I am restoring a 61 K10. Got it from CA off of eBay. It had a 350 engine which was blown and a TH350 xmission installed by someone in the past. I was trying to see if they had done anything to the Drivetrain. I jacked both back wheels up and spun one side. Only one side turned. It has really big tires so it might be possible that all that tire weight was enough resistance to keep the other tire from spinning or it could be an open rear end. What seemed really odd was that the drive shaft turned about 1.9 times per turn of the tire. Does not mater if one tire is on the ground or both in the air. I moved to the front, locked the hubs and I get less that 2 there. I was told by the guy I purchased it from that the guy that switched out the engine and trannie pulled sleds with it. With that info, I was thinking a 4 plus rear end might be in it. Figured I must messed up in the way I was trying to check it. What am I doing wrong?
Hi Gary and welcome to the site. Since it sounds like things have been changed on your truck, you may have to remove the rear cover of the differential and either count the teeth of the ring and pinion gears and divide them to see what you have or maybe you could see the stamped code on top of the axle tube on the passenger side of the differential assembly. But...if the ring and pinion were for some reason changed in your transmission, that would alter things. As memory serves I think 3.90 was the ratio most commonly used on the 1961 K10. You can also only jack one wheel up, mark the driveshaft and rear end with a bit of chalk so you can count the turns and rotate (transmission in neutral) how many turns it takes to equal 2 rotations of the free wheel. However many turns it takes to rotate the wheel one time will tell the story. Almost 4? Could be 3.90 or 4.11, depending on how accurately you did this. It isn't exact...but it will get you into the ball park. Note: if you have a worn-out positraction rear end this method may not work. Depends on how worn out it is.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
The stamped code looks like it has been welded over. I am working on the cab right now and I don’t want to start something else until I finish that. I plan to change the axle seals and bearings so I have to pull the cover to complete that task. Just seems really odd that one turn of the wheel equals less than 2 turns of the drive shaft.
If it behaves as you say, it's probably a 3.90. There will probably be enough brake drag to keep one wheel from turning. As noted above you have to double the number of pinion turns to get the ratio because the differential gears have a mathematical doubling function if you hold one side.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
If you're turning one wheel, with the other one on the ground, the spider gears will cut the driveshaft speed in half. It will take two turns of one rear wheel while counting the driveshaft rotations to get an accurate guesstimate of the ring and pinion ratio. Jerry
"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!
Update: with both tire off the ground I turned the right rear. Left rear did not turn. 2 turns of the tire was about 3.75. I walked over to the drivers side spun the tire and the right tire turned. Fairly sure the drum brake drag and heavy tires kept the left tire from turning when I spun the right tire.
(Gary. You are out of "moderated" status. Your next post will go right thru. We don't need to approve it. You can also send Private Messages (PMs). Good job on getting the photos in! )
~ Peggy M 1949 Chevrolet 3804 "Charlie" - The Stovebolt Flagship In the Gallery "We make a living by what we get; we make a life by what we give." -- Winston Churchill
The casting number on the housing tells you exactly nothing about the gear ratio. Either pull the cover plate and post the number stamped on the perimeter of the ring gear (41-10 for instance, indicating a 4.10:1 ratio) or turn one wheel with the other one on the ground and count the turns of the driveshaft. Be aware that the spider gears will be involved, so turn the wheel TWO revolutions while counting the driveshaft rotations. Pulling the cover is the most accurate way, and that also allows you to inspect the gears for wear and/or damage. Jerry
"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!
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