I also have some GMC tuneup specs for the 228, Message me and I can send them to you.

@dunfire data plate info.........MODEL  AC-152,  Serial # AC1521338,  Max GVW  4600

@hoseman-2 , et al, My guess is that your data plate, when found, will I.D. your truck as a 3/4 ton. GMC built some long wheelbase 1/2 ton pickups and maybe panel truck too, but my gut tells me your truck is a 3/4 ton. Ah, but it has 6 bolt wheels, you say. Chevrolet 3/4 and 1 ton trucks from 1937 (first year for these ratings) through 1942, use 6 bolt wheels. My guess is that GMC light trucks followed the same pattern. As a 3/4 ton, a Chevy would have had the 15 X 5-1/2  Artillery wheel with 7.50-15 tires. I notice you are running 15" Rally Wheels from a 1973-1987 Chevy/GMC K series (four wheel drive) 1/2 ton. These are most likely the 15 X 8 variety, although there were some Blazers equipped with a 15 X 7 version. I doubt you have the total tire height of the original equipment tire.

If your truck is, in fact, a 1/2 ton, it likely left the factory on 6.00-16 or 6.50-16 tires. You can go to Coker or any of the vintage tire vendors and find the hight of all the tires they offer when you click on the tire for the specs. I could provide set of 16" wheels if you would like to return to this format.

Your actual speed might differ substantially from the speed showing on your speedometer. A speedometer App on your cell phone will give you an accurate assessment of any speedometer error. My 1936 Chevy 1-1/2 ton is traveling 41 mph when the speedometer says 35. It is very comfortable at that speed. It has 5.43 gears and 6.50-20 tires. When the speedometer gets above 45 I can no longer bear the sound of the engine, even though I think statistically, it is fine. 

It is possible to build a 3.55 rear axle for your truck and retain the 6 bolt wheels. I have done it for a 1951 Chevy 1/2 ton. However I have learned to appreciate the slower ride like others have stated in previous posts.

As for your oil filter, my 2 cents worth (now priced at 5 cents, due to inflation, but still valued at 2 cents) is take it off, clean it up and give it a fresh coat of paint then proudly display it on a shelf in your garage. Change the oil every year or 1000 miles and live life on the wild side.

I don't think your Carburetor is original to your truck I'm thinking your truck might have been equipped with a Zenith carb, when new. Your carb seems to be one of the many versions of the Rochester B that were used as original equipment and aftermarket replacements in the 1950s.

I love your truck. I think with some attention to your carburetor and ignition, you will have a good running truck.

Mike

@dunfire Patrick, how can i get ahold of a copy of the GMC MAINTENANCE MANUAL that you copied these pages from? Is there a site, or a "store" who sells these manuals. Please let me know?

Greg

@dunfire how do i message you?  Are you on FB? Do you have an e-mail address you can share?

Greg

@35mike Mike, i increased the fuel pump discharge pressure and the spitting and sputtering went away....55 mph and still had pedal left but motor sounded like it was working really hard. Motor spec says 3400 Max RPM so i'm going to install a tach and see what is what.

New problem, after running about 5 miles at the high speed i watched my oil pressure gradually drop off from 35 to 0. i headed home on slow speed roads but the oil pressure never came back. Got in the driveway and popped the hood and no visible oil leaks and no noise from the rocker arm cover . waited 2 hours and fired it up and back to 35 psi. thoughts?

My next plan is to install a direct pressure oil line gauge and drop the oil pan to check out the pump suction strainer and generally check for sludge and crap in the pan.

Greg

Posted by: @hoseman-2

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@dunfire how do i message you?  Are you on FB? Do you have an e-mail address you can share?

 

Greg

If you are a club member you can do a Member Search under the Rosters button at the top of the page. There you will find his location and contact information. You can also click his name above then click the envelope icon on the right side of the page to send him a personal message within the forum.

If the engine coughs or sputters at any speed it is a sign the engine is not running properly and needs adjustment. I would start with the basics-a compression test followed by plugs, points, condenser and timing. 

Greg, sent you a private message.

    I did some math for different rear axle ratios and tire sizes vs top speed.  Click here:  http://home.znet.com/c1937/RPM.htm     The only difference I notice between GMC and Chevrolet pumpkins is that Chevy used New Departure ball differential side bearings and GMC used Hyatt roller bearings.              

    I also did research for casting numbers on Chevrolet engines.    http://home.znet.com/c1937/Cast.htm     I believe that GMC casting numbers on the left side of the block of OHV engines.  The OHV GMC serial number stamped by the ignition distributor will start with the displacement.   228, 236, 248, 270, 302?   1939 was the first year for the Over Head Valve (OHV) small GMC engines.  In 1938 GMC used a Pontiac flathead.  In 1937 GMC used an Olds flathead engine that had one more Cubic inch and one more HP than the Pontiac.