Upper Fulcrum Shaft Bushes C8672 - Sloppy Bores ?

[lowact]

The reason it is said that the bushes should not be tightened until the car is on its wheels is so that, in their normal position the bushes will not be twisted; suspension travel will then be accommodated by the least amount of twisting of the bushes. I.e. it is a position thing, not a load thing.

In their normal (static loaded) position the wishbones are ~level (horizontal) and the frame to which the bush housings are bolted are at angles of ~77 degrees off horizontal. Knowing this, you can fully tighten and pin the fulcrum shaft nuts before bolting the wishbone to the car; just ensure while you do it that the angle between the wishbone and the mounting face of the bush housing is ~77 degrees.

You don’t get a choice about how much to tighten the fulcrum shaft nuts and compress the rubber. The nuts have to be tightened until the distance between the mounting holes in the bush housings is the same as the distance between the mounting holes in the frame. You will find that, if you are using all of the proper and correct thrust washers, the holes will be aligned when the washers are hard up against the ends of the bushes inner tubes. Note that you absolutely need this. The way these bushes work, the inner tube twists with the wishbone; the tube is clamped to the wishbone by the fulcrum shaft nuts; otherwise the fulcrum shaft will twist inside the tube, squeal like a banshee and handle like a citroen.

Last but not least, there is absolutely nothing wrong, nothing is lost, by trimming the rubber. The torque wrench settings are specified, 60 for the uppers, 80 for the lowers. If you are at these levels before the bush inner tubes are fully clamped and mounting holes aligned, your only option is to trim the rubber a couple of mm and try again.

[rfs1957]

There is no rubber alive that will resist the requisite torque applied to the 1/2" UNF nuts that contain this assembly.

The whole point of the rubbers exceeding the length of the spacer is that, once deformed, they form shoulders to retain the upper wishbone in its position.

Cutting off "excess" is a mistake, unless you're adapting parts from a Citroen.

As for the 77°and assembling on the bench, sorry, we must live in a different hemisphere

(Ed - we do !)

Philippe - je t'ai fait un message privé.

[mgcjag]

Why would you consider fully tightening the wishbone bushes off the car?....you will have to loosen them again to fit and set your torsion bars.....Steve

[Philippe-J.]

Steve,

as far as your question is to me, my intention is to check the tightening of the rubbers off the car as it will be easier to find out if too thick of a shoulder is formed, and, at least, if the nuts can reach the split pin holes in the shaft. Then I will check the distances between the blocks as compared to the dimensions of the frames.
Of course I'll then have to loosen everything and tighten again when on the car.

Colin,

thanks for your advise but I am not quite sure about this 77° angle. What is it related to exactly?



As for the torque, where did you get these figures from? I did not find them in the workshop manual (pages J.xx).

[rfs1957]

Philippe, to test everything you can just clamp the shaft in a vice - no wishbone needed - and fit both fulcrum blocks, with requisite washers, then run the nuts up hard and tight.

Note that the OUTER washers have a 1/2” bore, and are meant to butt up against the shoulder at the end of the threads.

The rubber has no effect whatsoever on how the castellated nuts end up oriented, this is dictated uniquely by the length of the steel sleeve that is contained within the rubber.

As a matter of precaution, just check that the sleeves are slightly (1 or 2mm from memory) longer than the corresponding parallel shank of the shaft, otherwise you’re not tightening on the sleeve but on the shoulder of the shaft.

I promise you that this is all a lot simpler than you are making it, trust us !!!

As for the 77 degrees and the torque settings, I believe, with all due respect, that these are irrelevancies that just muddy the waters around what is in fact a desperately simple situation.

PS check that you have the correct thickness INNER washers, particularly, as they DO affect the relative separation of the blocks, and their alignment with your frame holes. They should be circa 1/8”, mine are a tad fatter at 3.30 for some reason.

Same for outside ones, though they are less critical. It would be perfectly acceptable to SHIFT, a millimetre here or there, your blocks ON their rubbers, if you needed to tweak the alignment.

[mgcjag]

Just for info Colin/Lowact has a S3..the series 3 service manual has a torque page....it shows the wishbone nut figures.....it is however quite a usefull page....however note that the S3 uses different upper wishbone bushes to a S1, S2 ...

[Philippe-J.]

Rory,

the rationale is now perfectly clear to me, thanks.
My actual situation not so , until I carefully check my parts. The only issue is: will the rubber beads be thin enough to let the nuts push the washes so as to butt up against the shoulders at the end of the threads? That I am not sure of from a first (too) quick try.
But now I know what I should get, that's a good step forward

[lowact]

Philippe - looking at your Fig.6., you can see that the rubber flange that is formed when the fulcrum nut is tightened is compressed between the bush housing on the inside, that is stationary, and the washers on the outside, that rotate with the wishbone. Ideally the washer would slide against the rubber however rubber is a lousy slide bearing surface and if the force required to compress the rubber is too much, instead of sliding the flanges will shear off.

If you are thinking “it must be ok ‘cos it’s how Jaguar designed it”; consider it is the inadequacies of this design that was the reason Jaguar changed to the S3 upper wishbone bearing arrangement which, imo, can’t be beat.

This issue (with bonded sleeve rubber bushes) is exacerbated if the rubber is harder or is polyurethane.
The solution is to trim the rubber, reduce the flanges to just a smidge longer than the inner sleeve. However this is only the 2nd best solution. The best solution is to ugrade to a properly engineered loose sleeve design, imo this is a no-brainer upgrade that every S1/S2 owner should do as a matter of course.
I.e.:
https://superpro.com.au/find/superpro-s ... 1063681367

Fully assemble on the bench, check that the mounting holes are at the correct distance apart and that the washers slide against the bush faces, bolt to the car.

On an S3, this angle is ~77 degrees, mainly because the frame post is not vertical.

If you know what it is for S1/S2 you can set your bonded sleeve bushes into their neutral position without having to do it on the car. Note there is not this requirement (to set the neutral position) with loose-sleeve bushes.

[Philippe-J.]

Having check the dimensions, I'd say my situation is not so bad eventually.
I tightened the slotted nuts so that the split pin holes in the shaft got flush with the depth of the slots. This was made without too much of a fight finally. And the distance between the washers was few tenths of mm longer than the length of the inner sleeves:



Now I released the nuts, waiting for the time to mount them on the car and do the final tightening under weight ... one day

Thank you Colin for your explanations, this option B is not nominal for me at the moment, but who knows?

[rfs1957]

You're nearly there ; forget the crenellations and the alignment of split-pins for now, what you want is to be both nuts tight so that the whole assembly becomes a block, there is nothing to measure or calculate

[Philippe-J.]

Yes Rory, my measurement demonstrates that I will be able to fully tighten the nuts, when it is time for the final mounting, up to a full contact between the washers and the sleeves, contrary to what I dreaded in the first instance