HO72 frustration

[stillsmokin]

I finally got may hands on an old 7200# third member from a friend of mine for a axle project I'm working on. This way I can swap out the 5200#third in the project axle. So I tore it down and started wire brushing the usual rust off the ring gear and discovered the drive side is shot. It looks like it hauled scrap iron for a living from day one (1949), while low on oil. Not all is lost, at least I have some parts I guess.

[Longhorn Man]

The 3rd member on every HO52 and HO72 were the exact same, load deflection bolt and all. The only thing I've seen between the two, is the brakes.

[jeffspower]

Not all of them have the deflection bolt. Early carriers & gears (50's?) are different than the later design. I can't remember the year they changed or the exact differences, but IIRC, the pinions are different length. You can't put an early gear set in a late carrier or vise- versa. But you can swap complete third members between early & late housings. I think the u joint to axle centerline measurement is different between the two also.

[jeffspower]

I just noticed you are a NE puller... do you pull with NPPA? If so, which truck is yours?

[stillsmokin]

Originally Posted by jeffspower

Not all of them have the deflection bolt. Early carriers & gears (50's?) are different than the later design. I can't remember the year they changed or the exact differences, but IIRC, the pinions are different length. You can't put an early gear set in a late carrier or vise- versa. But you can swap complete third members between early & late housings. I think the u joint to axle centerline measurement is different between the two also.

I'll second that statement. The 7200# has a load bolt the 5200# doesn't. The pinion bearing on the 7200# is tapered roller while the 5200# has ball bearings. The pinion is longer on the 7200# due to the taller stack up of the of the bearing. 7200# open carrier has 4 spider gears, 5200# has 2. 7200# third member and bearing plate are completely different due to extra holes for pinion bearing oil. The tail bearing on the pinion is different on early third members but, it looks like you can possibly install the later one into the bore. Ring gears are the same. FWIW I read somewhere that 5.13 gears only came in the 7200# but, I have a 68 5200# third with that ratio.

I don't run NPPA quite yet, I do go to some of the local events they tie into and was at Platte City, MO last year.

I thought 4.57's are supposedly the most common ratio for these?

[1969 GMC]

Originally Posted by stillsmokin

I'll second that statement. The 7200# has a load bolt the 5200# doesn't. The pinion bearing on the 7200# is tapered roller while the 5200# has ball bearings. The pinion is longer on the 7200# due to the taller stack up of the of the bearing. 7200# open carrier has 4 spider gears, 5200# has 2. 7200# third member and bearing plate are completely different due to extra holes for pinion bearing oil. The tail bearing on the pinion is different on early third members but, it looks like you can possibly install the later one into the bore. Ring gears are the same. FWIW I read somewhere that 5.13 gears only came in the 7200# but, I have a 68 5200# third with that ratio.

I don't run NPPA quite yet, I do go to some of the local events they tie into and was at Platte City, MO last year.

I thought 4.57's are supposedly the most common ratio for these?

I thought that about the deflection bolt but no, according to some on this forum the 52 could have it.

other than that, the 2 3rds i have agree with you. '65 4.57 '52 with a no-spin, and a '68 5.14 '72 with the load bolt, extra oil passages, open carrier with 4 spiders.

[stillsmokin]

Originally Posted by 1969 GMC

I thought that about the deflection bolt but no, according to some on this forum the 52 could have it.

other than that, the 2 3rds i have agree with you. '65 4.57 '52 with a no-spin, and a '68 5.14 '72 with the load bolt, extra oil passages, open carrier with 4 spiders.

I would love to see a 5200# 3rd with the load bolt. That would tell me that I could possibly use the good gears out of these 2 other 5200# third members here. I have seen a bunch of these rears never seen a load bolt one without the oil passage in the case.

I took a bunch of photos of 5200# and 7200# axles and compared parts with a 14 bolt FF as well. I also researched the GM service information as well. I was thinking of doing a tech post, what does everyone think?

Somebody has to have a load bolt third member with 4.57's close to me surely?

[Longhorn Man]

Good call Jeff... i was talking 67 - 72, I forget they made trucks before 67!

[jeffspower]

Originally Posted by Longhorn Man

I forget they made trucks before 67!

But we all know you don't acknowledge the '73 up trucks

[Longhorn Man]

73 and up what?

[westie 666]

Originally Posted by Longhorn Man

73 and up what?

There aint no body like a square body.

Had to say it.

[stillsmokin]

Originally Posted by westie 666

There aint no body like a square body.

Had to say it.

Yes, those are the trucks I grew up with and love. The rust not so much.
Anymore, if it was made in america it was cool. If it has a bowtie or GMC logo on it, it's all good.