HO72 confusion(taperd vs double row ball bearings)?

[daveinluray]

Hi
My 72 c35 has stated 11k axles but I am wondering if i dont have an axle swap
or something like that on this vehicle.

I have what looks like an ho72 though?
17 spline axle
10.5 ring gear(3768613 gm 7-36 6 1967 2) stamped in it)
5.14 ratio

Do ho72s have tapered pinion bearings(best I can tell from napa and the manual is they do)?

My manual indicates that the heavier axle(11K) has a double row ball bearing vs the tapered of the 7200k axle. I have the bearings of the larger axle however everything else seems smaller.

[daveinluray]

pic

[daveinluray]

fwiw
turns out HO72 changed bearing type between 67 and 68 with 11k axles and larger retaining the double bearing and the newer using a " straddle-mounted drive pinion is supported at the front by two opposed tapered roller bearings. The pinion
rear bearing is a roller bearing assembly consisting of
an outer race and roller assembly"

confusion was a 67 axle in a 72 or some mix of parts and chassis.

[bry593]

A C35 is GMC, while a C30 is Chevy. These are the same thing and should use an HO72.

Starting (I think) in 1971, both HO52 and HO72 used an opposed tapered bearing arrangement on the pinion. So yours being a ball bearing, has to be an earlier axle.

By the way, the HO52/72 ring gear measures 10.13" in diameter. I believe the later 14-bolt is 10.50". The later 14-bolt is essentially a redesign of the HO52/72, to remove expense of the welded axle housing.

[daveinluray]

Originally Posted by bry593

A C35 is GMC, while a C30 is Chevy. These are the same thing and should use an HO72.

Starting (I think) in 1971, both HO52 and HO72 used an opposed tapered bearing arrangement on the pinion. So yours being a ball bearing, has to be an earlier axle.

By the way, the HO52/72 ring gear measures 10.13" in diameter. I believe the later 14-bolt is 10.50". The later 14-bolt is essentially a redesign of the HO52/72, to remove expense of the welded axle housing.

thanks for the info. Looks like I have a 13 inch(DRW) drum but not certain yet as i have only eyeballed through the wheel with a tape. There was confusion on my part with, as mfg vs max capability, but have finally figured it originally had the 1 ton 7200 pound axle(at least the frame and cab i have did). I guess ill start using search HO72 vs 52 to see if it is still a HO72 or they went smaller.

[bry593]

HO72 used a bolt on the driver side of third member casting that holds a bronze thrust puck against the backside of the ring gear. This prevents deflection. If you don't have the load bolt, it is certainly not an HO72 regardless of year.

In 1971, GM consolidated HO52/72 so as to use up as many parts as possible in anticipation of the 14-bolt arriving in 1973. This meant the HO52 and HO72 were exactly the same except for the brake drum size. Both used tapered roller pinion and a ring gear deflection bolt.

All 1960+ HO52 used 11.15" diameter (measured on the inside) drums, and HO72 used a 12" drum. If your drum measures 12" on the outside, then it is probably 11.15" at the braking surface, meaning you have an HO52.

The good news is that all typical wear parts (seals, bearings, brake shoes, hardware, springs and drums) are available for the HO52, EXCEPT the ring & pinion.