MCA Suspension "Traction Mod"

[Ohio Enthusiast]

Originally Posted by RToyo86

Is there notable improvement to ride quality? primarily street driven in my yellow/B6 setup.

I installed the GP Sports one a few days ago, but with the rainy weather I don't have too much to report.

Ride quality does seem to be more compliant in the rear, especially on sharp bumps (like bulging seams or those rubber speed bumps). Before the rear always felt more jarring than the front when hitting those, now it's about the same or slightly better in the rear. Also, taking the aforementioned rubber speed bumps at an angle would shake the rear a lot, even at idle speed (~4 MPH). Now it's significantly better.

I'm on RCE Yellows with the stock '18 shocks and a bunch of stiffer bushings/inserts in the drivetrain and rear subframe (plus the GP Sports kit replaces the bottom Whiteline subframe bushing inserts - fronts are part of the relocating piece, rears are dedicated aluminum parts).

I'll be sharing more detailed impressions once weather improves and I get to drive the car more aggressively.

[norcalpb]

Originally Posted by dragoontwo

Looks like they include a different subframe bolt and some bushings.

This actually fixed my main grip with this product. The previous version would lock the chassis to the subframe via the unused trailing arm pick up point, which probably wouldn’t break anything, but that’s still a lot of undue stress on that tiny bracket.

The new design will work like a skateboard truck which will allow the MCA bracket to move with the subframe. I imagine the new bolts were designed with less threads because the amount of threads on the stock bolt may damage the bushings when the bushings are flexing side to side.

[autoracer86]

Originally Posted by norcalpb

This actually fixed my main grip with this product. The previous version would lock the chassis to the subframe via the unused trailing arm pick up point, which probably wouldn’t break anything, but that’s still a lot of undue stress on that tiny bracket.

The new design will work like a skateboard truck which will allow the MCA bracket to move with the subframe. I imagine the new bolts were designed with less threads because the amount of threads on the stock bolt may damage the bushings when the bushings are flexing side to side.

I wonder if that would introduce any downsides over the v1.

[norcalpb]

Originally Posted by autoracer86

I wonder if that would introduce any downsides over the v1.

Probably not, if anything the v2 will be the better overall piece as it functions more the way MCA had always intended. While the v1 consequently locks down the front half of the subframe to the chassis, which can be good for handling response, there are better, more direct ways of firming up the subframe such as bushings, inserts or stoppers.

That being said the v1 should not cause any issues whatsoever.

[RToyo86]

Couldn't help my self and ordered. Is there any recommended hardware I should replace not included in the kit?

[autoracer86]

Originally Posted by RToyo86

Couldn't help my self and ordered. Is there any recommended hardware I should replace not included in the kit?

I was reading from a post in a uk gt86 forum that the bolts holding the trailing arm on are stretch bolts.



"Went to fit it today. Its quite incredible the stock arm angle when the wheels are hanging.

You can see from the pictures the difference these mounts make. Once the weight of the car is back on the wheels the arm will be pretty much horizontal now.

Three things that aren’t mentioned in the instructions -

1) That its much easier to do this with the wheels off. I’d have saved a lot of time by starting with removing the wheels.

2) The torque settings (140nm for the large bolt going into the floor. 70nm for the two small bolts next to it and 110nm for the bolts either end of the trailing arm)

3) The bolts either end of the trailing arm cannot be reused as they stretch. I found this out the hard way. So the car is still on axel stands waiting for 4x new bolts to turn up. Part No - SU003-02819 (around £11 each!)"
- https://www.gt86.org.uk/forums/forum...ction-mod-kit/

[Ohio Enthusiast]

Originally Posted by autoracer86

I was reading from a post in a uk gt86 forum that the bolts holding the trailing arm on are stretch bolts.

"3) The bolts either end of the trailing arm cannot be reused as they stretch. I found this out the hard way."

Not sure how he determined they're stretch bolts. The repair manual marks them as non-reusable, yes, but so are the bolts holding the subframe to the car and the nuts holding those trailing arm bolts (which he didn't order). AFAIK non-reusable fasteners are not necessarily stretch bolts (or torque-to-yield). I do agree that the best approach would be to replace any fasteners that are marked as non-reusable by the OEM.

