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Old 09-10-2021, 11:33 AM
punkin punkin is offline
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Default Ford 9" Conversion

Hello all,

Working outside my comfort zone here but I was reviewing my equipment order for a new Ford 9" rear for my 68 Firebird. I notice in the descripton that the axles were going to be diffent lengths. The sales person told me this is due to the design construction of the 9" center section and that this is done to keep the driveshaft in the center of the car.

Does this sound correct? He also indicated that they could set it up so that that housing is centered and that the drive shaft would still work with respect to u-joint angles but I'm not sure what to do with this.

I don't want it to look goofy but if this is how it's done so be it.

I appreciate any recommendation/suggestions. Thanks!

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  #2  
Old 09-10-2021, 01:37 PM
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ZeGermanHam ZeGermanHam is offline
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If you look at how the 9" center sections are constructed, you'll notice that they are offset to the passenger side. This means that the driver side axle will be longer than the passenger side. This is done to keep the housing centered in the car, not the driveshaft. Here is what that offset looks like in my '66 GTO frame.



If you center the pinion yoke so the driveshaft is straight down the middle, you will then offset the differential housing, which may or may not cause clearance issues depending on application. Personally, I'd just buy a complete drop-in 9" from Quick Performance. I'll bolt right into your F-body.

https://www.quickperformance.com/GM-...e_p_21573.html

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Last edited by ZeGermanHam; 09-10-2021 at 01:45 PM.
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Old 09-10-2021, 01:46 PM
punkin punkin is offline
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Thank you very much for the reply. Some of the terms still don't register with me. Your car looks fantastic! If I'm seeing it correctly, it appears your drive shaft coupler is to one side slightly and the housing is centered.

I am purchasing a complete brake to brake rear and a bolt-in solution that is what I'm asking for. In the quote it descrbed axles being about 3 inches different in length when I asked about it here was the response;

The driveshaft will be in the stock location for an F body, but due to how the 9-inch is configured, the pinion is inherently offset, so in turn, the axles are different lengths, that’s true will nearly all Ford 9-inches. For example, if you wanted equal length axles, the pinion would be offset 2.18 inches (which is still within operating range of the u-joint).

I don't fully understand the reply. Is this sayning that the rear housing will be centered or is it saying that the drive shaft will be centered? Certainly I want function over appearance but if it looks goofy I want to address that sooner than later.

Again, I do thank you very much.

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Last edited by punkin; 09-10-2021 at 02:05 PM. Reason: punctuation
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Old 09-10-2021, 03:50 PM
JLMounce JLMounce is offline
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The F-body has a relatively small drive-shaft tunnel since from the factory, the leaf springs will keep the housing relatively centered compared to the converging 4 link found in an A body. If you take a look at the pinion on GM rear-ends, while they are not perfectly centered in the housing, they are relatively close, especially compared to a Ford 9".

The way your rear-end will be setup, the pinion will be in the same location as it would be with the factory GM rear. This means that the housing will be skewed off-center slightly to allow that placement. This is one of the reasons I decided to do a 12 bolt with Torino housing ends instead of a 9".

That said, the only time you're really going to run into any clearance issues with a 9" (or 12 bolt) is if you're trying to still use a factory style transverse muffler. If your exhaust system currently uses under the floor mufflers which is more typical of aftermarket stuff, you won't have an issue other than the fact that you'll have the housing off-center by a couple issues and one axle tube (and axle) will necessarily be longer than the other.

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Old 09-10-2021, 04:57 PM
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Quote:
Originally Posted by JLMounce View Post
The F-body has a relatively small drive-shaft tunnel since from the factory, the leaf springs will keep the housing relatively centered compared to the converging 4 link found in an A body. If you take a look at the pinion on GM rear-ends, while they are not perfectly centered in the housing, they are relatively close, especially compared to a Ford 9".

The way your rear-end will be setup, the pinion will be in the same location as it would be with the factory GM rear. This means that the housing will be skewed off-center slightly to allow that placement. This is one of the reasons I decided to do a 12 bolt with Torino housing ends instead of a 9".

