Original IRS Mounts vs. Replacements

…and they would be easier to install with the lower stud 5/8" long per the drawing, not 3/4" as on every one I have…

I am working on my XJS, and while this is the E-Type topic group, the IRS units are quite similar.

Instead of starting an XJS thead on IRS mounts and have mostly duplicate information (the bottom IRS mount metal piece is basically the same, the rubber issues are basically the same, the failure issues are basically the same, and the top mount metal piece is basically the same except for mounting holes) …

I was posting here as the information is essentially the same and applicable to both E-Types and XJSs (and other models with the IRS unit) with the exception of the upper chassis mounting holes.

Now that is the sort of thing my initial question was posing and is a simple solution to stiffen things up a bit and the car to handle

Hi Jerry …yes i know all that…in a post above you were asking for mount hole spaceing dimensions…without specifying that you wanted the dimensions for XJS…which are different…Steve

Sorry Danny, it’s taking a while… :roll_eyes:

To be fair there are parts out there that are stiffer but the ones I’ve seen will tend to make the car sit higher, which isn’t usually a recipe for improved handling. Those parts will also be harder to install.
I’m looking for a spec that gives better dynamics and easier installation, at my usual glacial pace. I did make a lot of chocolate yesterday.

I’m guessing he knew what the XJS mount dimensions were, just wanted to know if the e-type dimensions were the same? My understanding, compared to XJS mounts (CAC3067 or CBC5737), “genuine” e-type mounts (C17198) are different, however aftermarket e-type mounts (C17198x) are very similar to XJS mounts. The bases, including the enlarged elastomeric, are exactly the same as XJS mounts. The only difference is that an e-type upper bracket has been used instead of the XJS bracket.

Hi Colin…do you really think these XJS mounts have similar dimensions to after market E type mounts?

Not think, I know, I bought one to check this. The only difference is the shape of the inner bracket. The outer bracket, that bolts to the IRS, and the size and shape of the elastomeric is exactly the same.

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Yes, I was looking for a comparison between the two, hopefully with replies for each.

Currently, the measurements I took yesterday under compression, and will take today under tension, have very little meaning to factory static manufactured dimensions.

I may get to where I can remove one today and measure it in its static position.

Mine have been replaced at sometime, likely since I’ve owned it, as it is evident each has been removed and replaced/reinstalled (being as they don’t look 40 years old, I’m going with replaced).

After thinking about them from this discussion, I have a vague memory that Bob Sellers (my mechanic in Daytona Beach when I lived there) said he had to replace them, to which I likely said something like ‘Sure, no problem, thanks’. It was my DD and I had Bob keep it going (being an older British car, I got to know my mechanic quite well).

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Jerry…just so were all talking about the same measurement…This is the dimension that you asked about in your post above…it is clearly much larger on the XJS mounts than an E type mount

Steve, yes that is the measurement, between the holes, center to center.

From my compressed measurements yesterday, yes, the dimensions are greater for the XJS mounts.

Base to upper hole is 3.491".

Lower hole to upper hole was 2.665"

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IRS mount tension measurements, first with IRS suspension only, then with wheel (for its weight) hanging from it.

With IRS suspension weight only … 2.800":

With wheel hanging from suspension … 2.833":

As an aside, in looking at the mounts it seems that it would be easy to drill a hole clean through the rubber and metal and set a bolt to act as a fail safe if and when the rubber bonding were to give out, on the road or on the lift. Suitable slack to be included in the fastening of course.

Drilling a hole may be possible, but may also leave fissures that could work as a starting point for a cohesive failure (rubber splitting/tearing, leading to a split rubber pad).