Pinion Seal for 1972 mustang

[moparbrian]

All,

I inherited a 1972 mustang with a 351 engine and automatic transmission. My dad purchased it brand new in December of 71. The rear pinion seal needs to be replaced. Does this car come with a 9 inch or 8 inch diff? I need to know what pinion seal to purchase.

 

[Bentworker]

You should be able to use a vin decoder to identify the axle.

 

[Hemikiller]

351 cars had a 9" rear diff.

https://www.rockauto.com/en/catalog...2861,drivetrain,differential+pinion+seal,2380

 

[moparbrian]

ok, I looked at the tag on the diff and the door tag. The tag on diff shows "9". The door tag for axle shows "R"

 

[moparbrian]

Another question. What type of gear oil should I use for the differential? Viscosity?

Thank you

 

[Don C]

The R means you have a 3.25:1 locking differential.

You can get some good information about the Ford axles here:
https://www.diyford.com/ford-axle-history-identification-ford-differentials/
I also assembled some Ford code numbers, including the door sticker, here:
https://7173mustangs.com/threads/axle-diff-upgrade-variables.37633/#post-383821
Because you live in a moderate climate, just regular 90 weight should be fine. Because you have a Traction-Lok you should also add the friction modifier if you drain and refill the differential.

 

[Bentworker]

Be aware that the 9” uses a crush sleeve / pinion nut torque to set pinion bearing preload. Read up on it and be mindful of it when swapping the seal so that you don’t destroy anything.

Basically if you torque the daylights out of the pinion nut you will have bearing failure.

Right thing to do is set it up with a dial or inch pound torque wrench to the spec for used pinion bearings.

 

[moparbrian]

Thank you. I was planning on using a dial torque wrench and reverse the nut off. the dial will record the torque it takes to break loose. I will also record the amount of twists it takes to remove.

 

[Bentworker]

Fast forward to about 7 minutes to see measurement of preload with an inch pound torque wrench.

 

[Hemikiller]

Thank you. I was planning on using a dial torque wrench and reverse the nut off. the dial will record the torque it takes to break loose. I will also record the amount of twists it takes to remove.

From the 71 shop manual, on seal replacement. I've done this several times and it works out fine.

Use 85W90 gear oil with a bottle of Ford Motorsport friction modifier for the Traction Lok unit in your axle.

 

[moparbrian]

From the 71 shop manual, on seal replacement. I've done this several times and it works out fine.

Use 85W90 gear oil with a bottle of Ford Motorsport friction modifier for the Traction Lok unit in your axle.

View attachment 59760

Awesome info!!! Thanks!!

 

[Cleveland Crush]

All,

I inherited a 1972 mustang with a 351 engine and automatic transmission. My dad purchased it brand new in December of 71. The rear pinion seal needs to be replaced. Does this car come with a 9 inch or 8 inch diff? I need to know what pinion seal to purchase.

Take a look underneath to be sure, if it's factory original it will be a 9".

 

[moparbrian]

Take a look underneath to be sure, if it's factory original it will be a 9".

I did and it is a 9 inch diff.

Thanks

 

[Cleveland Crush]

You may want to consider a solid sleeve vs the crush style. Once the solid type is set up it will never go out of adjustment. It is reusable and allows future tear downs without the crush sleeve hassle. Solids are almost mandatory for higher HP cars especially with stick trannys.

 

[moparbrian]

You may want to consider a solid sleeve vs the crush style. Once the solid type is set up it will never go out of adjustment. It is reusable and allows future tear downs without the crush sleeve hassle. Solids are almost mandatory for higher HP cars especially with stick trannys.

Hello,

This sounds like a great upgrade. Do you have a link to the solid sleeve that you recommend?

Thank you

Brian

 

[Cleveland Crush]

Hello,

This sounds like a great upgrade. Do you have a link to the solid sleeve that you recommend?

Thank you

Brian

Hello,

This sounds like a great upgrade. Do you have a link to the solid sleeve that you recommend?

Thank you

Brian

 

[Cleveland Crush]

Jegs is one of many options

Pinion Shims & Solid Spacer Part Number: 555-61216​

, been running solid spacers for many years. If a future teardown is needed simply reuse spacer and retorque, no need to start from scratch.