11.25″ Brake Upgrade How To

11.25″ Brake Upgrade How To

The following brake conversion uses mostly off-the-shelf parts and a few simple fabrications. This conversion applies to 1984 through 1987 Fieros, all models. They are incompatible with the changes of the 1988 model year.

The rear calipers are selected to function with the stock Fiero parking brake cable arrangement. some people mistakenly rationalize that they never use the hand brake, therefore they won’t miss it. Definitely you should retain the emergency brake function. The Fiero requires that both pull to the rear. 1980-1985 Cadillac Seville calipers met the requirements. Be careful that the calipers you get are marked with casting numbers 020 and the other with 021. They are mirror images of each other in that one is a right and the other a left. In our application, the sides are reversed. We will re-use the parking brake levers and return springs from the Fiero calipers. No modifications are required.

The master cylinder selected is for late model Chevrolet C/K pickups and Blazer. It is made by Bendix and is of the same family of master cylinders as the stock Fiero unit. To look at the two, they are identical, varying only in bore size. Our choice is 1 1/8″ bore to pump more fluid to the larger caliper bores, thus maintaining a pedal stroke equal to the original. Installation is a perfect bolt in replacement.

Walt Zettner’s design has been improved on by PFF member Koburn. In Zettner’s design, the Fiero E-brake cable comes much too close to the CV boot. This was solved by designing the calipers to be rotated 5°. this allows the E-brake cable to clear the CV boot quite nicely. Minor trimming of the brake pads, however, is necessary. Two designs sufficed, one for the front pair and one for the rear pair. The accompanying .dxf AutoCAD drawings show the simplicity. The caliper brackets are flame cut from 3/8 inch mild steel plate. Machining consisted of drilling four holes and tapping two of them.

The fronts require spacers 1.00 OD x .50 ID x .435 inches thick to align the calipers with the rotor. you’ll need 0.450 or so thick spacers with Lebaron rear rotors. The test is to be able to freely turn the rotor with the calipers installed. Misalignment will cause the pads to drag. Your actual spacer thickness may vary, but if by more than a few thousandths, look for something bent or deformed.

The Fiero front rotors must be modified. Take them to a machine shop and have the rotor disk portion “parted-off” in a lathe, leaving the edge of the hub flange about 5/8 inches thick. This gives you a beautiful little hub with no brake disk. The studs are then knocked out and replaced with longer, 55 mm studs. The extra length is needed for the added thickness of the Lebaron brake disk, which is installed over the studs.

In Zettner’s write up, it mentioned putting passes of cast iron machinable weld in the bores to make the rotors fit the hubs. This is not necessary if you use four REAR Lebaron rotors, since the pilot diameter is the same as the Fiero’s.

Some things Koburn noticed on the Zettner write up .. It calls out the need for an 12Mx1.50 tap (I assume to tap your mounting holes in the new adaptors) the caliper bolts that came with the Cadillac calipers were 12Mx1.25. He calls out 1/2″ holes for mounting to the stock location but these need to be 7/16 for a closer fit as well as 7/16″ lock washers, not 1/2″ – however the bolts that thread into the stock fiero knuckles do seem to be 7/16″ thread.

nowhere in Zettner’s write up is there a mention of any grinding to the stock knuckle – however at least on the 86 there is a tab that sits just past the stock rotor edge that has to be removed for the Lebaron rotors.

Adjust the tap drill size accordingly. The balance of the job is bolt together and plumbing. The stock rubber hoses are not suitable for a high performance brake system and they are too short. Use the stainless braided hoses referenced in the Bill of Materials.

Caution: During disassembly and re-assemble, refer to the appropriate sections of your Fiero shop manual. If you are not a “brake” person, get help from someone who is. The lives of you and your loved ones depend on the quality of the work you do during this project. Always use jack stands and an adequate floor jack when raising the car. The Fiero jack is for on-the-road emergency situations only.

Check for fit and alignment on each step of the assembly process. Check for clearance of the brake hoses. Use rubber insulated straps to secure them out of harm’s way. Turn the steering, full lock to lock, watch for clearance, and beware of “banjo-string” tension on the hoses. Likewise, check for free rotation as you assemble each part, including mounting the wheels. It is embarrassing to finish up the job only to find that your wheels won’t turn.

There is no alternative to a perfect brake bleeding job for good brakes. I recommend a small hand-operated vacuum pump called a ‘Mity-Vac”. You can get these from many auto parts stores for about $20. Start with the right rear caliper (farthest from the master cylinder) and work to the caliper closest to the master cylinder. I suggest draining all of the old fluid and using all new DOT 3 or better brake fluid. Do not re-use the bled fluid.

Perform the obvious driveway slow speed brake checks first. Do several miles of start and stop driving to allow your pads to seat in before you try your 60 mph to zero test stops.

there is a bit of debate regarding the standard Fiero proportioning valve. Zettner’s write up stated that he left it alone and “performance is perfect, with no premature locking up, front or rear” but others have removed a seal from the brake valve to allow more fluid flow to the rear wheels. Some have even installed adjustable proportioning valves. I will try to update this with better information.

SOURCES AND REFERENCES:

All of the rotors, calipers, and the master cylinder listed in the Bill of Materials following are manufactured or rebuilt by CarQuest and are available at any CarQuest store. Shop around for at least a 20% discount for your parts. Work the best deal you can on the cores and/or core charges when buying rebuilt. The core charges for the rear calipers is significant.



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