Differential Pinion Shaft Collapsible Spacer

[angelw]

Hello All,
On other occasions in this Forum, I've voiced my opposition to the use of the Collapsible Spacer to set bearing Pre-load. Following are some of my thoughts on the matter.

The collapsible spacer is positioned between the set of two bearings. The logic applied to this arrangement is that the natural elasticity of the shaft is used to keep the system tight (the reason behind tightening nuts/bolts to a specified torque), but not apply that amount of torque as a pre-load force to the bearings. In effect, the collapsible spacer tends to keep the bearings apart and soaks up most of the torque so that its not all applied to the bearings. Using the Pinion Shaft and Bearing System as an example, if the 120lb/ft to 140lb/ft torque specified were to be applied to the bearings as a Pre-load, the shaft would require a lot of force to rotate and the system would fail in a short time.

So the hypothesis is that the collapsible spacer will collapse just the right amount so that the cones of the Taper Roller Bearings come into intimate contact with their respective cups, just prior to the specified torque being reached and that the remaining torque to be applied will put the bearings under the correct Pre-load. That all sounds fine if you say it quickly, but for that to happen, the following criteria must be satisfied, as per the original design:
1. The starting length of the spacer must be just right.
2. The wall thickness of the spacer must be correct.
3. The compressive strength of the material must be the same.
4. The amount of Pre-collapse must be correct.

Even the distance between the bearings will affect the result. The distance between the bearings has the potential to vary due to the cone setting distance of the pinion.

The above may have worked well enough back when the original equipment was available, but typical of much of the current After Market parts being produced, I’ve found these collapsible spacers to vary extraordinarily. In tests carried out using Pinions that wont be used again, I’ve observed results in excess of 200lb/ft torque before the bearing cones and cups made contact (Zero Endplay – Zero Pre-load).

Prior to the collapsible spacer being introduced, the Pre-load was achieved by shimming and the measurement of the torque required to rotate the Pinion; a very predictable method. With differentials that use the collapsible spacer, I replace it with a solid spacer and employ the tried and true method of determining the Pre-load by checking the effort required to rotate the pinion shaft.

When using the collapsible spacer system, I’d bet that very few would check what Pre-load the bearings are actually under, but blindly follow the instruction and torque the Companion Flange nut to the specified torque. One well known repairer and supplier of parts here in Australia when asked if they ever checked the Pre-load of the pinion bearing when the collapsible spacer is used, replied with pride that they check this on every diff worked on. Asked how they checked it, replied that they check the Pre-load with a dial indicator. At this point I declared them to be unique in the World, being able to measure less than no movement (my colloquial term for Pre-load) with a dial indicator. This is the type of chump that can be working on your car and actually charging for the privilege.

The additional time taken to adjust the Pre-load using a Solid Spacer is infinitesimal in the whole scheme of things and well worth it, knowing that the bearings actually have the correct Pre-load.

Regards,

Bill

[mgcjag]

Hi Bill.....great post with lots of detail as ever.......would the collapsable spacer be suitable if instead of tightening to the figure in the service manual and assuming the pre load was correct......you tighten gradually measuring pre load as you go untill you reach the desired setting.........im looking at this from a diy perspective where we dont have access to a machine shop to manufacture spacers/shims .......also for E type diffs what is the preload figures you work to for i/p and o/p shafts......these are not in the service manual as the less desirable torque figures are given and not the preload measurement and also the preload already attained by the oil seal........are the figures the same for the different E diffs

Also Bill just in general re tapered bearings i think you mention you prefer to set them with pre load...is there a general setting depending on the size of the bearing? or what would your recommendation be for front/rear wheel bearings.....thanks and all the best..Steve

[angelw]

Steve Wrote:

would the collapsable spacer be suitable if instead of tightening to the figure in the service manual and assuming the pre load was correct......you tighten gradually measuring pre load as you go untill you reach the desired setting.........im looking at this from a diy perspective where we dont have access to a machine shop to manufacture spacers/shims .......also for E type diffs what is the preload figures you work to for i/p and o/p shafts......these are not in the service manual as the less desirable torque figures are given and not the preload measurement and also the preload already attained by the oil seal........are the figures the same for the different E diffs

Also Bill just in general re tapered bearings i think you mention you prefer to set them with pre load...is there a general setting depending on the size of the bearing? or what would your recommendation be for front/rear wheel bearings.....thanks and all the best..Steve

Hello Steve,
The fellow in the video assembling the Output Shaft units did exactly that. He made no reference to the amount of torque being applied to the nut. However, given the length of the lever he was using and the apparent effort he seemed to be exerting, it would have been considerable.

You need to be aware that all of the force being applied by the torque used on the Companion Flange Nut is applied to the Pinion Shaft (disregarding some torque lost due to friction). The weakest feature of the shaft is the threaded journal that takes the Companion Flange Nut. At some point, if torque is continually increased, the natural elasticity of the material will be exceeded and that rubber band effect will be lost forever. In some of the tests I've carried out using the collapsible spacer, I've recorded torque figures in excess of 200lb/ft just to have the bearing cones make contact with their respective cups.

Prior to the introduction of the collapsible spacer, the shoulder on the Pinion Shaft that resists this spacer was closer to the Companion Flange by approximately the collapsed length of the collapsible spacer; thin shims were then used to set the correct bearing pre-load. When using the shim system, lets say that an excess of shims were used that resulted in 0.010" End Play with the Nut torqued to the correct figure of 120 to 140lb/ft torque. Exceeding these values will have negligible affect on the End Play. Accordingly, by reducing the thickness of the shims being used by the appropriate amount and maintaining the correct torque range value applied to the nut, the result is the correct pre-load of the bearings and the correct stretching force on the shaft.

