TR6 Frame cracking around lower control arm mount, have you checked yours?

[sqbsprite]

Being relatively new to the TR6, I am quickly learning some of its inherent dark secrets. First there was the differential mount cracking problem and the rear trailing arm bracket cracking issue. Now that I am rebuilding the front suspension, I learn about the need for additional braces required for the lower control arms. My frame was badly broken, not just cracked at the rear control arm mount on both sides. The right side had been somewhat welded, but without adding the additional support. I question if the use of shims behind the bushing mount might contribute to the stress. There were shims behind the brackets on the rear ward mounts where the fame was broken, but not the fronts. To me, the idea of putting shims here to make a small caster adjustment, was not a good one. The mis-alignment of the pivot points through the bushings, puts a lot of load on the bushing and bracket. It was obvious that the rubber bushing was being pushed more to one side. I could really see the alignment when I was re-assembling it with new bushings. The trunion pivot bolt did not want to align with the control arms which is what gives the caster adjustment. I would think that the caster angle is built in by the offset of the trunion to the upper arms. If so, then shins were required just to square things up. If that was the case, it should improve alignment between the arms and the trunion. Can someone explain this better to me?

 

[Darrell_Walker]

I've only used the shims to set the camber, so you use the same number front and back. The TR4As are even worse in this area than the TR6, as they used a single bolt bracket and no bracing at all. Another tip is to make up a backing plate for the back side of the bracket that is welded to the frame.

 

[ed_h]

The front side of the front mounts on my car had only small, anemic looking welds to the steering rack mount. This is an area that can be improved.

Ed



https://bullfire.net/TR6/TR6-29/TR6-29.html

 

[sqbsprite]

Just a follow up regarding the shims. I thought it was strange that there were only shims under the rear lower bracket. The right side had 4 shims and the left had 2. When I re-assembled it, I reduced the right to 1 and kept the left at 2. I set the car back on its wheels and made a couple trips up and down my drive to settle things. The result was excess negative camber with the left being worse. So I removed the shims and now it sits about right on both sides. For whatever reason a previous mechanic must have been trying to compensate for something that is no longer an issue with everything being new. I would think that shims should be placed equally on both front and rear arms when needed to adjust camber. I read in one manual that you could shim to adjust for caster, but I don't think it would be good idea. Something would probably be bent if caster was out. The car drives correctly now and I have dialed in the toe-in. I'll be watching for changes, but I think it's all good.