That said, the only time you're really going to run into any clearance issues with a 9" (or 12 bolt) is if you're trying to still use a factory style transverse muffler. If your exhaust system currently uses under the floor mufflers which is more typical of aftermarket stuff, you won't have an issue other than the fact that you'll have the housing off-center by a couple issues and one axle tube (and axle) will necessarily be longer than the other.
I thank you...I think this makes sense now. If I were to have them center the housing then the drive shaft would be at a greater angle (left/right) running through the tunnel and even closer to it at the rear. I imagine the extra angle is less than desirable as well?

My exhaust is going to another project maybe next year. It will need to be a custom thing anyways because of the bracing and trans cross-member changes. Being 2-3 inches off center shouldn't be too terribly objectionable from a visual standpoint (I hope). I've seen them in F-bodies before and never noticed. I just wanted to be sure this was a normal situation before I place the order.

I thank you gentlemen. The people on this forum are truly great.

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  #6  
Old 09-12-2021, 01:43 AM
Goatracer1 Goatracer1 is offline
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I have had a Currie 9 inch in my GTO for over 20 years now. It has the unequal length axles to center the drive shaft. Don’t over think it. Once under the car you can’t see it anyway.

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Old 09-12-2021, 11:46 AM
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Quote:
Originally Posted by punkin View Post
I thank you...I think this makes sense now. If I were to have them center the housing then the drive shaft would be at a greater angle (left/right) running through the tunnel and even closer to it at the rear. I imagine the extra angle is less than desirable as well?

My exhaust is going to another project maybe next year. It will need to be a custom thing anyways because of the bracing and trans cross-member changes. Being 2-3 inches off center shouldn't be too terribly objectionable from a visual standpoint (I hope). I've seen them in F-bodies before and never noticed. I just wanted to be sure this was a normal situation before I place the order.

I thank you gentlemen. The people on this forum are truly great.
Yup, you're going to actually have to really look at it to notice that it's offset in the car. The only people that would care about that sort of thing would be a concourse judge, and they'd knock you for having a 9" in the first place.

You're good to go!

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Old 09-12-2021, 12:10 PM
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I thank you...way past concourse. I'm in it for my own sense of cool and fun. That order is getting placed on Monday when they open up :-)

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  #9  
Old 09-13-2021, 09:46 PM
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If you tried to run a pinion offset of 2.18 your drive shaft would hit the tunnel in an F-body. The axles are 27 5/8 and 30 7/8, something like that.

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  #10  
Old 09-13-2021, 10:56 PM
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Thanks all, I ordered my rear from Currie today...another exersize in patience...told me it would be 10 weeks out

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Old 09-13-2021, 11:13 PM
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Holy cow. I miss the mid 00's. I ordered my Moser 12 bolt circa 2008 and it was delivered the next week.

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Old 09-14-2021, 02:59 PM
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It's such a widespread issue now. It only took me a few weeks to receive my Quick Performance 9" in December 2019, but more recently I've been waiting on items from other vendors for over 5 months. It's a real drag.

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  #13  
Old 09-15-2021, 01:26 AM
punkin punkin is offline
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Yep...its crazy. The transmission was a bit over 3 months. I've been meaning to rewire the thing so maybe I'll get started on that while I wait.

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  #14  
Old 09-23-2021, 11:45 AM
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One thing to note, depending on the housing center section design, it's possible, with the pinion centered, that you may have issues when you try to do a 3" exhaust. That also depends on the type of exhaust, due to how tight the U bend over the axle is.

Also, due to the fact that the axle tubes are larger in diameter, you will have to modify the spring retainer/shock plate, since the holes will need to be further apart.

I've run both 9" and 12 bolts in multiple cars, and if I had a choice, I would just go for a Moser 12 bolt. The center sections are new castings, and they use thick wall axle tubes, making it pretty indestructible. Cost difference is nominal.

When ordering, have the hybrid axles ends installed that use the 9" bearing with a 12 bolt flange. You will be glad you did later on when it comes to brakes, etc.

I also suggest narrowing 1" on each side, so disc rotors don't push the wheels/tires out.


.

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