Apologies - I meant to start new rubber bushing thread. Ignore
previous post and please repsond here with the points I’ve missed:
Doug, Alex, Bob (and possibly Alyn?)
Let’s get to the bottom of this one. We are 4-5 good people with a
lot of knowledge who are split into two camps on this and we can��t
both be right but we can all learn and enjoy doing so.
Sorting this kind of thing out is exactly what the forum is about
IMHO. I��ll start the ball rolling with my (non Mech Eng) view. I��m
vaguely familiar with this technology from its use 50+ years ago by
Greeves and BSA et al.
The idea of rubber in torsion suspension pivots is that you get a
waterproof and maintenance-free joint in an exposed part of the
vehicle. Bike suspension bushes often last the life of the vehicle
and quite a few cars too I guess? The main downside is that unlike
precision bearings or bushes, rubber can��t give totally precise
location and there tends to be a little ‘give’ in other planes
besides the one around which the lever is meant to rotate. They do
reduce vibration and harshness which we know Jag were trying to
eliminate. Greeves even used the rubber in torsion as the main
springing medium, let alone pivot, but that��s rare.
Points to consider:
- Why would a manual ever mention the strong caution of not
tightening until mid-laden, if the sleeve can rotate on the shaft
through has many degrees as required with no ill effects? There is
no mention of this kind of caution for any IRS pivot, for example.
The XJ, XJ-S and E-type manuals all say final tightening of the
pivot bolt must not occur until the car is resting on its wheels.
This is so that the bonded steel sleeves are clamped tight at mid-
position and therefore the rubber does NOT need to deflect, say, 30
degrees �V only 15-ish degrees in each direction. This is doable.
Even the upper wishbone bushes, which have a push-fit sleeve, are
not supposed to be tightened until the car is resting on its
wheels, although these are not rubber-in-shear bushes AFAIK.
- Where else, on any assembly, is a thin plain steel sleeve
asked to perform heavy duty, un-lubricated bearing duty around a
plain steel pin, with no provision whatsoever for maintenance? Even
door hinges are supposed to get a squirt of oil, but not wishbones.
Steel on steel is not a viable bearing surface in an un-lubricated
setting. A spring steel slipper bearing against a chain running in
an oil bath is one thing. A steel suspension bush wearing on a pin
with no surface treatment or lube is quite another.
- There is obviously zero movement once seized/rusted. If
the sleeve was the designed pivot, then when seized all the
suspension movement has to be taken up unexpectedly by the rubber
bush or the pin rotating in the subframe (which it doesn��t). I��d
expect rubber to crumble fairly quickly if it was being asked to do
something it was never designed for. However, many bushes with
seized sleeves are still intact.
- The bushes DO get shredded if people tighten the pivots
while the car is up on stands with its wheels dangling down (hence
the cautions in the manual to tighten only when the weight of the
car is on them). This highlights the fact the rubber is supposed to
be twisting, not the sleeve rotating, but it is only designed to
twist through half the arc, not the total range of movement. If the
sleeve were rotating on the pin it wouldn��t make any difference
tightening up the pivots with the car on stands.
- The only way parts seize with rust is through prolonged
immobility. Yet suspension bushes seize on the pivot pin even in
cars in constant use. Un-lubricated or poorly-lubed steel on steel
which is in constant motion typically wears rapidly �V giving clear
wear grooves like on door hinge pins or door lock mechanisms etc.
Has anyone ever seen a grooved pin or a sleeve worn thin from
rotating against the pin? They either come apart as normal or are
seized. They are never sloppy or worn. Do we check pins and sleeves
for wear, or is there any spec for the pin OD or sleeve ID in the
manuals? Not AFAIK.
- How come no Jaguar manual mentions lubricating the
sleeves or the pin before reassembly if this is supposed to be a
bearing? You and I may put anti-seize on but no Jaguar publication
mentions lubrication of the sleeve or pin.
- If the steel sleeves rotate around the pivot pins and are
free to spin, how come 45-50 lb/ft on the nuts doesn��t clamp them?
Where do the nuts are tighten against if not the sleeve? If the
sleeve is free to turn, how come there is no end float spec like
there is for the hub carrier fulcrums at the back?
Happy to hear the opposite side of course, so I learn more stuff
myself. Over to the ��spinner�� camp ��–
66 2+2, 73 OTS, 76 DD6 Coupé, 93 XJ12
Cambridge, United Kingdom
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