The Stovebolt Site Forums The Shop Area General Truck Talk Is my granddad's GMC 1/2 tonna 54 or 1st series 55?

I wanted to know if anyone could hell me decipher
if the build plate reveals a
54 or 1st series 55?
102-24 S Z3675

Open drive line would be 55 closed driveline 54

The Z series was 1954-1955 New Design GMC.
Approximately analagous to Chevrolet Advance-Design 1954/55st.

GMC differed from Chevrolet trucks in using a series letter rather than a year.

What are the engine serial number and the engine/head date codes?

Here is info on decoding the GMC truck serial number.

That low serial number would have been built in 1954.

Remember that factories were famous for using up inventory when series or years changed, resulting in trucks that were "change over exceptions".

102-24 would be a 1/2 ton longbed (Chevrolet trucks did not have longbed 1/2 ton trucks in that series).

Most likely you have an open drive-line/drive-shaft, whether 54 or early 55.

Did the 55.1 long bed have the u-joint enclosed in the ball, or were they exposed modern u-joints?

I do not know.

But, if the 55.1 GMC long-bed driveshaft was the the same as a 55st Chevrolet 3600 (same bed length), it had a fully open driveshaft (as the Chevrolet 3600 had for the first time in 1954).

From the 1954 GMC shop manual (I'll assume your copy is on order):

Model 101-22 has single a torque tube
Model 102-22 has split enclosed shafts connected via U-joint, rear shaft is identical to 101-22
Series 150-22 Front shaft is solid, rear is tubular. U-joint trunnions have needle bearing support rings.
Series PM150-22 AND UP Both shafts are tubular with the needle bearing trunnions.

When two shafts are used, there will be an extra crossmember with a center bearing supporting the front shaft.

I don't know what changes were made between the 54 and 55.1 versions of GMC trucks, but a lack of torque tube on a half ton may be the best evidence of a later model. You will find much arcane GMC knowledge at www.oldgmctrucks.com