What should I do next to get rid of the "unsettled" rear suspension?

[sms2022]

You mean this?
https://www.cjponyparts.com/upr-rear-vertical-link-billet-aluminum-pair-mustang/p/LCA9/

It has value but it's the last item on the Let's fix the rear end, list.

Gotcha. So you’d recommend the braces and white line bushing kit first?

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[shogun32]

Gotcha. So you’d recommend the braces and white line bushing kit first?

Yes. And the alignment dowels. Steeda/bmr and I thought Lethal had a kit too? It's stupid money for a bit of delrin rod, but I haven't yet Sat down and run off a bunch on my lathe.

https://www.steeda.com/steeda-s550-mustang-irs-subframe-alignment-kit-2015-all-555-4438.html

 

[MAGS1]

Yes. And the alignment dowels. Steeda/bmr and I thought Lethal had a kit too? It's stupid money for a bit of delrin rod, but I haven't yet Sat down and run off a bunch on my lathe.

https://www.steeda.com/steeda-s550-mustang-irs-subframe-alignment-kit-2015-all-555-4438.html

Unless you suspect (or have verified) that the rear subframe is more than a tad off, I really don’t see how the alignment dowels help unless you plan to drop the subframe somewhat frequently. Then I can see the value so that you make sure it’s lined up the same way every time. Are people’s rear subframes really that far off from factory??

 

[bnightstar]

What worked for me is: IRS Base Pack + FP Toe Link Bearing this made an insane difference in how the rear of the car is feeling. The IRS Base Pack (Alignment) helped the car during transitions left/right and the FP Toe Link bearing helped with car putting power down out of corners. Minimal NVH added.

 

[shogun32]

Are people’s rear subframes really that far off from factory?

Uhh you new here? It's a Ford...

Repeatability aside, you have to drop the frame to get the lockouts in, so might as well fix it the whole way. Also it removes massive slop and assists the braces in their task.

Without the dowels and Ford factory quality, your Steeda braces might not even go on, it's twisted so far off.

 

[bnightstar]

Unless you suspect (or have verified) that the rear subframe is more than a tad off, I really don’t see how the alignment dowels help unless you plan to drop the subframe somewhat frequently. Then I can see the value so that you make sure it’s lined up the same way every time. Are people’s rear subframes really that far off from factory??

The holes are too big when you transition the car you can feel how the subframe moves in the space around the bolts the dowels effectively don't allow the subframe to move when transitioning like in a left/right S type of corner. In other words the dowels help a lot with weight transfer side to side making the rear much more predictable IRS base kit helped me drop 0.5 sec from my average lap times that's insane difference.

 

[MAGS1]

Uhh you new here? It's a Ford...

Repeatability aside, you have to drop the frame to get the lockouts in, so might as well fix it the whole way. Also it removes massive slop and assists the braces in their task.

Without the dowels and Ford factory quality, your Steeda braces might not even go on, it's twisted so far off.

Ha! Yeah I’m new (sarcastic tone here) .

Fair point, if you’re already dropping it for the lockouts there’s no harm in adding the dowels. FWIW when I did my Steeda IRS braces I didn’t have to make any adjustments to the IRS to get them to fit properly. Maybe I have a unicorn car?

 

[Aless_andro00]

This is a daily driver but I drive it in a, shall we say, spirited manner at times. It's all for fun, not a track car. When I go on roadtrips I seek out the twisties. My last 2 cars were a 2013 Scion FR-S and 2017 Mazda Miata so you can see what type of car I gravitate towards.

Mods i've done to my 2023 GT Nite Pony Package (came with 255 Pirelli AS, so i guess it's not 100% a base car with 235s).

FRP track springs
FRP track shocks
Steeda Camber plates
Steeda Rear Camber adjustment kit
Steeda sway bars front and rear
FRP front control arms
FRP shock tower brace, paired with OEM cowl extension (PP1 setup)
PP1 brace (k brace?)
I think that's everything.

Riding on SVE SP1 19x10s, 275/40r19 PS4S square.

Alignment as follows, even on both sides unless specified L and R:
Front Toe: Toe out -0.07 deg.
Front Camber: -2.1 deg.
Caster: -7.1 deg L, -7.0 R

Rear Toe: 0.07 deg L, 0.08 deg R
Rear Camber: -1.6 deg L, -1.5 deg R


The car MOSTLY handles really well, surprisingly well and very solid for such a heavy car, but the new stickier tires really have exaggerated that feeling of the rear being disconnected from the front... it feels like there's a big hinge in the middle of the car and it just takes a second for the rear to catch up with what the front is doing. The front turns in like a motha****** though and feels fantastic. I just want the car to feel a bit more connected front to rear.

