How to Install the Steeda Mustang ‘Stop the Hop' Street Starter Kit

Wheel hop on the S550 and S650 Mustang comes down to how the independent rear suspension is mounted. The subframe attaches to the chassis at four points via soft rubber bushings that prioritize street comfort and isolate noise and vibration. Under hard acceleration or braking, that compliance allows the subframe to shift slightly and the axle to load and unload rapidly, resulting in wheel hop that breaks traction and stresses driveline components.

The Stop the Hop Street Starter Kit (MPN 555-4455) goes straight to the root of the problem. Instead of patching things up with stiffer half shafts or other driveline band-aids, this kit locks the subframe to the chassis with a trio of parts that work in concert: alignment dowels that fill the bolt hole voids and square the subframe to the body, billet aluminum bushing supports that take up the slack in the rubber bushings to stop vertical movement, and chrome moly steel IRS subframe support braces that tie the subframe directly into the chassis at five points per side.

This guide breaks down what comes in the box, the tools you'll need, how tough the job really is, and walks you through the installation step by step. If you're thinking about tackling this in your own garage, read through the whole process first. The work is straightforward, but you'll need to loosen the subframe hardware in a specific order, so knowing the sequence before you start is key.

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What's Included

The Street Starter Kit bundles three Steeda products:

• IRS Subframe Support Braces (555-5754): Five-point braces made in-house from chrome moly steel. Each brace bolts into factory mounting locations along the framerail and ties the front subframe mount and lower control arm mount directly into the chassis.
• IRS Subframe Bushing Support System (555-4437): A patented eight-piece kit machined in-house from billet 6061 aluminum with stainless steel hardware. The supports fill the voids in the factory rubber subframe bushings, preventing up-and-down movement of the subframe.
• IRS Subframe Alignment Kit (555-4438): CNC-machined delrin dowels that fill the factory bolt hole voids. These square the rear subframe to the chassis and limit side-to-side and front-to-back movement of the subframe under acceleration and braking.

Hardware List

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Tools List

• 13mm Socket
• 15mm Socket
• 16mm Socket
• 21mm Socket
• Socket Extension
• 5/32 Allen Wrench
• 18mm Wrench
• Torque Wrench
• Grease (Optional)

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Difficulty, Time, and What You're Getting Into

Steeda calls this a moderately difficult install, and you're looking at about three hours start to finish. A four-post lift makes life easier, but you can absolutely get it done on jack stands with the rear of the car up and solidly supported.

There are two things to know about this install. First, you won't need to cut, drill, or make any permanent changes. Every part bolts into factory locations, so you can always return the car to stock if you want. Second, installing the bushing supports and dowels means loosening and removing subframe bolts one at a time. The subframe stays put with the other bolts in place, but you have to follow the sequence to the letter. Never pull more than one subframe bolt out at a time.

You'll need a wheel alignment after the install, so plan for that when you're mapping out the job.

Follow along with photos with our full install guide.

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Phase One: Bushing Supports and Alignment Dowels

Phase one is all about installing the bushing supports and alignment dowels at the subframe mounting points. The steps below walk you through one side of the car, finish that side completely, then repeat everything on the driver's side.

• 1. Towards the front of the rear subframe remove the two 13mm bolts and the 21mm bolt holding the subframe bracket in place. Remove the bolts completely.
• 2. Towards the rear of the subframe, loosen, but do NOT remove the bolt completely. Only 1 sub frame bolt should be removed at a time.
• 3. Place the bushing supports both top and bottom in the front of the subframe. Refer to figure 6 for the correct orientation. The thicker support will go up top.
• 4. Before reinstalling the 21mm bolt, place the shorter Alignment dowel in the front of the sub-frame.
• 5. Reinstall the front bracket & 21mm bolt where the threads are engaged, but not tightened down. This allows the subframe to hang slightly to allow for clearance in the rear. Remove the rear bolt completely.
• 6. The two-piece bushing support will be installed in the lower rear section of the subframe. A bit of grease and some pliers will help get it into place. Then evenly tighten the two 5/32 allen bolts.
• 7. The thinner bushing support will be installed up top in the rear. The taller, thinner alignment dowel can be installed as well.
• 8. Tighten the two subframe bolts and torque to 129ft/lbs. The smaller bolts on the front bracket will be torqued to 41ft/lbs. Repeat the installation on the driver's side.

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Phase Two: IRS Support Braces

Once the subframe is squared up and the bushings are locked down, it's time to install the braces to tie everything to the chassis. Just like before, finish one side completely before moving to the other.

• 9. Remove the two bolts along the framerail.
• 10. Insert the threaded plate into the subframe as shown in figure 19.
• 11. Place the IRS brace up in place and use the longer bolt to secure it to the front subframe bracket. Leave this bolt loose.
• 12. Towards the front, install the two shorter bolts and large washers. Leave these bolts loose as well.
• 13. In the rear, install the smaller bolt & washer into the threaded plate you installed in step 10.
• 14. Place the nut on top of the subframe and the longer bolt & washer can be installed to secure it in place.
• 15. Once all the bolts are started, tighten down the center first, then tighten the front and rear bolts.
• 16. Torque the 2 rear bolts to 55ft-lbs. Torque the center and front two bolts to 45ft-lbs. Repeat this process for the driver's side.

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After Install

Get the car aligned. Moving the subframe mounting points changes the rear suspension geometry enough that an alignment isn't just a good idea, it's mandatory. Skip it, and you'll pay for it in tire wear and handling.

Once you've got the alignment dialed in, the difference is obvious the first time you put the power down on a less-than-perfect surface. The subframe stays locked in place, so the rear axle plants exactly where the suspension geometry wants it. Because the kit fills the voids instead of swapping in stiffer bushings, you get all the control. You don't add noise, vibration, or harshness in the cabin. That's the whole idea: fix the movement at the mounting points, keep the factory isolation, and leave the car just as comfortable as before. Now, the hop is gone.

Torque Specification Quick Reference