Eaton HO72/HO52 vs. 14 Bolt FF

[Short 3/4]

Originally Posted by Dave

I suspect that you may have a gear set that was made by aftermarket company some time ago to fit into the Eaton 3rds.
Or it could be a GM Canada thing, whereby there were definitely differences in production and equipment.
Having a GM part numbers would clear up any confusion on being original or aftermarket.
Thanks

Read in this forum somewhere (maybe even early in this thread) that the 3.90's were made for the NAPCO 1/2 ton conversions. If you have ever seen one, they are really strange looking as they retain the small 1/2 ton rear, with stock 3.90 gears, but use a modified Eaton for the front, so you have this rear that looks like it came out of a car, then a massive HO52 up front with 6 lug wheels. The 3/4 ton conversions look a lot more normal as the front and rears are both matching Eatons (with the usual 4.56 gears)
So that really makes sense why the 3.90 exists, and is so rare. I don't think anybody has ever found evidence of Chevy offering it as a RPO (I of course could be wrong on that point). NAPCO must have had them custom made for their conversions, and then probably they or the manufacturer had some others they sold as parts for the aftermarket.
This is the best theory on the subject I have come across, and it makes sense to me. What do you all think? Love to hear other opinions on this.
Tom

[Captainfab]

The 1/2 ton NAPCO conversions used the Eaton HO32/33 both front and rear. That is what came stock in the '55 second design thru 1962 in the 1/2 tons They look just like the HO52/72, just smaller. The 3.90 gears were the most common gear found in the HO32/33's.

Originally Posted by Short 3/4

Read in this forum somewhere (maybe even early in this thread) that the 3.90's were made for the NAPCO 1/2 ton conversions. If you have ever seen one, they are really strange looking as they retain the small 1/2 ton rear, with stock 3.90 gears, but use a modified Eaton for the front, so you have this rear that looks like it came out of a car, then a massive HO52 up front with 6 lug wheels. The 3/4 ton conversions look a lot more normal as the front and rears are both matching Eatons (with the usual 4.56 gears)
So that really makes sense why the 3.90 exists, and is so rare. I don't think anybody has ever found evidence of Chevy offering it as a RPO (I of course could be wrong on that point). NAPCO must have had them custom made for their conversions, and then probably they or the manufacturer had some others they sold as parts for the aftermarket.
This is the best theory on the subject I have come across, and it makes sense to me. What do you all think? Love to hear other opinions on this.
Tom

[Vanblindguy]

[QUOTE=jbclassix;5512266]Interchangeability... Sop far, only the brakes are interchangeable between the 14 bolt and the Eaton. I have seen a lot of requests for part numbers and how-to's for the Eaton brakes. Well, here is my how-to rebuild the brakes on the HO72 and HO52. NOTE: for the 71 and 72 HO72/52 axles this is a direct swap. 70 and earlier use smaller wheel studs and will require a hub swap, or the holes on the hub to be enlarged.


So if we were to go to, say, Napa and try to buy a backing plate, shoes, wheel cylinders to perform this swap What year would we ask for? 1973? 1974? 2WD or 4WD K20, or k30? or would any 14bolt 1973 -87 all work the same. I have a 2000 k2500 with a 14 bolt with drums would all the parts from it swap over? Seems like somewhere along the way the e-brake hook up is going to be different and so on.