Differential Pinion Gear Bearing Preload
 

nkaminar in Post #3 is correct, the torques in the following service bulletins are the torques necessary to turn the pinion resulting from tightening the jam nuts. In other words, you tighten the jam nuts until the torque to turn the pinion is reached.

While researching the 1932 - 1937 Ford Service Bulletins, I stumbled upon information regarding the tightening torque for the Model "A's" pinion bearing:

• January - February 1934 Bulletin states, "The correct torque for the stub mounted pinion, as used in the Models A, B and early 18 is from 35 to 47 Inch-lbs."

• August 1934 Bulletin states, "The passenger drive pinion bearing adjustment has been reduced five inch-lbs. Correct adjustment for the various axles is as follows: Model 40 12 to 17 Inch Pounds; Model18 Straddle Pinion 12 to 17 Inch Pounds; Model B-18 Stub Pinion 15 to 20 Inch Pounds; Model A 15 to 20 Inch Pounds; Model AA Timken Type 12 to 16 Inch Pounds; Model BB 3/4 Floating 12 to 16; Model BB Full Floating 12 to 16 Inch Pounds.

No reasons were given for the reductions in torque.

Re: Differential Pinion Gear Bearing Preload
 

Great info!!!

Re: Differential Pinion Gear Bearing Preload
 

Isn't the nut tightened to provide a certain torque to turn the drive shaft? I think that is the 15 to 20 inch-pounds referred to above, not the torque on the nut or jam nut.

Re: Differential Pinion Gear Bearing Preload
 

Interesting that this info should come up, as I'm in the middle of rebuilding my differential. I ended up with the pinion bearing preload at 17-18 in-lb as measured with a precision milk jug partially full of water hanging 8-1/2" off a breaker bar.

Supposedly the pinion bearing carrier is thinner where the second (forward) bearing rides, to allow for adjustment of the preload. It may be, but mine was still stiff getting that old bearing off and the new one on. The 17 in-lb was all I could get out of it even with "encouraging" the forward bearing rearwards. Seeing the info that Bob B posted, I'm happy with it.

FWIW, I had to shim the pinion gear rearwards 0.020" (put four 0.005" shims between the bearing and the pinion) to get proper ring gear engagement.

I think NK is correct - the nut to connect the pinion carrier to the driveshaft (taper with key) is nominal 100 ft-lbs.

Re: Differential Pinion Gear Bearing Preload
 

Bob, would it be possible for you to post scans of those pages here so that we can read the entire procedure in context?

It is not clear to me where the in-lbs of torque you are quoting are to be applied. If there are some drawings in the Bulletins that show this, it may help. Thanks!

Re: Differential Pinion Gear Bearing Preload
 

I revised Post #1 to reflect nkaminar's comment in Post #3. Also, I attached scans of the two service bulletins to Post #1.

Re: Differential Pinion Gear Bearing Preload
 

When I first started rebuilding Model A differentials back in 1988, I researched all the literature I could find in the Model A kingdom. Information written in the day by old Model A guys recommended setting the pre-load for both the carrier bearings and pinion bearings at 20-inch pounds read off a dial indicator. My experience has taught me that there is an acceptable window. I accept anything between 14- and 22-inch pounds. I have done hundreds this way.

Most garage mechanics do not understand pre-load and they put them together too tight. I have taken hundreds apart and found the results of that. Usually, it just spins the bearings on the carrier hubs. On two occasions I found the hub sheared off.

Henry's 40 horses will always break loose over tight bearings. If you cannot turn the bearings with your fingers, you got them too tight.

http://www.santaanitaas.org/wp-conte...r-Apr-2003.pdf

Tom Endy

Re: Differential Pinion Gear Bearing Preload
 

Apart from the numbers involved, that exactly reflects my experience. Every time I have someone say the diff is either running hot or noisy, I go straight to the pinion bearing and invariably, it has been set too tight. A new bearing set correctly and away they go.

Re: Differential Pinion Gear Bearing Preload
 

Personally I set the pinion a little less if the bearings are not new. The bearings and races wear into each other and will loosen up some. existing bearings are already seated.

Re: Differential Pinion Gear Bearing Preload
 

If you measured that with the drive shaft horizontal, you have to support the end of the shaft, and calculate the resistance of that support.

The bearings are slightly apart and if you add an overhung load such as the drive shaft, you are putting the bearings in a bind. The reading will not be accurate. It is best to have the drive shaft vertical and measure the torque with a beam style torque Wrench.

Re: Differential Pinion Gear Bearing Preload
 

Like one of these guys.

Re: Differential Pinion Gear Bearing Preload
 

Excellent point, and an excuse for a new tool! Actually, I measured on the Mitchell stub shaft, which is maybe a quarter the length of a driveshaft. I did not feel any binding effect, which I suspect I would have noticed on a full length driveshaft.

Re: Differential Pinion Gear Bearing Preload
 

KR Wilson made one too. They’re moderately easy to find.

Re: Differential Pinion Gear Bearing Preload
 

I made a tool from and old damaged drive shaft. I cut it down and welded a nut on the end. It is about 50mm, 2", longer than the pinion and still has the key fitted. I can loosely slide it into the pinion and turn with a torque wrench to check for pre-load.

Re: Differential Pinion Gear Bearing Preload
 

I really like the cute torque wrench that is shown in the illustrations that Bob added in Post #1.

Re: Differential Pinion Gear Bearing Preload
 

Dave - I've found that the preload changes a bit due to the torqueing down of the pinion carrier onto the tapered end of the driveshaft - seems to maybe expand the carrier a tad? Something to keep in mind doing it like you do. Clever idea, though.

Re: Differential Pinion Gear Bearing Preload
 

That’s the KR Wilson torque wrench.

Re: Differential Pinion Gear Bearing Preload
 

About how much change. Is it small enough, that if I keep the load at the bottom side if the tolerance, the change won't raise it to outside the upper end of the tolerance? I might have to make a C spanner adaptor and do a pre and post driveshaft fitment load check.

Re: Differential Pinion Gear Bearing Preload
 

Dave - I haven't measured it, but if you snug up the bearings to "no slop" on the carrier before installing on the shaft, after you install it onto the shaft I've felt a noticable increase in resistance to hand turning the race - maybe a couple inch-lbs? That's of course if you install the bearing assembly onto the shaft prior to inserting it into the banjo. If you install the carrier assembly into the banjo and then put on the shaft you won't see this.