Steering Rack

Rally cars slide a lot, and to catch a slide you have to get some opposite lock on quickly. To aid the quickly aspect of that you need a steering rack that moves the wheels as much as possible for the minimum amount of input from the driver. This of course makes it nervous in a straight line, as minimal inputs from the driver result in large amounts of wheel movement. The more a steering rack causes wheel movement for minimal steering wheel movement is referred to as a quick rack. The popular way of measuring a rack is Lock to Lock for steering wheel turns, so a 2.5 rack is 2.5 turns of the steering wheel causes full movement of the front wheels. The M3 rack is quite quick at this, although I can’t remember the number at this moment. However, this is not the whole story any longer, racks are now variable rate, and to aid straight line stability racks are slower in the middle, and quicker as you approach full lock. The M3 rack is now one of the slowest BMW make. Luckily most BMW racks are the same externally so you can easily swap from another BMW. The popular swap is from a Z4, but since everyone wants one they are rare and expensive. The other way of measuring rack speed is in mm/rev, ie mm of rack movement for one steering wheel rotation. The M3 is 34mm, the Z4 is 54mm, and as it turns out the E46 is 45mm. Not perfect, but available for a mere £85. I also found that Titan can supply a motorsport one with 63mm, but for £600 more than the E46 item. I decided that since £££s are disappearing rapidly at the moment the Titan one can be next year, and bought the E46 one. As I said this bolts straight on, but the story does not end there. I fitted it, and the front wheels pointed about 45 degrees outwards, meaning the E46 rack was much wider than the E36. A look around showed that the Track rod ends were much longer. To change them should be simple, but the Rod ends did not want to part company with the rack, on either rack. Tight to the point that I was lifting the car rather than undo the ends. Anyway, the technique is to use something heavy to hit against, an anvil would be perfect, but since I didn’t have one used a 10lb sledge worked, put the threaded part of the track rod end against it, and then pound on it with a lump hammer, whilst rotating the rod end, to loosen the rust that has welded the two parts together. After doing this for a while, put in vice, heat with blow torch, and apply the biggest pair of Stilsons you own on the end. I have read for road cars that adding some engine oil into the track rod end before screwing the two parts together allows the oil to seep out and lubricate the threads, not needed for rally cars as they are adjusted every week. This is not the end of the story either. After fitting the new E46 rack, and checking full lock the wheels now hit the chassis, as the rack had more movement. I removed the boots from the end of the rack and found there is a nut that holds the ball joint on the end, and a nice firm face on the end of the rack itself, so after some measuring we made up some 10mm wide strips of 3 or 4 mm aluminium, formed them into a circle around a suitable socket, then undid the nut on the rack, slipped the collars on and put the nut back on. This collar then prevents the rack from moving as far and prevents the wheels from hitting the chassis. Hopefully all the wheels will also miss. By the way these collars are generally referred to as Lock Stops, and you will hear rally drivers talking about having the car, “..on the lock stops”, meaning it was as sideways as it will get.

Fluid

I was sure when I built the car that I checked the pressure rating of the hoses, I can remember finding typical pressures. I somehow got this wrong as typical pressure is 2000psi, or 140 Bar, and the hose was rated at 1000psi, unsurprisingly this burst. With a new pipe made, good for 4000psi we have had no more problems. Note this rating is only required for the pipe from the pump to the rack. The pipe from the reservoir to the pump is at atmospheric, and the return from the pump to the reservoir is open ended so has very little pressure.

We now use competition fluid from Millers.

Cooling

Whilst on one event I noticed the power steering was quiet at the start of the stage, but started to moan during the stage, after 5 or 6 miles. Back in service I mentioned this with the crew who had a quick check of levels, and all was OK, so we thought and decided that boiling may be the issue. They did confirm the pipes were very hot.

The original plumbing for the rack had a long coil of hard pipe across the front of the crossmember. I decided at the time that this was probably a cooler, but since we only went short distances heat would not be an issue. This coil was also badly corroded and would have needed replacing anyway. Thinking about this with hindsight I probably do more steering in 10 stage miles than a 200 mile blast up the motorway.

So, an oil cooler was purchased, the front taken off the car and the existing engine oil cooler moved and the new one installed.