In practice, the consensus on the Internet seems to be that stretch/TTY fasteners are fine to reuse (even engine head bolts) at least a few times (supported by accurate length measurements (the "real" way to confirm stretch bolt degradation when you know the stretch specs) and yield torque measurements, as well as by anecdotal evidence). I've done quite a bit of suspension work on my BRZ and never replaced any hardware that was marked non-reusable. So far everything torqued correctly to the specs without any problems (including these bolts).

[RToyo86]

Noted thank you.
Photo from MCA shows that they provide new subframe to chassis bolt and upper bolt, so would I only need 2x bolts to freshen everything installed?

[autoracer86]

Originally Posted by Ohio Enthusiast

Not sure how he determined they're stretch bolts. The repair manual marks them as non-reusable, yes, but so are the bolts holding the subframe to the car and the nuts holding those trailing arm bolts (which he didn't order). AFAIK non-reusable fasteners are not necessarily stretch bolts (or torque-to-yield). I do agree that the best approach would be to replace any fasteners that are marked as non-reusable by the OEM.

In practice, the consensus on the Internet seems to be that stretch/TTY fasteners are fine to reuse (even engine head bolts) at least a few times (supported by accurate length measurements (the "real" way to confirm stretch bolt degradation when you know the stretch specs) and yield torque measurements, as well as by anecdotal evidence). I've done quite a bit of suspension work on my BRZ and never replaced any hardware that was marked non-reusable. So far everything torqued correctly to the specs without any problems (including these bolts).

Good to know. His post was the first I saw of anyone replacing those bolts the internet is full of opinions lol.

I am still not sure why you even need to undo that tiny that goes from the subframe to the body. Also personally I would support the subframe with a jack and go 1 bolt at a time. I have yet to see anyone even MCA support the subframe during install.

I followed every tip and trick I could find when doing my subframe bushings and it made the install pretty easy. Oh and speaking of stretch bolts I don't recall anyone saying to replace those big subframe bolts lol

[autoracer86]

Originally Posted by RToyo86

Noted thank you.
Photo from MCA shows that they provide new subframe to chassis bolt and upper bolt, so would I only need 2x bolts to freshen everything installed? I noticed that page is from V1 run, can anyone confirm if V1 had supplied hardware?

Yeah I think so. I will probably snag some new bolts myself as most of my stuff is pretty crusty looking

[Ohio Enthusiast]

Originally Posted by autoracer86

I am still not sure why you even need to undo that tiny that goes from the subframe to the body.

The MCA mod has an attachment point that uses that bolt (the little "cup" thing).

Originally Posted by autoracer86

Also personally I would support the subframe with a jack and go 1 bolt at a time. I have yet to see anyone even MCA support the subframe during install.

Supporting the subframe isn't really needed when doing one bolt at a time and only needing access to the bottom. I didn't support the subframe and had no issues threading the bolt back by hand until snug, doing one bolt at a time (and the GP Sport kit touches all 4 bolts (front for the mod and rear for the aluminum collars)). The subframe does droop a little with one bolt removed, but it's really minor.
You'd need to support the subframe for the subframe bushing insert kit (Whiteline KDT922) because you need access to the top of the subframe as well and need more clearance (hence removing two bolts at a time which causes the subframe to droop quite a lot).

[autoracer86]

Originally Posted by Ohio Enthusiast

The MCA mod has an attachment point that uses that bolt (the little "cup" thing).



Supporting the subframe isn't really needed when doing one bolt at a time and only needing access to the bottom. I didn't support the subframe and had no issues threading the bolt back by hand until snug, doing one bolt at a time (and the GP Sport kit touches all 4 bolts (front for the mod and rear for the aluminum collars)). The subframe does droop a little with one bolt removed, but it's really minor.
You'd need to support the subframe for the subframe bushing insert kit (Whiteline KDT922) because you need access to the top of the subframe as well and need more clearance (hence removing two bolts at a time which causes the subframe to droop quite a lot).

What's this little cup thing now ? Are we talking about where it connects to the subframe itself like where the big bolt goes ?

From looking at photos it seems to be you would remove the trailing arm bolt and the big subframe bolt and that's it beside the plastic cover if that's in the way at all.

Well needed or not easy enough to support it so there is no movement but again thanks for the insight

[DocWalt]

I see no need to replace the bolts that he mentioned, they're not stretch/TTY bolts.

[Ohio Enthusiast]

Originally Posted by autoracer86

What's this little cup thing now ? Are we talking about where it connects to the subframe itself like where the big bolt goes ?

Yep, that's what I was referring to.