128 Rear Disc Brake Conversion

Intro
I have heard plenty of folks say that the drum brakes are plenty for the rear of a 128, that the rear is "just along for the ride," etc, etc. Having driven a couple of rear-disc-equipped 128s, I know that they can benefit from the conversion. For autocross (slalom) racing or mild street driving, sure, it might not make a huge difference since you don't have much time to heat up the brakes and the drums are plenty adequate to lock the rear wheels. For mountain driving or track days the discs provide a more even temperature distribution between the front & rear brakes, and I think tend to be more predictable. Lowered cars (which exhibit less forward weight transfer under braking) will benefit from the increased rear braking more than a stock vehicle. Servicing a set of discs is also quite a bit easier than the drums. Cost is a bit of a draw - the initial conversion isn't free, but replacing rotors is arguably cheaper than drums (not that either wear that fast).

Conversion Details
The 128 Rear Disc Conversion was conceived of by long-time Fiat friend Dave Voss. He installed his original setup on his '78 128 Rally many moons ago (the same Rally which I currently own). I had copies made for my first 128 sedan, and later swapped them to my second '76 sedan.
Dave's genius was in using all Fiat components, with the exception of the fabricated brackets. The parking brake cable comes from a 124 coupe, mounting screws were 128 door screws, X1/9 brake hoses, 124 or X1/9 calipers, and X1/9 caliper bracket.

Dave's Disc Brake Conversion on my '76 sedan

I had removed the discs from my Rally to compete in a specific autocross class but now that the car doesn't compete in that class I decided to convert back. I had sold the original parts to a friend for his E Prepared Yugo so new parts had to be machined. While I was at it, I decided to simplify the conversion and get a little more clearance between the parking brake cable and unibody. I modeled the rear suspension in SolidWorks and came up with the revised kit.

Revising the Disc Brake Conversion in CAD

Conversion Process
Shown on the right are the parts required for the revised conversion. The phillips head 128 door screws were a bit of a pain to install (and somewhat tough to source) so I opted for readily available flat-head socket head cap screws. Other than that, as per the original conversion, you've got:

124 Coupe/Sedan Parking Brake Cable
Custom Adapter Plates (L & R)
Custom Rotor Spacers (qty 2)
M8 Flat Head Socket Cap Screws (qty 8)
X1/9 Rear Caliper Brackets (L & R)
X1/9 (or 124) Rear Calipers (L & R)
X1/9 (or 124) Rear Brake Pads (set)
X1/9 (or 124) Copper Crush Washers (qty 2)
X1/9 Rear Brake Hoses (qty 2)
Standard Fiat Brake Rotors (qty 2)

128 Disc Brake Conversion Parts

First order of business is to remove the brake drum. They can be pretty stubborn to remove, even with a puller (so get ahold of the biggest one you can!).
Removing Brake Drum

Removing the rest of the hardware is very straightforward. I disconnect the parking brake first. Once the axle nut is broken loose, the rear hub can come off and the four bolts holding the drum backing plate on can be accessed. Then just disconnect the brake hose.
Drum removed showing rear shoes & backing plate.

Not much to it...
The bare spindle.

Now the fun begins. First step is to bolt on the adapter plate with the flat head cap screws.
Mounting the adapter plate.

Next, the hub (with bearing) is installed.
Hub installed.

The custom spacer plate goes on to properly position the brake rotor.
Spacer installed.

Then the brake rotor is affixed with the locating bolts/pins.
Rotor installed.

An X1/9 rear caliper mounting bracket gets bolted to the adapter plate.
Caliper bracket installed.

Finally the pads are loaded and caliper mounted with its sliders.
Caliper installed.

All that remains is to hook up the brake hose and parking brake cable.
Another view of the installed caliper.

Conclusion
I took my rear-disc-equipped Rally on the roughly 1400 mile round-trip from my home in southern California to Ashland, Oregon and back for the annual Mirafiori gathering. This included an autocross and a fair bit of spirited mountain driving. The brakes worked quite well! Pedal feel is firm and consistent. Pedal effort is comfortable and travel minimal, which makes sense since it has the same master cylinder as a 124 and now has the same brakes as well. The one thing I still have to work out is a new configuration for my Addco rear swaybar brackets. I had to remove the ones that mount to the control arm to clear the calipers but they didn't need much clearance so I don't think it will take much to get them to work. Stay tuned...

