PSA: MCA traction mod failure

[Tatsu333]

Originally Posted by norcalpb

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

From what MCA told me when I inquired about upgrading when V2 came out, and from what is clearly visible, the difference between V1 and V2 was the addition of the polyurethane inserts where it bolts through to the subframe, and according to MCA that change was made primarily for user complaints of noise (which I never experienced). The overall construction and design are otherwise unchanged.

[Tatsu333]

From Justin at Just Engineering (who has been very responsive, by the way):

"The main goal of our design was to reduce anti squat and produce a more linear anti squat change during suspension compression (hence the longer length). But this had to also be legal according to the Formula D regulations. For road racing, the same theories apply, and the benefit is more stability and better feel of the rear during cornering.

So, the best way to do all of this was sort of a mix of the GK tech's design and MCA's design. We had seen their designs when I was designing ours and they're both good but each didn't meet the design goals we had.

The bracket is meant to be used with solid subframe bushings. Otherwise, the subframe will want to move while the bracket is trying to stay fixed."

When I asked him about using their brackets with OEM subframe bushings, he said:

"Good question! I don't think it'll break anything, it'll act like a solid bushing on those 2 front attachment points in the horizontal direction.

Of all the people who bought this from us, none of them have had problems with stock subframe bushings. So, this tells me that even if theoretically it isn't perfect, in the real world it still works perfectly fine."

With all that, I've decided to go ahead with them. They don't stock any pre-made units, so they will be fabricating and finishing mine sometime next week, and hopefully they'll ship out towards the end of the week or the week after.

[Racecomp Engineering]

Originally Posted by norcalpb

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

Originally Posted by Tatsu333

From what MCA told me when I inquired about upgrading when V2 came out, and from what is clearly visible, the difference between V1 and V2 was the addition of the polyurethane inserts where it bolts through to the subframe, and according to MCA that change was made primarily for user complaints of noise (which I never experienced). The overall construction and design are otherwise unchanged.

My V1 look fine after inspection. I may get a set of either the V2 or the GP Sports over the winter...I'll have to look into it a bit more.

- Andrew

[Tatsu333]

Originally Posted by Racecomp Engineering

My V1 look fine after inspection. I may get a set of either the V2 or the GP Sports over the winter...I'll have to look into it a bit more.

- Andrew

Mine also look fine structurally (no visible cracks or signs of fatigue), but the severe degradation in the finish over such little mileage with mine was a bit shocking. I'm also not putting the same kind of heavy track use on my car as some other users, but...I'm a bit paranoid. LOL

[autoracer86]

Just checked mine I also checked the tq on all the bolts. My MCA still look pretty much brand new and the bolts have not loosened

I have 16 track days and 6k street miles since install 6 months ago. So I would hope they still look good ha

[norcalpb]

Originally Posted by Tatsu333

From what MCA told me when I inquired about upgrading when V2 came out, and from what is clearly visible, the difference between V1 and V2 was the addition of the polyurethane inserts where it bolts through to the subframe, and according to MCA that change was made primarily for user complaints of noise (which I never experienced). The overall construction and design are otherwise unchanged.

So keep in mind I am not an engineer, but this is my theory. I think MCA makes great products, but I am not a fan of this one.

I've also never heard anyone complain of noise either, but IMO it's smarter from a business standpoint to say the change was to address noise than to say our old design was compromised, we are cancelling that design and releasing a new one.

Check this out:



The blue circled bolt is connected to the subframe and the orange circled bolt is connected to the frame of the vehicle. This could be considered to have the same effect as solid subframe bushings which prevents subframe movement, but with the traction mod there is much more leverage on a much thinner piece of metal than with a metal replacement bushing.

Below is an old YouTube video from Whiteline showing how much the subframe moves relative to the frame with stock bushings, which I imagine OP's Gen 2 has. The movement could be considered to be significant:

Now look at OP's failure:



The traction mod snapped in two right next to where the chassis mounted bolt goes, which is where the mod is most securely connected.

Looking at the V2's:



The chassis mounted bolt, not the subframe bolt goes through a poly bushing, which seems to prevent shock from subframe movement being transferred directly to the frame of the mod. But even with added flexibility, if the durometer of the poly bushings is higher than stock subframe bushings there will still be tension, but a failure becomes less likely.

I personally run GP Sports because with their design the new trailing arm mounting point becomes completely independent of the subframe.

[Tatsu333]

Originally Posted by norcalpb

The blue circled bolt is connected to the subframe and the orange circled bolt is connected to the frame of the vehicle. ..

...The traction mod snapped in two right next to where the chassis mounted bolt goes, which is where the mod is most securely connected.

