Rear Disc Brake Conversion
By Ryan Ballou
I've said in previous articles, making your car quicker is pointless if
you have no way to safely bring it to a stop. This was the reason for
upgrading to front disc brakes some time ago. Well as time goes on and
more has been done to the car the question of braking has come up again.
The only upgrade left is to go all out with four-wheel disc brakes by
adding on a set to the rear of the car.
Once again I have Mid
America Motorworks to thank for providing me with a set of their rear
disc brakes. Mid America carries kits for both IRS and Swing Axle applications
as well as kits with and without parking brakes. For a car that is driven
on the street the kit with the parking brake is a must and therefore that
is the kit type that I'll be covering. Keep in mind that when running
four-wheel discs you want to be using a late model dual circuit master
cylinder. Not a problem for me since my car came equipped that way.
The advantage of running four wheel discs vs. two discs and two drums
is that brake fade will be eliminated in all but the harshest driving
conditions, namely road racing. Wet weather performance will be increased
dramatically as disc brakes shed water when pedal pressure is applied.
Just try coming to a quick stop after going through a deep puddle with
drums, it takes quite a bit of effort. With discs, you have full braking
power almost instantly. Finally there is the little to no maintenance
required, as disc brakes need no adjustment. All you need to do is monitor
pad & rotor wear and replace as needed, along with regular brake fluid
The kit supplied by Mid America comes with nearly everything you need
for the installation. Included are a pair of rotors & calipers, a
set of brake pads, caliper brackets, new rubber brake lines (soft lines),
bearing housing seals, associated hardware, and a set of parking brake
cables designed for this application. You will need to purchase two new
brake lines (hard lines) 30" long, and if you have already gone with
stainless steel braided Teflon lines for the front brakes, then you'll
want to pick up a set for the rear as well. Mid America carries these
Teflon lines too, they are sold per each so order two.
The first order of business is to remove brake drum. This can be tricky
since the torque on the axle nut is 250 [ft*lbs] at a minimum. I use a
¾" drive breaker bar with a 4' cheater bar (my jack handle)
to break these loose. The nut size is 36mm, though in some cases it may
be less expensive to use a 1 7/16" socket, usually easier to find
as well. Put the car into 1st gear and use wheel chocks to keep the car
from rolling when doing this. With the drums removed you can take out
all the old braking hardware; shoes, springs, parking brake equipment,
I chose to leave the existing lines and slave cylinder connected until
I was ready to install the new lines to prevent making a mess by dripping
fluid everywhere. Just unbolt the bearing cap, pull the backing plate
out with the cylinder still attached, and push everything back out of
the way. Don't worry about bending lines, you'll be replacing them anyway.
If you haven't serviced your axle bearings in awhile, this is the time
to do it while everything is taken apart. I just did mine a year ago so
I'm leaving them alone for now. Clean up the bearing cap and mating surface
on the diagonal arm to prevent grease from contaminating the new paper
gaskets that will be used.
There are two thin washer type shims included in the kit. Deburr these
completely and slide them on the axle so the sit on top of the bearing,
one shim per axle. These will end up sandwiched between the bearing and
the outer bearing spacer that the rotor snugs up against. With this shim
installed you can set the caliper bracket in place with the mounting ear
facing inward and to the rear of the car. Install the new bearing seals
in the bearing caps and put the new O-rings in place (both included).
Smear a little grease onto the O-ring to prevent pinching it during installation.
Now set a new paper gasket in place on top of the caliper bracket and
install the bearing cap back on the hub assembly. Torque each of these
four bolts to 43 [ft*lbs]. With the caps in place you can reinstall the
outer spacer with the tapered side in towards the bearing. Be sure to
smear a little grease on it prior to installation.
Now you can install the rotors. Clean up the braking surfaces with some
brake cleaner while you can still reach everything. Be sure to clean and
deburr the recess that where the seal in the bearing cap will ride and
smear a little grease here also. Slide the rotor over the axle and install
the axle nuts hand tight for now.
Prep the calipers by installing the brake pads. These can be a little
tricky, but if you look at the pictures of the install you'll see they
just pop right into place. You can also install the metric adapters into
the calipers at the inlet hole. Be sure to use the copper sealing washer
provided so you don't have any leaks. Now you can bolt the calipers in
place with the provided hardware. Use a dab of anti-seize and torque these
to 50 [ft*lbs].
Almost there, we just need to install the new brake lines and we're done.
