Steeda S550 Mustang Adjustable Differential Bushing Insert System - Urethane (2015-2023)

15 Review(s)
$10.00 (6%)
Steeda Autosports has once again taken the S550 Mustang to the next level of performance and comfort with our exclusive Adjustable Urethane Differential Mount Bushing Insert System for all 2015+ Mustangs!

Part Number: 555 4443
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Steeda Autosports has once again taken the S550 Mustang to the next level of performance and comfort with our exclusive Adjustable Urethane Differential Mount Bushing Insert System for all 2015-2021 Mustangs! When our engineers sat down to design this kit, we had to come up with a way to increase performance without sacrificing too much drivability and preserving the cars street manners per the driver's preference.

Unlike our competitors' kits that take 3-4 hours to install and force you to permanently modify the rear IRS suspension with a Sawzall, Steeda's does not! Steeda's kit installs in under 1 hour, is adjustable and can be easily removed - it simply doesn't get any better than this!

Minimize pinion angle changes, increase traction, eliminate wheel hop and differential deflection with Steeda's new kit. Made from high-strength urethane to Steeda's exact specifications and durometers, our kit comes with 2 different bushing options - our red 'street' 80 durometer bushings and our black 'performance' 90 durometer bushings. Both bushing options will increase performance while the red bushings offer the least increase in NVH as compared to the black. Like all kits on the market, our kit can add noticeable NVH due to increased transfer of gear whine noise problematic to some Super 8.8 IRS differentials.

Steeda's kit adds the strength and support the OEM bushings need to perform the way our customers intended. Once again, this is not a permanent modification - there is no drilling, cutting or pressing required. Simply loosen and remove a couple bolts and this kit installs in less than 1 hour. Bushings are included for both the front and rear differential mounting locations. Grade 10.9 hardware is included with zinc-plated washers.

Note: For hardcore enthusiasts that want ZERO pinion deflection, try our 555 4440 kit. This kit features aluminum bushing inserts. For race-use only as it will increase NVH and gear noise.

Note: This product may increase noise, vibration, and harshness (NVH) after installation. NVH may increase slightly with red/street bushing inserts, but more aggressively with black/performance bushing inserts. This product itself does not generate any additional NVH, rather it transmits existing rear differential noise into the cabin by firming up the OE bushings.

Product Benefits
  • Limits IRS differential movement while increasing traction and eliminating wheel hop
  • Adjustable stiffness with red or black bushings
  • Easily removable, not a permanent modification
  • 100% designed, manufactured, and made in the USA
  • Installs in 1 hour or less
  • Also fits the Mach 1, GT350, GT350R, and 2020 GT500

Note: Due to changes in the OE subframe bushings, the bushing inserts will not fit 2021 GT500's or 2022 Mustang's

CA Residents: Cancer and Reproductive Harm WARNING

Today we will be installing the Steeda S550 Differential Bushing Insert System. Lift and support the car by the chassis on a vehicle lift or jack stands. Place a jack underneath the front of the subframe to support it independently from the car. To install the rear IRS differential bushing, you must loosen the 2 rear 21mm bolts that hold the subframe in place. You can only remove these 2 21mm subframe bolts, if the front subframe brackets and bolts are securely fastened. Doing 1 side at a time, remove the differential 18mm bolt. Once the bolt is removed, install the urethane bushing with the provided large washer. First, insert the short billet aluminum spacer into the rear urethane bushing, and then install the bushing into place where the factory 18mm bolt was removed. Repeat the steps on the other side. Torque the 110mm long bolts to 129ft.lbs. To install the front bushings, locate the main subframe bolts. 2 blue ones that are 21mm hex headed bolts. Remove the 2 front bolts and the 4 13mm hex head bolts (2 per side) securing the front subframe support bracket to the chassis, allowing the subframe to droop down in the front. With the IRS drooped down, you can now remove the front differential bolt. Remove only 1 at a time. You are removing 1 factory bolt and replacing it with 2 new bolts. Then install the 7/8 headed 14mmx65mm long bolt and the 7/8 washer with blue loctite. From the rearward towards the front, in the same manner the stock bolt was. Torque to 129ft.lbs. Take the longer billet aluminum spacer and insert it in the front urethane bushing. Fit the bushing into place from the front side where the original factory bushing. Grease is included for ease of installation and is not required for operation. Bolt the front bushing into place with the provided 7/8 headed 14mmx35mm long bolt and washer with loctite. Torque to only 35ft.lbs. Repeat the steps for the other front differential bolt. Once both front IRS differential bushings are installed, tighten back up the subframe support bracket and subframe bolts. Torque the 21mm subframe bolts to 129ft.lbs and the 13mm bolts to 41ft.lbs. Thank you for choosing Steeda, where Speed Matters!
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Fitment & Features


