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MGB Brake System Components

Some say that early April is way too early to start pushing brake parts. I feel otherwise…

Proper brake system overhaul takes time and effort. Why not get at it now, prior to driving season. We’ve got all the components on sale now. If you do your brake work now, you can do it all in an organized manner and end up with a first class job.

-Or you can buy it all at the height of driving season for higher prices, and then do a slap-dash job, just to get your car back on the road.

The choice is yours…

MGB Brake Master Cylinders

All of our Brake master cylinders for MGBs are TRW brand. We’ve gone down this road for a few good reasons:

There are some no-name master cylinders out there and they are cheaper. They come in plain boxes and they don’t carry a guarantee of any kind. Do you really want to risk your cars braking ability in this fashion? At Obsolete’, we don’t feel that way.

MGBs all came from the factory with Lockheed brand master cylinders. Lockheed has priced their master cylinders at levels that are no longer tolerable. They are simply too expensive! Added to that, I think that their production tooling is getting worn out. It means that their master cylinders may be more prone to leaking or failure (just my humble opinion mind you)

Since we seriously started selling TRW master cylinders some years back, I have noticed that there are a LOT less problems than there had been previously.

All of our master cylinders and related components are on sale now. Even with our foundering dollar, I think that most of these parts are on sale now at lower prices than they were ten years ago!



MGB 63-66 Brake Master Cylinder

This is the single-circuit master cylinder used on the early cars.

I am not a proponent of single-circuit brakes, but if you need a new master cylinder, here it is.

This is a reproduction cylinder. It has an Aluminum body and a plastic reservoir.

It looks like a poor excuse compared to the original Lockheed cylinder with the “tin-tank”.

That being said, we’d like you to know that the Lockheed brand cylinder is no longer supplied with the tin-tank either. The currently available Lockheed cylinder also comes with a plastic reservoir now…




MGB 68 – 74 Brake Master Cylinder

This is a high-quality TRW brand master cylinder.

Ten years ago, we were selling a Lockheed brand master cylinder and it cost three hundred bucks or more. At that price, there was lots of master cylinder rebuilding going on. I couldn’t blame anyone for trying when a new cylinder was so damn expensive. Anyone who has tried to rebuild one of these masters’ will know how much FUNNN it really is:

There are two snap rings (circlips) buried down deep inside the cylinder. They must be removed to get the “guts” out of the cylinder. They are next to impossible.

And did I forget to mention how much fun the “Spirolox” circlip is on the end of the piston rod is? That circlip has to come off so the return spring can be removed. I think you need to be a trained monkey to do this job. Nothing that six hands and many cut fingers won’t be able to accomplish!

And if that ain’t bad enough, the white nylon guide bearing in the cylinder above the second snap ring is often seized inside the bore. Just try and break it out in little pieces with a screwdriver. I know you’ll enjoy it!

Sadly, after all the effort to dismantle a cylinder and pull out the piston, most cylinders are rusty, pitted messes, not capable of being rebuilt…

We have brand new ones on sale now. What more can be said…

Fits any 68 – 74 MGB or MGB GT.

These are dual-circuit cylinders. May fit later 67 cars if they have dual circuit brakes.

Will fit 74 ½ MGBs too, as long as they DO NOT have a brake booster.




MGB 75 – 80 Brake Master Cylinder

This is also a TRW brand cylinder.

It is original for 76-80 cars, but makes a perfectly useable substitute for 1975 cars. Original cylinders for the 1975 model year are not available. The only difference was that the original cylinder had a somewhat wedge shaped reservoir, while the later one is more square.

Works just the same…



MGB Brake Pressure Warning Switch – 1975 models

Screws into threaded hole in the master cylinder body.

This is a BLACK plastic switch. Only fits 1975 models



MGB Brake Pressure Warning Switch 1976 – 1980 cars

Screws into the master cylinder body.

White plastic switch.




MGB – MG Midget Brake Light Switch – Lucas brand component

All 1968 -1980 B’s and Midgets use the same mechanical switch to operate the brake lights.

It has always had reliability issues…

That being said, it is an improvement over the hydraulic switch used in 63 – 67 cars. If you needed to change the brake light switch in an early car, it would involve brake bleeding!

There have been a number of different aftermarket switches over the years. For quite a long time, even the Lucas brand switch was an aftermarket item, sold in a Lucas box! The aftermarket switches have been noteworthy for their haphazard operation. Some are fine, and then there are the others…

In recent years, I wondered why the switches of our American competition cost ten bucks and ours cost close to thirty. Nope, it isn’t us being greedy. Most of the competition is selling aftermarket brake light switches. Some work OK and some don’t.

We just lucked into about twenty-five proper Lucas switches in original Lucas boxes.




MGB – MGA Brake or Clutch Pedal Spring

Pedal springs often getting damaged or broken. Sometimes they are missing entirely.

If you have a missing spring, the affected brake or clutch pedal will flop up and down, since nothing will be holding it up.

These have been hard to come by in the past, so we got some into stock.

Fits any MGA or MGB, brake or clutch pedal.

Also fits Midget 1275 & Midget 1500.




MGB – MGA Brake & Clutch Pedal Bushes

Pedal bushings have been unavailable during the past year or two. We finally got some in recently.

Most every car needs new ones…

The brake & clutch pedals pivot on a big long bolt, and there is a bronze bushing inside the hole in each pedal arm.

