28 or 31 spline

[alarmrick]

I have a 71 mach1 with a 351 4v, c6 and 9 inch rear. I am looking to replace the drivers side axle. Would the axle be a 28 spline or 31? Any suggestions on where to get one at a decent price would be appreciated. Thanks Rick

 

[Don C]

It would have come with 28 spline. Here's some information:
https://www.vintage-mustang.com/attachments/ford-8-and-9-inch-rear-ends-identification-pdf.766989/

 

[Doug's 73 Mach1]

31 splines were typically used with 3.50:1 ratio rear ends and up and included a "N" case "pumpkin". Check your rear axle code on your door data plate. That code can be used to decipher what gear ratio the car came with from the factory.

 

[Ron Tanzi]

Another option when in doubt is to just pull an axle and count the splines. On the bright side pulling a Ford 9" or 8" axle is way easier to do than on a junk GM 12 bolt diff among many others.

Ron

 

[boilermaster]

3.50 and up and Nodular case might be 31 spline, but my parts car does not follow that path.
1973 Q code, 3.50 gearing, nodular center section, Daytona pinion support, 4 pinion and one wheel peel and 28 spline axles .
just guessing it had the Daytona and nodular case because it was a toploader car.
Boilermaster

 

[Don C]

My '71 M-code came with a 3.50 traction-lok and has 28 spline axles. The only cars that came with 31 spline were with high performance engines, such as Boss 351s and 429s.

The link I provided above tells you how to determine 31 or 28 splines without pulling the axles.

West Coast Classic Cougar has 28 spline axles for $110 each
https://secure.cougarpartscatalog.com/d0oz-4234-c.html?sessionthemeid=26
https://secure.cougarpartscatalog.com/d0oz-4234-d.html?sessionthemeid=26

 

[timachone]

3.50 and up and Nodular case might be 31 spline, but my parts car does not follow that path.
1973 Q code, 3.50 gearing, nodular center section, Daytona pinion support, 4 pinion and one wheel peel and 28 spline axles .
just guessing it had the Daytona and nodular case because it was a toploader car.
Boilermaster

Me too - 73 Q-code, 4 speed, 3.50 gears, staggered shocks, one wheeler from the factory, has N-case and Daytona support, all original and 'numbers matching', but 28 spline.

Changed to a Trac Lok with the original N-case now

 

[alarmrick]

Thank you very much. Happy motoring!

 

[machattack]

It would have come with 28 spline. Here's some information:
https://www.vintage-mustang.com/attachments/ford-8-and-9-inch-rear-ends-identification-pdf.766989/

Thats a GREAT article. I learned more from this than any past experiences. Thanks Don for digging that up for us!

 

[Doug's 73 Mach1]

Another way to tell, is 28 spline axles have a deep recessed double "D" shape at the center of the hub the wheel fits over on outboard ends which can be seen with the hub caps off and/or wheels removed. 31 spline type do not, but look essentially flat on the face on the hub the wheels fits over .

 

[jasonwthompson]

Another way to tell, is 28 spline axles have a deep recessed double "D" shape at the center of the hub the wheel fits over on outboard ends which can be seen with the hub caps off and/or wheels removed. 31 spline type do not, but look essentially flat on the face on the hub the wheels fits over .

Careful with that, I have encountered what looked like 31 spline but they were in fact 28 once the axles were pulled and checked.

 

[Hemikiller]

Careful with that, I have encountered what looked like 31 spline but they were in fact 28 once the axles were pulled and checked.

The big car 9" rears have 28 spline axles with the "three dots" axle flanges.

 

[Doug's 73 Mach1]

Photo, 31 spline and 28 spline photo from 429 Mega site

 

[71ProjectJunk]

Photo, 31 spline and 28 spline photo from 429 Mega site

View attachment 63398View attachment 63398

I believe that after 1972 this method of ID'ing the axles can be incorrect. From what I have seen Ford after 1971 did make some 31 spline axles with the concave hole, so it does not always hold true for cars built after 1971.

 

[basstrix]

I believe that after 1972 this method of ID'ing the axles can be incorrect. From what I have seen Ford after 1971 did make some 31 spline axles with the concave hole, so it does not always hold true for cars built after 1971.

I've had personal experience with this and can say that there are 28 spline applications that use the the 3 hole pattern. The application I saw for myself, was a pickup truck axle.