Manufacturer: Steeda Autosports
Made in USA: Yes

Installation Information:

Level of Difficulty: Easy
Install Time: About 2 Hours
Tools Required: Basic Shop Tools
Install Video:

Vehicle Fitment:

Fits Model Year: 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023

Customer Reviews

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Average Customer Ratings


Stop the slop, stop the hop
My s550 is a convertible, and you could feel the rear end slop around on launches, and jump all around when cornering hard over choppy pavement. I use this car as a back county cruiser so I need more stability than stock offers, and the IRS is the basis of all stability. This kit along with the IRS Alignment Kit changes everything. Got it on sale, along with the bump steer kit. Rear end bites, takes power much better, front end corners and holds the line around the curve over expansion joints. This is the foundation of good performance: Hold everything together nice and tight.
Did you find this helpful?  1 of 1 Found Helpful
Use The Red Bushings For Street Car
If you are not used to it it is a very stiff drive at first even with the softer red bushings. I am fine with it now.
Did you find this helpful?  1 of 1 Found Helpful
Very good kit
Installed the red street pucks and can confirm that there's no NVH increase at all, at least with my setup, 6MT 3.55 gears.
Did you find this helpful?  6 of 6 Found Helpful
I have driven about 500miles using the black bushings. Live on a pretty rough road and have not noticed a change in NVH, but car does feel more rigid/planted. Very happy with product, easy to install
Did you find this helpful?  5 of 5 Found Helpful
planted rear end
I have had these in my 2017 GT PP for over 40k miles. I'd never go back to stock. I put the firmer bushings in as the car sees lots of track time and is my daily through summer and snowy winters. If you only add these and don't stiffen the rest of the drivetrain, you may regret it. Add the trans mount bushing and the shifter base bushing (or do yourself a favor and get the Tri-Ax). As soon as the whole driveline is stiffened, the clunk goes away, power delivery is smoother, and shifting is much snappier and less crunchy.
Did you find this helpful?  3 of 4 Found Helpful
Differential bushing kit
Great product, although I would have liked to see it combined with Steeda's through bolt kit which I also purchased to compliment this mod. Be warned though, this mod does require the IRS subframe to be lowered from the car in order to install it properly. I had to lower mine 10 1/2. I haven't driven the car yet, due to installing a slew of other Steeda parts, so I cannot report any data on NVH.
Did you find this helpful?  1 of 1 Found Helpful
Perfect fit
You don't really notice that these made any changes since I have done all the other Steeda suspension parts. But I can say install isn't difficult and you definitely notice the no movement when installed. I installed the street red bushings. And pretty happy with that feel for now. So I can talk about the black race set.
Did you find this helpful?  1 of 1 Found Helpful
Verified Buyer  
High quality
High quality product but I had to remove because even using the red street bushing supports, there was a significant increase in differential noise, both in terms of gear whine and frequent audible clunk sound when shifting (engaging or disengaging a gear).
Did you find this helpful?  11 of 12 Found Helpful
The difference is night and day
Hey guys I just recently installed the the Steeda IRS & Differential bushings (red bushings) along with the IRS alignment kit. All I have to say is WOW! I installed it myself in the garage. It was very straightforward and easy. The difference is night and day. The car would have some really bad exaggerated wheel hop. I didn't feel much confidence with the car on launch and handling. I almost started to question my driving skills. On handling you get a lot of the control back. The car becomes more predictable when the rear breaks loose. When launching, it dips and rips off the line with very minimal wheel hop to where the car can grip. It's a very very good confident feeling you get. The wheel hop I would say is about 95% gone. The 5% wheel hop that you do feel is very light and almost unnoticeable. Anyone who is in doubt or questioning on getting the kit, I highly recommend it and it's worth every single penny. You won't regret it!
