Upper Control Arms on IRS are slightly different / misalign with mounting brackets

Hello to all

I am building a complete kit MKIV with the IRS. The driver side upper control arm does not fit or line up with the mounting ears exactly … I’ve gathered this is a very common problem so went about spreading the driver side mounting ears but at some point have begun to worry that it is just too much spreading.

As an experiment, I took the passenger side UCA and attempted to line it up on the driver side, and it fit perfectly, actually perfectly on both sides. I then laid the UCAs on top of each other and concluded that the problematic UCA (driver side) is .15” wider than the passenger side one that fits easily. To be clear, the bushing widths are the same. The disparity is when I measure from the outter side of one bushing to the outter side of the other. See photo attached. The one with the grease on bottom is the driver side UCA that does not fit.

Is this disparity standard and acceptable? Is it further acceptable to modify the mounting ears to accommodate the wider width of the driver side UCA? Given the nature of the chassis and the angle of the UCA sub-arms, the entire modification would have to occur on the rear ear of the rear mount and in excess of 0.25”. Perhaps it makes more sense to order a new UCA?

Thank you for any and all thoughts. Attachment 195008

Lots of the parts, especially suspension parts, don’t fit perfectly. Some bending is required for a lot of it, but you shouldn’t have to bend too much to get your LCAs in.

I can’t tell from your picture whether it’s a welding issue, or if the actual mount tube is just a bit too long. If you can trim the tube to make it match the other side, I’d go that route. If it’s welded at a bad angle that makes the whole assembly wider, I’d reach out to tech support at FFR on Monday and see if they can get you a replacement sent out.

That makes sense to me. Perhaps this photo will provide more information. It looks like a welding angle to me, but curious as to your assessment.Attachment 195009

Yeah, looks to me like an angle issue. I’d wait for one of the folks who’ve built multiple kits to chime in with possible solutions. I’m sure you’ll have several opinions by the end of the weekend.

Very Common problem for those to not fit. Most seem to be able to spread the ears to get it to fit. I took a different path, details in my build thread, because of the mis-alignment I had the parts off by more than 1/8 inch in one direction only and I could not get the satisfactory fit with just spreading the ears. Both my passenger and driver side required the same treatment.

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Originally Posted by F500guy

Very Common problem for those to not fit. Most seem to be able to spread the ears to get it to fit. I took a different path, details in my build thread, because of the mis-alignment I had the parts off by more than 1/8 inch in one direction only and I could not get the satisfactory fit with just spreading the ears. Both my passenger and driver side required the same treatment.

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That was a clever solution outlined in your thread. My divergence likely is too large to grind down the bushings and sleeves but impressed how you did that.

To me that is a problem w/ the control arm. One arm fits both sides of the car while other does not, and it's off by 1/4"? No way. Call FFR and get a new arm. BTW most of the problems w/ fitting are that the mount ears are too close, and some where they are too far apart. OK spread them or close them down a bit/ But you need to bend both ears 1/4" in the same direction. If the other arm didn't fit either than the problem could be the frame ears. IMHO your problem is w/ the arm not the frame.

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Originally Posted by CraigS

To me that is a problem w/ the control arm. One arm fits both sides of the car while other does not, and it's off by 1/4"? No way. Call FFR and get a new arm. BTW most of the problems w/ fitting are that the mount ears are too close, and some where they are too far apart. OK spread them or close them down a bit/ But you need to bend both ears 1/4" in the same direction. If the other arm didn't fit either than the problem could be the frame ears. IMHO your problem is w/ the arm not the frame.

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I agree with your assessment. The fact that the other arm is perfect tells us the path of least resistance is to replace the arm. Hopefully they can get a new one out asap. Difficult to find a suitable component in the aftermarket.

They’re pretty good about getting parts out quickly if in-stock. With the custom geometry of the suspension, I have no idea of there’s a comparable aftermarket piece.

Rest assured though, even if you have to skip doing one corner of suspension for now, there’s plenty to keep you busy until the replacement comes in.