AU IRS front diff support bush upgrade

[CAT600]

Got a SOLID job done today.

When I pulled the tailshaft off to remove the gearbox hence engine, I was sort of relieved to find a part failing on the IRS of the car.

I say relieved because several months ago I had the original diff rebuilt after 140,000kms and some dragstrip action and I was concerned that something was not installed 100%. My concern started when I found what originally appeared to be a loose (vertical movement) front diff support bolt, but when I checked the bolt with a spanner, it was tight into the subframe. On closer inspection the top diff mount bush had been hammered by the launches at Heathcote and the front of the diff was able to bang up and down about 8-9mm, kind of like a slide hammer effect on a launch. Now this is the movement that kills halfshafts on the B-series cars and I was keen to resolve it. So I took some measurements off a new bush (pictured) and then made the solid steel spacer with a protruding top section.

Old vs New:





Now normally the standard bush would have a large gap all around the outside of it and only have contact in the middle where the threaded weld-in spacer hangs down from the subframe around 9mm, but my new setup, combined with a 5mm disc of rubber (to insulate NVH) will transfer the reactive torque of takeoff through the whole subframe tube AND spacer:





This is a prototype and was made a bit thicker to correct a slight tailshaft alignment issue on my project car, but if the design works, I am happy to produce a few of the correct alignment design for anybody that may want to buy one for their AU.

Not a money making exercise, just a bit of a hand for anyone that wants to drag race their IRS AU a bit more confidently