12 bolt carnage - The 1947 - Present Chevrolet & GMC Truck Message Board Network

6869704X4 · 04-14-2003, 11:20 PM

Can someone get the angle of the spring perches vs the pinion on a 70 12 bolt.
Mine failed pulling a stump out of the ground.
Also broke the pinion yoke.
Are the 73 and up u-joints bigger?

Mike C · 04-15-2003, 09:12 AM

This article will tell you how to set pinion angle:

http://www.carcraft.com/howto/91758/

Or this one for 4x4:

http://jniolon.clubfte.com/driveline...nephasing.html

I have broken 6 12 bolts in the Jimmy, including one trying to remove a stump. I really want to upgrade to 8 lug wheels, not because I need them, but just because. However, wheels and tires in addition to a front 8 lug setup will eat me up. So, in the meantime, if I break the 12 bolt again (or should I say when?) I am planning on installing a semi-floater 14 bolt with the 9.5" ring gear from a late 80's-early 90's light 3/4 ton truck. That should be significantly stronger for not much money and I can retain my current 15x10 inch rims. Most semi-flaoters were 4.10 geared in 3/4 tons, but Z71 1/2 tons will have 3.42 or 3.73. I have 4.10, so that works well for me.

6869704X4 · 04-16-2003, 01:42 AM

Thanks man, good article, heres a pic.

6869704X4 · 04-16-2003, 01:43 AM

front view

Dale DuBose · 04-16-2003, 11:52 AM

I'm running a 12 bolt. Did you break something in the dif or just a u-joint? I plan to go to 14 bolt rear D60 front.

6869704X4 · 04-16-2003, 12:04 PM

I'll put up more pics when I get the axle out. The front of the perches folded allowing the axle to rotate up. That caused the u-joint to bind and break the yoke.
I have a yoke from a later model 12 bolt but one of my buds said its for a bigger ujoint. Aint had a chance to compare it yet.

Dale DuBose · 04-16-2003, 04:37 PM

Bigger u-joint sound like a good idea, if you could get the driveshaft and t-case yoke to match.

**Canadian694x4** · 04-16-2003, 10:52 PM

Do you have some pics of your truck(s) that I could see?

6869704X4 · 04-17-2003, 09:43 AM

Sure, heres one just prior to incident.
I dont know who that fat bastard is.

Mike C · 04-17-2003, 10:50 AM

I bent the perches on my housing when I was running blocks. I welded a brace across the perches to reinforce them after straightening and leveling them best I could.

6869704X4 · 04-17-2003, 01:45 PM

Here is what Im gonna do for perches http://www.off-road.com/chevy/tech/perch/
The yoke on the driveshaft got tweaked so my plan is to order a yoke for the bigger ujoint.
A shop in town is going to make sure the shaft itself is still true, cut off the old yoke and weld a bigger one on it. Total damage $240.00

Hey MikeC
Somebody on the pirate board says the shims on the leaf pack caused this. I think he probably right. What about you? What gears were you running when this happend to you? Im running 4.56s.

Mike C · 04-18-2003, 09:21 AM

I was running 4.10. I don't see any way that the shim on the leaf pack could cause that. You are just putting too much torque through the OEM mounts because of gear and tire size. I have had no troubles since getting rid of the blocks which reduces the twist on the mount. That and the braces didn't hurt...

The boxed square tube spring mounts is what I was going to suggest for you. You can also use Mopar or Comp Engineering mounts and brace the ends to the housing with 3/16 steel plate if you don't want the extra height from the offroad design style perches.

6869704X4 · 04-18-2003, 09:49 AM

Got the axle out last night. The welds are OK. The front of the perches folded. We knew that already though.
Two things I noticed. The front ubolts were stripped and there was a definite indentation from the shims on the perches.
So, add the price of ubolts to the cost.

6869704X4 · 04-19-2003, 10:01 AM

Here are the folded perches. One of the replacements is next to them. Im cutting the notch to go halfway down the axle tube.
Back to work. Gotta hit the boneyard to find some ubolts and plates.

6869704X4 · 04-28-2003, 05:23 PM

Heres the way she sits now. I moved the axle back 1/2". Looks like I coulda moved it back a little more.

04-14-2003, 11:20 PM	#1
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	12 bolt carnage Can someone get the angle of the spring perches vs the pinion on a 70 12 bolt. Mine failed pulling a stump out of the ground. Also broke the pinion yoke. Are the 73 and up u-joints bigger? __________________ The more I learn about women, the more I love my truck.

04-15-2003, 09:12 AM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,714	This article will tell you how to set pinion angle: http://www.carcraft.com/howto/91758/ Or this one for 4x4: http://jniolon.clubfte.com/driveline...nephasing.html I have broken 6 12 bolts in the Jimmy, including one trying to remove a stump. I really want to upgrade to 8 lug wheels, not because I need them, but just because. However, wheels and tires in addition to a front 8 lug setup will eat me up. So, in the meantime, if I break the 12 bolt again (or should I say when?) I am planning on installing a semi-floater 14 bolt with the 9.5" ring gear from a late 80's-early 90's light 3/4 ton truck. That should be significantly stronger for not much money and I can retain my current 15x10 inch rims. Most semi-flaoters were 4.10 geared in 3/4 tons, but Z71 1/2 tons will have 3.42 or 3.73. I have 4.10, so that works well for me. __________________ 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

04-16-2003, 01:42 AM	#3
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Thanks man, good article, heres a pic. Attached Images __________________ The more I learn about women, the more I love my truck.

