Weekly Fun Question - Test Your 71-73 Mustang Knowledge

[cobra3073]

Since last week's "Fun Question" seemed to have been somewhat difficult, I have decided to pose another question relative to "rear ends" for this week. Here it goes.

You have been faithfully "improving" the performance of your classic '71 - '73 mustang with suspension modifications, a stronger engine and transmission upgrades. You finally take your "Baby" to the local "test and tune" and one of your young neighbors with her fox body mustang (running a bit of "juice") chose you and jump on you hard out of the hole. She ends up taking the win because you initially spun your tires off the line. In retrospect, you realize you were doing a lot of spinning at the line which you attribute to your stock "open" rear end. Additionally, with all your new engine power, you "let up" on the top end because you were doubtful about the durability of your stock 8" rear end.

You make the decision to remedy that problem immediately and head to your local "bone yard" the very next day to try and find a new 9" inch rear end (preferably one with traction lock) to replace your 8" open rear end.

When you arrive, you find a couple dozen Ford carriers (pumpkins) out of different Ford cars, trucks and vans lined up side-by-side on the shelf. The question for this week is:

How can you visually determine whether the carrier assembly is a 8" or 9" inch rear and whether it has a traction lock, just by looking at it?

Who will be the first to get the most obvious answer?

BT

 

[aasukisuki]

Since last week's "Fun Question" seemed to have been somewhat difficult, I have decided to pose another question relative to "rear ends" for this week. Here it goes.

You have been faithfully "improving" the performance of your classic '71 - '73 mustang with suspension modifications, a stronger engine and transmission upgrades. You finally take your "Baby" to the local "test and tune" and one of your young neighbors with her fox body mustang (running a bit of "juice") chose you and jump on you hard out of the hole. She ends up taking the win because you initially spun your tires off the line. In retrospect, you realize you were doing a lot of spinning at the line which you attribute to your stock "open" rear end. Additionally, with all your new engine power, you "let up" on the top end because you were doubtful about the durability of your stock 8" rear end.

You make the decision to remedy that problem immediately and head to your local "bone yard" the very next day to try and find a new 9" inch rear end (preferably one with traction lock) to replace your 8" open rear end.

When you arrive, you find a couple dozen Ford carriers (pumpkins) out of different Ford cars, trucks and vans lined up side-by-side on the shelf. The question for this week is:

How can you visually determine whether the carrier assembly is a 8" or 9" inch rear and whether it has a traction lock, just by looking at it?

Who will be the first to get the most obvious answer?

BT

This question is totally irrelevant because the scenario would never exist. Girls don't drive V8 Mustangs.

 

[RocketFoot]

This is a good question because I need to know that exact answer to determine what rear I have in the Mach (data plate is missing)

 

[cobra3073]

Well Jeremy, tell that to our very own "Gina" (72STANGGIRL - a member of this site) and my daughter who drives a 5.0L, with great skill I might add .

You probably need to "get out more."

BT

 

[73vertproject]

Ouch, Jeremy! :s

I agree, Barry - great question because I think I'm headed down the "rear end" road soon.

My first instinct says, "Get out your ruler and measure it" but I'll take a look around and see if I can come up with something better.

BTW, BT, I really enjoy the scenarios you create with the questions. I often see myself in them.

Doc


OK, try this. First, just take a look at the axle tag if it exists. That should tell you everything (look for the L within the gear ratio to denote traction loc - what we used to call "posi-traction" or just "posi".

If the tag is missing, you would see the the 8" to be much more oval-shaped, whereas the 9" is more rounded and almost always has two dimples, when viewed from the back.

To determine if it has posi, open them up and look at the spline covers. The posi will have recessed openings for 5/8" bolts holding the ring gear, and the open (non-posi) will have 3/4" bolts with a smooth cover.

Am I in the ballpark here?

Doc

 

[Twinturbomach1]

on an 8" you can get a socket and rachet on all the pumpkin bolts on a 9" you must use a wrench on the lower bolt due to the case design.

An open carrier looks different the posi carrier. The bolt heads are recessed into the carrier on a posi not just sitting on top of a flange like on an open unit.

In addition 28 spine axles interchange between 8 and 9 inch rears just a fun fact so save your axles when scrapping the old 8"

28 spline axles have a rectangle shape in the hub area 31 splines have 3 holes drilled ina strait line! easy way to tell without pulling the rear appart.

 

[cobra3073]

Doc and TwinturbomachI:

You are both "right" as to your responses. However, the question was a bit "tricky" in that it referred to the carriers being "out" and had to do with how you could tell "visually" if they were "side-by-side."

The response I was looking for is:

As TwinturbomachI inferred, there is a very distinct visual difference between the 8" and 9" as the 8" is oval shaped and the 9" is more rounded - - very easy to see when they are side-by-side.

TwinturbomachI is also "correct" about the bolts, BUT if the carrier is out the way to tell is by the bolts in the ring gear. If you can get an open end wrench on the bolts that attaches the ring gear, it is an "open" rearend. The Traction lock has recessed bolts through the ring gear which can only be successfully accessed with a socket wrench.

It should be noted that the vast majority of our mustangs had the 8" rear end from the factory. The 9" was generally found on the more performance-based (i.e., Boss, Mach I, CJ, etc) mustangs. However, the 9" carrier was used on many, many other full sized Ford, Lincoln and Mercury products and the carrier will bolt right up to our rearends. If you are building any kind of real power, you should think about changing to a 9" (if you currently have an 8").

Over the next week or so, I will develop a more in-depth tutorial on this subject to be placed in the "Data" section of the site.

GREAT responses Doc and TwinturbomachI!

BT

 

[aasukisuki]

C'mon guys, take a joke. Didn't you see the ?

 

[cobra3073]

We did, Jeremy - - didn't you see the ?

Got you!

BT

 

[aasukisuki]

We did, Jeremy - - didn't you see the .

Got you!

BT

D'oh!

 

[73vertproject]

Right on, BT!

I'll be happy to split the prize money with TwinTurbo, so please just send the check to OMG to apply to my future account, and I'll be a happy camper. Or, instead, maybe I'll get 1/2 a Rec.

Humbly yours,

Doc