I haven't done the FRP rear knuckle to toe link bearings which I am guessing makes a good difference here especially with beefier tires and suspension. I was thinking maybe also i made a mistake spec'ing negative toe in the front which makes the front end dive into a turn but the rear is positive which makes it lag behind slightly? I have seen parts like the Steeda IRS Rear Support Braces which im not sure help with this, or if that's more for wheel hop-i dont really launch the car hard so I dont care about wheelhop tbh. I don't want to go nuts with lockouts etc because I still want the car to be decently comfortable eating roadtrip miles and I dont want to hear it from the wifey when we take my car, so really loud solid mounts etc are no good for me.

Thoughts/suggestions? Let me know if I missed something.

Your car's handling might feel a bit off because of your current toe setup—negative toe in the front and a bit of positive toe in the rear. Negative toe in the front can make the steering really responsive but also a bit twitchy. Positive toe in the rear stabilizes things, but it might slow down how quickly the back end responds. If you try adjusting to neutral or even slightly negative toe in the rear, it could make the car feel more connected, with the rear following the front better. Making small changes like this could make a big difference.

 

[WD Pro]

The holes are too big when you transition the car you can feel how the subframe moves in the space around the bolts the dowels effectively don't allow the subframe to move when transitioning like in a left/right S type of corner. In other words the dowels help a lot with weight transfer side to side making the rear much more predictable IRS base kit helped me drop 0.5 sec from my average lap times that's insane difference.

The subframe does not move around the bolts, that's fixed once everything is torqued up, they even have teeth to bite into the frame. A picture (which also shows how well Ford align some of these cars at the factory) :

The dowels ensure concentricity (of the bolt shank and that toothed bush inner tube) when assembled, and repeatability for future disassembly / reassembly.

The movement is from the 'soft' bush that surrounds those items

WD

 

[TeeLew]

So by the sound of it you are saying the FRP toe link bearing adds that much NVH? That's surprising it adds that much.

It adds zero, IMO. It gives the rear a lot of stability. Lock the rear subframe one way or another. Add some rear camber.

 

[NightmareMoon]

I knew this thread was going downhill as soon as the OP mentioned rear suspension.

So everyone who ever spent a dime on a rear brace or alignment dowel shows up and says you have to do all that.

My 2c was that I got zero NVH from the LRCA bearing and toe bearing. If you do those last after 5 other stiffening mods, I could see it, but if thats all you do, the rear gets a little more predictable and NVH may not be impacted at all. It wasnt on my car.

Your alignment is pretty good but I’d add some more rear camber and a bit more on the front. I’d also zero the toe. Your springs and shocks are only mild upgrades, coming from the BRZ/miata you may want stiffer and better shocks and springs. I have some experience with those cars.

Doing the rear LCA bearing is a PITA. I wouldnt throw too much money at rear braces and bearings, if you do, my 2c is address the big LCA and toe link and then see if you’re happy.

 

[GrabberBargeCaptain]

Solid advice everyone- i like the smidge of negative toe in the front for some steering immediacy but i might try zero toe. I really dont want toe-in on the front. The car is extremely stable even on rough roads, at least at the speeds i drive it at. Maybe on a track the negative toe would cause wandering, not sure. I have yet to see abnormal tire wear but I only have 5k miles on it.

I'm pretty happy overall with the stiffness of the car overall and wouldn't want much more-the stiffer sidewalls on the PS4S bumped it up another notch. I'll reflect and see where I go from here. Definitely sounds like I should do that little donut bearing at minimum. LCA bearing: https://www.steeda.com/steeda-s550-...spherical-bearing-2015-2016-all-555-4117.html is this the one people are referring to?

I already have the alignment dowels, forgot to mention.

 

[Oakley]

1. ford racing toe bushings (huge PITA install but worth it)
2. some kind of subframe lockout
3. big bertha bolt kit and keltech diff bushings (only the rear ones)
4. steeda adjustable rear shocks

that cured 99.9999% of my wheel hop and floatiness.

I have the spherical bearings for the LCA's, dual rate springs, and front adjustable steeda shocks in a pile waiting to go on the car which should get it the rest of the way there.

 

[Dana Pants]

The toe bearings are easy to install IMO. The knuckles aren’t held on by any particularly troubling fasteners and a push-pull kit does the job in moments.

 

[CrazyHippie]

I have this exact problem and that’s the perfect description, like a hinge. My charger, on 10 year old rubber and weighing 1200lbs more, feels more planted in the corners. what I’m hearing is steeda brace for sure, white line bushings, and what about the upr billet irs links?

Hi, the Steeda Stop The Hop kits include the following:

Ultimate Street - Subframe alignment and support hardware, adjustable toe links, vertical links with Delrin (hard) bushings, subframe support braces.

Ultimate Handling: The same except that vertical link bushings are polyurethane (softer than Delrin) and they include rear diff bushings.

There are additional kits with varying components and I like that all of the kits are designed to work together.

Good luck!

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