Yes, by checking the amount of drag (pre-load) of the bearing, you can get the pre-load correct when using the collapsible spacer, but at what torque being applied to the Companion Flange nut and therefore, the stretching affect on the Pinion Shaft?

The correct pre-load, as measured as the torque required to just rotate the shaft is 8lb/in to 12lb/in.

The amount of pre-load is contingent on a few factors, so there is no value that is a panacea. The life of the bearing decreases with the increase of End Play. However, life will drastically diminish with excessive Pre-load. Accordingly, any value where End Play is eliminated will generally increase life of the bearing. For front wheel bearings, I use a figure of 6lb/in to 10lb/in torque to turn the hub (no wheel attached). But these bearings can't be pre-loaded by simply tightening the nut, as this would encourage the inner race of the bearing to spin on the Stub Axle. I achieve the bearing pre-load and locking of the inner rase from turning, by using a tapered spacer between the two bearings.

Pre-loading of the wheel bearings is not my recommendation, as the manufacturers of the Jaguar Car specify an End Play setting. This is simply how I prefer to set my wheel bearings.

I'm sure that you have observed a groove worn in the Stub Axle at 6 o'clock by the Inner Bearing when servicing your wheel bearings. This only happens because the bearing is rotating on the axle. Accordingly, this phenomenon can occur with bearings that are set with End Play. The tapered spacer I've referred to is of great benefit even when the bearings are set to have End Play.


Regards,

Bill

[mgcjag]

Thanks for the reply Bill...much appreciated and very well explained.....Steve

[AussieEtype]

I also live in the Landrover world and my truck has a sals in the front diff and the rear diff. In the 4wd world the advice is never to use a collapsible spacer for rebuilds if you want to maintain diff integrity.

Bills advice is spot on.

Garry

[mgcjag]

Hi Bill...just re reading your post above.....cant quite understand how the tapered spacer is working on the front wheel bearings.....any chance of a simple sketch......for my C type build i recently rebuilt a pair of front hubs.....the stub axels were really worn by the inner bearing turning..they were really loose and i replaced the stub axels....would like to consider dismantling them and fitting you spacer idea.....just need to understand it first....all the best....Steve

[angelw]

Hello Steve,
I manufacture these, but don't have any on the shelf to take a picture of, but will be running a batch in the next couple of weeks. I'm rearranging the layout of the machine shop and so most of the machines are not leveled nor wired up.

Basically its a sleeve, the shape of which follows the taper of the Stub Axle, but with plenty of clearance. It has a short, close fitting (sliding fit) parallel bore at each end that locates on the respective bearing journals. Final bearing adjustment (End Play, or Pre-load) is achieved with shims. It holds tight, the bearings between the Axle Nut and the face of the Stub Axle Carrier upright.

I also make Stub Axles where the Bearing Journals are an interference fit in the bearings (similar to the rear hub bearings), but you have to be content with having to use a puller to remove the hub and bearings from the Stub Axle when servicing.

Regards,

Bill

[mgcjag]

Thanks Bill....iv got it now......all the best...Steve

[lowact]

Prior to the introduction of the collapsible spacer, the shoulder on the Pinion Shaft that resists this spacer was closer to the Companion Flange by approximately the collapsed length of the collapsible spacer; thin shims were then used to set the correct bearing pre-load.

G'day Bill. Not sure how I managed to buy a S1 CWP for my S3.
Quaife via SNGB product code 8825.

Here is pic of new (S1, right) vs original (S3, left). Shoulder is closer to the companion flange (position) as you describe above.


Have you ever done this, fitted S1 CWP into an S3 diff, with shims instead of crush-sleeve? I cannot see why it wouldn't work except, in addition to the shims the S1 uses a "distance washer" (short tube) that is NLA. Might you have one of these?

[angelw]

Colin Wrote:

Have you ever done this, fitted S1 CWP into an S3 diff, with shims instead of crush-sleeve? I cannot see why it wouldn't work except, in addition to the shims the S1 uses a "distance washer" (short tube) that is NLA. Might you have one of these?

Hello Colin,
Yes I have; about 6 months ago. The client's S3 was equipped with a diff from an XJ6, without LSD and a 3.07:1 ratio; he wanted the LSD reinstated and the original ratio of 3.31:1. He sourced the parts and part of the package was the Crown-wheel and Pinion from a late S1.

The only difference between the S1 and S3 Pinion Shaft is the location of the shoulder that is either the stop for the collapsible spacer (S3), or distance washer and shims (S1). You won't have any problems with getting the S1 unit set up.

I haven't got a spare distant washer and I don't have an S1 diff stripped down at the moment. Accordingly, if you measure the distance from the face of the inner race of the Taper Bearing installed on the shaft, to the shoulder that the distance washer interfaces with, I'll work out what length the distance washer should be, taking into account a few shims and make you one.

Regards,

Bill

[lowact]

Thanks Bill, good news that I can use S1 CWP. It does seem to be a very economical way to convert an S3 to 3.07, S1 CWP's cheaper and more available than S3. Making a distance washer, thx very much for yr offer, i'll see how I go myself 1st, by boring out a 3 mm thick washer to 28.7 mm. Here are my dimensions fyi. Seems the only difference, apart from shims instead of crush-sleeve, is that a different outer bearing cone is req'd.