If you're using standard rubber lines up front then you can go ahead and
use the soft lines provided in the kit. If you're using Teflon lines up
front, then use Teflon lines in the rear as well so you don't disturb
the braking bias. You'll need to bend your new hard lines to fit, so I
suggest going out to the hardware store and getting a small tubing bender.
Go slow and test fit frequently. This is easier than you might think,
but you can't really undo a bend after you make it, so measure twice,
The last thing to do before bleeding the brakes is to install the new
parking brake cables. Slide the threaded end up into the tubing in the
car greasing it as you go. Pass the line through the mounting boss in
the caliper and secure it with the c-clip that is provided in the kit.
Adjust the cable in the car with the nuts halfway up the threads. Pull
the cable tight at the caliper and you will notice that the cable is way
too long to do anything. The best solution I could come up with was to
cut the cable off about 2"-3" past the lever on the caliper.
I used a cutoff wheel on a Dremel tool to avoid fraying the cable. Then
I picked up a set of cable stops from an automotive store nearby. These
look just like the stops used on the throttle cable at the carburetor.
Slide the stops up against the levers on the calipers. You don't need
any preload so just makes sure that both cables are adjusted to the same
length in the car and you can set the stops up against the lever and secure
them. I would suggest using a small propane or MAP torch to solder the
ends of the cables to prevent over time.
You can now bleed the brakes. Do this just like you normally would, start
at the passenger side, then drivers side. Go ahead and do the fronts while
you're at it so you're starting fresh with new fluid all the way around.
You should have a nice firm pedal somewhere between a quarter and half
travel. Any lower than halfway and you probably still have some air in
the system. It's normal to get bubbles stuck in the calipers when they
are new and dry so just keep at it until you get a good pedal feel.
Once the lines are bled you can reinstall the rear wheels and lower the
car. With the car back on the ground you need to put it back into gear,
block the wheels, set the e-brake and torque the axle nuts, remember 250
[ft*lbs] min. Keep a very close eye on the axle nut torque for the first
few weeks of driving. Between the shim that was added and the new rotor,
the metal will compress slightly and that nut will become loose. I checked
mine at the end of a week and it was probably down below 50 [ft*lbs].
A hard launch and I could have ripped the splines out of the hub in the
rotor. Keep checking this until it stops getting loose, about 3 weeks/3
adjustments in my case.
I've already put these through the paces since they were installed. Quite
a few rainy days and they performed flawlessly. No matter how much water
I went through the brakes were always there. Even got to use them in a
panic situation recently. Came to a complete stop from 40mph in such a
short distance it was scary. Overall, this was an upgrade that was well
worth the effort involved. Drive it like you stole it, but stop it like
you own it.
1-I had to use one of my original rims to break the axle nuts loose
since the Sport Bug rims I have now don't allow access to the axle
nut while installed. Without a huge impact wrench, you need the wheel
in place to help keep the car stationary.
2-With the drum removed you can see all the existing hardware
that needs to come off now. Remove the shoes and springs, and unbolt
the parking brake cable holder from the rear of the backing plate.
3-With the bearing cap removed the backing plate will pull off with
little effort. If you're not servicing your axle bearings then be
extra careful to avoid contaminating the grease while the bearing
is exposed. You can install the bearing shim now. It's just stamped
from a piece of metal stock so be sure to completely deburr it before
4-Clean up the bearing cap, install the new axle seal and set the
new O-ring in place. I'm reusing my axle seals since they were replaced
when I recently serviced my axle bearings.
5-Here we have the caliper bracket in place with the bearing cap and
new paper gasket installed. The steel spacer should slide in place
with a little effort, make sure the taper is facing inwards.
6-You'll see the recess cut into the hub of the rotor where the axle
seal will ride. You should deburr this area thoroughly and then give
it a smear of bearing grease.
7-The rotor installs just like the old drums did. Slide them in place
and get the axle nut as tight as you can for now.
8-This is what the pads look like when installed. You'll have to spread
the caliper apart to get them in place.
9-Installing the caliper is pretty straight forward. Slide it over
the rotor and hold it in place while you bolt it on
10-Bending the new hard line was a little tricky. I started at the
joint to the soft line and made one bend at a time. Bend then test
fit, then bend and test fit again. Keep going until you reach the
rotor. Once installed you can always 'manhandle' it to clear obstructions.
Be sure to check fit once the car is lowered. Mine was rubbing against
an oil line in my full flow setup, but only when the car was on the
ground and suspension was loaded.
11-These are the cable stops I used to hold the parking brake cable
in place. Make sure they are good and tight so the cables don't slip
out when you need them most.
12-Finally a little solder on the end of the cable will keep it in
one piece over time.