Installing the IRS – it’s only a matter of 8 bolts …

 Rear Suspension  Comments Off on Installing the IRS – it’s only a matter of 8 bolts …
Aug 232013

I had been waiting on the completion of the front suspension components so that everything would be in place to transform it from a bodyshell to a rolling chassis; installing the front & rear suspension as well as the engine over a weekend. I even dared think we might be able to have a stab at starting the engine.

I had read and re-read all the available manuals a number of times to produce a detailed list of tasks that needed to be completed prior to and over the installation weekend.

Adapting the IRS trolley to fit under the IRS cage and raising the platform heightThe first task was to adapt the original IRS trolley I’d made; reducing its footprint to a little larger than the base plate of the IRS cage so it wouldn’t get in the way during installation, giving it sufficient ground clearance to allow the trolley jack to be inserted underneath and raising the height of the cage so the wheels could be put on while on the trolley.

I’m not sure about the need for the latter but it made sense at the time! The aim was to be able to lift the IRS and trolley to meet the chassis.

A number of other tasks before the weekend involved the IRS unit which had been sat on its trolley for over a year. Even though it was dry stored, the caliper plating had already deteriorated in this time. These were removed and painted in a tough, silver caliper paint and a remote bleed kit fitted.

The IRS cage had also picked up a variety of scuff marks when it had been delivered and moved around. It was therefore given three coats of 2 pack black paint and two clear satin coats. I didn’t have the luxury of a spray booth so boards and boxes were used in an attempt to keep bugs and leaves off while it dried.

Masking up on the smaller trolley Attempt to keep bugs off Re-painted – not much different!

The planning was finally over and the installation weekend had arrived. Much needed help was drafted in, John had been granted a pass for the dereliction of parental duties who then managed to persuade Martin to travel down to complete the line up. Both had ample engineering knowledge to complement my tea making skills!

Four Metalastik mounts connect the corners of the rear suspension cage to the chassis. Restricted access during the fitting the IRS unit is overcome by pre-fitting the rear mounts to the chassis and the front mounts to the IRS cage. ‘All’ that remained was to raise the IRS to the chassis and fit the remaining 8 bolts. I had foolishly assumed this would take an hour or so at most.

John and Martin assessing how to overcome the fitting problem None of the bolt holes were close to lining up. Hmmm. The IRS was removed and all the mounts then fitted to the cage in order to compare the centre to centre distances. The C2C distance between the mount holes was 6mm greater than the chassis holes.

As they are attached at an angle of 45 degrees, this would need each rubber mount to compress by √2 x 3mm to obtain hole alignment. So they became the prime suspect in the fitting problems.

A few tests of a mount in a vice suggested that it might be possible to achieve the necessary compression in the rubber section but exactly how was still to be determined. So the decision was made to continue rather than abandon the installation weekend.

The front of the chassis was raised in relation to the rear in an attempt to use the weight of the car to compress the rubber in the rear mounts. It still wasn’t sufficient – we needed more weight in the rear. A few moments later, Martin and I were standing in the boot while John assessed whether this had achieved anything other than a comical moment.

Eventually each bolt was persuaded one by one until the IRS had been fitted. A successful method was to insert a screwdriver into the second bolt hole to lever the first bolt hole into alignment and then tap the bolt home. I later found out that such fitting issues were far from uncommon.

We just needed to connect the radius arms to complete the job. Unsurprisingly they were also a country mile off fitting on to the cups on the chassis and were also twisted in relation to the cups because there was no load on the suspension. The solution was a three man job. John applied a tourniquet to draw the IRS cage forward so the radius arm and cup aligned. At the same time I rotated a G-clamp attached to the radius arm while Martin fitted the retaining bolt.

Just the radius arms to go Applying a tourniquet to pull into alignment G-clamp was also needed

Almost the entire day had been taken up with fitting the rear suspension but at least we had the satisfaction of finally lowering the car onto two of its new 5″ wheels. I had been wildly optimistic on what could be done in a day but nevertheless was pleased with what had been achieved.

The front suspension and engine would have to wait for another day ….

