control arm attachment tabs

[Bill Waters]

I wonder if those of of you with the 2015 IRS option have the same issue as I do.

The tabs where my upper and especially lower control arms attach are not square. While I can force the control ams between them and bring the tabs into proper registry with the inner sleeve either by slightly bending the tabs or by bringing the tabs into proper position by tightening the attachment bolts, either of these actions causes the tabs to press on the poly bushing flanges (since they were not square to begin with) disproportionately as they are pulled up against the inner sleeves. When fully tightened, the pressure on the outer bushing flanges causes the bushings to remain in one position while the control arms rotates - i.e., not the bushing turning with the control arm around the inner sleeve as they should. I presume that this will improve with full lubrication of the area between the outer bushing flanges and the tabs, but the angle of the tab against the bushing flange may not allow that to be true. Has anyone else had this problem, and has the problem resolved with more lubrication and use?

[ncbuilder]

I hope someone chimes in here about this problem/situation. This is of particular interest to me because I am about ready to order a kit set up for the 2015 IRS.

[edwardb]

I didn't notice anything unusual when I assembled mine. I did have to tweak the tabs a bit to get things to fit together. I found nearly every assembly step on the new IRS the fit was extremely tight. They are obviously using some very close tolerances there. But once assembled, seems to be OK. Have you called FF and asked their opinion about what you're seeing?

To ncbuilder, the 2015 IRS is a sweet setup. I wouldn't let this or other questions/issues change your mind about ordering it.

[Bill Waters]

I haven't called FFR yet, as I am leaving town for a few days and will have internet, but not cell phone access where I am going. I thought someone else might have experienced the same issue and had worked things out.

It's not just the poly bushing clearances on the mounting tabs; I had to add an additional 1/16" thick, 5/8" ID washer in front of the 1/4" spacer in front of the spherical bearing on the toe arm, as well. Maybe I should just pull the tabs up by tightening the bolts to remove this amount of excess clearance, but that seemed suboptimal.

But I agree with edwardb, ncbuilder. The 2015 Mustang-based IRS is a terrific setup. I have built several kits and have redone the suspensions in a number of production cars, and the tabs/control arm fit-up is always imperfect.

It's worth commenting that the fit between the differential housing and 4 mounting points was perfect. I mention this because this it's a difficult (physically) aspect of the IRS build and any deviation from perfect alignment would be both very noticeable and difficult for the builder.

If no one else has any experience to share, I'll call FFR at the end of the week.

Also, I realized I posted this in the Build Threads section, but meant to do so in the general Roadster section. An administrator may wish to move it.