stavinski

My tailshaft seal is leaking badly enough that it puts a drop on my garage floor about once a day. I'm reading about lots of newer ones failing on here, anyone know if it's a simple replacement on the '66 top loader 4 speed manual or if the whole assembly has to come down to get the prop shaft out to replace it? Reading on here, looks like newer ones can be done from under the car without dropping trans easily. Can't find info on '66.

Also, anyone have a suggestion for how to tell which 4 speed it is? Which seal I need to buy? Auto parts stores ask about 28 spline or 31. Do I have to take it apart and learn to count to figure that out? I think once I find out how hard the job is, I will buy both seals and use whichever one fits once I get the other one out :^) If I can save $10 by figuring it out ahead of time, much appreciated.

lil bull

You can take the driveshaft out and see the splines on the end of the trans. You should be able to pry the old seal out and then tap the new one in place easy enough.

slipkid

Order the seal from Glazier Nolan. It has a perimeter flange that you do not get with NAPA and the like....

Al Newman

The National brand seal # is (or was in 2006) 470059.
Best,
Al

jlg2002

There were 3 different 4 speeds used in 66 according to the FSM: a Dagenham for the I6 engine and 2 different Ford units for the V8's. I would expect the 31 spline would be for a HP car and the 28 spline is for everything else.