This page created: August 1, 2006

Courtney Waters courtney@mirafiori.com

Back to Court's Main Page

Intro I have heard plenty of folks say that the drum brakes are plenty for the rear of a 128, that the rear is "just along for the ride," etc, etc. Having driven a couple of rear-disc-equipped 128s, I know that they can benefit from the conversion. For autocross (slalom) racing or mild street driving, sure, it might not make a huge difference since you don't have much time to heat up the brakes and the drums are plenty adequate to lock the rear wheels. For mountain driving or track days the discs provide a more even temperature distribution between the front & rear brakes, and I think tend to be more predictable. Lowered cars (which exhibit less forward weight transfer under braking) will benefit from the increased rear braking more than a stock vehicle. Servicing a set of discs is also quite a bit easier than the drums. Cost is a bit of a draw - the initial conversion isn't free, but replacing rotors is arguably cheaper than drums (not that either wear that fast). Conversion Details The 128 Rear Disc Conversion was conceived of by long-time Fiat friend Dave Voss. He installed his original setup on his '78 128 Rally many moons ago (the same Rally which I currently own). I had copies made for my first 128 sedan, and later swapped them to my second '76 sedan. Dave's genius was in using all Fiat components, with the exception of the fabricated brackets. The parking brake cable comes from a 124 coupe, mounting screws were 128 door screws, X1/9 brake hoses, 124 or X1/9 calipers, and X1/9 caliper bracket.
Dave's Disc Brake Conversion on my '76 sedan
I had removed the discs from my Rally to compete in a specific autocross class but now that the car doesn't compete in that class I decided to convert back. I had sold the original parts to a friend for his E Prepared Yugo so new parts had to be machined. While I was at it, I decided to simplify the conversion and get a little more clearance between the parking brake cable and unibody. I modeled the rear suspension in SolidWorks and came up with the revised kit.
Revising the Disc Brake Conversion in CAD
Conversion Process Shown on the right are the parts required for the revised conversion. The phillips head 128 door screws were a bit of a pain to install (and somewhat tough to source) so I opted for readily available flat-head socket head cap screws. Other than that, as per the original conversion, you've got: 124 Coupe/Sedan Parking Brake Cable Custom Adapter Plates (L & R) Custom Rotor Spacers (qty 2) M8 Flat Head Socket Cap Screws (qty 8) X1/9 Rear Caliper Brackets (L & R) X1/9 (or 124) Rear Calipers (L & R) X1/9 (or 124) Rear Brake Pads (set) X1/9 (or 124) Copper Crush Washers (qty 2) X1/9 Rear Brake Hoses (qty 2) Standard Fiat Brake Rotors (qty 2)	128 Disc Brake Conversion Parts
First order of business is to remove the brake drum. They can be pretty stubborn to remove, even with a puller (so get ahold of the biggest one you can!).	Removing Brake Drum
Removing the rest of the hardware is very straightforward. I disconnect the parking brake first. Once the axle nut is broken loose, the rear hub can come off and the four bolts holding the drum backing plate on can be accessed. Then just disconnect the brake hose.	Drum removed showing rear shoes & backing plate.
Not much to it...	The bare spindle.
Now the fun begins. First step is to bolt on the adapter plate with the flat head cap screws.	Mounting the adapter plate.
Next, the hub (with bearing) is installed.	Hub installed.
The custom spacer plate goes on to properly position the brake rotor.	Spacer installed.
Then the brake rotor is affixed with the locating bolts/pins.	Rotor installed.
An X1/9 rear caliper mounting bracket gets bolted to the adapter plate.	Caliper bracket installed.
Finally the pads are loaded and caliper mounted with its sliders.	Caliper installed.
All that remains is to hook up the brake hose and parking brake cable.	Another view of the installed caliper.
Conclusion I took my rear-disc-equipped Rally on the roughly 1400 mile round-trip from my home in southern California to Ashland, Oregon and back for the annual Mirafiori gathering. This included an autocross and a fair bit of spirited mountain driving. The brakes worked quite well! Pedal feel is firm and consistent. Pedal effort is comfortable and travel minimal, which makes sense since it has the same master cylinder as a 124 and now has the same brakes as well. The one thing I still have to work out is a new configuration for my Addco rear swaybar brackets. I had to remove the ones that mount to the control arm to clear the calipers but they didn't need much clearance so I don't think it will take much to get them to work. Stay tuned...
This page created: August 1, 2006 Courtney Waters courtney@mirafiori.com Back to Court's Main Page