Alignment & Support Kit vs. Insert Bushings vs. Replacement Bushings vs. lockout kit?

[rpinkstn]

I"m looking for input on the best method to align and support the IRS subframe assembly in an S550.

2017 Mustang GT Premium
6R80 automatic transmission
Chasis and suspension are 100% original except for the PP1 strut tower and firewall braces.
The car is a DD and might see a drag strip or road course once or twice a year at local events.

I plan to replace the shocks and struts soon but I want to address the IRS subframe first. What is the best option for aligning the IRS subframe and reducing the amount of movement? Reading through several threads on here as well as manufacturer's product descriptions, I'm not sure which product is the best option for this car. I've looked at the following products from Steeda:

Subframe Alignment and Support Kit (Steeda P/N 555-4450)
Link: https://www.steeda.com/steeda-s550-subframe-alignment-and-support-kit.html

IRS Subframe Insert Bushing Kit (Steeda P/N 555-4045)
Link: https://www.steeda.com/steeda-555-4045-mustang-subframe-insert-bushings

IRS Subframe Replacement Bushings (Steeda P/N 555-4046)
Link: https://www.steeda.com/steeda-555-4046-mustang-subframe-replacement-bushings

I've also seen several threads mention an "IRS cradle lockout kit" although I didn't find one on Steeda's website, only on BMR's website. There are a lot of options that all seem to address the same issues. How do you choose which product is the best option?

Based on my previous experiences with basic GM G-body suspension mods I would just choose the IRS Subframe Replacement Bushings (Steeda P/N 555-4046) and call it done but I found several posts where people said the aftermarket polyurethane bushings were too hard and transferred rear-end noise into the car. I don't know if that's correct.

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[s550_kenny]

I was also researching this and was looking into the BMR cradle lockout kit so I'll be watching this thread.

 

[tdstuart]

Replacing the bushings is kind of a pain in the ass. I see people commonly do inserts rather than replacing the bushings.

It looks like if you replace the bushings you wont need to do the alignment kit as the hole diameter will already be tighter.

 

[shogun32]

IRS Subframe Replacement Bushings (Steeda P/N 555-4046)
Link: https://www.steeda.com/steeda-555-4046-mustang-subframe-replacement-bushings

This is a copy of whiteline's kit (KDT953) they quit making. You will need to literally cut and burn out the Ford original just like you do for the Camaro.

For much less effort, get the white line bushing inserts (KDT943) instead. Then Steeda centering sleeves and a brace. Cb005 or Steeda, pick one.

The bmr or other Steeda bushing inserts are harder material and will transmit some minor unobjectionable amount of road noise. If you want Acura quiet you're in the wrong car to begin with.

You also want to fix the differential mounts. Here too I recommend whiteline instead of Steeda or bmr.

 

[rpinkstn]

Thanks for the responses, good info!

As far as burning the old bushing out, this is how we did it on the G-body cars. No big deal. The front A-arms and rear trailing arms are stamped steel parts and were easy to remove from the vehicle. Then we just burned out the old rubber bushings with a torch. I've watched a couple of videos of replacing the IRS cradle bushings on an S550 and I see now that it does look like a much more involved process since the entire cradle has to be removed from the vehicle (at least that's what it looks like has to happen from the videos I've seen).

Regarding noise, I wasn't really too concerned about it., but a few threads I read made it sound like it was a major issue. I have a 3" cat-back exhaust system on it already so not looking for "Acura quiet". In the G-body cars, we always replaced the factory rubber bushings with polyurethane bushings (usually Energy Suspension) and never noticed any additional road noise or ride harshness. It was a cheap, easy upgrade that was absolutely worth it, especially on the cars with higher mileage on the suspension. This is why I was originally leaning toward just replacing the bushings rather than adding bushing "supports". However, it does look like a lot more work for not much benefit over the bushing supports.

Follow-up question: What is the difference between the "bushing inserts" and "bushing supports"? I can see the support kit includes two oval shaped pieces vs all round pieces. Other than that, the pieces appear to be similar other than color and price.

Sorry for rambling. I'm bored a work this morning.

 

[shogun32]

What is the difference between the "bushing inserts" and "bushing supports"? I

Synonyms. Yes the whole IRS has to come down if doing replacements. Unless you're very talented.

 

[Magony15]

The Whiteline KDT 953 is better than Steeda's and it still is available on their website. It aligns the subframe and eliminates the need for braces. I can launch my MT82 without wheel hop. No change in NVH.

 

[rpinkstn]

The Whiteline KDT 953 is better than Steeda's and it still is available on their website. It aligns the subframe and eliminates the need for braces. I can launch my MT82 without wheel hop. No change in NVH.

Excellent picture! Thank you for your post. That looks like a lot of work there with really nice results.

 

[rpinkstn]

If I don't want to mess with dropping the entire rear subframe to replace the bushings, I'd like to install either the BMR Level 1 Cradle Bushing Lockout kit (CB010) or the Steeda Subframe bushing support kit (555-4437). What is the *functional* difference between these two kits?

