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  #1 (permalink)  
Old 08-17-2003, 02:25 PM
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9" or 12 bolt

I am currently in the process of building a '50 Chev pickup, street rod style. This is my first project and I have been reading a lot of the info posted here and really appreciate the info I've seen.

My question is for possibly using a 12 bolt GM rear end under my truck. I have found a TON of info on Ford 9" rear ends. Widths, how to ID, ratios, what can and can't be narrowed, etc., etc.

So far I have not found information like this for GM rear ends.

My search has been centered around the 79 to 81 Lincoln or Granada with rear disk brakes. These rear ends are listed at 62" overall width (measured at the outside of the axle flange).

If a GM 12 bolt turns up before a Ford 9" does, I would hate to pass it by due to my lack of knowledge.

Any suggestions?

Thanks in advance

H2Os50

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Old 08-17-2003, 03:11 PM
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The ford 9" rearend was quite possible the best differential ever built. It is so adaptable to work in anything, and the parts availability is extraordinary. It will far outlast a GM12 bolt. You may have a hard time finding a 9" with factory disk brakes because that is a part in high demand. But you can get any nine inch once you know the width that you have to have. 1966-1977 Ford Bronco's probably have the narrowest housings. And you can get an aftermarket bolt on disk brake set-up from Summit Racing for $450-$1000 dollars. If you find, a stock 9" disk set-up it will cost you at least that much extra anyway. But you should be able to build the rearend you are looking for, for less than $1000. Of course you can always spend more!
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Old 08-17-2003, 05:27 PM
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I"m not sure I agree with bowtie the ford 9 inch's reputation was built around the versons used in the high performance big block cars. It is true that the ford 9 inch has part selection 2nd to non which is nice and they are quick any easy to swap gears on but honestly on the street how oftain are you swaping gears anyway. If you going with a limited slip the eaton posi is also far supiour to fords unit and as for far outlasting the 12 bolt thats a bunch of b*ll sh** the only thing you have to watch is that axle shafts don't start being dug into by the bearing because over time the hardend outer surface wears though. This is a minor problem how ever. I'm not saying that the ford 9 isn't a very good rear but I think the 12 bolt is a better choice, besides who wants to lower them selves to using ford parts
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Old 08-17-2003, 09:44 PM
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Arrow

The choice is yours, but there is absolutely NO WAY that a 12 bolt even comes close to the strength of a 9". It isn't the ability to change gears that makes them so popular,it's brute strength and superior design. The number one cause of failure in any rearend used in a hard application is pinion deflection. The only rearend that is designed to eliminate or reduce it is the 8" and 9" rearends. If you look at their design you'll notice that they have a bearing support on the end of the pinion not present in most others. That's why so many rearend companies make bolt in 9" housings for so many GM and Mopar cars. I don't think any make a bolt in 12 bolt for any car other than those originally equipped that way.
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Old 08-17-2003, 10:14 PM
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I'm not disputing that of the 2 the ford 9" is the Superior design but I think it is chosen far to often and it does have some inherent weaknesses. for example the stalk carrier and 3rd member made out of grey cast iron with is crack prone where the 12 bolt uses nodular iron 2nd the chev is 31 lbs lighter 3rd it is more efficient. The ford 9 inch used a vast array of quality of the internals where pretty much all 12 bolts came with the same stout pieces. another point is that the ford tac-loc is a piece and last but not least the 9" has fewer spines on the axle shafts. Now most of these problems can be over come but it requires money being spend so if your on a big budget then the 9" and need all the strength you can get then a built 9" is the way to go other wize a 12 bolt will serve you nicely
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Old 08-17-2003, 10:21 PM
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In my 55 years on this planet, I have learned a few things and one of them is to avoid people who say to use "anything, but or nothing but". To say that it is a lowly thing to use ford parts on a chevy and visa versa is just a show of hotrodding ignorance. The only brand superiority is in the persons head that is dealing the crap. Now that that is off my shoulders, the ford 9", the chevy 12 bolt and the Dodge dana 60 are all good strong rears. The strength of all of them is overlapping. The dana being the strongest followed by the 9" then the 12 bolt. On the other hand, the 12 bolt is the lightest, followed by the 9" and then the dana. All have their strong points. I am partial to the 9" only due to the fact that I have built about 4 of them and I am most familiar with them. The reason I built them is because they were available at the time. What ever you can find that will more closely fit your needs, by all means use it. By the way, If you do end up wanting a 9" disc rear, do not pay the price for the lincoln rear. Disc brakes can be added to a 9' for about $300 and that is all new parts. You don't need Wilwood brakes on the street, hell, I don't even use them on my bracket car. Hope this helps.
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Old 08-17-2003, 11:50 PM
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Thanks for the help!

With this info I will expand my search for the Ford 9" rear end with or without disk brakes.

It sounds like if I find a ford 9" without disk brakes, just add them later. No need to pay a premimum price for a rear end with disk brakes just to rebuild them.

If I watch what I'm doing with my shopping, I should be able to build a 9" to suit my needs. I'm no slouch with a torch and welder and I have access to a machine shop. This will help if I wind up narrowing one to fit under my truck.

H2Os50
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Old 08-21-2003, 12:47 AM
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Well here is my two cents worth if it helps you at all. I recently put a 55 Chevy pickup together. I chose the 9" for a couple reasons. I wanted 350-1 gears, those are quite common in Ford trucks. Secondly width was just about perfect while still using stock fenders and box without tubs.
Try buying a 12 bolt and see how over priced they are due to the old supply and demand thing.
Lastly I just thought I would mention that if you get a pickup rearend they should have the big drums etc. I have put front discs in and used rear drum. That truck stops like you would not believe! That being said I really have to question why you would want disc on the rear unless it is for show reasons?
My thinking is all that extra dough being spent on rear disc could be spent on other more important thing like.........Nitrous??
Good luck with that Chevy!
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Old 08-21-2003, 09:19 PM
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h2o
I was at my local junkyard today and I found two 9" 's with disc brakes. They were set up for coil suspension but could be converted to leaf springs pretty easily. If you are interested I am going by there tomorrow anyway I will ask how much he wants for them. I live about 3.5 hours away from you so picking one up would be no problem.
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Old 08-22-2003, 12:01 PM
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12 Bolt

I have a buddy that owns a rearend shop in San Jose, CA and I talked to him about this because I am in the process on my 68 Camaro right now as well. From what he told me (and I believe him he has been doing this for 15 yrs) the 12 bolt is a better choice if you are looking for something strong and reliable. The Ford 9" is a great rearend but if you are not looking to change 3rd members often do not own an 8 sec or faster car and want to save that extra 50 hp that the Ford 9" robs go with the 12 Bolt...

Just my .02

Whytry
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Old 08-22-2003, 02:30 PM
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If price is not a consideration, go with the Ford. But if money counts, consider that your truck is light, particularly in the rear, and it is pretty unlikely you would break either one of them in that chassis even with huge hp. And you could use the pickup truck version of the 12 bolt which weighs a little more, but has larger axles and bearings.

The one argument for the Ford which makes sense though is that the Ford does not use C Clips and therefore the axle can't come out if it breaks which is pretty unlikely.

Anybody with a mig welder can narrow a rear end or put calipers on a drum original. I can talk you through it.
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Old 08-26-2003, 08:26 AM
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Propanic,

I thought I was emailing you from this site. Turned out the email went to the web master.

I get to most major towns in AZ every month. If you get by the junkyards again, email me at h2os50@qwest.net and I'll make sure that I stop where your at.

Thanks for the help.

H2Os50
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