The bushings become worn and loose.

It can cause your pedals to actually vibrate under the dash!

More importantly, worn bushes cause lost pedal movement and it just doesn’t feel right.

In the case of a marginal clutch, it can result in less than full release of your clutch. This is especially true if you have a little wear in the clutch master cylinder and clutch slave cylinder pushrods.

Installing new pedal bushings is not too bad of a job. On a chrome bumper B’, you’ll need to remove the pedal box cover and then remove the big thru-bolt that secures the pedals. You then remove the pedal return springs under the dash. This will then allow you to lift up the pedals and slide the old bushings out and install new ones.

Not too bad of a job really.

Fits MGA brake or clutch.

Fits all MGB for the clutch.

Fits 63 – 74 MGB or MGB GT for the brakes.


MGB – Midget & TR6 – Spitfire Brake Differential Pressure Warning Switch Block (4-way or 5-way Brass Block Thing)

There seems to be a lot of confusion about this component.

Every year we get lots of calls about this subject right around the middle of May, coincidentally with the start of driving season!

Contrary to popular belief, this unit is NOT a proportioning valve. The brake fluid flow to the front & rear brakes is separately “metered” by the primary & secondary circuits inside the master cylinder. That is why there are two separate sets of brake piping from the master cylinder, all the way out to the brakes on the front & rear wheels.

The most common problem that we hear about is that the plastic pressure-warning switch has failed and is “leaking” brake fluid. If you consider that the pressure-warning switch has a simple plastic body and no sealing washer, it should be apparent that this switch is NOT designed to withstand hydraulic pressure at all. Brake fluid leaking out around the plastic switch indicates that the sealing o-rings on the shuttle piston have failed inside the body of the unit.

Inside the brass block there are fluid channels connected to both inlet and outlet ports. (These ports have threaded holes into which the brake pipes screw in.)  Between the two separate “circuits” in the valve block there is a machined channel. A shuttle valve with o-ring seals sits inside this channel.  The shuttle valve is hydraulically “balanced” by pressure on both front & rear brake system circuits. If one brake circuit fails (the pressure drops), the shuttle will be pushed sideways by the hydraulic force exerted on it by the other “circuit”. As the shuttle moves in its bore inside the casting, it pushes against the pin on the end of the plastic switch. The switch contact then closes, completing an electrical circuit. This causes the brake system “IDIOT” light on the dashboard to glow. I suppose that the brake pedal falling to the floor and little or no braking being available might be another indication of trouble…

Here is what you get when you take the warning switch block apart. The shuttle piston is plain to see. In most cases, the failure of the shuttle o-ring seals causes brake fluid leakage around the plastic warning switch.

You can buy a new pressure warning block unit. The cost is frightful. Expect to spend upwards of $500 for a new one!

Differences between 4-way TR6 units and 5-way MGB units

The brass block switch units are pretty well identical on these cars. I’m referring to original Brass components, not the cast iron replacement assemblies that I’ve seen on occasion.

The TR6 only uses a 4-way fitting because the front brake pipes are split with a brass adaptor fitting on the chassis. In the case of an MG, the unit is a 5-way fitting as both front brake pipes come out separately from the warning block. The casting for both units is identical. On the TR’, the threaded plug that seals and retains the shuttle piston is blanked off. On an MG, the plug is actually drilled and tapped for a brake pipe.


Conveniently enough, mine just failed…

The symptoms were simple enough: mushy pedal, and hardly any brakes.

I jacked up the car and examined the brake calipers and the brake hoses. Everything looked good. Then I had an assistant pump the brake pedal while I looked around. Suddenly I saw a few bubbles coming up from that plastic warning switch on the brass block. It is a good telltale sign. You know that the shuttle seals have failed as soon as you see that happening.

They don’t make these things too accessible for service. Here’s my advice:

Suck out as much brake fluid as possible from the master cylinder first.

Use any sort of a suction tool that will work.  Undo the brake pipes from the side of the master cylinder. They are the easiest. Put plenty of rags down underneath the master cylinder to catch the inevitable drips of brake fluid. It eats paint!

Unscrew the two brake pipe fittings at the base of the brass block that conduct the fluid to the front and rear brakes. Then undo the single bolt that secures the brass block to the underbody. Disconnect the electrical connector off the top of the switch.

Pull the brass block assembly, complete with the short master cylinder pipes, up and out from under the master cylinder.

Get in there with hot water and soap and immediately clean up any dripped brake fluid-before it wrecks your paint.

The brass block can then be dismantled and overhauled with a new seal kit and reassembled.



Brake Pressure Warning Switch Block Seal Kit

This kit contains the small shuttle valve o-ring seals as well as a copper sealing-washer for the end plug.

The shuttle piston uses only two o-rings. The kit contains o-rings for both early & later shuttle piston designs, so it is sure to fit yours!

Installation is easy and this repair may be the answer to a “dodgy” brake hydraulic system.

Fits TR6 – TR250, Spitfire & GT6, MGB 69-74 & Midget 68-74



Brake pressure Warning Light Switches

These are the plastic switches that screw into the four-way or five-way brass block.

These are replacement type switches, but they both fit properly and the electrical connections are “as-original”.



TR6 69 – 76 and MGB 68 – 74 Brake Pressure Warning Switch