1966 Rear axle and differential identification.....NEED HELP!!!

[poochie883]

I'm about to take apart the rear differential of my '66 Q code (428 CID) Thunderbird, but I want to drive it while I still line up the parts I need for the rebuild. There is no code tag on the differential, so I'm left wondering what's actually in there. All I know from the door code is gear ratio. Can anyone help me out?
Are '66 Q codes all 9 3/8" diffs?

Which do I have (9" or 9 3/8")?

How many spline are the axles?

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[captrick]

Hi Poochie, More then likely you have a 9"differential in your car. The bigger rear ends were installed in trucks. If I remember correctly I think they offered a 2:78 to 1 gear ratio in those cars. If it had the trailer towing package I think it was a 3:25 to 1 ratio. I am pretty sure they were all 31 spline axels. The 29 spline axels were used in he Fairlanes and Mustangs. It is easy enough to check, jack up the rear from one side so as the gear oil goes down to the other wheel and remove the tire and brake drum. spin the axel so as the hole in the axel flange lines up with the bolts holding the backing plate on, they should be 3/8 bolts and you will need a 9/16 socket. Once you get all 4 on the off put the drum back on backwards and put the lug nuts on very loosely and use the drum as a slide hammer to take the axel out. Then just count the splines and put the axel back in, tighten up the 4 bolts replace the drum and tire and you are good to go. Good Luck Rick

 

[Clint66]

Hi Poochie, I have a Q car and redid the rear end in it. They have a 31 spline 9" rear end. The most common gear ratio is 3.00 to 1 in these cars. I also have two Town Landau's with the same rear end in them. You can get seals and oil from most auto stores. I got everything I needed from Napa. There isn't much to it. Pull the axles replace the seals and take the third member out replace the gasket. You will have to make sure when changing the yoke seal to set the depth and torque it correctly. Don't over tighten it.

 

[poochie883]

There are 6 differentials combinations according to my '66 manual. On page 4-24 it lists two 9" and four 9-3/8".

 

[CuzCrash]

Hi Guys, This exactly the same issue I have. I also have a 1966 Q Code Town Hardtop with a 3:00 to 1 rear end and need to rebuild it, but I don't have any axle tag on the housing. What are the axle tag codes on your Q codes? Many thanks.

 

[Francis Mitchell]

My 1966 Tl has this tag info on the drivers side of the 10 stud differential under a nut. Tag info:
WEF-H
3.00 5LB 401
It is, of course , 9 3/8 as indicated by the code.
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