Your picture didn't come through in the post. More info on the car would be helpful too - year, original V8 or 6-cylinder, etc. Here's a picture of a small bearing 8" rear end in a '66 (has the same brakes you just bought being fitted with the MS brackets). Notice how the axle tubes narrow down from 3" to 2 3/8" diameter just next to where the jackstand is.

All Mustang original 8" AND 9" rears were small bearing.

As McStang indicated, your pic did not post.  If I remember, you have a factory V8 65.  If so, it is probably an 8" rear.  Looking at it from the rear (pun intended) the center housing will be oval with large dimples at 3 & 9 o'clock.  The 65/66 mustang 8" rears were tapered, and had a smaller diameter where the ubolts clamp the spring & shock plate.  After 50 years, at a minimum, I would replace the pinion seal and axle bearings.

Oops, there's the pic.  Yup, 8".
 

Last edited by TimC (2/23/2015 3:11 PM)

That's an 8 inch rear end.

jkordzi wrote:

Greg B wrote:

Shelby took  1963 Ford Galaxie 9" rears and axle tubes from 6 cylinder Salisbury rears and used them to make the 9" Shelby rear.  

I thought he just started w/ specially ordered factory Ford Mustangs, which came w/ 9" differentials just like the hi-po Mustangs.

 Greg B. is Correct....Beginning as a stock Mustang with a 4-speed manual, the cars were shipped to Shelby American, where they received the high-riser manifolds, had their stock Ford Falcon live rear axles replaced with heavy-duty Ford Galaxie rear axles, and were given larger, metallic-lined rear drum brakes and Kelsey-Hayes front disc brakes.

True74yamaha wrote:

The only other thing you may want to do is choose if you want a different gear ratio. Now would be the best time to decide on what you wanna do.

Copy that, as of now (according to the date code) gears are 3:0? Seems like they would be good for a cruiser but would I be missing out on some low end? What would be the most ideal gear ratio if I say am putting a semi-stock 5.0  with a T-5?
 

Tire height makes a difference too.  In general, a production Ford T5 with a reasonably tall tire will like a 3.73 gear.  If its a Z-spec T5 then 4.11 may be more the order due to the lower first gear ratio.  The idea is not to get a first gear that takes you from 0-20.  The best way to figure it is to multiply the first gear ratio by the rear gear ratio.  An ideal ratio is in the 9:1-10:1 range.  Lower and it will struggle to get out of the hole.  Higher  and first will feel very short.

Now if you are running a short stock tire size you may be more comfortable with a 3.55.  Tire height changes the effective gear ratio; its just something else of which to be aware.

TKOPerformance wrote:

Tire height makes a difference too.  In general, a production Ford T5 with a reasonably tall tire will like a 3.73 gear.  If its a Z-spec T5 then 4.11 may be more the order due to the lower first gear ratio.  The idea is not to get a first gear that takes you from 0-20.  The best way to figure it is to multiply the first gear ratio by the rear gear ratio.  An ideal ratio is in the 9:1-10:1 range.  Lower and it will struggle to get out of the hole.  Higher  and first will feel very short.

Now if you are running a short stock tire size you may be more comfortable with a 3.55.  Tire height changes the effective gear ratio; its just something else of which to be aware.

Ok, so back to this- I am thinking tire size will most lilkely be a 235 45 r17? I am also thinking a 3:55 rear gear as from doing some research and talking with Rose Hill Performance, he says 3:0 will be pretty "boggy" on the freeway? Anways, now to do some research to see best places to buy new gears and any other items needed for the swap?  Am I even capable of doing a gear swap- we shall see? I will be removing the rear end this weekend to do the rear brake swap as my parts have arrived, so now is the time....
 

devovino wrote:

TKOPerformance wrote:

Tire height makes a difference too.  In general, a production Ford T5 with a reasonably tall tire will like a 3.73 gear.  If its a Z-spec T5 then 4.11 may be more the order due to the lower first gear ratio.  The idea is not to get a first gear that takes you from 0-20.  The best way to figure it is to multiply the first gear ratio by the rear gear ratio.  An ideal ratio is in the 9:1-10:1 range.  Lower and it will struggle to get out of the hole.  Higher  and first will feel very short.

Now if you are running a short stock tire size you may be more comfortable with a 3.55.  Tire height changes the effective gear ratio; its just something else of which to be aware.

Ok, so back to this- I am thinking tire size will most lilkely be a 235 45 r17? I am also thinking a 3:55 rear gear as from doing some research and talking with Rose Hill Performance, he says 3:0 will be pretty "boggy" on the freeway? Anways, now to do some research to see best places to buy new gears and any other items needed for the swap?  Am I even capable of doing a gear swap- we shall see? I will be removing the rear end this weekend to do the rear brake swap as my parts have arrived, so now is the time....
 

3.55 gears are the most common with all t5 trannies . . it is a good balance between good acceleration and low rpm at 70 mph with most tires . . your tires are 25.7" tall

if you are not a street racer and want more of a freeway gear than 3.40's are good.

there is a problem with some brands of gears making a whining noise . . for gears that do not make a whining noise, I would only use Motive or US Gear . . Ask the seller if the Motive or US Gear gears they sell are made in either the USA or Italy . . Motive makes some in both China and Italy . . I’m not sure about US Gear.

Do NOT use KOYO bearings . . use Timken.
 
Phone 1-847-663-1701
http://www.strangeengineering.net/website/contact-strange
 
Phone 714-528-6957
http://www.currieenterprises.com/
 

Last edited by barnett468 (3/04/2015 7:20 PM)

jerryF wrote:

The gear you choose should depend on how you're going to use the car.  I started with a 3.55 gear which is a  fun sport gear, but my near stock 5.0 & T5 just doesn't need the rpm. I changed to a 3.25 for those long bash trips on the interstate. For my car, it was the way to go... the 3.25 is lot more comfortable at 78mph, plus I gained 2 mpg consistently.   If you're gonna hot rod around town, the 3.55 may be a better choice.
 

Definetly something to think about, I guess I would like a little of both- but cant have your cake, however, the speed limit here in Oregon is 55- even on the interstate. Lame I know, but I often find myself doing well over that but something to think about.
  Now my question, I was uninstalling the axles from the Diff. the bearing came out with the Axle, and are stuck on pretty well.  I reinstall the new bearing into the diff shaft not on the axle correct?
  Also, I am going to take the third member apart, is there any way to tell definitively what the gear ratio is? I was thinking in the last 50 years, the gears very well could have all ready been switched out?

Also, I notice on the housing, the numbers read C2OW-E?  Cant find any information on those numbers?

Last edited by devovino (3/07/2015 1:12 PM)

A hydraulic press is needed to remove the bearings off the axles and to re install new ones. 

As far as determining the gear ratio , you divide the number of teeth on the ring gear (big gear) by the number of teeth on the pinion ( small gear). So it's as simple as just counting the teeth and dividing.

Last edited by MachTJ (3/07/2015 8:10 PM)

josh-kebob wrote:

The C20W-E is the casting number for a standard 8" diff the pinion support.

The axle bearings are "pressed" unto the axle so, what you have is normal. There's a retaining ring pressed on next to the bearing......

What bearing are you attempting to replace?
 

I am installing rear discs with MS bracket (much like the picture above) and it states you need to replace the outer diff bearing seen in my last picture.

Jkordzi, thanks for the input. So it sound like the shop should press on the bearing/inner retaining at the same time? Making sure not to forget the outer retainer.

As for the rear end gears, i am going to  pull the housing and do some counting to verify the gear ratio is still 3.0, who know it might have been changed over the years, and the tag is missing which tell me it has been accessed?