Leaf spring swap (reverse 3/4 ton swap) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

eric67m · 11-08-2007, 12:43 AM

I have a 1967 K10 which had almost rusted out leaf spring eyes. My old set up was 1/2 ton springs, 4" blocks and a 12 bolt rear axle (6 lug). I picked up a set of springs and U-bolts from a 1968 K20 3/4 ton with a Eaton HO52 (8 lug rear end).

I am in the process of removing the old springs and replacing with the newer springs but keeping my old 12 bolt axle. The old U-bolts were rusted on so I cut them with a cutting torch. When replacing with the new U-bolts I noticed that they are a wider spacing and leave a gap around the front and rear of the axle. Should I replace my U-bolts and use the closer spaced top plates from my original set up? The springs, U-bolts, top plates in the pictures are from the 3/4 ton Eaton set up the axle is a 12 bolt.

Is this a problem?

I appreciate your input and knowledge.
Eric

earl87gta · 11-08-2007, 01:23 AM

the 3/4 68 springs are wider are the ubolts tite to the springs? the 68 rear springs are 3in wide it looks in the pic like those may not be a 3in wide spring so they may be from a newer truck then a 68. it should be ok this way a lot of guys do it. The only way aroun dit is to have a spring shop make you a set of cutome springs that are 3in wide. I dont think there are any out of the box lift kits for the 67 to 68 trucks with rear lift springs. if you ever change the front out you will find your front springs stock are 2 1/2 wide not 3 like the 69 up trucks.

**special-K** · 11-08-2007, 06:21 AM

The u-bolt will be different for each rear you have.You need to go with new 1/2t u-bolts.They should be replaced when swapping springs anyway.The 3/4t rear has bigger tubes/bigger u-bolts.

eric67m · 11-08-2007, 07:23 AM

I think Special K hit the nail on the head. I think the Eatons rear end tubes are larger diameter. The springs look like the same dimensionally as the 67's that came off. They are also hourglass tapered. The ends were the same width and the center appears to be the same. I will try to take some measusrements tonight on the U-bolts.

Thank you guys.

1969K10 · 11-08-2007, 08:13 AM

You need to get U-bolts that match your axle better. don't know about where you're at, but I've got a semi tractor shop here in town that custom bends U-bolts for less then $5 each. And they've worked perfect every time. Just something to look into for cheap U-bolts.

OLDCHEV4X4 · 11-08-2007, 08:15 AM

My rear u bolts on my 1/2 and 3/4 ton are square and come down from the top. And the spring plates are on the bottom. Your's look like newer style spring plates on a older truck. The u bolts should be tite to the spring and the axle tube. Otherwise you could shear a center pin if you go off road or work your truck.
I converted to a top spring plate on my race truck for ground clearance. They came off of a 1975ish 1/2 ton truck.
I have been told that you should never reuse spring u bolts. I have with no problems so far, but i keep retorqueing them.

1969k10stepside · 11-08-2007, 04:35 PM

Quote:

Originally Posted by OLDCHEV4X4

My rear u bolts on my 1/2 and 3/4 ton are square and come down from the top. And the spring plates are on the bottom. Your's look like newer style spring plates on a older truck.

The 67-68s were that way..In 69 through 72 they were like yours with spring plates on the bottom

eric67m · 11-08-2007, 11:00 PM

I will look into the semi truck custom bent option. I am always looking for a less expensive way.

I took measurments off of the old and newer springs. It would appear that the only difference is between the u bolts.

Old 1/2 T, 2 leaf, front and rear eyebolt width 3 3/16, 2 1/2 at the axle,
U bolt plate 3 1/16"

Newer 3/4 T, 3 leaf, front and rear eyebolt width 3 3/16, 2 1/2 at the axle,
U bolt plate 3 5/16"

What about rolling some 1/8 thick flatstock to take up the difference in axle diameter? Do you think it would be ok to lightly run the truck on road with the U bolts this way until I get them properly replaced?

OLDCHEV4X4 · 11-09-2007, 07:25 AM

"The 67-68s were that way..In 69 through 72 they were like yours with spring plates on the bottom" <quote>

My 67 C-30 has them on the bottom too. ??

earl87gta · 11-08-2007, 04:32 PM

I didnt even notice that they were not around the axle tube I was just looking at the spring perch and top plate. Yap have to agree time for new u bolts.

**special-K** · 11-09-2007, 08:12 AM

Just get new u-bolts.It`s recommended anyway,even when size stays the same.
I think the inverted u-bolts were pre-72.

11-08-2007, 12:43 AM	#1
eric67m Registered User Join Date: Apr 2005 Location: Monroe, WA Posts: 298	Leaf spring swap (reverse 3/4 ton swap) I have a 1967 K10 which had almost rusted out leaf spring eyes. My old set up was 1/2 ton springs, 4" blocks and a 12 bolt rear axle (6 lug). I picked up a set of springs and U-bolts from a 1968 K20 3/4 ton with a Eaton HO52 (8 lug rear end). I am in the process of removing the old springs and replacing with the newer springs but keeping my old 12 bolt axle. The old U-bolts were rusted on so I cut them with a cutting torch. When replacing with the new U-bolts I noticed that they are a wider spacing and leave a gap around the front and rear of the axle. Should I replace my U-bolts and use the closer spaced top plates from my original set up? The springs, U-bolts, top plates in the pictures are from the 3/4 ton Eaton set up the axle is a 12 bolt. Is this a problem? I appreciate your input and knowledge. Eric Attached Images __________________ 67 K10, lwb, fleetside, 327, 4spd, 205, cab and 3/4 frame swap, 14 bolt, big window, and a "rustoleum roll job"

