[BERRY251]

What is so special about a ford 9" rear? I hear alot of people talking about them and putting them in there cars but why are they so popular, are they extremely tough and durable or something?

[Vintage 68]

I would say they have a reputation and following simular to the Small Block Chevy - and for most the same reasons ...

1st - they were used for many years across the complete Ford vehicle line. They can be found in most ford cars and trucks from the late 50's into the 80's.
So, like a small block, they can be found in lots of variations that can be easily adapted to many vehicles and for very reasonable prices.
They tend to be very reasonably priced if you go looking for them at wrecking yards.

2nd - they are very well engineered, again like a small block, and they stand up to increased HP output (or input in this case) with minor modifications to the stock configuration - again, like a small block ...

3rd - their popularity has lead to many aftermarket performance companies offering excellent replacement parts that can be had for low prices and used to improve the internals of the assembly.
Popularity of a given design means more companies are willing to invest in tooling to make parts for it, the economy-of-scale will allow them to make money off their investment very fast in most cases - again, like a small block ...

4th - GM's use of a weaker design 10-bolt in most standard production vehicles requires an upgrade if you intend to put some serious HP into the rearend and expect it to live - so I guess GM has some responsibility in creating this 'need' for a replacement rearend.
As 12-bolts are relatively rare, harder to change ratios on and usually more expensive to aquire and modify, there is a ready market for a stronger readend assembly.

5th - It takes a Ford off the road ...
Really, it's underneath and you can't really see it in most applications, so "Chevy" guys don't feel to bad about putting one under there and abusing the heck out of it ...

The 9" has come in several different design variations over the years. Some are stronger that others and some are just about as bad internally as having a 10-bolt when it comes to putting large HP through them.
The axle sections come in various widths and have different side bearing sizes depending on their original application.
These axle side bearings are pressed onto the axle (v.s. ride on them as in the GM design) and are retained in the axle section by bolts v.s. the weaker "C-clip" retention design GM uses in 10 & 12-bolts.
There are several axle spline counts - 28 and 31 are the most common in stock applications. I've used aftermarket with up to 40 splines.
The 9" Center Sections (also called 'drop-out', 'pumpkin', 'third member' & etc ...) come in several designs. The stronger units have three (3) Pinion support bearings, with the third being on the geared end helping support the pinion for higher loading ability - these aren't "bullet proof", the end straight roller bearing is prone to failure (I have one in my shop now) and the bearing housing is prone to breaking if subjected to repeated shock loading, such as clutch dumps with sticky rear tires.
The aftermarket has addressed this issue with reinforced bearing support designs and other improvements that make their offerings better than using a stock ford casting in most cases for racing and HP use.
Having a removable center section makes repairing, regearing and at-track gear swaps much easier.

Hope some of this helps explain it - others will also hopefully chime-in with other reasons;
John

PS - I guess there's also that - ' I've got a 9" ' thingy that gives it a good ring too

[pdq67]

He forgot to mention that a 12-bolt due to the gear tooth profile design is about 3 percent more eff. to turn than a 9".. (I.e., take's about 3 percent less power to turn it)...

That said, (I think), you can even get a 9" with 12-bolt gears in them b/c of this..

pdq67

[BERRY251]

Vintage68 thanks for all the info, pretty interesting! It might be something to look into then! and I like the 5th point "it takes a ford off the road!" LOL

[Larger Dave]

This is a condensed version of a Q & A spanning many weeks and pages on another forum that I think answers all the 9" Ford vs GM rear end questions. I didn't write every word but it raises questions that need answering.

10 and 12 bolt GM rears are basically weak everyone "KNOWS" that 9 inch Ford rears are stronger. A 12 inch can not handle more than 450 hp.

I beg to differ on the statement "it's still not as strong as the 9". The "new" Moser 12 bolt will handle up to a thousand horse with the 33 spline axle package. A stock 30 spline 12 bolt still is and always was stronger than a stock 9" (people only stopped using them because there were no more around). Even a custom built 9" without a Ford part in it isn't that much stronger than the "new" Moser 12 bolt. The Moser is a all new non-GM high nickel casting with heavy fully welded axle tube walls and no C-clips. I've used one for years with over a thousand horse in a 4000 pound car and it hasn't given a moments bother. It also doesn't suffer from the parasitic drag that the 9" does so more of your horse power gets to the ground than goes into frictional losses. I'd choose a Dana 60 over a Ford 9" any day of the week, and the Dana 60 is a real boat anchor at 287 pounds compared to the 185 pounds for the 12 bolt.

