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Tweaking Toe On A Rear Twist Beam

AKA: Fixing wheel alignment on a car without adjustable alignment—like a 2015 Honda Fit—with SPC's toe shims

Oct 30, 2018

We celebrate the mindset—the ethos, really—that if OEMs don't give us what we want, we'll find a way to do it anyway. That's what the aftermarket is for, an industry that has spawned all kinds of modifying goodies for every part of your car, whether you want to go fast, go sideways, go anywhere, or just look like you do. And the aftermarket is there to help you correct things, too—we were reminded of this recently when a coworker approached us about finding a way to fix the rear toe settings on his 2015 Honda Fit daily driver.

See, the Fit—like a lot of cars these days—has a rear torsion beam (also known as a "twist-beam") suspension, which is typically a stamped-steel member that stretches underneath the car across its width and replaces a more traditional independent rear suspension (or IRS), another type of setup that's commonly found on front-wheel-drive cars—or at least it was, anyway. OEMs employ these beams primarily because they are cheaper to mass-produce than a multi-link system (they use fewer bushings, there's no need for a separate anti-roll bar, etc.) The down side is alignment geometry is factory-set and not generally adjustable. By design most twist beams limit simple rear wheel alignment adjustments, like camber and toe.

We don't know how the toe got out of whack on our '15 Fit, but when we took it in for an alignment we were told the left rear was toed in, 9/32 of an inch out of spec (see the before measurements in the photos above). Initially, the shop performing the alignment tried to sell us an entirely new beam (!) but we wanted to look at our options. We're glad we did, because SPC Performance has a product that corrects our situation for a fraction of the price.

A new-from-the-factory Fit rear twist beam assembly will run you north of $600, while a salvaged or knockoff version will obviously run you less. For less than $200, though, you can pick up SPC's rear plastic shim set for the Fit (PN #71790), and with a little bit of elbow grease and some help, fix that toe yourself. These fixed change, wedge-profiled shims come in an 18-piece kit that includes two each of a series of toe shims that will adjust from -0.5° to +0.5° in 1/10° increments, and camber shims that will adjust from ±0.25° to ±1.0° in 1/4° increments. Combine up to two shims to dial in both toe and camber.

Tweaking toe on a rear twist beam flange bolts Photo 8/15   |   Tweaking Toe On A Rear Twist Beam Flange Bolts

SPC says installation should only take us about a half hour per side, but thankfully we're only correcting the left side, so we start by putting the rear in the air and removing the wheel. The goal is to slip the shims in between the rear brake backing plate and the beam where the two are bolted to one another, effectively pushing out the front edge of the wheel, which means we had to remove the brake drum as well to get at the so-called "flange" mounting bolts (indicated by arrows in the above pic). This drum came off pretty easily but in some cases you may have to tap the drum around its edges with a mallet in order for it to rattle free; in worst cases, you may have to thread a bolt into the holes on the face of the drum in order to push it off of the brake.

Ideally, we imagine for the easiest access we'd probably have to remove the entire brake, but that would mean disconnecting lines and having to bleed the brakes eventually—basically adding more time to this job. Our compromise was to leave the brake fluid and parking brake lines intact but create enough slack in them to be able to pull the brake away from the beam just enough to slide in our shims.

Tweaking toe on a rear twist beam wheel speed sensor pickup Photo 9/15   |   Tweaking Toe On A Rear Twist Beam Wheel Speed Sensor Pickup
Tweaking toe on a rear twist beam parking brake cable Photo 10/15   |   Tweaking Toe On A Rear Twist Beam Parking Brake Cable

We for sure had to unbolt the wheel speed sensor pickup from behind the backing plate—if left in place, we likely wouldn't have been able to pull the brake away from the beam very far (when installed, the pickup actually sits in a channel on the hub, which is why you need to take it off). Re-installing the sensor was actually the hardest part of this entire endeavor, mainly because the access hole for it was made for toddlers' hands (so tiny!) In addition, we unbolted the parking brake cable from torsion beam for more slack.

Tweaking toe on a rear twist beam rear toe shim positive end Photo 11/15   |   Tweaking Toe On A Rear Twist Beam Rear Toe Shim Positive End
Tweaking toe on a rear twist beam rear toe shim negative end Photo 12/15   |   Tweaking Toe On A Rear Twist Beam Rear Toe Shim Negative End

The four flange bolts came out and then we were ready to pop in our shims. Via one of several conversion calculators on the Internet, we figured out what the variance was in degrees (remember, we got the measurements in inches), and then figured out we needed one 0.5° shim and one 0.1° shim—which actually turned out to be a little overkill in the other direction, so we went back after a follow-up alignment and pulled out the 0.1° shim. Positive or negative change is marked on the shim—correction marks that should be oriented at the front outboard top corner when installed—and SPC recommends not stacking more than two shims at a time. SPC's shims are also reversible.

Tweaking toe on a rear twist beam brake torsion beam Photo 13/15   |   Tweaking Toe On A Rear Twist Beam Brake Torsion Beam
Tweaking toe on a rear twist beam toe shims torsion beam drum brake backing plate Photo 14/15   |   Tweaking Toe On A Rear Twist Beam Toe Shims Torsion Beam Drum Brake Backing Plate

We have our helper gently tug the brake out so it separates from the beam, and then we're able to introduce our shims. The shims'(s) holes should line up with the holes for the flange bolts (if not, you probably just need to flip the shim). From there, it's the reverse order to put everything back together—re-bolt the backing plate and re-secure the parking brake line and wheel speed sensor pickup, slip on the brake drum, and finally put on the wheel.

Tweaking toe on a rear twist beam alignment measurements Photo 15/15   |   Tweaking Toe On A Rear Twist Beam Alignment Measurements

Green is good! Our toe is back within spec, this time a 32nd out but within factory tolerances, which is all we're really looking for. Before this scenario came up, we had no idea we could fix toe on our rear twist beam cars with such a simple kit—but now that we know, we're spreading the word!

Sources

Specialty Products Company (SPC)
Longmont, CO 80504
800-525-6505
https://www.spcalignment.com
Bob Hernandez
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