What kind of differential is it?

[64galaxiemann]

My 1970 chevy longhorn has a differential That has a "adjustment screw" on the side of the carrier, where the pinion is located. I accidentally removed it thinking it was for filling the differential, I quickly replaced it. Does anyone know who made this differential? What is this screw used to adjust? Any web sites for info, anything would help...Thanks

[STOCKISH]

The differential in your truck is called an Eaton ho72. It is damn near bulletproof. The bolt on the side with the nut on it is an adjustment for ring gear deflection. There is supposed to be about 2 thousanths clearance between the back side of the ring gear and the flat lug on the end of the bolt you pulled out. When the truck is under heavy load it keeps the ring gear meshed tightly with the pinion gear. GM stopped making it in 72 and started with the 14 bolt in 73. 14 bolt axles will fit in it if you use 14 bolt spider gears or locker from a 14 bolt. It should have 10 spline axles and pinion gear.

[64galaxiemann]

Can you adjust it without taking the diff appart? I had alittle bit of rear gear noise before I removed it, after I replaced it I noticed it was not any noiser. I figure if it is accessable from the outside I can adjust it installed..What do you think? The posi works great so I think someone has already been in the differential. Thanks for the help...

[Stocker]

Originally Posted by 1972SuperCheyenne

The differential in your truck is called an Eaton ho72. It is damn near bulletproof.

It is an Eaton, but probably an HO52 (assuming C/K20)... I believe HO72s were only on C/K30 trucks. I think the internals are the same anyway. If nobody chimes in, a search should tell you the difference between HO52 and HO72.

I can't tell you anything about adjustment, sorry. But if you have a limited-slip Eaton, consider yourself lucky. They are hard to find.

[1969 GMC]

Originally Posted by Stocker

It is an Eaton, but probably an HO52 (assuming C/K20)... I believe HO72s were only on C/K30 trucks. I think the internals are the same anyway. If nobody chimes in, a search should tell you the difference between HO52 and HO72.

I can't tell you anything about adjustment, sorry. But if you have a limited-slip Eaton, consider yourself lucky. They are hard to find.

If its a longhorn, it very well could be a 1 ton, so I wouldn't rule it out. I'm sure someone here knows the hard and fast rule for the ring gear deflection bolt, but I have one H052 chunk that has no bolt, and one H072 chunk that has it, so I will assume the one tons got it...but I could be wrong.

The 52 vs. 72 use different kinds of bearings, but otherwise seem to be the same, with the exception of brakes.

I have heard mention of a posi for these on here, but never seen one. However there was a No-Spin as a factory option, which is actually a Detroit Locker.

I believe the service manual gives a spec for the load bolt, but I do not know what it is.

[phoenix37]

Originally Posted by 1972SuperCheyenne

The differential in your truck is called an Eaton ho72. It is damn near bulletproof. The bolt on the side with the nut on it is an adjustment for ring gear deflection. There is supposed to be about 2 thousanths clearance between the back side of the ring gear and the flat lug on the end of the bolt you pulled out. When the truck is under heavy load it keeps the ring gear meshed tightly with the pinion gear. GM stopped making it in 72 and started with the 14 bolt in 73. 14 bolt axles will fit in it if you use 14 bolt spider gears or locker from a 14 bolt. It should have 10 spline axles and pinion gear.

I want to put a detroit locker in my rear axle. Do they make one for the Eaton HO72 or do i need to go with the 14 bolt?

[Longhorn Man]

I've had 3 HO52 rears, 2 from '70 longhorns, and one off a 72 longhorn, all had the preload bolt, then the one HO72 under the 70 C/30... also with the preload bolt.

[STOCKISH]

I've rebuilt lots of these and never saw a 52 with the preload bolt. You can adjust it in the truck just take the rear cover off and have at it. Internals are different as far as bearings go. It should have a Detroit locker from the factory in any posi ho72