Identifying Differential

[jpaz]

So that means it has an open differential. If it was a posi then both wheels would spin, but one would spin in the opposite direction of the other.

 

[Stanglover]

He said earlier that it came with a code 6 axle, 3.00:1 open.

 Ah, yes he did. However I was referring to the axle that is in the car now. I should have made that clear.

 Geoff.

 

[Stanglover]

So in that case, if it were me, I'd be looking for a Ford 9" Traction-Lok with a 3.50:1 ratio or at least a 3.25:1. 429/460 are gas hogs, so I wouldn't want the revs up too high on the highway.

 Just my thoughts on that.

Geoff.

 

[red351]

The old seal and bearing should have a part # on them.

 

[DarthRevan39]

No dice on the tag. I don't have a deepwell socket but it looked like one would fit if I tried it. The whole underside of the vehicle was painted black (yeah I know its a cardinal sin to buy one thats been painted like that to hide rust, but the rust looked/looks quite minor. Couldn't get a good picture of the hogs head.

 

[DarthRevan39]

The old seal and bearing should have a part # on them.

Honestly, that would be to smart for me to take them out and just look at the part number.... Lol

I guess part of the idea was to know what to buy before I took it apart because I'm afraid of getting it too far apart where I can't even get it properly towed if need be. Is there a part number on the outside of the bearing so I could just take the axle out again and look and the seal should probably match or come as a set?

 

[DarthRevan39]

So in that case, if it were me, I'd be looking for a Ford 9" Traction-Lok with a 3.50:1 ratio or at least a 3.25:1. 429/460 are gas hogs, so I wouldn't want the revs up too high on the highway.

 Just my thoughts on that.

Geoff.

It does drink gas about like I drink beer lol, somewhere between 8 and 14 mpg, leaning closer to the 8.

 

[Stanglover]

So in that case, if it were me, I'd be looking for a Ford 9" Traction-Lok with a 3.50:1 ratio or at least a 3.25:1. 429/460 are gas hogs, so I wouldn't want the revs up too high on the highway.

 Just my thoughts on that.

Geoff.

It does drink gas about like I drink beer lol, somewhere between 8 and 14 mpg, leaning closer to the 8.

 That sounds about right. I have a friend with a 73 Torino with a transplanted 429 and it does about 10 mile per IMPERIAL gallon, so 8 US mpg sounds about right. That's why I don't have a 429/460. It's bad enough with a 351 4V.

 

[Don C]

It sounds more and more like it's an 8", so will take the small bearing. If you used a 9/16" socket to remove the backing plate/bearing retainer that makes it pretty certain, along with the tapered axle housing tubes.

Only the high performance cars (427s, 429CJ, 428CJ,Bosses etc), including Galaxies, came with the 31 spline axles and large bearings.

You can also look at the illustrations in this thread

https://www.7173mustangs.com/thread-what-size-bearing-when-ordering-disk-brakes

 

[DarthRevan39]

It sounds more and more like it's an 8", so will take the small bearing. If you used a 9/16" socket to remove the backing plate/bearing retainer that makes it pretty certain, along with the tapered axle housing tubes.

Only the high performance cars (427s, 429CJ, 428CJ,Bosses etc), including Galaxies, came with the 31 spline axles and large bearings.

You can also look at the illustrations in this thread

https://www.7173mustangs.com/thread-what-size-bearing-when-ordering-disk-brakes

Thanks. I just saw another video that had an early 8" and it looks exactly like mine.

I guess the next question is, is there any concern that the 8" won't hold up to the 429/460 power output or should it be ok?

 

[red351]

Depends how easy you are on it. Ford had a reason for using 9" on all 351 and up.

 

[Don C]

Yes, there are some concerns about it. There's a reason that Ford used the 31 spline 9 inch differentials behind high performance engines, and the 28 spline 9 inch behind 351Cs.

It will partly depend on the rear end ratio and the tires you will be using. Large diameter and width tires hook up better, more traction means more load on the differential and the rest of the drive train. Another factor will be the shape and diameter of the axle shafts, some of the 28 spline axles do not maintain the same diameter for the full length, but narrow down between the splines and the hub. A low gear ratio (numerically high) differential has smaller pinion gears which also means weaker.

If I were running that engine I would definitely run a 31 spline 9 inch, either stock or aftermarket like Currie or Moser. And, if I were planning on frequent trips to the drag strip step up to 35 spline axles.

 

[1sostatic]

Yes, there are some concerns about it. There's a reason that Ford used the 31 spline 9 inch differentials behind high performance engines, and the 28 spline 9 inch behind 351Cs.