Did you find this helpful?  9 of 9 Found Helpful
I am pleased to say the thud is gone
So I was unaware that people had seen an improvement in the thud after installing the diff bushing so I hadn't really paid attention to it at all. My car is a GT PP with a ver obvious and annoying thud. Well, after paying more attention to it today I am pleased to say the thud is gone. That being said, I did notice a more pronounced shift if that is possible. Maybe a little more notchy, but I like it. Feels like the shifter drops into place easier. Bushings look to be a great investment and mod!
Did you find this helpful?  4 of 4 Found Helpful
I am beyond happy!
Got my Steeda differential bushing kit installed today...and I am beyond happy! I decided to go with the red Street bushings because I was afraid of NVH and I'd say the thud is 95% gone. It is at a point that I feel like if the car had come this way from the factory, I'd have never even noticed it. Such a joy to drive now and not hear that damn noise! I really think each car must do it to a different degree and mine was particularly bad because I just can't imagine anyone accepting that sound in a car otherwise so nice. I'm sure that with that kit or the Steeda aluminum bushings the sound would be 100% eliminated but I'm completely happy with it now and with the red Steeda's there is ZERO added NVH. Don't believe those that say you'll have to live with that awful sound. You don't. Haven't tested out the wheel hop but if that's better then that's just icing on the cake!
Did you find this helpful?  3 of 3 Found Helpful
I am a Steeda believer
The car is a totally different handling car. Took the wife for a ride today and she said it is smoother than before. Much less bouncy. That is good news to me. Cause if the wife is happy I am happy. But I will say that these mods have really changed my confidence in the car. I had one little 30mile spirited section with S curves on my way home that normally when they say 45mph.. you can take them at 55mph... I took them at 70mph and the car was just planted solid. No roll, no rebound and no breaking loose on the rear when I accelerated from the apex. It just transitioned smoothly and predictably. Now the only thing the wife did notice was the gear whine. Yes the Red differential bushing will cause some gear whine, but I have been told that replacing the stock gear oil in the rear end will help quiet that noise down. We will see as I will most likely change mine out here in the next week. Amsoil or Royal Purple is what a lot of people recommended. So, all in all, if someone is on the fence about these suspension upgrades, just do it. The guys at Steeda are top notch and know their stuff. Almost all of them have Mustangs and the owner even races them. A final shout out to [email protected] What a great help he was. He made sure everything was ready and there, his recommendations were spot on. David, again, Thank you man. I can hardly wait for the next batch of Steeda goodies come out.. Count me in already. I am a Steeda believer.
Did you find this helpful?  2 of 3 Found Helpful
Definitely worth purchasing
I installed the red bushings Friday night while installing my Borla S Type cat back. The red have no added HVH. Great street setup. Immediately on first take off noticed the rear axle was more solid. Definitely worth purchasing.
Did you find this helpful?  1 of 1 Found Helpful
Solid Mod
Give yourself 3 hours to do this mod. No real increase in NVH Manual drive line slop is reduced further with these. SOLID MOD buy these. Not sure I would ever need the Aluminum ones but I bet I could swap them in an hour now that I'm familiar.
Did you find this helpful? 
No more chirp chirp chirp!
No more chirp chirp chirp! Went for a nice ride to check it out. I did a burnout and a hard take-off and it was very solid, no hopping. The most important thing was cornering for me. I went into a large parking lot, took a hard turn accelerating out of the exit purposefully braking the backend loose. Before, with the wheel hop, it was hard to control. It took a lot of working the wheel. Now it is easy! Thanks again [email protected] for the recommendation!
Did you find this helpful?  4 of 4 Found Helpful
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