Fail Safe IRS mounts?

Has anyone tried to make add-on pieces that would keep the IRS from falling off when the car is on a lift and the rubber mounts have separated?

While I am a long way from doing any work on the IRS, I was thinking about the IRS as I will be lifting the kitty up for a belly rub to remove the engine and transmission.

Anyone seen or had ideas for such? I haven’t actually seen if there is space, if any, for such, I’m just thinking ahead for possibilities.


I’ve thought about this from time to time.

Some motor mounts have [for lack of better description] a latch or finger that prevents unlimited movement in the event of the rubber separating. I’ve thought that something similar could be divined for our IRS mounts.



Interesting idea.
Maybe an idea is to remove the stud, and replace it with a bolt that goes all the way through both pieces. You will have to add a counter lock nut or weld it on the one side so it’ tight and have some space on the other side for free movement.

I know this doesn’t help, but one nice thing on a Cabriolet is the ladder-bar stiffener below the IRS, which means that failure of the mounts prevents the IRS from falling.

Use safe working practice…raise the car then put a support under the IRS…

I have had both my XJ-Ss up on my 2 post hoist many times, which means the back wheels and the IRS are not supported.
Why do the mounts not give way ?
I think if you pulled them apart you will find the two metal parts that bolt one to the chassis, one to the IRS are assembled in an interleaved “claw” configuration.
Rubber is injected between the claw halves such that both when the mount is compressed as the car is lowered onto its wheels, and in extension when the wheels are off the ground, the rubber component is always in compression.

It has to be, because rubber is not strong in tension but reasonably strong in compression. The engine mounts would be similar.

No “claw”…the mounts are just 2 pieces of steel bonded together by rubber


Some sort of safety cable, could be an alternate solution.

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I agree that there is no claw-type configuration built into the mounts, but that is exactly how I imagine a mount could be redesigned to prevent separation of the bonded rubber.

Those are some of the things I was thinking about.

I started with an external claw and latch or hook & loop, then a steel safety cable.

Cutting off the stud and through bolting would place all upward movement against the bolt, which would then rubber isolation for both vertical and lateral movement.

Which lead me back to hook & loop as being the easiest to make. The hook could be a flat piece with one end bent outward and upward (>90° bend), with the loop being a flat piece with an oversized hole to allow the hook to move around within the hole.

The hook could be mounted to the body bolts.

Long time ago chevy’s had a recall to add a loop of steel cable.
It limited engine travel if a mount failed.

On my car, I just use Metalastics.

Maybe something like this on each side of IRS each mount?


A metal cable between the bolts would be nice. I always thought a chain would be it but just realized it‘d cause noise… steel cable between two bolts, just long enough, good idea.

Jerry, too complicated and no real benefit… ideally in milled aluminium?

They do come apart. Be safe.

In almost 30 years of XJS/XJ6/XJ12 ownership, across probably a dozen cars this just never been a concern.

You buy the car, replace them as part of your day one reboot (along with coolant hoses fuel hoses brake hose etc etc etc), and don’t worry about it again.

Re-engineering not required.


Two separate pieces. I would likely make them, if I made some, out of 1/16 steel flat bar. Easy to make and would not weigh much, They would bolt on with the existing bolts and nuts.

Obviously, I would need a mount in my hands to make sure the pieces were bent as needed to hook within each other will having sufficient clearance for movement, yet make contact with each other to take the weight off the rubber when the IRS was ‘hanging free’ on the mounts when the car is up on a lift.

I’ve thought above using steel cable, but (to me), seems too awkward to make (with the equipment I have). I would need strong large eye ends which would crimp onto the steel wire, and a hydraulic crimp for the crimping.

If one had the hydraulic crimping tool and then ends, cut the steel cable the correct length, crimp the ends on, and bolt into the existing holes. This would likely be less expensive.

However, with such a short length of steel cable, getting the correct length to take the weight of the IRS when the car is on a lift would, I suspect, be so short and still that the steel cable would resist bending and reduce the effectiveness of the rubber mounts.

I could also be missing something there too?

While not a concern, why lift the car and have the IRS hang from the rubber, and why have to independently support it with stands whenever the car is lifted? Why unnecessarily stress the rubber in tension when it is was designed for compression?

Sorry, I meant to say that the mounts come apart. Yours is fine, just seriously overengineered. I would make the cable just long enough so it is not under tension when the IRS hangs freely. It should not impede anything - the other question is if noise transmits through a cable?

Seems to me that, supporting the weight of the IRS when the car is on a lift, would be the first design feature to consider - eliminate the/a cause of the rubber mounts tearing and separating … take the weight off the rubber (eliminating cause of cohesive failure of the rubber itself) and of the rubber to the metal (eliminating cause of adhesive failure of the rubber/metal bond).

To be fair if they can’t take the weight anymore, they should be replaced. A safety gadget would make finding out… easier.

Four beefy braided ground straps at each corner would suffice.