Brake master, replace original single with dual?

Hello Folks,
Has anyone replaced the early single outlet master cylinder with the later master with two outlet ports? I imagine that would be a little safer?? If so do the mounting holes match the ones in the chassis?


Wes Keyes
York, Maine

You’d have to very careful, to get brake balance correct, by using different sized master bores, like Sprites did.

Hi Wiggles,
I need to replace the brake lines anyway because they are pretty rusty. If I used a later dual master and match the brake line setup of the later system I would be OK right? Or am I missing something obvious?

Thanks for your reply.


The mounting holes in the chassis bracket do NOT match.
Nor do the holes in the LHD heat shield. Took me awhile to figure out what was wrong with the one I got from one of the majors.

BTW the tandem master is a single bore size, and the wheel cylinder pistons are all a single diameter.

Its only safer if you blow off a hose. Otherwise the tandem folks seem to report more problems than the single folks on this forum.

Thanks folks,
I guess I’ll leave well enough alone for now.


Wes Keyes

Really? The slaves all had the same diameter?

Paul, on TRs, there are various sizes seemingly sold indiscriminately, My wife had to quit driving my TR3
agter I installed a TR6 OD transmission. had installed smaller diameter slave (sold for the TR6) The pedal pressure was high enough that her bad knee could not deal with it.

Yes, all 120s have all 1.125" diameter wheel cylinder bores front and rear, and all use the same #2762 rubber cup seal.
The tandem folks have reported problems with the tilt valves, which are not part of the single master.
On the other hand, I once had a problem with my single system; the brakes locked up and I could not move the car for an hour, but that turned out to be due to my use of DOT 5 silicone brake fluid, which swelled the seal in the master and impeded the release of the pressure.

How did they deal with brake balance?

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Careful design and experimental testing at the MIRA track, with help from Lockheed. The 120 has twin leading shoes in front, and leading and trailing shoes in the rear.
Drum brake system design involves a lot of trigonometry and calculation of forces applied to the shoes. Probably beyond the scope of this forum.
BTW when you have your shoes relined, duplicate what was there, don’t allow the shop to line them toe to heel, or if they do, trim them off when you get them back. Too much lining can shift the center of pressure and reduce their effectiveness.

Actually, you reawakened a loooong forgotten memory (it’s been at LEAST 35 years since I did any 120 brake work). The design of the single leading and twin leading shoes, plus the differing material length, is the same way DKW did it, but they also used different-sized slaves.

Drum brake system design is starting to be a lost art.
Later Mark V with sliding pivot shoes has front twin leading shoe wheel cylinders with 1" bore and rear leading/trailing shoe wheel cylinders with 1-1/8" bore.
Mark VII with vacuum assisted brakes has 7/8" bore rear wheel cylinders, which will fit in a Mark V. Guess who bought one from a foreign parts store guy who said they were the same, and drove around with it on the left rear for years and wondering why the brakes seemed a little bit squirrelly.

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Sorta, but I for one, will not mourn their passing, as I do not mourn the death of carburetors, points and condensers: even our buses now come with air discs, and they are, as is the engineering norm, better designs and stop the bus a whooole lot better.

I was talking to a fellow mechanic, and he says the last shop in Denver with an drum arcing machine has gone out of business.

The importance maybe not so much their passing so much as their preserving as another step in the evolution of human understanding. Hydraulic drum brakes all around were state of the art in my youth. Front discs in combination with rear drums appeared later, later still discs in all four corners. I did my driver’s test in a 1957 Bel Aire. No power assist and drums all around. It wasn’t an unsafe car, unless you decided to drive it really fast.

I’ve always thought that disc brakes are over hyped. Yes discs are better at getting rid of heat in racing situations and brake fad, but largely irrelevant for street cars imo. Drove different 4 wheel drums for many years and never felt in danger because of stopping distances. They could lock up the tires in panic stops as good as anything.

Try driving a C3 corvette with the common at that time, 4 wheel discs and no power booster. I’d take a good 4 wheel drum system over that anytime. Insane pedal pressures required.

You’re probably aware that Jaguar went back to the single system after the short term use of the tandem system in the XK. Even Jaguar didn’t like it.

Anyone have a recommendation for a good flaring tool?

Napa has the full kit, or you can buy just the mandrels.
Search the archives, as I know we have discussed the method of using this tool. I made all new cunifer lines for my Mark V.

A friend of mine recently got his 1960 Rambler back on the road, after rebuilding the engine and brake system (his aunt bought it new, and it was the car he learned to drive in).

I helped him along the way, and when I took it for a drive–was the first time in a loooong time I’d driven a car with unassisted drum brakes–I was made aware of inferior they are, to disc brakes.

They’d stop the car, no doubt, but they take a different mindset and driving technique.

Yes, it’s an art, one that is rapidly disappearing, and one restorers will have to keep alive in the small niche of that design, but… thank gawd we’ve progressed past them.

There is a reason drum brake technology is fading into history.

Thanks! I think I have this kit, same kit as sold by a bunch suppliers with different colored cases, maybe. Anyway, I’m not 100% that it produced leak free formed ends, but I should know this pretty soon. My supposedly custom fit for my application tubing kit, fit almost nothing. I ended up having to do a lot of cutting and reforming of flared ends. I regret not spending the bigger bucks for a better tool.

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Not entirely true Jaguar going back to single system they were sort of forced to as the American mechanics made such a mess of working on the twin system.
If you read the Jaguar service bulletins early 1950’s there passionate calls for mechanics to read the service bulletins on how to work on them ie undo the tilt valves before ripping the piston out!
When they could they went back to a twin system the 3.8 litre E type.
A little to complex for the time - they do work perfectly when rebuilt an bled.