Plaid Valve Covers....straight from the west coast Factory Rep.
 

When I was 14, I bought a 1963 custom cab, big back window 1/2 ton pickup from a retired factory Rep. He had bought the truck he had driven around the west coast from GMC when he retired. It had just turned over 100,000 miles. He made me promise never to sell her, then proceeded to tell me that his truck had lots of modifications to get better mileage, handle better, and be as reliable as it could be made to be since he traveled the entire west coast and mountain region. He said that it was one of the early trucks off the line and soon after his first trip and needing some valve train attention (heavier springs?) it was given a 3:23 rear end, a custom carb (that I have never found parts for) and 4 more cigarette lighters. He told me that the Valve train upgrades would be marked by the plaid valve covers later once more started coming back for the upgrade. GMC went with the advertising slogan "thrifty as a Scott". The new 305E had better mileage than the earlier 305 V6 engines, and was a bit lighter. I still have Betsy. 365,000 miles and going strong! I have everything I need to restore her. Picture 1 is 1980, 2 is last week.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

I have 3 1963 GMCs now. Two 1/2 ton trucks that rolled off the same line Oakland, CA line the same week, and a 3/4 ton that rolled off that same line a month later. All 3 are custom cabs with power steering. Bonnie will be getting a 351E put in her since I got her with a 1958 283 that is going in my 58 Chevy 1/2 ton long step side. http://20210730_194200

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

When I decided some years ago to help my 305 run easier, I put in 3.23 in my DANA 44. Since I've put in a 700R4, she really likes the low RPM. I was wondering if back in the day GMC realized they should have went with the lower rear gears 3.23 all along?

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Interesting information on your ‘63’s. Have my g-father’s ‘63 3/4t, 4 wheel drive that we used on our central Tx farm, 78K miles. It was/is a farm implement (PTO) and 5:11 front/rear end, 4 speed, from the factory. Has anybody seen this before? Just wondering how unusual it is to have such a low geared trans for that time period? We hauled cattle and horse trailers w/ it as well, even hooked up a shredder once or twice.





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Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Nice looking truck! Great to keep it in the family like that. I'm guessing you have the optional SM420 transmission which was actually a very common option back in those days. I suspect the majority of our trucks have them.

According to the original 1963 factory sales brochure, the only available differential ratio available for the 3/4 ton 4x4s was a 4.56. So if you actually do have a 5.11, it must have been either a special order from the factory, or a later conversion. The sales brochure does show an optional 5.14, but that's only for the 2WD one ton trucks.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Robert, Can you get a picture of the front differential? If they changed out the Spicers for H-072 rear and NAPCO front axles, you could have a 5.14 final drive ratio with parts that would have been available at that time.

Bob

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Ed & Bob, I thank you gentlemen for your informative and insightful information - invaluable and very much appreciated!! The rear is indeed 4.56 and tomorrow I’ll back it out and check out the front end which I’m sure will be the same. Everything is original w/ exception of the split-rim wheels. What venerable old trucks these GMC’s are - love driving it around Tulsa. The 305E V6 in these beasts always conjures interesting questions from people who don’t understand why there isn’t a V8 under the hood, as I guess many Ford and Dodge trucks had at the time. Great resource this entire forum, thank you again!! Wish I could get a look at that ‘63 brochure that outlines all the options - fascinating stuff!!https://uploads.tapatalk-cdn.com/202...5efdfa27db.jpg
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Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

My 1963 3/4 ton came from the factory with 3:73 posi. I filled the wheel wells with 265/70/16s and she goes down the freeway at 2800 rpm at 70 MPH. Jenny gets 15 MPG.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

The Eaton third member swap was very common at the dealership. Later in 1972 some 3/4 ton trucks with the automatic came with 3:73 gears. 20 minutes and my 68 C30 dually flatbed dump with 5:11 gears went from 40 top speed to 70 top speed and from 5 MPG to 15 MPG.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

If you consider how some of these old pickups were used they really needed those 4. or 5. something axle ratios, and the relatively low top speeds to make the 120+/- 305's work that hard.
In a 3/4 or 1 ton a 351 would be a better engine choice, I had mid-1960 GMC pickup sales brochures decades ago, I'm not sure there was a larger engine option.
Today it's crazy the performance you can get in a pickup, like my 2018 Ram 1500, 5.7L 345 cid V-8, 395 hp, 410#/ft torque, 3.92 axle ratio runs 80 mph at 2000 rpm. And it tows like it says KENWORTH on the grill.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Very well put and so true!


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Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Thinking about having the ole 4.56 gears replaced, just for more top end and mileage. W/ 4x4 I’m wondering what would be easy and ideal for the road? Thinking your 3:73 posi might be the way to go?


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Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

If you have an Eaton and are staying with Eaton rear, the third member from a 1970 or newer will bolt in the front. The factory automatic trucks had the 3:73 posi option in the C30 service trucks/ catering trucks.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

If you have an Eaton and are staying with Eaton rear, the third member from a 1970 or newer will bolt in the front. The factory automatic trucks had the 3:73 posi option in the C30 service trucks/ catering trucks.

Re: Plaid Valve Covers....straight from the west coast Factory Rep.
 

Both of my 300-6 powered Ford F-150's had 3.50/3.55 final axle ratio with 235-75R-15 tires, the engines had to wind up pretty good, 2500-2600 to run 65 mph which REALLY hurt mpgs. One had a little Carter YF-1 1 barrel carb, other was factory EFI and supposedly made around 20 hp more than the carbide truck. Carb =125 hp, EFI = 145. Both got around 14 mpg if I drove 55-60, try to run 65-70 and get 11. The carb had ALL kinds of bad habits, I ended up converting it to manual choke which reduced but didn't eliminate them all. The EFI was much better. A co-worker with a similar EFI truck and a 4 speed over-drive Trans claimed 17-18 mpg vs my 14.
SON had a '93 F-150 LIGHTNING pickup, 351 Windsor with higher flowing GT-40 induction system good for 20-30 added HP, 4.10 final drive ratio, 275-60R-17 tires, and the E4OD auto Trans had a .71:1 overdrive ratio. I got 14 mpg commuting to work one week, SON would draft other cars & trucks and get 18 mpg.
The V-6's are a low end torque engine, I wouldn't go any lower than a 3.00 axle ratio, but without and overdrive gear in your transmission a 3.23 or 3.55 ratio would be good.
My 2018 RAM 1500 has 3.92 axles, cruises 80 mph at 2000 rpm in 8th gear, a .67:1 ratio, 7th is .87:1, 6th is 1:1. it has 275-60R20 tires. I get 15 mpg around town and 17-18 mpg on Interstate. Towing it pulls like my '96 F250 Diesel did but the MPG is less. But it takes gas to make 395 hp. ENGINE MASTERS did an episode on the latest 5.7L Hemi, They were impressed, I am too.