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identify this differential
#1350368 Tue Mar 17 2020 03:25 PM
Joined: Aug 2019
Posts: 20
R
New Guy
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

Attached Files
differential.jpg (396.05 KB, 260 downloads)
Pic 2.jpg (529.79 KB, 267 downloads)
pic 3.jpg (425.11 KB, 253 downloads)
Last edited by Rick Brown; Tue Mar 17 2020 04:45 PM.
Re: identify this differential
Rick Brown #1350439 Wed Mar 18 2020 12:42 AM
Joined: Aug 2019
Posts: 20
R
New Guy
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

Last edited by Rick Brown; Wed Mar 18 2020 12:43 AM. Reason: correction
Re: identify this differential
Rick Brown #1350484 Wed Mar 18 2020 05:29 AM
Joined: Apr 2005
Posts: 2,527
C
Shop Shark
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.


Evan
Re: identify this differential
coilover #1350518 Wed Mar 18 2020 04:11 PM
Joined: Aug 2019
Posts: 20
R
New Guy
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

Re: identify this differential
Rick Brown #1350526 Wed Mar 18 2020 04:57 PM
Joined: Sep 2011
Posts: 702
B
Shop Shark
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).


BC
1960 Chevy C10 driver 235 T5 3.73 dana 44
1949 GMC 250 project in waiting
1960 C60 pasture art
G.M dealer tech since 1980 & counting
Re: identify this differential
Rick Brown #1350562 Wed Mar 18 2020 08:22 PM
Joined: May 2005
Posts: 7,165
B
General Purpose
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.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: identify this differential
Rick Brown #1350686 Thu Mar 19 2020 03:51 PM
Joined: Aug 2019
Posts: 20
R
New Guy
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

Re: identify this differential
Rick Brown #1350687 Thu Mar 19 2020 04:04 PM
Joined: Jan 2013
Posts: 1,642
S
Shop Shark
Coil overloads Bart,lol
Somebody needs to hunt the guy that did that down and give him the what fer!

Last edited by sstock; Thu Mar 19 2020 04:07 PM.

1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
https://www.youtube.com/watch?v=Bli...n05i04t1aokgm4p04jiwgffwhyyih5xbk0h00410
1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration
Re: identify this differential
Rick Brown #1350697 Thu Mar 19 2020 05:32 PM
Joined: Mar 2007
Posts: 690
T
Shop Shark
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. wink


Craig

Come,Bleed or Blister somethings got to give!!!
Q:"What yah runnin"
A:"3/8 drive Black and Decker aquarium pump motor" (the movie HOTROD)

59' Apache 31, long term project (30 years and counting)
Re: identify this differential
Rick Brown #1350700 Thu Mar 19 2020 05:41 PM
Joined: May 2015
Posts: 2,367
K
Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums
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. eek


Kevin
First car '29 Ford Special Coupe
#2 - '29 Ford pickup restored from the ground up.
Newest Project - 51 Chevy 3100 work truck. Photos [flickr.com]
Busting rust since the mid-60's
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