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#58093 03/21/2006 11:41 AM | Joined: Jan 2006 Posts: 33 Junior Member | | Junior Member Joined: Jan 2006 Posts: 33 | Hi, I tried to determine my axle ratio by putting a mark on bot the driveline and the tire, jacking up the back end and spinning the tire one rotation to count the driveline revolutions.....one turn of the tire got me a little less then 2.25 turns on the driveline......that can't be right can it? It didn't feel like it was slipping or sticking...I'm told it's an Eaton ten bolt axle. That's all I know at this point. Though I DO know the engine is screaming at 20 in second gear. The number cast on the front of the case is 3883379 if that helps any. | | |
#58094 03/21/2006 2:07 PM | Joined: Nov 2004 Posts: 121 Wrench Fetcher | | Wrench Fetcher Joined: Nov 2004 Posts: 121 | Did you have both tires off the ground? If you had one jacked up and the other on the ground, the wheel will turn twice as fast. Based on you saying the engine is screaming, you might have a 4.56 rear end ratio. | | |
#58095 03/21/2006 2:41 PM | Joined: Oct 2005 Posts: 1,317 Shop Shark | | Shop Shark Joined: Oct 2005 Posts: 1,317 | Just a suggestion....one turn of the wheel will make it difficult to accurately determine the ratio. Jack up both wheels. Try turning the wheel 10 times while counting the driveshaft revolutions. Divide the number of d/s revs by 10 and you should have the number.
I've found it's just as easy to pop the cover and read the ratio and other pertinent info off the outer edge of the ring gear. A bit messy but the numbers are stamped, easy to read and eliminate any guesstimates. BTW...if both wheels turn the same direction you've scored a posi diff. | | |
#58096 03/21/2006 7:08 PM | Joined: Jan 2006 Posts: 33 Junior Member | | Junior Member Joined: Jan 2006 Posts: 33 | yes, both wheel were off the ground. I think I'll just take off the cover plate | | |
#58097 03/21/2006 9:34 PM | Joined: Mar 2005 Posts: 1,029 Member | | Member Joined: Mar 2005 Posts: 1,029 | The only time you need both wheels off the ground is if the vehicle has a limited slip differential. If it doesn't, what usually happens is that either the opposite wheel will rotate counter to the direction you are turning and the driveshaft won't rotate at all or the opposite wheel won't turn and the driveshaft will only turn half the revolutions you might expect. | | |
#58098 03/22/2006 1:45 AM | Joined: Sep 2003 Posts: 343 Member | | Member Joined: Sep 2003 Posts: 343 | What year and make of truck are we talking about here BTW?
Jim
1954 GMC 1/2-ton Longbed
1971 Pontiac LeMans Sport
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#58099 03/22/2006 11:59 AM | Joined: Jan 2006 Posts: 33 Junior Member | | Junior Member Joined: Jan 2006 Posts: 33 | 1966 Chevy C20. I had both wheels off the ground when I checked. | | |
#58100 03/22/2006 2:45 PM | Joined: Sep 2003 Posts: 2,384 Shop Shark | | Shop Shark Joined: Sep 2003 Posts: 2,384 | I would guess 4.56,,brian | | |
#58101 03/22/2006 4:27 PM | Joined: Nov 2004 Posts: 1,552 Shop Shark | | Shop Shark Joined: Nov 2004 Posts: 1,552 | 64fleetside:
According to the 1966 Silver Book from General Motors, the standard equipped rearend ratio for the '66 C20 was 4.57 and optional equipment was a 4.11. I hope this helps. | | |
#58102 03/22/2006 4:55 PM | Joined: Sep 2003 Posts: 2,384 Shop Shark | | Shop Shark Joined: Sep 2003 Posts: 2,384 | I knew I was close if he counted 2 1/4 turns on one wheel. He probably has the standard 4.57,,brian | | |
#58103 03/22/2006 6:40 PM | Joined: Jan 2006 Posts: 33 Junior Member | | Junior Member Joined: Jan 2006 Posts: 33 | Why would I only get 2 1/4 turns from turning just one wheel? Rear ends are still quite mysterious to me.................  | | |
#58104 03/22/2006 11:42 PM | Joined: Mar 2005 Posts: 1,029 Member | | Member Joined: Mar 2005 Posts: 1,029 | That's the way differentials work in order to allow you to turn corners without scruffing tires. One wheel turns faster that the average speed determined by the ratio and the other has to turn a slower speed which is the complement of the faster turning wheel, so if one wheel is stationary the other turns at double the speed that the ratio would yeild. | | |
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