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Several club members have provided narratives about replacing their Gen1 xB’s rear drum brakes with disc brakes. Various setups and parts combinations have been used to make the exchange. Following is information about the rear disc brake configuration I installed on my 2005 xB.

I purchased rear disc brake assemblies off a 2003 Toyota iSt (NCP61-HHPGK) in 2009 and installed them in 2011. The JDM model iSt was marketed in the U.S. as the Scion xA. It was sold equipped with rear drum brakes instead of rear disc brakes. The iSt, xA, and Gen1 xB platforms share several components.

The change involved removing the xB’s rear drum brake assembly and bolting in the iSt’s rear disc brake assembly, then connecting the brake line, ABS, and parking brake cable. Both vehicles use the same rear axle hub/bearing and the same rear axle beam.

xB rear brakes use a flexible hose attached to a metal brake line on the body. The hose connects to a junction block mounted on the rear axle beam. A short metal line from the junction block terminates at the stationary brake cylinder. iSt rear brakes use two inline flexible brake hoses. One runs from the metal brake line on the body to a junction block on the rear axle beam. The second runs from the junction block to the floating caliper.

I used a single flexible hose 21" long, including fittings. This eliminated the junction block along with two potential hose points of failure. One end attaches to the metal brake line on the body using a 10mm female inverted flare with a groove for the lock-in clip. The other end attaches to the caliper with a banjo fitting measuring 10mm wide by 8mm thick.

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The floating caliper moves inward slightly when the brake is applied and further as the pads wear down. As a result, the banjo fitting is angled 22.5 degrees away from the caliper for the fitting to clear the axle beam. Built into the banjo fitting is a positioning pin which fits into a socket on the caliper for proper alignment.

The iSt parking brake is a self-adjusting duo-servo design. Brake shoes attach to the combination caliper mount/backing plate. The rotor hat serves as a drum for a lever actuated secondary shoe, and a strut applied primary shoe.

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I used my xB’s parking brake cables, which required four changes. If I had used iSt parking brake cables, none of the four changes would have been necessary.

The parking brake cable housing fastens to the backing plate. The xB housing has a 90-degree angle offset for the fastener. The iSt housing has a 45-degree angle offset for the fastener and is positioned on the opposite side of the xB’s

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I drilled a hole for the xB housing fastener to attach to the backing plate at its pass-through opening. The opening was lengthened by 1/8” to allow the housing end to fully seat. During installation, the iSt fastener hole, and the newly made pass though opening gap were sealed with heat resistant silicone.

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The xB parking brake cable end stop is larger than the iSt’s. To fit the iSt actuating lever the xB’s stop was trimmed using a small rotary grinder.

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The xB cable wire extends 5/16” further than the iSt’s wire. For proper cable alignment behind the secondary brake shoe, the difference required compensating. 1/8” was reduced by the backing plate pass-through modification. Another 3/16” was reduced by using a rotary grinder to cut three coils off the xB wire’s return spring.

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Originally, I painted the calipers black and had the rotors slotted and zinc plated. The rotor has an opening for access to the parking brake self-adjuster. It is used for initial shoe adjustment and for backing the shoes off, if necessary, before rotor removal. A rubber dust plug covers the opening.

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The 3/8” thick caliper mounting plate is located between the axle hub/bearing and the axle beam. This results in each wheel being moved 3/8” outward. All axle hub/bearing mounting fasteners were replaced with 3/8” longer Grade 8 bolts.

In 2011 my xB had 18” rims, 1.5” lowering springs, and 215/45R18 tires. The passenger-side wheel hit a fender liner bolt when the car went over a speed bump. I replaced the liner bolt with a low-profile fastener to resolve the clearance problem.

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In 2018 I returned the xB to 15” rims, stock springs, and 185/60R15 tires, with no clearance issues for the original fender liner bolt. I later swapped the iSt calipers for matching 2004 Celica GTS calipers. Both the GTS rear calipers and the xB front calipers were powder coated red, then I rebuilt all of them.

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Overall, the swap was easy and quick. Most of my effort was for cleaning and preparation of the used parts. Since the install, my xB has been driven over 70,000 miles on local streets and highways and on multiple 1,000-mile Interstate trips. The brakes have performed flawlessly and without an issue. Stopping is strong, smooth, and the braking bias feels excellent.

No hydraulic brake system changes or adjustments were necessary for pressure proportioning or metering.

Original xB axle hub/bearing was used without any change. No modification was necessary to the rotor center opening to fit the axle hub/bearing.

The caliper required no change, nor did the combination caliper mounting plate/backing plate. No change was needed to the xB rear axle beam assembly.

Total initial cost was just under $400, including used disc brake assemblies, new hub to axle beam bolts, new brake hoses, and performing my own labor. It did not include rotor slotting and plating. Caliper powder coating and rebuilds were performed seven years later.

I searched extensively online for information on replacement parts and did not locate any U.S. based source listing for Toyota iSt. I located and bought iSt parking brake cables from a supplier in Belarus but have not yet installed them.

iSt part numbers were identified on in 2011. This week the data was verified on the same website. For 2021 parts availability and prices, I checked Along with some superseded part numbers, one cylinder assembly shows as discontinued.

For a source of new or used replacement parts, there are other vehicles whose rear disc brake parts match the 2003 Toyota iSt. These include 2003-2006 Toyota Matrix XRS, 2005-2006 Toyota Corolla XRS, 2000-2005 Toyota Celica GTS, and the 2000-2005 Pontiac Vibe GT. The Vibe was jointly produced by Toyota and General Motors.

Along with fasteners, clips, tensioners, and pins, matching components include caliper, mounting/backing plate, disc pads and shims, parking brake shoes, and parking brake actuating levers and return springs.

Their rotors do not interchange as they are for five-lug wheels. I do not know whether any of the above vehicles’ five-lug axle hubs can be used with the xB axle beam. I also do not know if any of their parking brake cables work on the xB.

New part data is listed in the table below. Where multiples of a part are required, prices reflect the combined cost.

Brake Pad Kit
Anti-Squeal Shim Kit
Brake Fitting Kit
Disc (2)
Right Hand Parking Brake Plate Sub Assembly
Left Hand Parking Brake Plate Sub Assembly
Parking Brake Shoe (4)
Brake Flexible Hose Gasket (2)
Right Hand Shoe Adjusting Screw Set
Left Hand Shoe Adjusting Screw Set
Compression Spring (4)
Shoe Hold Down Spring Pin (4)
Shoe Adjusting Hole Plug (2)
Right Hand Parking Brake Shoe Lever
Left Hand Parking Brake Shoe Lever
Parking Brake Shoe Strut (2)
Cylinder Slide Pin (Sub) (2)
Caliper Slide Pin (Main) (2)
Right Hand Cylinder Assembly
Left Hand Cylinder Assembly - DISCONTINUED
With Hole Pin (4)
Clip (2)
Tension Spring (2)
Tension Spring (2)
Tension Spring (2)
Tension Spring (2)
Right Hand Flexible Hose
Left Hand Flexible Hose
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