11-08-2007, 01:23 AM	#2
earl87gta Senior Member Join Date: Dec 2003 Location: Kingsport TN Posts: 4,641	Re: Leaf spring swap (reverse 3/4 ton swap) the 3/4 68 springs are wider are the ubolts tite to the springs? the 68 rear springs are 3in wide it looks in the pic like those may not be a 3in wide spring so they may be from a newer truck then a 68. it should be ok this way a lot of guys do it. The only way aroun dit is to have a spring shop make you a set of cutome springs that are 3in wide. I dont think there are any out of the box lift kits for the 67 to 68 trucks with rear lift springs. if you ever change the front out you will find your front springs stock are 2 1/2 wide not 3 like the 69 up trucks. __________________ Earl 68 2500 4x4 GMC Burb

11-08-2007, 06:21 AM	#3
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Leaf spring swap (reverse 3/4 ton swap) The u-bolt will be different for each rear you have.You need to go with new 1/2t u-bolts.They should be replaced when swapping springs anyway.The 3/4t rear has bigger tubes/bigger u-bolts. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

11-08-2007, 07:23 AM	#4
eric67m Registered User Join Date: Apr 2005 Location: Monroe, WA Posts: 298	Re: Leaf spring swap (reverse 3/4 ton swap) I think Special K hit the nail on the head. I think the Eatons rear end tubes are larger diameter. The springs look like the same dimensionally as the 67's that came off. They are also hourglass tapered. The ends were the same width and the center appears to be the same. I will try to take some measusrements tonight on the U-bolts. Thank you guys. __________________ 67 K10, lwb, fleetside, 327, 4spd, 205, cab and 3/4 frame swap, 14 bolt, big window, and a "rustoleum roll job"

11-08-2007, 08:13 AM	#5
1969K10 Senior Member Join Date: Jul 2004 Location: Clarks Hill, Indiana Posts: 733	Re: Leaf spring swap (reverse 3/4 ton swap) You need to get U-bolts that match your axle better. don't know about where you're at, but I've got a semi tractor shop here in town that custom bends U-bolts for less then $5 each. And they've worked perfect every time. Just something to look into for cheap U-bolts. __________________ 1969 K10 - V8, 465, 205, 12 bolt, D44 2002-current 1969 K20 - V8, 465, 221, Eaton, D44 2012-current Nothin' but drums on all 4 corners! past horses in the stable 72 C10-short step (97-02), 68 C10-long fleet (06-12)

11-08-2007, 08:15 AM	#6
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: Leaf spring swap (reverse 3/4 ton swap) My rear u bolts on my 1/2 and 3/4 ton are square and come down from the top. And the spring plates are on the bottom. Your's look like newer style spring plates on a older truck. The u bolts should be tite to the spring and the axle tube. Otherwise you could shear a center pin if you go off road or work your truck. I converted to a top spring plate on my race truck for ground clearance. They came off of a 1975ish 1/2 ton truck. I have been told that you should never reuse spring u bolts. I have with no problems so far, but i keep retorqueing them. __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania

11-08-2007, 11:00 PM	#8
eric67m Registered User Join Date: Apr 2005 Location: Monroe, WA Posts: 298	Re: Leaf spring swap (reverse 3/4 ton swap) I will look into the semi truck custom bent option. I am always looking for a less expensive way. I took measurments off of the old and newer springs. It would appear that the only difference is between the u bolts. Old 1/2 T, 2 leaf, front and rear eyebolt width 3 3/16, 2 1/2 at the axle, U bolt plate 3 1/16" Newer 3/4 T, 3 leaf, front and rear eyebolt width 3 3/16, 2 1/2 at the axle, U bolt plate 3 5/16" What about rolling some 1/8 thick flatstock to take up the difference in axle diameter? Do you think it would be ok to lightly run the truck on road with the U bolts this way until I get them properly replaced? __________________ 67 K10, lwb, fleetside, 327, 4spd, 205, cab and 3/4 frame swap, 14 bolt, big window, and a "rustoleum roll job"

11-09-2007, 07:25 AM	#9
OLDCHEV4X4 Registered User Join Date: Apr 2000 Location: Chester County PA, USA Posts: 1,228	Re: Leaf spring swap (reverse 3/4 ton swap) "The 67-68s were that way..In 69 through 72 they were like yours with spring plates on the bottom" <quote> My 67 C-30 has them on the bottom too. ?? __________________ 72 k/10 short wideside 72 k/5 Blazer 72 K/5 Blazer - obstacle course racer 72 custom/10 8' bed 70 K/5 Blazer 67 C-30 GMC Flat bed 86 GMC K2500 Plow Truck 85 GMC K3500 84 M1008 85 M1008 77 G30 Motor Home 72 Sears 12hp Tractor Glenmoore, Pennsylvania Last edited by OLDCHEV4X4; 11-09-2007 at 07:26 AM.

11-08-2007, 04:32 PM	#10
earl87gta Senior Member Join Date: Dec 2003 Location: Kingsport TN Posts: 4,641	Re: Leaf spring swap (reverse 3/4 ton swap) I didnt even notice that they were not around the axle tube I was just looking at the spring perch and top plate. Yap have to agree time for new u bolts. __________________ Earl 68 2500 4x4 GMC Burb

11-09-2007, 08:12 AM	#11
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,851	Re: Leaf spring swap (reverse 3/4 ton swap) Just get new u-bolts.It`s recommended anyway,even when size stays the same. I think the inverted u-bolts were pre-72. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 11-09-2007 at 08:12 AM.



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