12 bolt on craigslist

[Dapper Dan]

Hey guys, I have been thinking about swapping out my 10 bolt for a 12 bolt. I found this one for $50 http://baltimore.craigslist.org/pts/1468753391.html

What should I look for? or are all 12 bolts basically the same and is that a fair price? Thanks for the help

[68Timber]

Since he's not sure what it came from, measure the total width and the spring perch width against yours. $50 sounds like a steal. If you pull the diff cover and it's not grenaded I'd take it home.

[thirdstreettito]

Originally Posted by BRUISER

Since he's not sure what it came from, measure the total width and the spring perch width against yours. $50 sounds like a steal. If you pull the diff cover and it's not grenaded I'd take it home.

Yup.

[71swb4x4]

I would hold out for one with posi. Why do you want to upgrade to a 12 bolt? It seems like a lot of answers to that question will also lead to a posi of some sort.

[Dapper Dan]

Originally Posted by 71swb4x4

I would hold out for one with posi. Why do you want to upgrade to a 12 bolt? It seems like a lot of answers to that question will also lead to a posi of some sort.

I would like posi but for 50 bucks i thought i could buy the posi later. Would that be a mistake?

[cableguy0]

i would grab it for 50 bucks so long as the width is correct. you have all the parts needed. could use it as is for now. pull the cover count the teeth on the gears. if it has the ratio you want the only thing you will need is a posi unit. and have the rear setup. you cant go wrong for 50 bucks. if i had somewhere to stash it i woulda bought that rear myself.

[68Timber]

Originally Posted by cableguy0

i would grab it for 50 bucks so long as the width is correct. you have all the parts needed. could use it as is for now. pull the cover count the teeth on the gears. if it has the ratio you want the only thing you will need is a posi unit. and have the rear setup. you cant go wrong for 50 bucks. if i had somewhere to stash it i woulda bought that rear myself.

+1, for $50 you can have a 12-bolt and if you find a 3.73 posi 12-bolt later, you can sleep easy knowing you can get your $50 back easy.

But I've got the feeling it's already sold.

[Dapper Dan]

well I just got off the phone with him he still has it. He said it spins freely, but he has never run it. Ended up being too wide for what he needed

I had been planning on doing a flip kit but would it be better to just weld new spring perches on the 12 bolt?

Lastly, he said it measures 57" from backing plate to backing plate. I measured my 10 bolt at 58" but I was under the truck in the dark at the time and I am not sure where he measured from. does that sound about right?

[78-5.3]

Originally Posted by Dapper Dan

well I just got off the phone with him he still has it. He said it spins freely, but he has never run it. Ended up being too wide for what he needed

I had been planning on doing a flip kit but would it be better to just weld new spring perches on the 12 bolt?

Lastly, he said it measures 57" from backing plate to backing plate. I measured my 10 bolt at 58" but I was under the truck in the dark at the time and I am not sure where he measured from. does that sound about right?

yup from the flange plate face to flange plate face

[cableguy0]

even if it is narrower 1/2 inch on each side smaller isnt going to even be noticeable.

[Dapper Dan]

If I were to weld on new spring perches how would I set the pinion angle? Anyone know an easy way? Could I get away with setting them parallel with the old ones? That looks like what the flip kits do or am I mistaken

[HOGDADDY]

Originally Posted by 71swb4x4

I would hold out for one with posi. Why do you want to upgrade to a 12 bolt? It seems like a lot of answers to that question will also lead to a posi of some sort.

Yes why would you want a 12 bolt? It has been my understanding that they(12 bolt truck) are no stronger than a 10 bolt rear.

[2tons of fun]

Originally Posted by Dapper Dan

If I were to weld on new spring perches how would I set the pinion angle? Anyone know an easy way? Could I get away with setting them parallel with the old ones? That looks like what the flip kits do or am I mistaken

1 you need to look to see what wheel parttern it has for starters.





as for the pinion angle. having the truck on level gorund will make it easeir but you need to have the full weight of the truck on the suspension. you can jack it up but you need to put the stands under the axle and not the frame of the truck.

go to the hardware store and get a angle finder, they are cheap.

1 put the finder on the back of the trans find angle .

2 put the finder on the yoke of the axle. rotate the axle till it is the same plane as the trans.

depending on how your finder is labled this can get confusing. just rember that 1 + 2 must = 90 or 180 *

if you still cant get it, call a drive shaft shop, they will help you out.

