GMC Rear swap options? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevykevy · 09-07-2016, 10:49 PM

I have a 1968 GMC with the leaf spring set up. Thinking of putting the 71-72 front disc set up which would be a 5 lug pattern.

Will a 71-72 GMC rear (5 lug) bolt right up? Shocks in same location?

Mike C · 09-08-2016, 07:13 PM

Yes. You can also buy conversion axles for your existing housing and new drums which may or may not be cheaper depending on how easy it is to find a donor 5 lug leaf housing.

You never said 1/2 ton 6 lug but that is my assumption here.

I put a 72 housing and axles in my 69 not just for the bolt pattern but wider housing that is on the 70 and up. This was needed to fit the wheel/tire combo I had in mind.

chevykevy · 09-08-2016, 11:18 PM

Thanks Mike. Ill try to find a 71-72 rear to start.

CastIron · 09-09-2016, 01:02 AM

I've wondered the same thing. Anybody know if 73 and later would work? I seem to remember that those have the springs in a slightly different location, but I don't know if that is accurate.

**special-K** · 09-09-2016, 07:27 AM

Quote:

Originally Posted by CastIron

I've wondered the same thing. Anybody know if 73 and later would work? I seem to remember that those have the springs in a slightly different location, but I don't know if that is accurate.

Not as a bolt-in, but it's not a big deal to move spring saddles and shock mounts. You can also buy 6-lug disc brake kits for the front. I think 6-lug half tons are cool...it's totally a GM thing! They finally caved in and started doing what the others did in '71.

Mike C · 09-09-2016, 11:43 AM

1/2 ton spring perches on the square bodies should be same, but shock mounts need relocating.

Not near as many 67-72 2x4 leaf trucks so haven't investigated this further since I was able to find a 72 housing. Something else to consider is that 71-72 will have perches for the narrower 2 1/4" spring vs the 2 1/2" spring on the 73 and up.

Coley · 09-09-2016, 12:08 PM

Quote:

Originally Posted by special-K

Not as a bolt-in, but it's not a big deal to move spring saddles and shock mounts. You can also buy 6-lug disc brake kits for the front. I think 6-lug half tons are cool...it's totally a GM thing! They finally caved in and started doing what the others did in '71.

...yeah, its funny that GM was 6 bolt, then went to 5 bolt in 1/2 tons for 25+ yrs....then went back to 6 bolt again...lol.
It would have been nice if they had a transition year with a 6 bolt/disc brake set-up in 1970 or thereabouts.

All Good
Coley

volksworld · 09-09-2016, 11:58 PM

the spring perches on the square body rear are 1/4 inch further apart than the earlier rear ....way back when i just forced them in cause the springs in my tow truck had so much arch....when i restored the truck and dropped it i made 1/8 inch spacer plates between the spring hangers and the chassis ....had to replace the hangers anyway due to accident damage and worn out bushing bolt holes (from the spring shop that "repaired" the damage and never tightened the bolts properly) so in this case it was easier than moving the perches....square body has one shock in front of the rear and the other behind it so one mount needed to be cut off and swapped around

09-07-2016, 10:49 PM	#1
chevykevy Registered User Join Date: Jan 2004 Location: Wyoming Posts: 641	GMC Rear swap options? I have a 1968 GMC with the leaf spring set up. Thinking of putting the 71-72 front disc set up which would be a 5 lug pattern. Will a 71-72 GMC rear (5 lug) bolt right up? Shocks in same location?

09-08-2016, 07:13 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	Re: GMC Rear swap options? Yes. You can also buy conversion axles for your existing housing and new drums which may or may not be cheaper depending on how easy it is to find a donor 5 lug leaf housing. You never said 1/2 ton 6 lug but that is my assumption here. I put a 72 housing and axles in my 69 not just for the bolt pattern but wider housing that is on the 70 and up. This was needed to fit the wheel/tire combo I had in mind. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

09-08-2016, 11:18 PM	#3
chevykevy Registered User Join Date: Jan 2004 Location: Wyoming Posts: 641	Re: GMC Rear swap options? Thanks Mike. Ill try to find a 71-72 rear to start.

09-09-2016, 01:02 AM	#4
CastIron Registered User Join Date: May 2013 Location: Oregon Posts: 326	Re: GMC Rear swap options? I've wondered the same thing. Anybody know if 73 and later would work? I seem to remember that those have the springs in a slightly different location, but I don't know if that is accurate.

09-09-2016, 11:43 AM	#6
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	Re: GMC Rear swap options? 1/2 ton spring perches on the square bodies should be same, but shock mounts need relocating. Not near as many 67-72 2x4 leaf trucks so haven't investigated this further since I was able to find a 72 housing. Something else to consider is that 71-72 will have perches for the narrower 2 1/4" spring vs the 2 1/2" spring on the 73 and up. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

09-09-2016, 11:58 PM	#8
volksworld Registered User Join Date: Apr 2011 Location: formerly NY currentlyNC Posts: 389	Re: GMC Rear swap options? the spring perches on the square body rear are 1/4 inch further apart than the earlier rear ....way back when i just forced them in cause the springs in my tow truck had so much arch....when i restored the truck and dropped it i made 1/8 inch spacer plates between the spring hangers and the chassis ....had to replace the hangers anyway due to accident damage and worn out bushing bolt holes (from the spring shop that "repaired" the damage and never tightened the bolts properly) so in this case it was easier than moving the perches....square body has one shock in front of the rear and the other behind it so one mount needed to be cut off and swapped around __________________ 1970 short step c10 leaf spring 454



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