Hey Don , How ya doin'?

Here is my version of Darth Vader's 2.75 Nut-sack  (another "2" in the VIN)



Now, it is a 9" ...(my wife doesnt think I have 9 inches, but WTF! looks like 9 to me  )

 ...My bag of bolts, as you know, is an April 1971 Dearborn "02" body, "M" code 351C std 4V with FMX trans, and a grotesque guy behind the wheel 



How would a numpty like me know if it is 31 spline or 28 ?

plz be gentle  :whistling:

 

[73pony]

If stock it was a 28 spline. Which is fine for what you are running.

 

[Don C]

The best way to be 100% sure is to remove an axle and count the splines.

However, you can be 99% sure by looking at the end of the axle. In this picture the axle on the left, with the Double "D" shaped slot in the center of the hub, is a 28 spline axle, and the one on the right with the 3 holes in a row is a 31 spline. Now, the reason for the 1% doubt, 8" axles all have 28 splines and most have the 3 holes in a row. An 8" axle of the same length will fit in a 9" housing.

 

[Stanglover]

IF you decide to go look for another 9" rear axle, here are the dimensions you would be looking for taken from mine. Sorry I don't have a fancy drawing program to make it look all neat and tidy, but you get the idea. Between the inside of the brake backplates measured 53 1/4" and the between hole centers on the mount plates was 43" (approx, just a quick measurement) I believe there were several axles with these dimensions used on other Ford vehicles, possibly Bronco, F150's etc. I'm sure Don C or Don from OMS can confirm, but there should be options out there, not just Mustangs. I'm going to suggest you order, or buy from a vendor like NPD, Kevin Marti's book, The Mustang and Cougar Tagbook (1965-1973). In it you will find just about every tag listed for our cars. There are way too many axle tags for me to list here. Someone may already have a complied list of axles and cross references they can post for you.

Geoff.



upload image

 

[DarthRevan39]

The best way to be 100% sure is to remove an axle and count the splines.

However, you can be 99% sure by looking at the end of the axle. In this picture the axle on the left, with the Double "D" shaped slot in the center of the hub, is a 28 spline axle, and the one on the right with the 3 holes in a row is a 31 spline. Now, the reason for the 1% doubt, 8" axles all have 28 splines and most have the 3 holes in a row. An 8" axle of the same length will fit in a 9" housing.

This is probably a dumb question, but if I get a new 9" differential, and with that new axles, I'm guessing that I will also have to get new wheel hubs (or the new axle will have it attached) and I will need new wheels, tires (tyres for you wierdies out there), and drum brakes (unless I upgrade to all disc) for this new configuration?

 

[Don C]

The hub is part of the axle. You get the bolt pattern you need for your wheels, which for stock wheels is 5x4.5" (5 lugs on a 4.5" [114.3mm] diameter}. You'll likely need to get new backing plates for drum brakes (unless your new axle also has small bearings), good time to upgrade to discs. You'll also need to get the correct width, which is 61.25" from outside of hub to outside of hub.

 

[DarthRevan39]

The hub is part of the axle. You get the bolt pattern you need for your wheels, which for stock wheels is 5x4.5" (5 lugs on a 4.5" [114.3mm] diameter}. You'll likely need to get new backing plates for drum brakes (unless your new axle also has small bearings), good time to upgrade to discs. You'll also need to get the correct width, which is 61.25" from outside of hub to outside of hub.

Whats the potential damage if I don't swap to a stronger differential and all the extras that requires right away? If I'm not too hard on it, should it hold up, or am I sitting on a ticking time bomb?

 

[Hemikiller]

The hub is part of the axle. You get the bolt pattern you need for your wheels, which for stock wheels is 5x4.5" (5 lugs on a 4.5" [114.3mm] diameter}. You'll likely need to get new backing plates for drum brakes (unless your new axle also has small bearings), good time to upgrade to discs. You'll also need to get the correct width, which is 61.25" from outside of hub to outside of hub.

Whats the potential damage if I don't swap to a stronger differential and all the extras that requires right away? If I'm not too hard on it, should it hold up, or am I sitting on a ticking time bomb?

I beat the living be-jeezus out of an all original 3.00 8" behind a stout 4 speed 351C for a couple years. Nothing ever broke, because traction was always an issue. If you put sticky tires on it, you're going to eventually break it. 

IMO, drive it and enjoy it, just make a plan for a 31 spline 9" upgrade for the future.