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I lucked out and found a 12 bolt on craigslist.  It’s out of a 1970 Chevelle with an axel code of CCW 09*5B,  and a casting #3859038MF.  If my research is correct it originally had a ratio of 373 and was an open rear.  The seller told me he thought it was a 331 posi unit.  Upon opening the rear it has Richmond gears and after counting the teeth it was a 354.54 ratio or as Richmond confirmed 355, and is a posi unit.

After reading multiple threads here I’m a little confused, some say that the upper left control arm will have to be changed, others say it will work fine.  Has anyone done this type of exchange and did or didn’t they have an issue with the control arms?

Thanks

J

 

 

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The upper Control Arm on the Diver Side Rear has a notch cut into it as clearance for the 12 Bolt.  You can notch the 10 Bolt Control Arm but you weaken the Arm.  Pics indicate difference.

Doug

Rear_Upper_Arms_10Bolt_001_small.jpg

Rear_Upper_Arms_12_Bolt_001_small.jpg

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1 hour ago, 72-CLASSIC_RIDE said:

The upper Control Arm on the Diver Side Rear has a notch cut into it as clearance for the 12 Bolt.  You can notch the 10 Bolt Control Arm but you weaken the Arm.  Pics indicate difference.

Doug

Rear_Upper_Arms_10Bolt_001_small.jpg

Rear_Upper_Arms_12_Bolt_001_small.jpg

That’s what is great about this club, concise advice,

thanks

J

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How much would it really weaken it? If its not a real high horsepower car I have to think it would be ok to just grind that little bit off and put a washer or shim on it. Any other thoughts on this?

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Hi. Nice score! Just bolt it in with the 10 bolt arms. It will bolt right in. 

I have installed way to many rears in my time like this. Especially if you don't mind if you have the factory correct arm or not. The stock 10 bolt upper arms will work. 

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I have heard the 10 Bolts being used with a little modification on the 12 Bolt Rears but can't say how well they held up.  Considering this is a Flex/Stress point, I just wouldn't feel comfortable over time and would think twice before lighting them up.  They changed the configuration for a reason, right?  JMO

Doug

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I have gone 10 teens in a drag car with 10 bolt arms on a 12 bolt for many years. I'm sure they made the different arms for a reason. I'm just saying  they work the same. 

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One lucky dog!!  12 bolt posi  with 3:55 gears. I still have my 3:42 posi 10 bolt in mine. Always thinking I'll change it out for a 12 bolt. UMI  Upper control arms on mine.post-259-0-06116300-1484180397_thumb.jpg

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ruff, ruff, lol turns out the guy worked as an engineer at a job I had applied to be the chief at. small world.  thanks for the advice.  other spending needs have come into the equation so I think I’m going to do this a little more piece meal and just do the uppers at this point

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Yesterday I removed the outer bearing, went to the store of the father of the kid I’m putting through college lol (parts store) and purchased new bearings, ordered new axels and hope to have the rear ready for install this weekend or early next week.  Still need to decide on the control arms and bushings.

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On 1/15/2020 at 8:07 AM, Traveler said:

Yesterday I removed the outer bearing, went to the store of the father of the kid I’m putting through college lol (parts store) and purchased new bearings, ordered new axels and hope to have the rear ready for install this weekend or early next week.  Still need to decide on the control arms and bushings.

Hows this going any new progress?

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Thanks for asking.

The axles arrived last Friday, installed the studs, cleaned the axle tubes, checked the carrier bearings, prepped the cover and the rest of the rear for the final push.  I ran into a little issue with the brake cylinders, they must be original as the bolts that hold them to the backing plate seem to have shrunk, they are not metric or sae, started to get physical with them and remembered I had one of those gadget tools (a socket full of pins) that may work so I don’t have to chisel or grind them off.  We have hit a cold spell here and my garage isn’t heated (oh poor me lol) so I took the last couple of days easy(helped my brother paint his home on Monday).  So today I feel guilty for being lazy yesterday.  I hope to solve the brake issue in a hour or two then finish prepping the bearings for install, put in the axle seals and axles, c clips..., add the gear and posi lube and close it up.

I then have to wait for the control arms to arrive to install the rear, I have everything else I can think of, maybe.  I ordered ‘inline’ brake lines they arrived, got drums, brake shoes, axle bearings, hardware kits, middle hose, the only thing I may need is the emergency brake stuff off of the 10 bolt.

I spoke with a gentleman in Delaware who will rebuild the 2004R and take care of the internals such as a hardened input shaft, bigger band, larger clutches, a TCI kit that eliminates the lock up control issue(allows overdrive without external control) and the correct speedo gear for 275/60R15’s, and the bracket for column shifter.

The last decision I have to make is two fold, upgrade the 350 with heads, cam, intake or go the 383/400 route.  The second choice is going carb or efi, which will determine which type of gas tank.

I started with a $5k budget and have gone halfway through it if I do the trans upgrades.  If I just throw the 2204R in ($120 TCI stuff) I can do any of the above and stay in budget without the efi.  383/400 is $3500 with carb, upper end on the 350 is $2500, trans $950, efi and tank/fuel pump/lines/electrical is around $1600, just replace the tank $150.   I estimate I have $5k-$8k equity in the car as I got a good deal, so my budget was low to begin with. Decisions, decisions,lol.  I’m blessed to have such problems. 

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What is this budget you speak of :rofl:What ever you figure something is going to cost you can almost double it and you will find something else you will need also (snowball effect) That's why I haven't started my motor and front end project yet, still collecting parts.

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I laughed at the budget thing too, thought how commendable you're able to stick to it. Same experience I've had in the past, double your projections (at least) and it's in the neighborhood. As said, glad to have such problems...

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In my professional life I managed million dollar budgets which taught me to establish budgets with wants and manage budgets to needs.  I’m doing the same thing with this project, at least I’m hoping to. Do you remember what Mike Tyson said, “Everybody has a plan until they get punched in the mouth” lol. Hopefully my wants won’t cause me to get punched too hard by my needs😊

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9 hours ago, Traveler said:

 Hopefully my wants won’t cause me to get punched too hard by my needs😊

By that logic, I'm pretty black & blue at this point, with no end to the beatings in sight :grin:

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Sorry all, sometimes the old me still comes out.  Ya know I decided to retire from who I had to be so I could be who I wanted to be, that money post was more an internal exercise that slipped through to bore/amuse the rest of you.  Again sorry 😢

 

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Rear was done yesterday sans a little cosmetics, on to the brakes, hopefully today.  

The control arms are due in by the end of the month, then the fun part comes, the install.

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No need to be sorry J. I think I can speak for most of us when I say working on old cars has a tendency to snowball into something more in depth, time consuming, and expensive than the original project we envisioned. In my experience when it comes to budgeting out a project I like to collect all the parts, materials, and supplies I project I will need before I dig in to the car itself. That way at least all the major components I anticipate I will need are already on hand and I can stay close to on budget. I rarely ever do, but at least I am close. Inevitably I find something I want to correct, upgrade, or make prettier once I get started and there goes my budget. Its pretty much a part of the hobby, at least for most of us.

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51 minutes ago, Traveler said:

Sorry all, sometimes the old me still comes out.  Ya know I decided to retire from who I had to be so I could be who I wanted to be, that money post was more an internal exercise that slipped through to bore/amuse the rest of you.  Again sorry 😢

 

No need to say sorry, it was all in fun. A lot of us have blown the budgets right out of the water at one time or another. I'm still curious if the upper control arm works from 10 to 12 bolt because I have a 12 bolt on deck also.

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