Vibration at 60mph

[Laith]

I swapped a z3 rack into the car the other day using the original tie rods to keep the geometry right.

Everything went in fine bar a leak from not using new crush washers on the banjo bolts (which I have ordered). I also put in an LSD with no issues. The car is a 92 cabrio manual 320.

Right now the fluid is on the low side and will be topped up in the morning, but I noticed on the motorway I got a steering wheel vibration. It starts at 60mph (most of the time) and gets worse then better with more speed.

Now I don't think I knocked a wheel weight off and I measured the rack length with the old tie rods on.

Could it be the low fluid? Or could it be the geometry is really out thanks to the slightly different height of the z3 rack fit?

My plan is to:
1) replace copper crush washers
2) refill fluid
3) take for front end tracking on a hunter machine
4) front wheel balancing.

Am I approaching this problem correctly?

[Brianmoooore]

Vibration at this kind of speed is wheel related. It's the speed at which one revolution of a wheel is close to the resonant frequency of the suspension.
ANY work on the front suspension requires the tracking to be checked. If the tracking is correct after swapping the rack, it's almost entirely by chance, however accurately you measured things. No fancy equipment is required - just a length of string, some scraps of plywood and a level surface.
You should have used spacers or washers to place the new rack exactly where the original one was, or bump steer will occur.

[Laith]

Brian you're a legend.

So a wheel balance is in order as a priority. I'll probably take it to a shop for geometry, I know a place that will do it for £35..

With regards to the spacers for bump steer - I noted there was not that much space between the rack and top subframe tab. I will try and fit some spacers in there - do you know what overall size I need?

Not experiencing any more bump steer than before though..