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Old 12-18-2019, 11:35 PM   #1
gratefuldog
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14 bolt axle in a 3/4 ton '71 Sub

Hi folks-
over the course of several very busy months this year, I swapped out the 4.56 Eaton HO-50 (or -70?) axle in my Sub for a 3.73 GM 14-bolt axle, and ended up with rear disc brakes in the process.

Unfortunately, I didn't take many pictures since I was focused on the work. I think the ones I did take will adequately 'splain the process.

I'm sure I'm not the first guy to do this, and it's probably been done better, but here I go:

First step was to get the axles side by side on the bench. (Sorry, no pics..)

Measured the (old) trailing arm pads, and proceeded to fab new ones.




Then it was making a wooden fixture off the old axle so I could get the trailing arm pads and the Panhard rod bracket in the right spots. The new axle is 2 inches wider (wheel flange-to-flange), so measurements were taken off center. With the (old) trailing arm pads level, the pinion angle was noted.

Next step was torching and grinding the old bracketry off the new axle. The good folks at GM welded these on to stay; cutting it all off was a *****. The Porta-band helped a lot.

New axle was laid into the fixture, with the pinion at the correct angle. Pads were tacked, checked, checked again, and welded. And a Panhard ("tracking") arm bracket was made.




About this time, I started looking into rebuilding the rear drum brakes that came with the 14 bolt.

After learning that one drum was shot, and the other had .005 left, I started looking at disc conversions.
I got caliper brackets from Ballistic Fabrication, and '77 K30 rotors, calipers, and hoses from Rock Auto.


(Side trip: here's a "field expedient" spanner I made up to snug down the wheel bearings.)


I also ended up shaving the lower pumpkin flange, and installing a Motobuilt "13 bolt" cover (This thing is stout!)
Then it was time to go home.


I'm pleased to say that everything bolted into the truck without issue.

The brakes -surprisingly- seem to work really well without an additional proportioning valve. There is no "emergency" brake -it's a manual transmission; I can (at least) slow it down with the motor- and I solved the parking brake problem by installing a ball valve in the rear brake line... works great.

I hope maybe this helps someone; questions, comments, and snide remarks are welcome
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Old 12-19-2019, 01:14 PM   #2
LockDoc
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Re: 14 bolt axle in a 3/4 ton '71 Sub

Quote:
Originally Posted by gratefuldog View Post
Hi folks-
over the course of several very busy months this year, I swapped out the 4.56 Eaton HO-50 (or -70?) axle in my Sub for a 3.73 GM 14-bolt axle, and ended up with rear disc brakes in the process.

Unfortunately, I didn't take many pictures since I was focused on the work. I think the ones I did take will adequately 'splain the process.

I'm sure I'm not the first guy to do this, and it's probably been done better, but here I go:

First step was to get the axles side by side on the bench. (Sorry, no pics..)

Measured the (old) trailing arm pads, and proceeded to fab new ones.

Then it was making a wooden fixture off the old axle so I could get the trailing arm pads and the Panhard rod bracket in the right spots. The new axle is 2 inches wider (wheel flange-to-flange), so measurements were taken off center. With the (old) trailing arm pads level, the pinion angle was noted.

Next step was torching and grinding the old bracketry off the new axle. The good folks at GM welded these on to stay; cutting it all off was a *****. The Porta-band helped a lot.

New axle was laid into the fixture, with the pinion at the correct angle. Pads were tacked, checked, checked again, and welded. And a Panhard ("tracking") arm bracket was made.

About this time, I started looking into rebuilding the rear drum brakes that came with the 14 bolt.

After learning that one drum was shot, and the other had .005 left, I started looking at disc conversions.
I got caliper brackets from Ballistic Fabrication, and '77 K30 rotors, calipers, and hoses from Rock Auto.

(Side trip: here's a "field expedient" spanner I made up to snug down the wheel bearings.)

I also ended up shaving the lower pumpkin flange, and installing a Motobuilt "13 bolt" cover (This thing is stout!)
Then it was time to go home.

I'm pleased to say that everything bolted into the truck without issue.

The brakes -surprisingly- seem to work really well without an additional proportioning valve. There is no "emergency" brake -it's a manual transmission; I can (at least) slow it down with the motor- and I solved the parking brake problem by installing a ball valve in the rear brake line... works great.

I hope maybe this helps someone; questions, comments, and snide remarks are welcome


Looks good! Yeah, the problem with the HO52/72 is parts availability. I'm not that familiar with the 14 bolt stuff but I bet it is a lot easier to get parts for, for now anyway....

LockDoc
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Old 12-24-2019, 07:48 PM   #3
ManNamedJed
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Re: 14 bolt axle in a 3/4 ton '71 Sub

Very Nice! I did a similar swap recently. Are you going to do anything for a parking brake?
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Old 12-26-2019, 02:06 AM   #4
gratefuldog
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Location: North Hollywood, CA
Posts: 15
Re: 14 bolt axle in a 3/4 ton '71 Sub

This lovely little chunk of stainless steel is my parking brake:

It's plumbed in like this:


That little ball valve came from Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Last edited by gratefuldog; 12-26-2019 at 02:09 AM. Reason: tryin' to make the picshures werk
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Old 12-26-2019, 11:58 AM   #5
ManNamedJed
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Re: 14 bolt axle in a 3/4 ton '71 Sub

Nice. I like it. Thanks for sharing pics. I have the cadillac parking brake disc calipers, but I haven't gotten around to getting them working as the old parking brake cables don't reach.
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Old 12-26-2019, 03:49 PM   #6
Killer Bee
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Re: 14 bolt axle in a 3/4 ton '71 Sub

Quote:
Originally Posted by gratefuldog View Post
This lovely little chunk of stainless steel is my parking brake:

It's plumbed in like this:

That little ball valve came from Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
first off I'll say that I admire your fab skills..

but I'm going to have to strongly disagree with this hydraulic 'line-lock' parking brake idea..

this runs afoul of just about every alphabet-agency safety reg but furthermore, it's just an outright bad idea..

there's good reason eom's use mechanical systems for this function..

if you've already ran through this debate, I'll let it go with having spoke my piece..

if you're genuinely not away of the safety reasons, I'll be glad to share..

good luck!
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Old 12-26-2019, 09:06 PM   #7
gratefuldog
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Re: 14 bolt axle in a 3/4 ton '71 Sub

Killer Bee-
Thanks- The fab skills have been developing over decades...

As to the "line-lock": I have considered all the "safety" aspects that I could think of, but I'm willing to hear you out. We may end up disagreeing, but lets not get into a 'flame war.' Make your case.
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