1961 Ford 9" interchangeability?

[keithnh]

Just got my very rough 61 home. Transmission and rear 3rd member were not included in purchase. I do have likely original 61 axles and housing complete. Bought a book on 9" but it does not provide enough interchange info for me to hunt the missing 3rd member assembly. Believe transmission was a Cruise-o-matic. Appears original engine (61 390 FE) someone dolled up at least was included. I will break apart and have checked for serviceability. Like to know if the early 9's take a special 3rd member. Or basically how to hunt for one to replace mine. Hoping for a 3.25.

 

[74 Harley]

When it comes to a 9inch, they will all fit. The bigger deal is to make sure you get one with side gears for 28 spline axles. If memory serves stock was a 3.00. Depending on where you are I may know of one laying around.

 

[Mrjagrock]

Traded my 3.00 9 inch for a 3.50 with Pos-a traction- not good for highway but great for take-off. Make sure spline number on your axles are the same as the third member you are buying- plenty around but not cheap for a good one.

 

[keithnh]

Not sure what I have now. Reading some I see 3.25 was a common ratio and would love to find a 3.25posi 3rd member. I am now not sure I even have a t-bird hsg-tubes +axle setup because the axles appear to be close if not correct for length and spline count is far less than 28 or 31. It is a front loader setup but axle spline count is 20 or under and looks like a keyway( or completely broken off splines. Hoping I have correct hsg to mate with car and at least axle lengths right so I can use to shop for 3rd member AND axles set .. I think my best bet?? PS .. Im in Pittsfield NH supposedly a Thunderbird guy living in town off Concord Hill road. Searched for him today, had alot of dogs chasing me 🙂

 

[68stangcjfb]

I'm not sure what you have there but that is definitely not a 9 inch Ford. It should be more of an oval shape with a more of a flat top and bottom. The axles should have 28 splines. The photos I provided are of my 1960 9-inch rear.

 

[keithnh]

Thank you, possibly it is a partial rearend that someone swapped for the original complete. Might be numbers on the axles or buried under rust somewhere on hsg I can ID with. Does have a rectangular raised portion on rear of hsg I read was a way to differentiate an 8.0" from a 9". The axles are in there tight with either 4 or 5 bolts behind the wheel flange. They seem undisturbed but must have been removed to take the 3rd member assy. Wonder if there was an econo-rear option in 1961 so something other than 9" was used? Seems like the level of crud /rust commensurate with the rest of the underbody. I am not planning on a dragstrip application but would like stout enough rear for a healthy 390 streeter .. that fits correctly.

 

[74 Harley]

That probably came out of a smaller car, I am thinking falcon. Put under the bird to make it movable. The stock 390 put out 300 hp, there were no smaller engines available.

 

[68stangcjfb]

I'm 99% sure that's not a Ford rear end. The only drop out center section Ford car rears are the 8 inch, 9 inch and the sometimes seen big car 9 3/8. Your best bet is to find a complete 9-in rear out of a 1961 through 1966 Thunderbird. There may be detail differences through those years but I'm sure it will bolt in with minimal issues. And you can always change the gear ratio and install a limited slip differential if you want to.

 

[aa010175]

The 1961 has a one only year of rearend. Different seals size. The 1962-63 are the same. 1964 and newer has a different rear end. Hope this make sense. Dave

 

[KD0SGO]

Just got my very rough 61 home. Transmission and rear 3rd member were not included in purchase. I do have likely original 61 axles and housing complete. Bought a book on 9" but it does not provide enough interchange info for me to hunt the missing 3rd member assembly. Believe transmission was a Cruise-o-matic. Appears original engine (61 390 FE) someone dolled up at least was included. I will break apart and have checked for serviceability. Like to know if the early 9's take a special 3rd member. Or basically how to hunt for one to replace mine. Hoping for a 3.25.

The 9" Ford is probably the most sought after for high performance car builds, and considered to be virtually (but not actually) indestructible. It was used in new stuff from the 60s to the 90s as I recall. The simple way to identify a 9" 3rd member is to examine the pinion housing. If you can get a socket on the studs (lower left of the pinion)on the housing, it is not a 9". There are a couple of the mounting studs that require an end or box wrench. Most F series half ton pickups used a 9" as standard, as did most, if not all of the big cars and wagons. Big block Mustangs and Cougars also used a 9", with either a 3.00 or 3.25 ratio. Many big cars with automatic trans came with a ratio of around 2.73, unless it was ordered differently. The rear is more than strong enough for any Ford engine, and many others. It is being used in racing even today. First thing to check is if the axle shafts will actually fir the splines of the side gears. Several spline counts were used, but I don't know enough about axles to tell you which.
Lastly, the "flat top" housing was pretty widely used in F series, E series, and the Pony Cars. For clearance, I assume.

 

[keithnh]

Thanks all for input, guess I need to find some numbers if I can. Brought hsg home and will wash, Evaporust and brush try to find any numbers on axles or hsg and measure. Will try to learn/take "standard measurements" and attribute time spent to my rear-end familiarity/rebuild bag of tricks. Did want to learn 9" rebuild when I saw empty hsg in car, as well as fiddling with an FE 🙂 Called Moser yesterday and Yukon Gear(didnt get thru) .. still a mystery what I actually have. Does anyone have a photo of a 1961 rear-end hsg they could post? If 61 was a one only year seems strange there would be such a difference in hsg from the 60 in post 5.

 

[keithnh]

Looks like I might have a GM T55 housing ... Tri-5 GM pickup ... had 17 spline axle, front load , with nearly circular pumpkin. Had a 9 3/4" ring I believe. Haven't found any numbers. Not bent or beat up visually. If I get positive ID and doll up abit maybe can get some money towards correct 9". Aggravating because the mount pin to pin nearly right on. 3rd members dont look cheap enough to fully assemble. Have buddy at junkyard who may have a suitable complete alternate from a newer vehicle. Do have another bud who can modify spring perches to t-bird dimension if I can find a very close axle dimension. Got to get my measuring tools/skills dead-on.