by Demon Tweeks
The dimly lit workshop is cluttered with bits of old Cooper racing cars.
It is nearly midnight. Outside it rains heavily. Two elderly men are seated on empty 20 litre drums staring at a MK6 Cooper JAP with the right front wheel removed.
The bald one, approaching a hundred, speaks softly to his old friend and confidant Uncle Des.
“You know something Desmond?” Chas McGurk mutters sadly, “these Coopers should stop a whole lot better than they actually do!”
Revived by a recent Mars Bar, Uncle Des shows interest in Chas’s surprising statement.
“What do you mean?” Des quizzes. “I thought they had pretty good brakes!”
“Not really,” Chas goes on. “Our Coopers weigh less than 400 kilos with driver and fuel. They have 8 wheel cylinders, 8 leading shoes, working in 4 good cast iron linered drums with 2 master cylinders!
Above: Mk6 Cooper brakes as Des and Chas saw them
On paper that’s as good as you can get! They should stop on a sixpence……. but they don’t! Even with really good linings we have to lean pretty hard on that brake pedal, much harder than you would expect. It’s not a big problem at sprints and hillclimbs, but it’s a different story when you need to knock off a hundred miles an hour in a hurry at the Mallala hairpin.”
Anxious to help and always up for a challenge, Des leant forward carefully on his drum and asked for a torch. He studied the Cooper’s exposed brake set up for some time.
Impatient for a verdict Chas prompted him. “What do you reckon?” he said.
“I think it’s got something to do with the brake shoes,” Des said. “I don’t think they self- energize much…… or at all.”
“The brake shoes,” Chas repeated, seeking clarity, “what’s wrong them?”
Des took a deep breath and got started. “This is only a theory,” he warned, “but this is what I think. What we are looking on this car and most other Coopers, is a Lockheed twin leading shoe set-up straight off a Morris Major. Is that right?”
“I believe so,” Chas nodded.
“Well,” Des continued, “let’s compare this arrangement to a typical Norton twin leading shoe brake. The Norton has both brake shoes located on the backing plate by fixed anchors at their trailing ends, so that when actuated they pivot outwards. As the leading edge of the linings makes contact with the rotating drum, a natural self -energizing action of the brake shoes takes place, and the result is a powerful effective brake!”
Chas, who was following Des’ dissertation with great interest nodded. He was right on it!
“But that’s not what’s happening here,” Uncle Des went on. “The shoes on the Cooper are not fixed. They are floating! They move around. They don’t pivot, and when these brakes are applied and the lining makes contact with the drum, instead of energizing the leading edge of the shoe like the Norton, I reckon these shoes simply slide in the direction of drum rotation and wedge the trailing end of the shoe against the blind end of the opposite cylinder.”
Silence followed Uncle Des’s hypothesis. “And you reckon,” Chas said after considerable thought, “that the self- energizing effect of this form of leading shoe arrangement is minimal?”
“I would make so bold,” Des admitted shyly, “to suggest the trailing end of the shoe could be doing most of the braking.”
Chas exhaled slowly. “That’s a big statement,” he grinned.
“I will give you supporting evidence,” Des continued confidently.
“If you Google Lockheed Brakes of this design you will find this proud boast. Lockheed state, and with some emphasis, that this design is a ‘Non- grabbing brake!’
“Now what does that suggest? The logical inference is that it has little self- energizing tendency! And something else! Do you remember those good looking twin leading front brakes Triumph and BSA put on their bikes in the 70s? They used exactly the same Lockheed shoes that are on the Coopers! The only difference was they were mechanically operated.”
Chas nodded knowingly. “They looked good,” he said, “but they were a hopeless bike brake.”
The two seniors lapsed into a reflective silence. Then Chas asked the $64 question.
“Should we tell anyone about this? And would they believe us? I suppose we could run it past Brian and Garry and Steve and Terry and see what they think? They’ve all got one of these things at home.”
“And while we are talking,” Uncle Des interrupted, “there’s something else weird about these brakes.”
“Please don’t tell me,” Chas said, shutting his eyes tight so he couldn’t hear. “What?”
“Have a look at these wheel cylinders,” Des said. “Notice anything odd about them?”
Chas gave them the once over. “No,” he confessed. “I can see they are early Morris 7/8” single ended Lockheed brake cylinders, but what’s odd about them?”
Uncle Des prodded a nearby cylinder with his Phillip’s head screw-driver and said, “They’ve got no bleeder screws,” and handed Chas the torch for a closer look.
Chas checked. Des was right! Eight brake cylinders with no bleeder screws! The brake hose supplied oil to a brass union on one wheel cylinder which fed an external pipe to another brass union on the other wheel cylinder. The only bleeder screw present was screwed into the last brass union at the end of the line making it possible when bleeding for fluid to completely bypass the cylinders!
Chas shook his head as he tried to work it out.
Des helped clear his thoughts with a brief summary. “The way this is plumbed,” he said patiently, “means that when you bleed the brakes, it’s very difficult to get all the air out of the cylinders, because there’s only one hole in the cylinder and that’s where the brake fluid enters. With no separate bleeder screw, any trapped air will be trying to get out through the same hole as the oil is trying to get in! Right?”
Chas worked on it for a minute and then gasped, like when Archimedes discovered why boats float.
“That’s why it’s so hard to get a decent pedal when you try to bleed these brakes, and why you’ve got to adjust the shoes up tight to get the wheel cylinder pistons right in, and clamp off the hoses and bleed one wheel at a time, and kick the pedal hard and fast. And what makes it worse, the cylinders all point in different directions. Up, down and sideways. And remember these cylinders were ever only used on the Morris front wheels in a horizontal position.”
There was another long silence. It was longer than usual. Uncle Des and Chas looked at one another.
They were both thinking the same thing. ‘Why do we do this to ourselves?’
They smiled as they said ‘Goodnight’.