Tweet
A while ago I fitted a 6 degree rear beam (only camber adjustable) to my cossie, with poly bushes for the beam mounts. I had the car aligned and camber was set correctly. After that the toe was -0.03° on the left and +0.21° on the right. After the alignment guy did all settings I noticed he set the front wheels also parallel. I said I wanted to have it toe in a bit, but as he already took all the alignment stuff off the car he said just try it and if it's not good come back and I'll set it with more toe in. Since the toe on the rear is not adjustable I needed to put a shim between the bearing carrier and left arm anyway, so a good reason to come back after doing that. (BTW, with the wheels parallel on the front was indeed not nice at high speed, wandering all over the place)
So I put the shim between the bearing carrier and the suspension arm to give the left wheel a bit more toe in. When I went back the new settings were +0.13° on the left, +0.21° on the right. (+0.21° matches about the 1.5 mm toe in per side)
I also told the alignment guy I was taking the car to the track the day after. He was interested to see what that would do to all the settings, so he said I could put it back on the alignment setup afterwards. So that is what I did last Saturday and I was quite surprised by the readings. The toe on the left was now about +0.33° and the right +0.03°.
Seeing that the total toe (about 0.30°) was still about the same it seems like the beam has moved underneath the car slightly. The only possibility that I can think of for the beam moving is that the beam mount bushes move a bit. How I see it is that the beam is kept in place by the top of the metal sleeve going into the hole in the chassis leg. Since the beam bush can deform by forces the sleeve should also be held at the bottom. At the bottom the beam guide plate holds the sleeve in position. But the guide plate itself is only held by the two M10 bolts which are only torqued up with 41 - 51 Nm. So I can imagine that the rear beam pushes the guide plate away, especially on the track where the forces on the beam are higher than normal. In total the toe moved 0.20°, on the distance between the beam mounts this would be about 5 mm total movement (2.5 mm each side). This does seem like a lot, but I guess it's not impossible.
With solid beam mounts the bush can no longer deform and the top of the bush should be able to do all the work I guess. Now I'm really wondering about changing to solid mounts. Have other people ever experienced the beam moving slightly?
So I put the shim between the bearing carrier and the suspension arm to give the left wheel a bit more toe in. When I went back the new settings were +0.13° on the left, +0.21° on the right. (+0.21° matches about the 1.5 mm toe in per side)
I also told the alignment guy I was taking the car to the track the day after. He was interested to see what that would do to all the settings, so he said I could put it back on the alignment setup afterwards. So that is what I did last Saturday and I was quite surprised by the readings. The toe on the left was now about +0.33° and the right +0.03°.
Seeing that the total toe (about 0.30°) was still about the same it seems like the beam has moved underneath the car slightly. The only possibility that I can think of for the beam moving is that the beam mount bushes move a bit. How I see it is that the beam is kept in place by the top of the metal sleeve going into the hole in the chassis leg. Since the beam bush can deform by forces the sleeve should also be held at the bottom. At the bottom the beam guide plate holds the sleeve in position. But the guide plate itself is only held by the two M10 bolts which are only torqued up with 41 - 51 Nm. So I can imagine that the rear beam pushes the guide plate away, especially on the track where the forces on the beam are higher than normal. In total the toe moved 0.20°, on the distance between the beam mounts this would be about 5 mm total movement (2.5 mm each side). This does seem like a lot, but I guess it's not impossible.
With solid beam mounts the bush can no longer deform and the top of the bush should be able to do all the work I guess. Now I'm really wondering about changing to solid mounts. Have other people ever experienced the beam moving slightly?
So because of that I was thinking left toe was suddenly +0.33° and right toe was +0.03°, while in reality left toe was probably +0.13° and right toe +0.20°. So no problems at all with the beam mounts moving. 
Comment