Outboard Pinion Bearing
 

I purchased a Motive Power ring and pinion set, and note that the pinion outboard bearing journal does not have the same step relief machined as does the original. This has been noted by others as impeding the proper bearing preload setting on assembly.

The part I received had a journal diameter of 1.5765", the old part measured 1.573", as this part was received, it would have had to have been pressed on as can be readily realized by these dimensions.

To solve this problem I fashioned a mandrel to hold the pinion gear in the lathe from the end of the old drive shaft which is being replaced in this overhaul. This mandrel will be utilized also in the process I am working through to simplify differential setup. (At issue being the awkwardness of handling the full length drive shaft in the process, more on that on a later post.) The part was set up to a tolerance of .00025" total run out in the four jaw chuck. At 1.573" the Timken bearings being used are still a bit more than a slip fit. The final dimension that I turned this part too was 1.5725" and has the desired slip fit sought after.

This is a very important detail and should be maintained for proper preload set up. As others have noted it would indeed be very difficult if not impossible to have properly set the preload with this part as supplied.

Re: Outboard Pinion Bearing
 

I have been overhauling Model A differentials since 1988. Just when I think I have seen it all, another strange phenomenon shows its face, usually caused by the reproduction folks.

See the attached article.

https://www.santaanitaas.org/wp-cont...-Grief-PDF.pdf

Tom Endy

Re: Outboard Pinion Bearing
 

The taper on mine was correct Tom, attached is a photo of the installed drive shaft. In this photo, the thread protrudes about .125" beyond Henry's castle nut, having been torqued to 100 foot-pounds.

The step turning on the journal took every bit of five minuets to correct on the lathe. That is of course after the twenty minute set up time........

Re: Outboard Pinion Bearing
 

Tom,
meant to ask also, you suggest the use of Indian Head shellac on housing gaskets. Do you apply between multiple thickness pack gaskets, or just on the surface in contact with the housing?

Re: Outboard Pinion Bearing
 

I put it on both sides of each gasket.

Tom Endy

Re: Outboard Pinion Bearing
 

Did you actually machine the new pinion or just use emery paper? I put my side gaskets on dry, with a tiny bead of silicone just inside the axle housings. I once used old and dried V8 gaskets (because that's what I had) and they fit nicely. Follow Tom's advice, he has done many A diffs!

Re: Outboard Pinion Bearing
 

We have found this same thing for probably the last 7-8 years, ...maybe even longer. While this may seem controversial to some, in the end I'm not sure it really is that big of a deal. Before me telling why I feel that way, let me start by going thru this. Because of finding this about the Pinion size, we have found over & over that many Model-A driveshafts are bent which I feel is an area that causes driveline vibrations that many people just assume is "typical Model-A". I would be interested in what you find on yours and what Tom has found in all the units he has rebuilt over the years.

Now back to the Pinion. The first time or two that we machined the new Pinions, we just used the customer's driveshaft and chucked the end by the taper in a 4-jaw, indicated it in, and then cleaned (straightened or re-centered) the center hole in the threaded end. The driveshaft stuck back thru the hole in the chuck. With a live center now on the other end, it seemed to work well, albeit very time consuming considering what we gained. Then at some point I made a mandrel to spin the pinion between centers on my crank grinder. It worked well grinding to a perfect 'sliding fit' however again, a lot of wasted time & effort. Then somewhere along the way we just started putting the mandrel in the lathe chuck and instead of machining we used a crankshaft polisher to quickly remove a thou or so.

So in the end, here is what we determined. When the Pinion is chilled, the inboard bearing will slide right on and fully seat. Next, with bearings fully oiled, slide the outboard bearing on partially and then use the first nut to press it into the race. Set your preload into your diff. housing. Now here is something you need to think about. After about 10 miles of driving, is the preload on those Pinion bearings exactly like you set it, -or did the preload loosen. My experiences are they loosen just enough where all of the effort was for naught. Therefore, if I feel I have pushed the outboard bearing on a tad too tight, then I seat the first pinion nut and then back it off by just a tad. This is all done by feel, but back the nut up maybe 5°-10° of rotation just to remove some of the preload pressure, and install the lock washer. When everything is said & done getting the lockwasher tabs bent, its going to affect the preload again. Then, when you drive it, the new bearing races, the new bearing's rollers, the bearing preload, etc., etc. are all going to move ever so slightly where the preload will lessen. So my point now is we hit them quickly with a piece of emory cloth to remove a few tenths and then go right to assembly. We don't waste time going through the hassle of fitting bearings any longer.

Sure, it seems like the proper way to make the Model-A rear end set-up perfect however we have found is that 30k, 40k, 50k. -or whatever miles later, the ones that we didn't spend the time making the pinion bearings slide vs. the ones that we just spent any extra time on all sound(ed) the same when driving and it hasn't seemed to make any differences on temps on the differential housing exterior. Ultimately, I think that in a nutshell is why there has not been much said about this before.

Re: Outboard Pinion Bearing
 

The seal had cut a line on my old drive shaft to the extent that it would either have to be sleeved or replaced to hold oil again. The deciding factor here was that I chucked it between centers on my lathe and quickly realized that it was bowed in the middle. Rather than try to straighten, and given that the new part is available I chose to replace it.

I did utilize about 10" from the pinion end to make a mandrell to mount the pinion in the lathe to turn the step I noted on Henry's original part. This shaft is 1.125" OD, so on one end I did index a 1" hex, on the other a 1.125"-14 thread was turned for about 2.5". Besides it's use on the pinion, it is also to be used in the fixture I have designed to overhaul these types of differentials. I will be posting much more detail on this process and what purpose these machining operations are meant to provide in the near future.

Your findings are appreciated and duly noted, thank you for sharing them. I completely understand the time considerations you must consider. I have spent a considerable amount of time and effort to tool up for this style of differential, I expect to gain it back on subsequent overhauls. I also am doing this for myself, and my time is not being billed as it must be in a flat rate job shop with payrolls to make. To cut this pinion like Henry's took about 25 minuets including setup once the tooling was available. With it fit like this the pre-load setup took maybe 10 minuets tops, this would not be the case I would think in the as supplied state. This time savings must be considered also.

In my case, to obtain a nice snug but slip fit, there was .004" removed from this part. Trying to pull that in with the nut would be difficult, and trying to remove it with emery cloth would be very difficult to keep it square and round.

More to follow, I look forward to your thoughts and comments. Thinking outside of the box is what usually make us improve on whatever it is being undertaken.

Post #6, no, I did not cut a new pinion. No emery paper was used, the smaller dimension given was turned with carbide insert tooling.

Thanks to you all......