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Hi guys wondering if someone could answer this for me? what is a n-case is that differnent from a regular 9in rear, I've seen posts on 9in nodulars wasn't sure the difference, also will all 9in third members interchange from one housing to another assuming axle splines are the same(car to truck or other way),i've got 28 spline 3.00 non locking rear i would like to find a used third member with same spline axles to take in and have the gears i want put on it so i've got two setups for my car. But not sure what cars or trucks to look for a doner
 

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the "N" on some 9 in. means it's a nodular carrier, alot stronger, practically bullet proof. All 9 in. centers will interchange with each other with the same splines. If it's just the carrier, then it doesnt matter. Good gearing came in trucks, some even had posi's, they are a good place to look for "N" cases as well. 9 in. came in almost every V8 car and truck from mid 60-mid 80's.

Rick
 

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9" applications

Dark, actually, 9" rears are generally found under cars with engines of 351 and up. Most 289/302 cars will have 8" rears.

There are many different 9" center section types. First of all, there are the small and large pinion bearing versions. Then there are the 28 and 31 spline axle versions (although you can just change the side gears and you can swap from 28 to 31s or vice versa). Then there are the positraction and open rear versions. Then there are the various types of posi units. Ford used the Equal-loc in the 50s-mid60s, then the traction lock from then on. Both of these types used clutch plates and steel plates under spring tension. For extreme performance use, there is the Detroit Locker. This is a 'clutchless' posi unit. Some 4x4 trucks even got the Gleason-torson unit that used helix gears.

OK, then we get into the different strength cases. The case itself will have different reinforcement ribs, alloy content, etc. The 'N' case is actually Nodular Iron, which is a lot stronger than normal cast iron. A Nodular iron case is identified by a large 1-1/2" tall 'N' cast in to the case in between the reinforcement ribs.

Straycat,

Go junkyard scrounging! in cars up to 1979, you can find a posi rear by looking at the door data sticker. Look at the section 'AX'. Genearally, a letter for an axle code will denote a posi rear. There are code-breaker cheat sheets out there to help you with your codes. You can also crawl around the rear end pile in most yards and read the tags on the rear ends. There is a metal tag attached to one of the center section bolts that will tell you about the rear end. The top line tells what the application was. (Who cares!) The bottom line will start off with a gear ratio. 3.00 is a 3.00 open rear. A 3L00 would indicate a 3.00 posi. The first digit may be partially obscured by the nut. Take a sharp knife with you to scrape any rust off the tag so you can read it easier.
 

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Lets make it clear Senior Motor head

I know you have to know the differance Cougarcj but lets clear up what you said. You CAN NOT just change the side gears to change between 28 and 31 spline axles. You have to have the proper carrier to match the side gears you are using. The carrier holes where the axle slides through it are smaller on a 28 spline than on a 31. That being that way a 31 spline axle will not fit through the hole in a 28 spline carrier.

I used to get around that in my dirt cars ( which are not as hard on rear end gears as drag cars are) which we used to use the inexpensive mini spools, by having my friend who owned a lathe, chuck the easy to find 28 spline carrier up and machine out the carrier to accept the 31 spline axles with a 31 spline mini spool.
Also the N on a nodular case is between the ribs because to the best of my knowledge the N case is the only one to use 2 vertical ribs on the front of it. All the rest only had one. Thats the way I usally found them to be and its a easy way to tell from a distance what it is.

Straycat 22, dont worry about the N case unless you have a high powered drag motor. There not worth the extra expense for a street car in my opinion. Like Dark said trucks are a good place to look. Early ( late 60's to early 80's) F100 4x4 pickups and Broncos with 6cyls and 302's are a good place to look for a 28 spline traction lock pig. You will have to change the front yoke to the car style though. mm
 

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and now for my question...

Do you ever have to chop off pieces of the axle tubes to get the width correct to fit with the tires in their proper location, if so what vehicles should I steer clear from? My brother has the 9 inch from his 56 truck he might let me have - would that be a direct swap? Also I'm planning for a 450 -500 hp engine - would this be a candidate for a nodular case? thanks a bunch - Chad
 

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Chad, unless you plan on back halfing and tubbing your car, for get about the 56 rear. Those housings have to be precision fitted and welded when you shorten one. If you dont have a 9 already just find one for your year Cougar or Mustang, It will keep your life simpler and cheaper. Yes 500 hp could stand a N case if you plan on some hard launches. mm
 

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modifiedmark did you tear up the mini spools i hear they can't take alot of power drag or roundy
unless it's on dirt cause the wheels are spining if they hook up with any real power they will break could u help me on this thanks maybe i'm way off on this thanks
 

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MM,

Actually, they made some carriers in 28 spline that were the same axle bore size as the 31 spline. Also, the WAR case looks the same as the 'N' case, with the two vertical reinforcing ribs, but no N. In fact, I even have one of those cases. The WAR case is not the same as an 'N' case though. One of the car magazines went so far as to do tests on the various style cases and the WAR case was the weakest. I wish I would have saved those magazines... Also, I forgot about the 2-pin vs 4-pin posi units.

