Narrowing IRS


To get the Ghia through the engineers inpection I need to address the issue of tyre to arch clearance. It had been noted by the engineer that I need to increase the clearance by approximately 10mm. There are a number of ways of acheiving this, most of which I have considered at some point, but all of which have some kind of compromise. My plan was to cut back the inner lip of the wheel arch and raise the suspension a little, but his was far from ideal. However, given the alternative - narrowing the IRS arms, it was the easy option.

Having now not looked a the Ghia in at least three months, I've now got a new found enthuusiasm to get it on the road, and to address the issues highlighted by the initial engineers inspection. I've decide to address the clearance issue properly by narrowing the IRS arms. A nominal 10 or 20mm is pretty easy to acheive by simply moving the bearing carrier in the arm. This is acheived by grinding the welds from the carrier, moving it inwards and re-welding in the new position.



The benefit of this modification is that the result will look stock as the modification to the arm is very subtle. It also retains the strength in the arm when compared to other narrowing modifications involving cutting anf re-welding the arms. The only drawback is that the maximum amount that the bearing carrier can be moved inwards is limited by the shape of the arm itself. From what I have read a maximum of 29mm is possible using this method. More if modifications are made to the arm to clear brake calipers etc.



The other consideration when narrowing the rear track is that the length of the drive shaft will also need to be reduced. This can be acheived in a few different ways. The left driveshaft from a Type 3 auto is shorter than the stock driveshaft and can be used, or alternatively some off of the shelf custom length driveshafts can be ordered from someone like Chirco. Failing that, you could get some scratch made.



The CV joint itself also allows for some lateral movement. This is to compensate for the change in distance between the gearbox flange and drive axle spigot as the suspension moves through its travel range. The only issue is that I am not sure what the tolerance range is, although I can imagine that it would only amount to a few millimetres.

My plan is to modify the spare IRS arms and then swap them over with those on the car but before I do this I need to get in the pit to take some measurements from between the wheel / tyre and the bump stop towers as the clearance is already quite small. I don't want to simply transfer the problem elsewhere.

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