Pinion Assembly

[steve davidson]

Did you get the AC bearings from a bearing factor or similar? The ones Austin used on all but a few late cars are narrower on the outside race than the "off the peg" AC bearings. If  you have the standard width bearings, as well as that gap, the pinion mesh will be different by the difference in the width of one of the bearings.

The ones that Seven Workshop (and others) sell are ground down to the correct width.

https://www.theaustinsevenworkshop.com/p...-ac-thrust

Hi Stuart,  The bearings came from our Club supplier here in Queensland.  I think I'll pop the bearings back out for measure.  Thanks for the advice.

Steve

Hi Steve, the specially machined pair with narrow outer rings are held in the Melbourne Club Spares as Part Number 0394a - sold only as a pair.   

Tony.

Hi Tony,

Thanks for the notes above.  I guess you know Trevor who looks after our parts up here, I'm pretty sure the set he gave me came to him as "second hand" from someone who'd had them and then not used them.  So their exact origin is unclear.  I pulled them back out again tonight and found that the outer race of the new ones are 0.626" while the old ones are 0.592", so that seems to explain the reason for the gap between the locking ring and the torque tube body.  The both look to have the same width.  Thoughts?  Is this gap an issue and why do the have to be an exact match?

With respect to the orientation of the bearings I'm going to say there is a one face that is "thicker" than the other, i.e., the balls could not be extracted past this "thick" face but they can be pulled out past the "thin" face (if you take the carrier with it).  The "thicker" face has the bearing ID stamped on it.
When I pulled the unit apart these "thicker" faces sat back to back, I asssume this is the correct orientation and the inner distance piece on the pinon end and the bearing retaining nut on the input end ensure that the bearings can not seperate.  Sound right?

Thanks

Steve,

I just checked a pair I recently removed from a '31 axle, they are (as you say) 0.592" on OR, and 0.622" on IR.

My (R&M) bearings are marked THRUST on the side which has the smaller gap between inner and outer races. (The inner races are the same diameter, but the outer has a 'lip' on the 'THRUST' side).

The correct orientation on assembly is 'thrust' faces together, this is known as a 'back to back' arrangement.
http://www.skf.com/uk/products/bearings-...index.html

If you clamp the inner races between your fingers in this orientation, there should be a slight pre-load between the outer races. If you turn them 'face to face' the outer races will be loose with a gap between them. Both layouts are used in general engineering but 'back to back' is more rigid arrangement and better suited to supporting overhung loads (such as a pinion drive).

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Hi Chris KC

I have a few pages copied from Woodrow and the Companion but not covering the diff. I was aware of the radial clearance for one ac race (and have found diffs carefully shimmed!) but curious about the end float. I cant find the A7 Journal on any Club sites but it may be there.
Would be interetsed if you (or someone) would  repeat or print the book or bulletin instruction please.

"In the case of the latest type of torque tube i.e. that with the dual purpose bearings at the rear end, the process is somewhat different.

Transfer the races on to the new pinion, or fit new ones if necessary, and tighten down the nut which fits on to the thread on the pinion shaft. Lock the nut in position with the lockwasher, or in the case of a few of the earliest type, with the setscrew let into one of the faces of the nut.

Now insert the pinion and races into the tube and tighten down the ring nut until it bears tightly on the bottom face of the torque tube end.

In the event of new races being fitted, .001 to .002 of an inch end clearance must be left in the outer race of the bearing. The best way to obtain this clearance is to drop an eight-thousandths shim into the torque tube end before inserting the races. Tighten down the ring nut as far as it will go, and with a set of feelers, test the clearance between the faces of the ring nut and the torque tube end. This should be from .005 to .006 of an inch.

In the event of the clearance being greater than .006, remove the pinion and races and file the requisite amount off the end of the torque tube. If there is less than .005, file the end of the torque tube until the required clearance is obtained (Sic). Drive out the pinion when the correct clearance has been arranged and remove the shim, which will no longer be required. Replace the pinion and races without the shim, and tighten down the ring nut. This will leave .0015 to .002 of an inch end float in the outer race of the bearing. Replace the key in the keyway and fit the flange, as with other types"

(Austin Service Journal - March / April 1932)

The companion adds a dire warning that this clearance allows the 'free' bearing to align itself with the one which is radially located, that the bearing pair must locate the pinion robustly in an axial direction, and that this tolerance is critical. Ergo that the ring nut must be de-burred properly before trying any of this!

The 750 Companion is a very worthwhile investment!

Thanks very much for the in-depth explanation above, I now have a much better idea what Angular Contact (AC) bearings are and why their orientation is important.  Is the reason they are sold as a matched pair because if they had different widths the load lines would not converge on the centre of the shaft and deviation here will induce a bending force in the shaft?
I’m still confused about what to do if the is clearance less than 0.005?  Filing the torque tube makes sense in my mind if the clearance is greater than .006, but if it’s less wouldn’t you need to take it off the ring nut?  Or maybe it’s just as east to make up a brass shim of the required width and put it in where the 0.008 shim was installed for the dry fitting. 
Thoughts?