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I replaced the pinion shaft oil seal on the differential of my 51 300. The nut that held the yoke in came off with very little torque (too easy). I need help figuring out what to torque the nut back to. The book says to torque it from 300 to 325 foot pounds. This seems way too high. The book says to note the torque it takes to overcome the friction of the new seal and add 2 1/2 to 3 foot pounds too it for a total of say 4 1/2 foot lbs. This can't be the overall torque for the nut. I read it to mean the torque it takes to over come the seal drag plus the bearing friction after the torque on the nut is correct. There is no way to measure over all force to turn the pinion shaft that I know of without removing the rest of the universal and leaving only the pinion shaft in the housing.


Can Anyone help me? What should I torque the nut to if nothing else has been changed except the seal?


Thanks, Bob

G'day Bob, It does appear to be a confusing issue but the preload of 30 - 35 inch pounds preload on the pinion bearings is intended to be measured for the carrier assembly on a vise or stand only. You cannot check the pinion preload if you have a differential in a vehicle with the axles, axle bearings and seals assembled, the preload and friction of all of those components would be in the order of 20-30 ft lbs and you would be unable to separate the individual component torques.
Therefore, if you have changed the pinion seal only, you should torque the 3/4, 16 TPI pinion universal joint flange nut to the specified 300 to 325 ft lbs. This places the collapsible spacer in the correct tension to achieve the 30- 35 inch pounds preload of the pinion bearings. It takes a decent bar to generate the torque, together with a friend to hold the UJ flange, but it can be done. You may have to borrow a LARGE torque wrench to generate that torque, together with the biggest shifter and pipe or similar to hold the UJ flange. Good luck and best regards Peter Toet.

The 2 to 2 1/2 lbs is the preload. In other words the amount of effort it takes to turn the internal gearing. I've never replaced just the seal without punching marks to realign the nut with. As I remember, it was something like 60 or 70 lbs. Sorry I'm not much help with the total torque.

I finally had time to check my Service Counselors and found they list 200 to 270 lbs. Boy, was I way off. Sorry.

I do not know if the Packard differentials are the same as early Cadillac ones, but I had an experience replacing the pinion oil seal in my 1939 Cadillac Sixty Special. It was not a straight-forward job. The complication was that once the spacer had been collapsed by tightening the pinion nut to set the pinion bearing preload, it would no longer provide the proper preload when retightened. To overcome this, a fellow Cadillac owner suggested using shims to restore the length of the spacer so that when it was retorqued, it would again be the proper length, and provide the proper preload. The tightening involved two parts; first, tighten the pinion nut with a considerable torque reading (200-300 lbs). To assure that it was not too tight or too loose check the overall torque to turn the pinion nut, with the brakes completely backed-off, to indicate a small torque reading in a few INCH pounds. Failure to provide the proper bearing preload would result in premature bearing failure. Included with this is a procedure that I helped him write describing the procedure to follow.

Obviously, the procedure document did not upload with this reply. If anyone is interested in the procedure, please contact me and I will send it to you.

Thanks for all the response. I have a few more questions for you guys. Does the yoke bottom out on a shoulder cut on the pinion shaft? In other words when you torque the nut to the 200 to 300 foot pounds are you applying that pressure to the bearing or are you just tightening the the nut against a shoulder stop on the pinion shaft behind the yoke. With out some kind of shoulder it would be like tightening a wheel bearing nut to 300 pounds. Way too much. The book says wheel bearings are supposed to be torqued to 20 foot pounds and then backed off one flat of the nut. Sense I'm not replacing any of the internal parts the idea of a spacer installed in front of the yoke makes good sense to me. It would allow for the crush sleeve to crush a little more hence resetting the bearing preload.

A side line story to this is I once replaced the pinion seal on my 1955 Olds 88 and was not sure how tight the nut should be so I set it like you would set a wheel bearing nut. Needless to say the nut was not tight enough and backed off because of normal vibration. I was on a trip and noticed some slop in the drive train but kept on plugging a head . I got to where I was going and pulled off the freeway. I got a couple of blocks and the nut fell off. The whole drive shaft pulled out of the differential and dropped down and fell out of the car. Couldn't believe seeing my drive shaft on the street from my rear view mirror. That's mainly why I am paranoid about doing this again. I'm really lucky this happened at 10 to 15 MPH on a surface street and not on the freeway at 75.


Bob