Mini spools. Funny you should mention those. I was running one in the 9" in my 74 Camaro drag car. I was running [email protected], putting somewhere near 440hp to the ground. Never had a problem with the mini spool and I was also running 28 spline axles. I mentioned all this in a post a couple of months ago. The 28 spline axles are more forgiving and will twist whereas the 31 just snap with no real warning. I painted a stripe down the length of the 28 spline axles and was looking for a sign of twisting. I never went more than 1/8 turn. Yes, this was a real low-budget car, but it did alright for itself.
 

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Cougarcj, what you say maybe true. What I have learned about Ford 9"s is there are no absolutes. I will say that in almost 20 years of stock cars and a ton of 9" pigs later I have never seen a 28 spline carrier with a 31 spline sized hole in it. I forgot about the war cases, but there not to common if I remember right.

As far as the mini spools go, no I never had a problem with one and I have seen only a couple people that I know of that have had any trouble with one. I have run them myself on dirt and asphalt. I remember seeing one tear the axle splines out of one and I seen one break the pinion pin in one. They make a high strentgh pin for them but by the time you get into all that you might as well buy a spool. The ones I seen break were in some sportsman cars that weigh around 2800 lbs and up with 10-12" tires and 5-600 hp. Remember my modifieds only went 2000-2300 lbs on 8" tires. As far as drag racing I would not think they are the best way to go, they still put alot of force on the pinion pin. mm
 

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Is the traction lock diferential the best kind for what I'm looking for? - Which is both tires turning off the line but when I turn I don't want anything jerky going on around the turns. I'd go with a Detroit Locker but I hear those are loud, but I'm not sure exactly what they mean by loud and I don't think I've ever heard one up close - does it sound about like timing gears in your engine, or is it worse? Oh yeah and it has to handle the power I throw at it ;) thanks - Chad
 

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Chad,
The Detroit locker does ratchet to allow for slipage and yes, it will clunk, bang, and make all sorts of noise going around turns. It is also kinda hard to set yourself into a turn and then have the locker go into convulsions back there. It loads/unloads the tires making for strange cornering handling.

A traction lock is the way to go for the street. However, the posi clutches do wear out over time. They are replaceable, but it is a PITA to do so. You gotta take the rear all the way apart and separate the actual ring gear carrier halves to gain access to the clutches. It is best to do this when you're setting up your rear end and then you're good for about 50,000 miles, depending on how much cornering you do. I'd say that 99.9% of the 9" posi units you'll find have traction locks. When looking for 9" posi 'pigs' or center sections, look under full size trucks or vans and the old (up to '78) full size cars or station wagons. Generally, the trucks will have better gearing (3.00-3.70 gears) and the cars will be 2.40 (yikes!) to 3.25 gears. Most cars will have 28 spline axles, vans about 50/50, and pickups generally will have 31 spline axles. If you get a 31 spline posi unit, you can swap out the side gears for 28s and you're good to go unless you want to spend the extra bucks and get a set of aftermarket 31 slpine axles because you're surely not going to find original 31s for your car very easily (or cheaply)! You can't just use the truck axles for a couple of reasons. First, most are a 5 on 5-1/2 bolt pattern (except some early F-100s), and second, they'll be much too long for your car.

Beware of the old 50s-60s equal-loc. You can't get parts for them, so once the posi clutches are wasted, you're stuck. Even I get stuck once in a while! ;)

Another good street posi unit is the Gleason-Torson. They're usually found in the front diff of 4x4 trucks that actually have a posi in the front. Not too common though. They use worm gears in a constant mesh so there's nothing to wear out and they're smooth. I see ads in the 4x4 on off road magazines for them every so often, going for around $450 for the posi unit itself.

Leave the mini spools and full spools to the racers. They do not allow for any slippage, and make cornering a bear. The tires have to do the slipping!

Oh, and whatever you do, don't let anyone talk you into making a 'poor-man's posi' by telling you to weld the spider gears!
 

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TRrue N cases have a second vertical rib cast into the body of the carrier also they are much stronger due to the nickel content in the case material. don't be fooled by some 9 in. cases that have 2 vertical ribs but no large N cast into it. those cases are only grey cast iron and do not have the high nickel alloy of the true N case.
 
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