differential question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

86SILVERADO · 10-17-2003, 03:53 PM

Heres a good one. I went to check the gear ratio on my dump and I jacked up the rear end and spun the tires around twice but my driveshaft only moved about an inch. I do know the gear ratio is not .125:1 so I am wondering what the heck is wrong with this picture. I have been driving this truck all over since I got it inspected a few days ago with no problems so I do not think there is anything majorly wrong with the diff. Anyone have any ideas? I will probably pull the cover soon just to take a look but I do not want to do it if I don't have to. It is the eaton HO 72 I think unless they made another one for the one tons. It looks like it would have a nine or ten inch ring gear in it from the size of the housing. Might as well post a pic.

**Yukon Jack** · 10-17-2003, 04:07 PM

I believe with an open diff, both tires are going to have to be rotated at the same time to get a correct reading.

86SILVERADO · 10-17-2003, 04:18 PM

Thanks Yukon,

That did the trick, It's a 410. Do you know if you can still get posi units for the one tons? I seem to remembr reading somewhere that eaton does not make them for the larger axles anymore.

Dean · 10-17-2003, 04:25 PM

They do not make new ones anymore, but you can find them around if you know what you are looking for. I've picked up quite a few lockers over the years. Don't forget to look at the pre-67 trucks also. They used this rearend for a long time.

And don't let rusty teeth scare you if you do fine one. Swapping your good 4.10 gears with it is not a big deal on these.

86SILVERADO · 10-17-2003, 04:38 PM

Thanks Dean,

are they eaton or the detroit lockers? I guess I have to pull the cover and see how many splines on the axle in order to start looking. GM was using this axle since the fourties right? I do not think I want one that is that old but I will start looking. Maybe I will post on the parts board.

kiley · 10-20-2003, 01:43 AM

I remember reading on this board in sometime in April/May that this axle ran from 60-72.

**JIMs70GMC** · 10-20-2003, 04:34 AM

It's a detroit locker.

86SILVERADO · 10-20-2003, 07:15 PM

Thanks for the replies.

Rod · 10-20-2003, 10:00 PM

The detroit lockers of this vintage look like this one of mine. 17 spline. There spring loaded so to keep them around you put a bolt and nut with big washers through the middle of it all.

Rod · 10-20-2003, 10:07 PM

Heres a detroit locker disassembled but I dont think this one was exactly correct ... but they all pretty much look the same inside except for spline counts anyway in these older ones.

Rod · 10-20-2003, 10:23 PM

And when you first get a unit in a whole piece it looks like this.
And its gotta weigh over 75 pounds.

Hooter · 10-20-2003, 11:32 PM

i have seen a lot of 60-66 one tons in my area with the "no spin" plate on the glovebox door, so they can't be overly hard to find

10-17-2003, 03:53 PM	#1
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	differential question Heres a good one. I went to check the gear ratio on my dump and I jacked up the rear end and spun the tires around twice but my driveshaft only moved about an inch. I do know the gear ratio is not .125:1 so I am wondering what the heck is wrong with this picture. I have been driving this truck all over since I got it inspected a few days ago with no problems so I do not think there is anything majorly wrong with the diff. Anyone have any ideas? I will probably pull the cover soon just to take a look but I do not want to do it if I don't have to. It is the eaton HO 72 I think unless they made another one for the one tons. It looks like it would have a nine or ten inch ring gear in it from the size of the housing. Might as well post a pic. Attached Images

10-17-2003, 04:07 PM	#2
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,686	I believe with an open diff, both tires are going to have to be rotated at the same time to get a correct reading. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

10-17-2003, 04:18 PM	#3
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	Thanks Yukon, That did the trick, It's a 410. Do you know if you can still get posi units for the one tons? I seem to remembr reading somewhere that eaton does not make them for the larger axles anymore. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!

10-17-2003, 04:38 PM	#5
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	Thanks Dean, are they eaton or the detroit lockers? I guess I have to pull the cover and see how many splines on the axle in order to start looking. GM was using this axle since the fourties right? I do not think I want one that is that old but I will start looking. Maybe I will post on the parts board. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!

10-20-2003, 04:34 AM	#7
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	It's a detroit locker. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

10-17-2003, 04:25 PM	#4
Dean Senior Member Join Date: Jan 2000 Location: Cincinnati, Ohio Posts: 1,492	They do not make new ones anymore, but you can find them around if you know what you are looking for. I've picked up quite a few lockers over the years. Don't forget to look at the pre-67 trucks also. They used this rearend for a long time. And don't let rusty teeth scare you if you do fine one. Swapping your good 4.10 gears with it is not a big deal on these.

10-20-2003, 01:43 AM	#6
kiley Registered User Join Date: May 2003 Location: Keizer, OR Posts: 103	I remember reading on this board in sometime in April/May that this axle ran from 60-72.

10-20-2003, 07:15 PM	#8
86SILVERADO Registered User Join Date: Dec 2002 Location: Hills of Western Mass Posts: 626	Thanks for the replies. __________________ 86 Silverado C10 back to 305 power! 67 C30 Dually Dump, with 350 transplant, Rockhauler 05 Duramax 3500 "If at first you don't succeed, try a bigger hammer" Member of the 1-Ton club!

10-20-2003, 10:00 PM	#9
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	The detroit lockers of this vintage look like this one of mine. 17 spline. There spring loaded so to keep them around you put a bolt and nut with big washers through the middle of it all. Attached Images __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

10-20-2003, 10:07 PM	#10
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	Heres a detroit locker disassembled but I dont think this one was exactly correct ... but they all pretty much look the same inside except for spline counts anyway in these older ones. Attached Images __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

10-20-2003, 10:23 PM	#11
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	And when you first get a unit in a whole piece it looks like this. And its gotta weigh over 75 pounds. Attached Images __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

10-20-2003, 11:32 PM	#12
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	i have seen a lot of 60-66 one tons in my area with the "no spin" plate on the glovebox door, so they can't be overly hard to find __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

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