[cableguy0]

the 12 bolt rear is definately stronger than the 10 bolt.

[msgross]

I found a 12-bolt with posi for $35.. ok that was a lucky day but yes, you can weld new perches to it. Do you have leaf or coil rear?

I'd check the gearing and if it's not what you want then hold out for it. The ratio is stamped on the ring gear (ie 41:11 = 3.73) just divide the numbers. The gears might be rusty or chipped, brakes mught be bad etc..

I sold my open 12-bolt 3.73 with 6 lugs for $40 or $50 at carlise, couldn't give it away...

[Dapper Dan]

Thanks for the help guys but it is a little too late I went and picked it up today. I started thinking twice about it, but inside it looked good

once I got it home and got a good look at it I found it has 307 gears. It looks like it was out of a 71 truck from the numbers I looked up so I'm not sure it will fit right in my 87. it does have leaf spring perches but they are on at a weird angle.

Probably should have passed on it but live and learn! I think I'll throw it in the back yard and maybe one day use it to build what I want

Thanks again everyone

[cableguy0]

are you sure they arent the perches for the truck arms? they are on an angle on the bottom of the housing. is there a mount on top of the housing for a track bar? you might be able to trade someone on here. lots of guys are looking for a 3.07 gear with fuel being the price it is.

[msgross]

if they are at weird angles it was probably a coil spring truck. You can cut them off and weld on a set of regular leaf perches.

[HOGDADDY]

Originally Posted by cableguy0

the 12 bolt rear is definately stronger than the 10 bolt.

The truck 12 bolt has a pinion gear that is smaller than the the 10 bolt rear.

1.438 (12 bolt truck) versus 1.625 (10 bolt) ring gear diameter which happens to be same size as the 12 bolt passenger cars' 12 bolt rear.

But the ring gear is bigger in truck 12 bolt at 8.875 same as passenger car 12 bolt whereas the 10 bolt is 8.5.

Is it really that much stronger with a smaller pinion gear?

[cableguy0]

how many 12 bolt rear end failures have you seen? 10 bolts fail constantly in trucks.

[2tons of fun]

i broke the **** out of mine.

[N2TRUX]

Lets keep this post positive and informative please.

[menace121978]

Originally Posted by cableguy0

even if it is narrower 1/2 inch on each side smaller isnt going to even be noticeable.

IMO, the 1/2 inch on both sides is HUGE. our trucks already have an off set track width. the rear tires sit in too much already. ideally you'd want a wider rear out of a newer body style(cant remember the exact year) if your going to go through all the trouble of welding new perches. just my couple pennies...

[Dapper Dan]

[QUOTE=cableguy0;3679847]are you sure they arent the perches for the truck arms? they are on an angle on the bottom of the housing. is there a mount on top of the housing for a track bar?

I think you are dead on. I have never seen a coil spring suspension but that makes sense

[QUOTE=menace121978;3681027]IMO, the 1/2 inch on both sides is HUGE. our trucks already have an off set track width.

I would agree with you but it is the same, we were measuring from diff points on the backing plate. I'm running staggered rallies now to make up for that

[kevinmfduane]

i just drove up to gaithersburg yesterday and picked up a 3:42 posi to replace the open 3:08 in my 83 ($200 with a 72 c-10 seat and 3 truck rally caps).

i figured i would have to cut off coil perches, and weld on leaf perches upside down (flip kit) but when i got there i did not see what i thought would be coil perches, i saw the same perches you have on this rear. my 83 seams to have the perches at 90% of the rear (have not comfirmed too cold to get under truck). can someone confirm what the perches in the above pic are??? guy said the rear came out of a 72 1/2 ton which i thought had coils but he claims it was leaf sprung. either way i have an open 12 bolt 3:08 to trade someone who can swap in my new posi rear, in the D.C area.
[quote=Dapper Dan;3681149][QUOTE=cableguy0;3679847]are you sure they arent the perches for the truck arms? they are on an angle on the bottom of the housing. is there a mount on top of the housing for a track bar?

I think you are dead on. I have never seen a coil spring suspension but that makes sense

Originally Posted by menace121978

IMO, the 1/2 inch on both sides is HUGE. our trucks already have an off set track width.

I would agree with you but it is the same, we were measuring from diff points on the backing plate. I'm running staggered rallies now to make up for that