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Old 12-01-2012, 10:30 PM   #1
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Default IRS upper shock mount - Permanent fix

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Howdy all,
For some time now I've been aware of the dreaded IRS upper shock mount problem, as most of you blokes probably have.

The standard mount is quite a substantial metal unit, with a good portion of it vulcanised in rubber. There are actually 3 metal sections to it -

1 - A top hat which is the section that bolts to the underside of the chassis.
2 - The bottom part of the main body, which is vulcanised to the top hat.
3 - The spring saddle, which is press fit (into rubber) inside the lower section of the main body.

This unit is flawed in several areas IMO -

1 - There is an aluminium sleeve within the main rubber section which is able to 'float' within the rubber. The amount of float is determined by how much packing *(washers) sit between the rubber and shock fastener.
2 - The upper and lower sections of the main body are joined only by rubber which is vulcanised to both pieces. No other mechanical contact is in place.
3 - The spring saddle is lightly press fit into the lower section of the main body, however this is also lined in vulcanised rubber.

This amount of rubber is certainly beneficial for low NVH levels, however it does not benefit rear suspension control, or longevity.

Minor complaints have been noise from the top of the shock being a loose fit inside the aluminium sleeve.
Vagueness from the rear suspension, lacking feedback, due to the shock not being able to use it's full damping capability because of the amount of give in the rubber.
Extra sag due to the deflection in the rubber between the 2 sections of the main body.

It is not fully understood why the 2 main sections are joined by rubber, the only explanation being to reduce NVH. However the spring mount already contains a rubber upper spring saddle, and normal practise for upper mounts on shock absorbers is to use 2 small self locating rubber disks.
With the standard system we have 3 rubber isolation systems at work.

Many users change the units on a regular basis, having a fairly short life span.
If left long enough, complete failure could result due to rubber breaking down over time and the sections then separating.

I have designed an improved version of the mount, using the existing unit, totally disassembling it, and replacing 1 of the sections with 2 new parts.
The new unit has no flex, as the spring mount is fully welded to the upper body.
Isolation still exists for the spring via the rubber upper saddle, and for the shock via conventional rubber disks.

The new design is many times stronger, has zero flex, uses off the shelf user serviceable upper shock rubbers, and is inexpensive.
Considering it will outlast the life of the car, it is a very inexpensive 1 time purchase.

I have trialled a pair on my own AU3 XR8 220 over many months, with excellent results. No knocking, no slop, no vagueness, and no noticeable increased NVH.
The last point about NVH may vary from car to car, as my XR8 is already suspended with a sports bias, and louder than standard exhaust.
A Fairlane user with standard suspension and exhaust may notice increased NVH.

It should also be noted that this system can be tightened up a little further by using the conventional practise of fitting poly upper shock rubbers, with of course the associated increase in NVH.

If you poked your head underneath your car, or just know the AU suspension well, you would see that there is nothing revolutionary about what I have done, as it is essentially the same upper mount system as the Watts Linkage live axle, and even very similar to the front of the same vehicle.

I haven't worked out final pricing yet, as I have a few minor things to deal with to speed up the process, however it won't be a lot as 90% of the job is done by myself. Parts cost is small, as there is only 2 pieces of metal, 2 rubbers, and a washer.
I'm guessing somewhere in the vicinity of $200-$250 for a pair, with a small amount of that being donated to the AFF CHARITY CRUISE.

I can obviously only do this on an exchange basis as I need to re-use most of the original unit.
If anyone has old units they can donate to me, I will happily pay a small amount so I can have some on the shelf ready to go.
It is obviously beneficial for me to do many at a time, to save on part and labour cost.

I am also happy to assist with you making them for yourself, I'm not doing this for the money, I'm doing it to help a fellow Ford enthusiast.

We can make a list of interested people here, and then we can work out the logistics of gathering some mounts to do a run.
Several members from the T series section had already shown interest a week or so ago.

Photo 1 shows the standard original on the left, with the break up of pieces of the re-manufactured unit on the right.
Photos 2 and 3 show the re-manufactured units either side of a standard original.

Last edited by Sox; 12-01-2012 at 10:53 PM.
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