The big boys abandoned the 9" years ago because they are too weak to hold up to more than two thousand horse power. Though it looks like a 9" in the rear of those top fuel cars it is actually a purpose built 11" rear end. They took the 9" design and super sized it (as in would you like fries with that).

You don't even have to take the brakes off the car to install another 8.5" 10 bolt or 12 bolt GM rear end. Just unbolt the backing plates and let em hang, remove and install rear end then bolt up the backing plates, and drive !!!! Its really that easy. Your brakes will work with a 9 inch if it is ordered correctly. You still must get the correct housing ends to use the Chevy brakes. You will also have to bore a hole in the center of the backing plates to 3.150 inches in diameter to go over the axle wheel bearings.

No! I'm not short changing the 12 bolt, it is still the best option bar none. I've got a thousand horse (with juice) 582 in a lead sled of an Impala (that’s 3700 pounds of lead sled Impala and 430 pound of lead butt driver) that I can put into the low 9's with slicks and have never had a problem with my 12 bolt. I've been racing more than 40 years with big block torque monsters, and have never owned a 9". In all that time I have broken only two 12 bolts and one of those was stone stock. I know that everyone thinks 9" inch rears are God's gift to the world of racing, but I have never figured out why.

You say it's 100 pounds more than the 12 bolt?? How much does the 8.2 10 bolt weigh compaired to the 12bolt? If I WAS considering the nine bolt how much more would the Dana weigh compared to that?

You can never get a straight answer to this question because no one runs a stock 9". Matter of fact there are precious few to any stock parts in any 9" rear end especially if it is made for a non-Ford application. I have three examples of rear ends I have pulled and weighed. Maybe gravity is different were you live (remember the higher up you go the less a item weighs).

Complete drum to drum the 10 bolt weighs on average (that means the one I weighed was an average rear end out of a '74 Nova with multi-leaf spring perches attached) 179 pounds.

An open rear 12 bolt out of a '70 Chevelle weighed 185 pounds, missing the passenger side drum.

9" weighs 230 pounds (Currie Fab 9 housing, Nodular case) Off of Curries web site.

Any way you slice it the 12 bolt is lighter and just as strong as anything you could bolt up. The 9" has a minimum of a 3% higher parasitic drag cost than the Spicer design (We know them as 10 bolts and 12 bolts but it also applies to the Dana rear end; most people say the 9" will cost you at least 4% off of whatever horse power you make just to spin it). And My favorite reason to use a 12 bolt under a Chevy; it is genuine GM product so it looks right (less filling - looks right -- less filling).

Please note that they forgot to weight the 9" axle with the backing plates, wheel cylinders, brake hardware, shoes, and those pesky cast iron brake drums on that weight chart.

This is an example of how the car magazines; which some say are basically just infomercials for the advertisers, slant things in favor of the product they are showcasing. They did not lie (there are laws against that kind of behavior), but a fast reader would be prone to over look the disclaimer in the parenthetical brackets.

As I pointed out when it came to weights and measures for a 9" it all depends upon what you are measuring because no two are alike. The 9" currently being sold is a concept not a product. It can be anything from a fabricated titanium housing, with a magnesium and aluminum cased carrier sporting gun drilled axles and a titanium spool to a slab of wrought iron and cast iron, with forged tool steel propeller shafts off a tug boat being used by some cow poke that he built for his 4x4 to crawl around a bit in Utah. There really needs to be some definitive standard as to what a 9" inch rear is and add or subtract weight as you modify it (with the modifications noted).

I have a hard time believing that the 9" is costing me 4% of my rear wheel power. Would swapping to a 8.5" 4.10 turn my 11.75@117 second daily driver/tow car into a 11.60@119 second monster? We already get 417 rwhp from our relatively mild 331" road race motor, would this mean 434 rwhp? Other than speculation, is there any definitive A-B-A testing of this supposed loss?

