Getting the best out of standard suspension components for touring driving today

Hi Clive…iv never had a problem setting correct ride height or rear camber…my comments in posts above were purely about useing the setting link at the rear as described in the Jag service manual…really just an answer to the question you asked about the holes in the rear mounts…if you actually try to set the rear useing the link as per the service manual you would find it impossible…Steve

Mine too - I was suggesting it should be possible to “calibrate” a convenient ride height as an easy reference point for camber, avoiding the need for setting links or weighty friends. My reference was this chart of camber vs ride height, which allows translation from nominal camber at nominal ride height to another pair of values, at the ride height you choose.

This chart is developed from a published drawing to illustrate the principle- a precise owner might choose to create his own from on-car measurements.

Maybe more appropriate here - I’ve changed some features of the IRS mount to increase cornering stiffness, can I change anything that would make it easier to install?
230407 diff mt


Clive, I will get your shocks measured this weekend and get those specs to you.

Pay close attention to this video from about 40 minutes on: it’s got some cool suspension mods that you might find…Interesting!

Yes, they are interesting. Thanks.

I’m not sure of the purpose for the air cylinder, or if that was the simplest way to achieve it. Probably missed the point again.

They’re clever boys with imagination and a good workshop - good starting point.

Looking at dimensions of original and Gaz front dampers, following an interesting discussion on a thread set up to discuss bushing materials:

A Gaz front damper I recently bought for testing is significantly shorter than an original Girling unit, allowing the suspension to move approx 1 inch further in bump travel. If my numbers are correct that will tend to put more work (stress) into the bushing. Is that a potential risk for owners using stiff bushes (of the fixed, not rotating sleeve design), perhaps using their cars in rougher conditions, to experience more bushing strain with Gaz front dampers?
This condition could be reduced by controlling excess bump travel, perhaps with an additional piece of jounce bumper. A section of shaped foam could give more progressive ride feel, and would also constrain the geometry changes (toe, camber etc.) within the design limits.

I understand the rebound travel is correspondingly shorter for the Gaz, but I don’t think that will compensate because the major energy is dissipated in the bump stroke.

Clive, Thanks for introducing this post link to me. Who knew bushings could be so engaging!! It took me about 3 hours to scan through the postings. Luckily I was only looking at the pictures! Good news I finished acquiring all the replacement parts for my front suspension, the last three from an Israelis chap actually here in the Detroit area, so now I have a much better idea of what bushings are going into them and why.

It’s a well kept secret John.

I planned to make a stiffer subframe mount today but the trial mix suggested the PU constituents hadn’t endured storage well, so I’ve ordered another set. On the positive side, the colour was good - it was very blue.

From the postings It appears you feel there is a significant advantage to be gained stiffening the rear end mounts. Do you feel there are any downsides?

My theory is that making the mounts at the rear of the rear subframe stiffer than the front pair will give a small amount of helpful steer in response to cornering loads. I really don’t know how significant that will be, I’m scraping for ideas because there’s so little available for change at the rear. I’m making that suggestion from a purely theoretical view, based on figures, charts and “feeling” based on experience that doesn’t include any XK-E mileage at all. My analysis suggests useful gains in response and stability feel, the extent of those depending on the actual stiffness values.

The question is how to achieve that front:rear difference. The Jaguar mount was the stiffest of the three I tested - I wouldn’t suggest fitting a softer one at the front because I feel you’d lose handling precision. Going with the Jaguar mount as the front pair then requires a stiffer mount at the rear - as far as I know such a thing is not currently available so I went into the realm of the hypothetical by cobbling up a pair with polyurethane inserts on top of the original rubber. One of our intrepid members will evaluate these at a suitable time. If it’s useful my assumption is that any development of the idea would involve revisions to both the shape and material. I’m currently making a jig to mould such a creature in PU.

The data doesn’t suggest any downside in the dynamics although that doesn’t cover every aspect - the stiffer mounts could transmit more road or driveline noise to the structure, although I think that’s low risk because they’re still flexible material. They could be more difficult to install. My parts are engineering samples, real-world use would need to consider long term durability.

Some might also see downside in getting advice from a self-proclaimed engineer you’ve never heard of, who lives on the other side of the world and freely admits to having never driven the car in question. That’s fair too.

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To put in context with some numbers - I bought three mounts from one of the leading suppliers, described as Genuine, Aftermarket and Uprated. My tests gave the following results for lateral stiffness:
Genuine: 620 N/mm (3550 lbf/in)
Aftermarket: 246 N/mm (1400 lbf/in)
Uprated : 600 N/mm (3450 lbf/in)

If your baseline is standard Jaguar mounts, there’s no obvious way to fit stiffer ones - unless my data is bad and the “uprated” mounts really are stiffer. I’m open to better data, but until then I’ll believe mine.

If you happen to have the (soft) Aftermarket parts fitted then you could fit either of the others in the rear position to get the steer effect I’m suggesting. But you might be better simply fitting them all round to get greater total stiffness and leaving the steering subtlety I’m suggesting to a later date - I can’t tell you which approach would be better.

I can tell you which would be best - Jaguar at the front and stiffer at the rear. With additional PU “wings” I got the lateral stiffness up to 1000 N/mm (5800 lbf/in). That should give a noticeable gain.

I’m now working on getting that level of stiffness with a simpler mount construction. And a simpler test setup.

The only downside i can think of for stiffer IRS mounts is to install them you need to compress the material between the metal plates. Any one that has put in new mounts compared to old knows the difference


I understand it can be a challenge, where does the difficulty occur? How do people typically resolve it?

Podgers, brute strength and levers.


On 2+2 cars there is much less room between the IRS cage and the chassis. …so you cant refit the IRS as shown in the service manual…you must fit all mounts to the chassis first then raise the irs cage up onto the mounts…this is a much easier way to fit the irs and can easily be used on non 2+2 cars…care must be taken to protect the thread on the protruding stud on the bottom of the mount…a thin steel sleeve works…this method make IRS refiting a much easier job…Steve

In my ignorance I’m curious where the dimensional mismatch, if that’s what it is, occurs. Presumably the U-sections fitting to chassis rails are quite accurate and reliable, so is it the variation in position of the mounts relative to subframe that requires some “technical adjustment”?
I’m wondering if the design intent was to put some preload on the mounts when installed and secured?

Hi Clive…the actual fixing point are exactly the same…the 2+2 cars have rear seats so the bulkhead behind the seat is much closer to the irs cage…so you cant get a hand in to fit the nuts on the mount to chassis fixing you can on the non 2+2 cars…Steve …ps photo 2+2 car

Understood thanks. It seems it’s not a straight “lift up, line up holes, insert bolts and tighten” on any model? I’m curious if you always have to struggle them in the same direction and whether it was a deliberate design to put some preload in the mounts.
Thinking of many Triumph cars of that era where the steering rack mounts were supposed to be preloaded outward before tightening, to give some lateral preload and supposedly improve the steering connection feel.

Nice colour! :+1:t5:

Hi Clive…no preload intended by Jaguar as far as im aware…to the IRS mounts…what you need to remember is that not all mount are dimensionally the same when sat side by side…so some will be more awkward to fit than others…also for most diy restorers this is not a “regular” job…i think thats the basics for many struggling…also as i mentioned fitting as per the service manual is more difficult than pre mounting all mounts to the chassis and straight lifting the cage…good tools also help…anyone thats done the job once will find it much easeir the second time…and so on…as with any of these "difficult"jobs the professionals(experianced) dont have a problem that the diy guys do…Steve