 

[shogun32]

What is the *functional* difference between these two kits?

nothing. The Steeda version is a bitch to install.
But let me help you further in your quest. The answer you're looking for is spelled WhiteLine.
https://whitelineperformance.com/products/kdt943-bushing-kit

and while you're at it, get their Diff inserts as well.
Hot damn, they've discontinued KDT934 as well.

The Differential 'pucks' you want the black RED version from Steeda. Unless they also make their own version of the 934. In any event some amount of 'singing' will result when you hit the resonant frequency. For example if I get off the throttle at 70mph in 5th or 6th the diff will sing. It's not loud or conversation killer but it's definitely there. Get back on the gas and it goes away. At lower speeds, eg. 50-60mph it's probably singing but it's hard to hear.

 

[rpinkstn]

@shogun32

Thanks for posting all this information today. Things are slow at work right now so I'm deep down the rabbit hole on this subject.

BTW, Lethal Performance still shows the KDT934 diff. inserts in stock here: https://www.lethalperformance.com/w...-voiding-of-oem-bushing-whiteline-kdt934.html

Thanks for that recommendation.

As for the Whiteline subframe insert bushings (KDT943), it looks like those are polyurethane rather than steel or aluminum like the BMR and Steeda pieces - is that correct? I would expect that to allow the IRS subframe assembly to move around much more than the BMR "lockout" and Steeda "support" kits. Can you elaborate on why you'd recommend the Whiteline pieces over the others?

Thanks,

 

[shogun32]

Can you elaborate on why you'd recommend the Whiteline pieces over the others?

they are softer, and impart less noise. the harder versions you get vibration from the diff and the wheels via the IRS into the body. It's not huge at all, but it's there. Plus let I looked the WL version was a fraction of the price. All my cars (except the M1) were done with WL parts to much satisfaction. Ok, the GT got the Steeda 'support' which is why I know they are a bitch. I've also done the CB005/CB072 on another car. And the Steeda IRS bracing on the GT and now M1. So I've used all of them.

don't neglect to get the alignment dowels. If you're gonna drop the IRS, you might as well do all the useful bits.

 

[rpinkstn]

they are softer, and impart less noise. the harder versions you get vibration from the diff and the wheels via the IRS into the body. It's not huge at all, but it's there. Plus let I looked the WL version was a fraction of the price. All my cars (except the M1) were done with WL parts to much satisfaction. Ok, the GT got the Steeda 'support' which is why I know they are a bitch. I've also done the CB005/CB072 on another car. And the Steeda IRS bracing on the GT and now M1. So I've used all of them.

don't neglect to get the alignment dowels. If you're gonna drop the IRS, you might as well do all the useful bits.

@shogun32
Thanks again for taking the time to post all this information today. Very helpful!

 

[chuckhammer]

I went with UPR's version of the diff bushing inserts. Their kit is $55 and includes red (softer) and black (stiffer) poly pucks. I'm running the red ones. I used to hear a touch of diff whine at highway cruise speeds with the windows up and radio off. I've since switched out the OEM diff fluid for Redline 75W-110 and now that noise is gone.

Ditto what's already been said about doing it all at once. Springs, too, if you were planning on it. Use the alignment dowels when you bolt it back up and then go get an alignment. One and done.

There are a couple different options for the alignment dowels. BMR's are a stiff poly whereas Steeda's are hard Delrin. The Steedas are two different sizes with the smaller diameter ones meant for the rear holes so they can slip past the flange on the bottom. That means they have slightly more slop than the BMRs. However, if you're already lowering the subframe you can just drop them in from the top to avoid that hassle.

A 2' crow bar with a pointed end and a spare, small jack (~1.5T) are very handy when doing this job. They let you maneuver the subframe into place with fewer curse words and busted knuckles. It has to be positioned very accurately for the bolts to go through the dowels and thread into the chassis.

 

[rpinkstn]

I went with UPR's version of the diff bushing inserts. Their kit is $55 and includes red (softer) and black (stiffer) poly pucks. I'm running the red ones. I used to hear a touch of diff whine at highway cruise speeds with the windows up and radio off. I've since switched out the OEM diff fluid for Redline 75W-110 and now that noise is gone.

Ditto what's already been said about doing it all at once. Springs, too, if you were planning on it. Use the alignment dowels when you bolt it back up and then go get an alignment. One and done.

There are a couple different options for the alignment dowels. BMR's are a stiff poly whereas Steeda's are hard Delrin. The Steedas are two different sizes with the smaller diameter ones meant for the rear holes so they can slip past the flange on the bottom. That means they have slightly more slop than the BMRs. However, if you're already lowering the subframe you can just drop them in from the top to avoid that hassle.

A 2' crow bar with a pointed end and a spare, small jack (~1.5T) are very handy when doing this job. They let you maneuver the subframe into place with fewer curse words and busted knuckles. It has to be positioned very accurately for the bolts to go through the dowels and thread into the chassis.

@chuckhammer

Thanks for the info. Just ordered the UPR IRS bushing lockout kit, location sleeves and differential insert kit. It was all on sale and had free shipping. Looking forward to getting these parts installed!

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