As to the 4% parasitic drag. Were do you think the strength of the 9" comes from. Surely you are not going by just the diameter of the ring gear because the 12 bolt is the same size. In fact Strange sells a 9" rear end equipped with the ring and pinion out of a 12 bolt Chevy to overcome the parasitic drag issue. No the strength of the 9" Ford design lies in the fact that it located the pinion gear low on the ring gear so that it engages two teeth of the ring gear at a time instead of the one tooth at a time that the Spicer design uses. Because it is dragging twice the number of teeth across the ring gear it has more friction. That friction is what we call parasitic loss. And yes it has been measured and compared a number of times.

The problem in testing is depending upon how you set up the rear end (back-lash, side load, pinion depth and crush on the bearings) there is a difference even between two similar rear ends made by the same person using the same parts. Because of this the 9" guys throw there hands up and say "See, I told you it's inconclusive." even though hundreds of tests all indicate a 3-4% loss.

In closing there are three reasons to consider a 9" rear.
1.) NO C-Clip
2.) They use a spanner nut instead of shims to set up the rear.
3.) They are a Hotchkiss design so you can change a gear ratio in twenty minutes in your drive way if you have another pumpkin all set up.
BUT
1.) There exists 3.150" large Ford bearing ends to weld onto the 12 bolt axle to fix the C-clip issue.
2.) I don't set up my rear ends anymore (got lazy and it drives me nuts trying to get it "right") so I don't care how they do it.
3.) How many people can really afford $2,400 for each gear ratio they want to run to be sitting in a box waiting to be changed out (avg. price of a fully built 9" pumpkin able to support the same power as a 12 bolt rear).

Big Dave with a little help from his friends (such as Freddie aka "Big Gear Head")

[BERRY251]

Thanks again!

[377camaro]

Well, that about sums it up, haha. It's funny that you bring this up because I have a 9" sitting off to the side getting ready to put into my camaro.

[onovakind67]

I'm swapping a 12-bolt out in a 69 Camaro for a Fab9 setup so I should have a chassis dyno comparison in a couple of weeks.

[Vintage 68]

Originally Posted by Larger Dave

... I beg to differ on the statement "it's still not as strong as the 9"...

Wow Dave - who said that

I thought his question was 'what's special about them & why are they so popular' ?
So I formulated my answer around that - not, how much money you can throw at either one if you want to put big HP trough it ...

[Larger Dave]

I have always assumed that people turn to 9" rears because they are looking for a stronger rear end; often never consider the 12 bolt (or the 8.5" 10 bolt if only a souped up small block in front of a TH350). My mistake if the change to a 9" is strictly for cosmetic reasons.

Cost is always an issue. People are quick to say how they scored a 9" out of a car for a pocket full of change and then overlook the considerable amount of money needed to bring it up to par (able to handle the same torque as the 12 bolt rear with comparable parts). Or under sell the upgrades they made in their rear-end because you will not need the expensive parts that they used, because they're assuming your ride isn't as bad as theirs is; so you obviously will forgo them and save all that money (which is wrong on two counts -- assuming your ride isn't as bad as theirs, and that you won't want the best).


Larger Dave

[oger]

Stock 12 bolts have the problem of all Spicer types. The case itself springs open if abused enough. If you look at most truck Spicer 60s that had posi they are spung but I am sure that a 3/4 ton work truck gets seriously thrashed. I have had no experence with the aftermarket 12 bolts but I bet they are really bullet proof. A 9in in stock form (except the trick factory race stuff) has a very weak housing and a case that is very prone to cracking. The aftermarket makes pretty much bullet proof pieces for a 9in and the price has gotten a little better. A stock 9in if you don't abuse it too bad it will live and gear changes are so simple if you ever own one you will never even think about a Spicer type again.

[sc68z28]

So a nodular case 9" with 35 spline axles, does the pinion gear shaft become the weak point?

[oger]

I would say you found a weak link. What type of gearset were you running?

[sc68z28]

Originally Posted by oger

What type of gearset were you running?

It was a Motive Gear, 3.0 to 1. With a 3.25 1st gear. I had just changed rear tire size from 26 x 10, to 28 x 11.5, and was just starting to get a grip (pun) on a traction problem. It broke at the start line, the car moved about 1".

The new gears are also by Motive Gear, I change to 3.25 to 1.

[big gear head]

The standard 9 inch pinion shaft has 28 splines. A standard 12 bolt pinion shaft has 30 splines. A pro gear for the 9 inch can be had with 35 splines, but can't be run on the street, and 3.89 is the cut off point for the 35 spline pinion.