1985 SAAB 900 REAR DISC BRAKES

        Wandering around in the salvage yard with an MGB rear hub in my hand, I spotted a black 1985 Saab 900 2-door coupe that still had all its alloy wheels under it.  A bit of work & I confirmed that the bolt pattern for the wheels was the same as my B.  A bit more work and I confirmed that the rear rotor will slip over an MGB hub!

        So, armed with 2 old Saab rotors, their calipers and caliper mounting bolts, I headed home..."

Installing Rear Disc Brakes on an MGB

From This:                      To This:
         

Only Requires This:
 
&, a few bolts!

PARTS LIST

PARTS #

PRICE

19620593
(Advance Auto)

$52.99*

19620496
(Advance Auto)

$52.99*

5672031
(Advance Auto)

$53.49 each

$100.00 pair

Already on MGB Rear End

323-255
(Moss Motors)

Acquired w/old calipers from salvage yard

Right - WIL120-2280

$55.99

Left - WIL120-2281

$55.99

       First, I suppose any rear brake caliper could be used so long as you can design a bracket setup; heck, for that matter, a Midget caliper could be used.  The main issue, in my opinion, isn't the caliper; its the rotor.  It has to fit over the MGB rear hub.       

        Another thing about the rotor: the MGB front rotor is 10-3/4" in diameter where the Saab rear rotor is 10-1/2".  That's a pretty stout rotor for the rear brakes.  So, a proportioning valve will definitely be necessary.

       The 2-pot Saab calipers are a bit smaller than original equipment 2-pot MGB front calipers, and about the same size as Midget calipers.  As I'm using Rover SD-1 4-pot calipers on the front of my car, the Saab rotors are sufficiently smaller to not overpower the front brakes (a real concern when building a 4-wheel disc brake setup).

        The MGB-GT V8 original front rotors are 10-3/4" in diameter where the Saab rotors are 10-1/2".  The rotors are basically the same size but the calipers are not meaning that the rear brake pads will have less surface area than the front.

        First, remove the entire MGB factory brake setup to include the backing plate.  Replace the 'back' (in relation to rear of car) 2 bolts that were used to attach the backing plate to the rear axle.  Hang onto the 2 'front' bolts; they'll be used to attach the caliper bracket to the axle.

        Second, after drilling and threading 2 small set screw holes in the MGB rear hub to hold the Saab rotor on it, slide the Saab rotor over the hub.  You can actually use either the MGB set screws or the Saab screws to hold the rotor to the hub.  I chose the MGB screws because they are longer.

        The Saab integrates a mechanical parking brake in the front brake setup.  It's wrapped around the hub and clamps onto the caliper to push one side against the rotor.  That won't work with my set-up.

        One has to ask oneself, "For what do I need a parking brake?  To stop the car in the event of brake failure?  To ensure the car doesn't roll on an incline?"  Well, aside from the fact that parking brakes are required by most states, one can be used to stop a vehicle in the event of catastrophic brake failure or to keep a car parked on a hill or idling while in neutral from moving.  And, bracket racers can use a parking brake to lock the wheels on one axle while they apply power to the other axle.

        As dual brake systems have almost eliminated the need for a parking brake since its rare for both systems to go out at once, I decided that I want a parking brake to ensure the car doesn't move when on an incline or at the beginning of a race.  In the event of catastrophic brake failure of both systems, bury me in my MG!

        However, I must also meet Alabama guidelines concerning a parking brake:

"Section 32-5-212
Brakes.
Every motor vehicle when operated upon a highway shall be equipped with brakes adequate to control the movement of and to stop and to hold such vehicle, including two separate means of applying the brakes, each of which shall be effective to apply the brakes to at least two wheels and so constructed that no part which is liable to failure shall be common to two; except, that a motorcycle need be equipped with only one brake. All such brakes shall be maintained in good working order and shall conform to regulations not inconsistent with this section to be promulgated by the Director of Public Safety. Any person violating this section shall be guilty of a misdemeanor.

(Acts 1927, No. 347, p. 348; Code 1940, T. 36, §35.)"
 ______________________________________

          After reading the law, my daughter - the lawyer - informed me that a line lock won't work as my park brake; however, it will be a neat thing to just have for locking down the front tires as I turn up the rear ones to get a jump on Corvettes at traffic lights when they start believing their own press releases & think they're bad!

LINE LOCK:

       So, I trudged off to visit some of our local street rodders (no, not the Japanese 'buzz bomb' kids, the American muscle car guys my age!) to see what they use.  And, there, I learned more about 'line locks.'

        A 'line lock' is just a little electrical solenoid that, when activated by a button, maintains up to 3,000 pounds of hydraulic pressure on the chosen brakes (front or rear).  Most bracket racers place the 'line lock trigger' on the gear shift lever where its within easy reach of their thumb for staging out of the start lights.  They also usually integrate it into the front brakes so the rear wheels are free to start their run up without the car moving.

        So, while I'm not certain how I'm going to build a setup for my parking brake; I know I'll put a line lock in the front brake system (activated by a switch on the shifter) so I can lock them and apply power to the rear wheels for a quick take-off.  Corvettes be warned!
______________________________________

REAR PARK BRAKE:

       But, back to the parking brake issue.  Wilwood Engineering offers what it calls a 'mechanical spot caliper' for custom parking brake applications.  Wilwood describes it as:  

"The single piston floating Mechanical Spot Caliper is compact, lightweight and widely used in Parking Brake, Karting, Recreational and Light Industrial applications. Its two position, cam-actuated lever permits right or left, front or rear mounting, and accommodates two settings for leverage adjustment. The 1.2 pound Mechanical Spot fits rotors with diameters from 6.00" to 13.00", thickness from .25", and is supplied with pads installed. The caliper is available black or polished."

        The price is reasonable ($50-range) and they may be just what I'm looking for.  So, its on to a Wilwood representative for answers.

        And, pretty informative they were.  In addition to confirming that the Wilwood spot caliper would work in conjunction with the MGB parking brake cable setup.  A quick phone call to Summit Racing (1-800-230-3030) got them on order.

        Next is bracket construction. 

15 December 2005:  Okay, the brackets are finished.  We used a Pontiac Fiero bracket setup to get the angle right for the Wilwood sliding calipers.  Here are a couple of photos:

        Now, I've got to slide up under the car & see how they'll interact with all the other stuff back there.

STAY TUNED!