I have a question. My truck is a 1953 GMC 3-ton (9700 or 450) with a 292 from a '66. I found a 1977 GMC c6500 and want to know if it's 5-speed trans will (easily) connect to my engine. Would also be nice to know the weight of it. I've included pictures since I don't know what the exact engine and trans is in the '77.
Alex - Here's a little info (below) I was able to find from a couple of resources on your "donor truck", including a VIN decoding chart (which may not be 100% accurate for a Canadian GMC) and a dealers sales data chart for 1977 Medium Duty Canadian GMCs which is probably the most accurate for the truck between the two.
The 2nd source shows the engine should be a GM (Corporate) 366 Big Block and the 5 speed was one of several available transmission options.
I don't know if the bell housing pattern for your 292 will match the Big Block pattern. Also no experience with if that 5 speed will mount up to your bell housing or not, but I'm doubtful.
Someone with more knowledge/experience with the late Big Truck 70's engines and transmissions will need to chime in to offer some hopefully helpful insight.
Bets of luck in your search.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
The 292 has the same Bellhousing bolt pattern as the Chevy V8's ( SBC and BBC are the same).
Many of the 5 speeds offered in Heavy Duty Truck didn't have an O/D. The 5th gear was a 1 to 1 ratio, it just gave the Truck a wider gear range.
Some information on the Transmission would help a lot.
Last edited by TUTS 59; 09/16/20252:25 AM. Reason: Spelling
~ Craig 1958 Viking 4400 "The Book of Thor" Read the story in the DITY 1960 Chevrolet C10 "A Family Heirloom" Follow the story in the DITY Gallery '59 Apache 31, 327 V8 (0.030 over), Muncie M20 4 Speed, GM 10 Bolt Rear... long term project (30 years and counting)
Come Bleed or Blister, something has got to give!!! | Living life in the SLOW lane
The 366 and the "tall block 427" were commonly used in big trucks in the 1970's and later. There are even special spacer plates sold to allow aftermarket intake manifolds to be used on the truck engines. Some racers prefer the tall blocks to allow for the use of longer stroke crankshafts. The engine in the picture has the governor-equipped Holley carburetor that was original equipment on both engines.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Hy Alex, some of the tall deck (366, 427) engines have block adapter plates and larger bellhousings to accommodate larger flywheels and clutches, some of the five speed transmissions have larger input shafts as well, as has been stated, overdrive versions of the five speed truck transmissions are few and far between, good luck.
Clark, Spicer and New Process were built for GM application. They came in both direct and overdrive 5th. Since your truck is not original the only way to see what clutch you have is to take it apart. A 5speed will not weigh a whole lot more than a 4 speed. Why do you want a 5 speed. If you want to go faster you will need a 5 speed OD. Top gear in a direct 5 speed is the same as a 4 speed.
I did some more research and had another look at it. You might be right, considering 1st is marked as Low.
Really hoped to get a higher 5th gear, since it is revving high at just 80km/50mph. Plus, the trans is leaky and pops out of 2nd. While my rear axle is good, including the brakes and tires on it. But it sounds like an axle swap for one with taller gears in the diff would be a more likely find. Too bad I couldn't just change the gears in my 2-speed diff that I have, but doubt there is enough room for a larger gear.
(Attached two photos of the 5-speed and one of my 4-speed.)
Is the rear axle in the C6500 good? It might well be a taller ratio than what you have, which is likely a 7 point something to one. Especially if it's a two speed.
The photograph looks like a New Process 540 with 5th direct. Your top speed would be the same as with a 4 speed. RATIOS ARE - 7:41-4:05-2:40-1:48 -1:00. Reverse 7:85
Regarding the axle, can you photograph the old and the new? GM made the spring pads the same width for a very long time. I swapped the worn out T150 (banjo shaped housing, no side bearing races exist for it) for a later T170 (round housing, bearings somewhat still exist), it just bolted right in, even the U joint and brake line. The T170 is probably what's under the '76. When I did the swap back in the '90s, it was the modern option and you could still buy taller gears for it at the dealer. Now of course, it's totally deprecated however you can at least get bearings for it, and one with a taller than usual 6.50:1 ratio occasionally pops up on Vander Haag's.
At least with the T170 you get Bendix style brakes, mine even had self adjusters IIRC. Brake parts are commonly available for it, too. Went from 15x4 to 15x5, it seemed to stop a little better.