Aug 212013

This is more of a retrospective post as the IRS rebuild was originally completed in line with the indicative chassis completion date of May 2011 given by Hutsons. I had stripped and painted all the components but needed a specialist to address the differential. By chance I decided to get it done by Alan Slawson from AJS Engineering.

I wasn’t aware at the time but one the two Jaguar World books that persuaded me to buy the E-Type included a section covering the IRS rebuild. Alan was the person they entrusted to do their rebuild so it seemed fitting he would also be doing mine.

When I arranged to pick up the diff I asked him if he would be prepared to do the full IRS rebuild. Although he was semi-retired he agreed, as long as I wasn’t in a rush for it. The aim was to free me up to tackle the 101 other things needed to be ready for the return of the chassis.

In the end Hutsons took much longer than hoped due to a very healthy backlog of restorations. It was shame really as I’d have preferred to rebuild it myself and would have had ample time to do so. Several months after dropping the parts off, Alan had completed the IRS and even drove over from Essex to drop it off. At his suggestion Gaz adjustable shock absorbers were fitted in preference to the Koni Classic ones I’d supplied.

Also at his recommendation was to rotate the larger radius arm bush through 90 degrees. The rubber section has two elongated holes which are normally orientated so they are front and rear. Rotating the bushes so the holes are at the sides marginally increases the fore and aft stiffness, which is in the direction of forces through the radius arm. I subsequently found out that this is common practice.

The IRS unit is quite a heavy unit so I knocked together an amply sized trolley using two sheets of 22mm chipboard. Great for moving it around but the down side of its generous proportions was that it bent significantly under the weight.

Aug 312012

The section in the service manual for removing the independent rear suspension (IRS) unit gave the false impression that it was simply a matter of disconnecting the handbrake cable, the hydraulic pipe and prop shaft, undoing the roll bar mounts and knocking off the radius arms. The IRS cage could then be lowered after unbolting the four cage mounts.

It probably is that simple for well maintained cars but mine had seized solid, resulting in bloodied knuckles and much cursing. In fact I couldn’t even get the wire wheels off as they were rusted to the hub splines! The brake connections and prop shaft were fairly easy to undo but everything else was struggle after struggle! The radius arms connect to cup fittings secured to underneath of the floor pan by what look like rivets. However the radius arms had well and truly rusted to the cups. Wooden wedges were hammered in but they still refused to budge.

I later found out from the E-Type forum that they are not rivets but something called Huck bolts, which are designed to shear in the event of an accident. I also found out others’ tricks to release the radius arms from the cups once the retaining bolts have been removed. Too late for my removal but no doubt they’ll be very useful in future. The first is to drive the car slowly backwards and forwards, with the aim that the changing loads breaks the radius arm/cup bond. The second is to chock the rear wheels and then jack up the front creating a load in the radius arms.

I briefly tried applying heat but all this did was burn the rubber bushes, producing acrid smoke. They eventually came free after applying penetrating oil over a period of several weeks and then jumping up and down on the end of a very long lever, inserted between the floor pan and the radius arm. To the untrained eye, the jumping up and down in a frustrated, childish manner while shouting ‘aaaargh!’ might have come across as a method of last resort …. but it worked!

The next setback was the removal of the roll bar. The bolts securing the mounting brackets were also seized but as they angled slightly downwards it wasn’t possible to apply penetrating oil so that it could soak in. Again I tried using localised heat but, like the radius arms, the bushes started to burn. By this time patience was in short supply, so I gave up and ground off the bolt heads to release the roll bar brackets.

The bolts securing the four IRS cage mounts had also rusted but fortunately they could be still undone. The main problem was the confined space so initially they could only be undone a 1/4 of a turn at a time. As I’d been unable to get the wheels off, it was rather an unconventional removal. Wooden blocks were placed under the cage’s base plate and the car raised away from the supported IRS.

The final dismantling of the IRS was equally unconventional for the same reason. The wheels and hubs were removed with the drive shafts and lower wishbones still attached and taken to a local garage so the hubs could be pressed out of the wheels. There was quite a build up of oil on the differential which suggested some of the seals might have perished. Although they’re interchangeable, and I didn’t know at the time, the aluminium hub carriers are not correct for the E-Type, which should have straight rather than sculptured sides.

 Posted by at 8:49 pm