04-16-2003, 01:43 AM	#4
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	front view Attached Images __________________ The more I learn about women, the more I love my truck.

04-16-2003, 11:52 AM	#5
Dale DuBose Registered User Join Date: Oct 2002 Posts: 27	I'm running a 12 bolt. Did you break something in the dif or just a u-joint? I plan to go to 14 bolt rear D60 front. __________________ I need all the help I can get.

04-16-2003, 12:04 PM	#6
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	I'll put up more pics when I get the axle out. The front of the perches folded allowing the axle to rotate up. That caused the u-joint to bind and break the yoke. I have a yoke from a later model 12 bolt but one of my buds said its for a bigger ujoint. Aint had a chance to compare it yet. __________________ The more I learn about women, the more I love my truck.

04-16-2003, 04:37 PM	#7
Dale DuBose Registered User Join Date: Oct 2002 Posts: 27	Bigger u-joint sound like a good idea, if you could get the driveshaft and t-case yoke to match. __________________ I need all the help I can get.

04-16-2003, 10:52 PM	#8
Canadian694x4 Born To Lose Club Join Date: Feb 2003 Location: Calgary, Alberta/Oxenden, Ontario, Great White North Posts: 13,306	Do you have some pics of your truck(s) that I could see? __________________ Brian Smith - "Born To Lose" 1969 Chevrolet K10 LWB Fleetside - Proud Owner For 20 Yrs - 1 of 208 Built & Sold In Canada! - 283 V8/350TH/NP208, 2" All Spring Lift, 32" Good Year MT/R's. 1972 GMC K2500 Custom LWB Fleetside - Proud Owner For 2 Yrs - 1 of 571 Built & Sold In Canada! - 350 V8/SM465/NP205, 4” Rough Country Lift, 33” Interco TSL Thornbirds 2007.5 GMC Sierra SLE 2500HD 4x4 - Proud Owner For 15 Yrs - 6.6L V8 Duramax Diesel/Allison 1000, 2" Lift, 33" Mickey Thompson MTZ's. 2008 Yamaha Raptor 700r - Proud Owner For 13 Yrs - ITP Mud Lites. 2015 John Deere 1025R - Proud Owner For 6 Yrs - 24HP Diesel/H120/54D/260B/SB1154.

04-17-2003, 09:43 AM	#9
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Sure, heres one just prior to incident. I dont know who that fat bastard is. Attached Images __________________ The more I learn about women, the more I love my truck.

04-17-2003, 10:50 AM	#10
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,714	I bent the perches on my housing when I was running blocks. I welded a brace across the perches to reinforce them after straightening and leveling them best I could. __________________ 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

04-17-2003, 01:45 PM	#11
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Here is what Im gonna do for perches http://www.off-road.com/chevy/tech/perch/ The yoke on the driveshaft got tweaked so my plan is to order a yoke for the bigger ujoint. A shop in town is going to make sure the shaft itself is still true, cut off the old yoke and weld a bigger one on it. Total damage $240.00 Hey MikeC Somebody on the pirate board says the shims on the leaf pack caused this. I think he probably right. What about you? What gears were you running when this happend to you? Im running 4.56s. __________________ The more I learn about women, the more I love my truck. Last edited by 6869704X4; 04-17-2003 at 01:48 PM.

04-18-2003, 09:21 AM	#12
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,714	I was running 4.10. I don't see any way that the shim on the leaf pack could cause that. You are just putting too much torque through the OEM mounts because of gear and tire size. I have had no troubles since getting rid of the blocks which reduces the twist on the mount. That and the braces didn't hurt... The boxed square tube spring mounts is what I was going to suggest for you. You can also use Mopar or Comp Engineering mounts and brace the ends to the housing with 3/16 steel plate if you don't want the extra height from the offroad design style perches. __________________ 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

04-18-2003, 09:49 AM	#13
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Got the axle out last night. The welds are OK. The front of the perches folded. We knew that already though. Two things I noticed. The front ubolts were stripped and there was a definite indentation from the shims on the perches. So, add the price of ubolts to the cost. __________________ The more I learn about women, the more I love my truck.

04-19-2003, 10:01 AM	#14
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Here are the folded perches. One of the replacements is next to them. Im cutting the notch to go halfway down the axle tube. Back to work. Gotta hit the boneyard to find some ubolts and plates. Attached Images __________________ The more I learn about women, the more I love my truck.

04-28-2003, 05:23 PM	#15
6869704X4 Registered User Join Date: Jul 2002 Location: SE NM Posts: 769	Heres the way she sits now. I moved the axle back 1/2". Looks like I coulda moved it back a little more. Attached Images __________________ The more I learn about women, the more I love my truck.



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