engine RPM will be below the optimal power band of this engine between 50-60 MPH. A vacuum gauge will verify this.

Thanks 52Carl. You are confirming what the fellow at the differential shop indicated that I am best to stay with the 3.90 which makes it easier anyways. Thanks for your input