...The chassis mounted bolt, not the subframe bolt goes through a poly bushing, which seems to prevent shock from subframe movement being transferred directly to the frame of the mod. But even with added flexibility, if the durometer of the poly bushings is higher than stock subframe bushings there will still be tension, but a failure becomes less likely.

Yeah, what I meant by "subframe bolt" is the bolt that attaches the subframe to the body, not the Traction Mod bracket to the subframe. We're talking about the same bolt location.

I agree that the V2 would allow for more movement around that bolt, and that MCA's communication to me could very well have been a CYA way of explaining a fix for a different issue. If anything, though, I would see that introducing a possible second point / mode of failure with the head of the bolt being somewhat less supported than the original design / more leverage being put on the shaft of the bolt as it passes through the OEM reinforcement bracket that ties that bolt location to the chassis if there is any horizontal or twisting force being applied. It essentially puts the head of the bolt kind of "free floating" (albeit with tension applied through the bushing). That said, given the orientation of the bolt and the subframe bushing, you'd expect that virtually all movement there is vertical, so that might be a non-issue.

Originally Posted by norcalpb

I personally run GP Sports because with their design the new trailing arm mounting point becomes completely independent of the subframe.

From what I understand, that has been the argument against this design from those that don't like it because they feel that mounting point *should* move with the subframe in concert with others in the rear suspension, as it does with the OEM design.

Then there's the GK Tech design that's different again, and the Just Engineering one that I've ordered that's also different...

So which is better?

They're all different approaches to the same idea of relocating that mounting / pivot point to reduce anti-squat, and each has their own compromises. What seems to be universal is that the idea of reducing anti-squat is worthwhile on this chassis, and having experienced the effect, I definitely agree with that!

For me, I have always been a little worried about the material thickness used in the MCA bracket, and with the corrosion seen on mine with so little mileage, I have been a little *more* worried than before. That combined with this reported failure is why I'm now exploring alternatives.

[norcalpb]

Originally Posted by Tatsu333

Yeah, what I meant by "subframe bolt" is the bolt that attaches the subframe to the body, not the Traction Mod bracket to the subframe. We're talking about the same bolt location.

I agree that the V2 would allow for more movement around that bolt, and that MCA's communication to me could very well have been a CYA way of explaining a fix for a different issue. If anything, though, I would see that introducing a possible second point / mode of failure with the head of the bolt being somewhat less supported than the original design / more leverage being put on the shaft of the bolt as it passes through the OEM reinforcement bracket that ties that bolt location to the chassis if there is any horizontal or twisting force being applied. It essentially puts the head of the bolt kind of "free floating" (albeit with tension applied through the bushing). That said, given the orientation of the bolt and the subframe bushing, you'd expect that virtually all movement there is vertical, so that might be a non-issue.



From what I understand, that has been the argument against this design from those that don't like it because they feel that mounting point *should* move with the subframe in concert with others in the rear suspension, as it does with the OEM design.

Then there's the GK Tech design that's different again, and the Just Engineering one that I've ordered that's also different...

So which is better?

They're all different approaches to the same idea of relocating that mounting / pivot point to reduce anti-squat, and each has their own compromises. What seems to be universal is that the idea of reducing anti-squat is worthwhile on this chassis, and having experienced the effect, I definitely agree with that!

For me, I have always been a little worried about the material thickness used in the MCA bracket, and with the corrosion seen on mine with so little mileage, I have been a little *more* worried than before. That combined with this reported failure is why I'm now exploring alternatives.

I agree that connecting the trailing arms to the frame is something that departs from the original engineering of the car, but I'm just guessing it's OK since BMW does that with their cars.

[Tatsu333]

My Adjustable Traction Arms from Just Engineering just arrived. Initial pics on my journal page here.

I'm hoping to get them installed tomorrow. If not, my next opportunity will be sometime mid to late January...

[Tatsu333]

Ended up getting the new parts installed this morning because I wasn't willing to wait until late January...LOL.

Step-by-step install and pics on my journal page here.

Initial Driving Impressions

Doesn't feel any different in terms of ride or NVH vs. the MCA Traction Mod and stock arms. The subframe being tied in a bit more with the new bracket seems to have reduced a little bit of drivetrain bounce when accelerating away from a stop, but other than that, no really noticeable difference. Maybe felt like it put the power down a little better than even with the MCA Traction Mod installed, but that could totally be in my head, and I didn't push things too hard, because I'm on my snow tires right now.

Everything feels straight (LOL), but I'll definitely get an alignment done sometime between now and spring when I'll be putting new all-seasons on the car, because this will almost certainly have had some effect on toe at the rear. No rush since I only drive about 300-350 km per month, and won't be pushing hard on my snow tires anyway.