PSA: MCA traction mod failure

[Code Monkey]

Installed 9/18/2018 on my 2017 BRZ at 12,290 miles.
Taken off May 2022 at 27,570 miles.
Installed 5/15/2022 on my 2022 BRZ at 825 miles.
Taken off 11/16/2025 at 16,030 miles.
Both cars heavily tracked.

Left side cracked, right side broken apart.

If you have this mod on your car, my advice is to inspect/remove immediately.

[bmacfrs]

Maybe that make the product from GKTech more attractive. https://us.gktech.com/products/86-gr...-mod-arm-combo

[redlined600]

What do you have for subframe bushings?
To me it looks like the base mounts to the arm/inner sleeve/bolt which are fixed and the flanges mount to the subframe which are moving (due to bushing deflection). If that's the case, the failure makes sense.

Thanks for pointing this out.

[Code Monkey]

Whiteline subframe bushings on the '17, OEM subframe bushings on the '22.

[Racecomp Engineering]

I'll have a look at mine tomorrow morning.

- Andrew

[Tatsu333]

Between this reported failure and my experience with corrosion of the brackets despite very low mileage, I've gotten really nervous about the durability of my MCA Traction Mod V1. So, I've decided to replace it with something else.

In searching around this morning, I came across this option that I had never seen before:

https://www.justengineering.ca/shop/subaru/frs-brz-gt86-gr86-adjustable-traction-arms/

With it using a similar configuration to the MCA's but with what looks to be MUCH more robust materials and finish (and it being a Canadian shop in Quebec producing it ), I decided to pull the trigger. It's a bit pricey, but both relocates the pickup point and replaces the trailing links, so it saves the cost of the STI trailing links as well.

Of note is that it moves the pickup point both down by 50mm AND forward slightly, and the new trailing link is longer as a result. They say the forward position and longer arm are "to reduce the toe gain curve as much as possible to so it became more linear."

Anyway - there's a little over $600 CAD I didn't really have available now gone, but it will give me a bit more peace of mind...LOL.

[Ohio Enthusiast]

Originally Posted by Tatsu333

https://www.justengineering.ca/shop/subaru/frs-brz-gt86-gr86-adjustable-traction-arms/

With it using a similar configuration to the MCA's but with what looks to be MUCH more robust materials and finish

This looks like a combination of the MCA mod (attaching to the original mounting point on the subframe) and the GP Sport mod (attaching to the frame). I wonder what side-effects this will have - it seems to be tying the subframe very rigidly to the frame.

As the price also includes arms with spherical bearings it's actually quite good. Some folks reported that trailing arms with stiffer bushings make the pickup point relocation mods shine, so this should be a nice mod.

[Tatsu333]

Originally Posted by Ohio Enthusiast

This looks like a combination of the MCA mod (attaching to the original mounting point on the subframe) and the GP Sport mod (attaching to the frame). I wonder what side-effects this will have - it seems to be tying the subframe very rigidly to the frame.

I've never quite understood the argument against / around the GP Sports ones (and now these) in that regard, because there already is a stamped metal bracket / brace tying in that subframe mounting bolt to the same point that these traction mod variants do. They both just replace that piece, where it's left in place with the MCA Traction Mod.

I do like that with these vs. the GP Sports ones, there is the extra structure tying to the original trailing link mounting bolt. My worry with the GP Sports design when I was comparing them back in the day was that the relocated mounting point was just kind of floating off the end of the flat bracket, and this addresses that. Not that there is a ton of load going through that pivot, but it just made me a little nervous...

Anyway - we'll see how it goes once I receive the new setup!

[Ohio Enthusiast]

Originally Posted by Tatsu333

I've never quite understood the argument against / around the GP Sports ones (and now these) in that regard, because there already is a stamped metal bracket / brace tying in that subframe mounting bolt to the same point that these traction mod variants do.

The OEM bracket only supports the bolt, not the subframe itself. The GP Sport piece has a shape that goes into the subframe bushing void and acts like a stiffer insert (compared to Whiteline KDT922, for example).

As far as I understand the concern is because all the suspension arms in the rear are mounted to the subframe, not the chassis. The GP Sport mod moves the trailing arm pickup point to the chassis, which could mess with the suspension as the subframe shifts but the trailing arm doesn't.

With that being said, I have the GP Sport mod on my car and I don't notice any issues, but I don't track a lot and only had for a year and a half and 10,000 miles.

[redlined600]

TBH, I don't think any of the relocation brackets are optimal because they all fight the OEM design philosophy in some way or another.
I guess if you have rigid subframe mount bushings it's a moot point.

[StraightOuttaCanadaEh]

Have you informed them of this? Perhaps they can change the type of steel being used or welding method or some other facet of the design. I would like to get one in the future

[NoHaveMSG]

Originally Posted by Tatsu333

I've never quite understood the argument against / around the GP Sports ones (and now these) in that regard, because there already is a stamped metal bracket / brace tying in that subframe mounting bolt to the same point that these traction mod variants do. They both just replace that piece, where it's left in place with the MCA Traction Mod.

I do like that with these vs. the GP Sports ones, there is the extra structure tying to the original trailing link mounting bolt. My worry with the GP Sports design when I was comparing them back in the day was that the relocated mounting point was just kind of floating off the end of the flat bracket, and this addresses that. Not that there is a ton of load going through that pivot, but it just made me a little nervous...

Anyway - we'll see how it goes once I receive the new setup!

I’ve personally not a big fan of the way the trailing arm mounts on the GK kit to the chassis. It seems like it is putting a lot of sheer load on the mounting point even with the brace on it. Of course we haven’t see one fail so I am probably over thinking it.

[RToyo86]

I would recommend some fluid film or rust protection spray, I did mine spring 24 and soaked it the day I installed it. Cleaned it up this spring to install subframe inserts and did not see corrosion.

[norcalpb]

The V1 MCA traction mods were poorly designed IMO. The V2 fixed this from happening though.