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MG MGB Technical - Brake Problems

Last night i replaced a bit of piping from the carb to the engine on my 80 MGB (i'm pretty sure it was the vacuum hose). Started the engine, everything worked fine, including the brakes.

Now this morning when i start to go to work, there are no brakes. Zero. Zip. Nada. There's no pressure behind the brake peddle. There's plenty of brake fluid in the container, but no brakes.

Could a brake servo just stop working overnight?

It's just total madness. I fix one problem and another one springs up in it's place.
Chris

When you say there's no pressure behind the pedal, do you mean it goes straight to the floor when you put your foot on it? Even without the servo assistance, the brakes should work pretty well and stop the car with very little difficulty (I tend to run out of traction way before I run out of braking force).

If the pedal hits the floor, either you have a sudden massive leak in the hydraulic side, or the rubbers in the master cylinder have ceased to seal properly. Either is a pretty remarkable thing to happen overnight. If it's the rubbers in the MC, you can usually get some brake pressure back by tapping the pedal hard rather than applying it softly - this forces badly-fitting seals outwards to fit the cylinder.

Did you see lots of white smoke when you started the engine?

Hope this helps,
--
Olly
Oliver Stephenson

This morning, the pedal hit almost to the floor, and then i got some braking power.

Now when i try it it seems to have regained a little more power.

When i first tried it, it was 4am and quite cold out, now it's about 1pm and slightly warmer.

I couldn't check under the hood this morning due to the fact i was supposed to be at work! And now that i've checked under the hood and saw nothing had disconnected, and there's no liquid leaks anywhere i'm a bit stumped.

No white smoke when i started the engine...

I was thinking maybe i just need to bleed the brakes?

I'll try pedalling the brakes to see if more pressure returns.
Chris

You've got a leak! The pedal to the floor and then some brakes is the dual-circuit arrangement doing its stuff. At a guess, I'd say that it's on the rear circuit, probably a slave cylinder gone so you can't see anything. Look carefully at the M/C resevoir. You'll see it's partitioned into two. I'll bet that the front half is empty, even though the rear half (which is all you can see through the filler cap) is mostly full.
When you've found and fixed the leak, remember to partially unscrew the warning switch from the bottom of the M/C to allow the piston to reset before bleeding.
Incidently, the "brakes" warning light on the centre console should have come on here...
T J C Cuthill

You'll have to bear with me as i *still* don't have a haynes manual to know exactly what i'm looking for...

The M/C reservoir you mention, that's the little tank for the brake fluid, right?

If that's the case, roughly where would i be looking to find the leak?

Thanks!
Chris

Chris. Not having a Haynes manual, or, better yet, a Bentley manual, might be an indicator that you should let someone else find the problem in your brake system. Not having the basic reference manual and having to ask if the brake reservoir is the little tank on top of the MC, perhaps, indicates that this particular project is slightly more advanced than you should attempt right now. All of us learn about working on cars by undertaking various projects and either doing them correctly or making a mistake and having to do the project over again. Mostly, when you make a mistake, you are only out time and, sometimes, the money you spent on the parts you damaged.

With brakes, however, making a mistake can result in your being killed, injured or killing/injuring someone else. Not, necessarily, a good early learning project, especially when there is a problem in the system.

The brake master cylinder reservoir is the white, rectangular shaped piece on top of the master cylinder. It has a white, plastic knob similar to the one of the clutch master cylinder. The first thing to do is remove the cap and check for fluid in the reservoir. If the reservoir is full, you do not have a system leak, but may have a bad master cylinder. If one of the chambers of the reservoir is empty, you trace the line, or lines, from that chamber and try to find where the leakage is. Sometimes, you may have to bleed the system, then have an assistant step on the brake pedal and hold it down to put pressure on the system, allowing you see where the leak is more easily. If you can, use some simple green (it has never damaged paint or rubber lines/bushes on the cars I have used it on) on the lines, brake hoses and the areas around them. The most likely places for a leak are at the junctions where the hard lines hook to the master cylinder or the rubber hoses hook to the hard lines. Sometimes, the hardlines will be cracked and you will just see a little brake fluid being forced out of a hairline crack. This is not common. Cracked rubber hoses that connect the hard lines to the moving parts of the systems (front calipers or the rear axle hard lines) can crack and leak. Bleed nipples can loosen allowing fluid to leak out and air to leak in. Calipers seldom self destruct, but wheel cylinders can quite easily, contaminating the rear brake shoes while doing so.

The basic principles are easy. Find out if there is missing brake fluid (if not, a MC problem) and, if there is missing fluid, clean and check until you find where it is leaking from. On the RB master cylinders there is an additional area to check. This is the brake failure warning switch which is attached to the MC. Many times, this part of the circuit is not rebuild when someone rebuilds the main portion of the master cylinder. There are two rubber O rings in this part of the circuit which, if not replaced, allow brake fluid to leak out through the brake failure warning switch. You normally notice this first when you notice paint damage on the inner fender under the switch.

By troubleshooting the system yourself, you may save a little money and will have a better idea of what is wrong. Whether you decide to do the work yourself or have it done for you is a personal decision. Decide wisely, as you are playing with your life. Les
Les Bengtson

Les, what is green? I'm assuming it's not a reference to the pure, unadultered Green discovered by Percy in a Blackadder sketch :o)

Sound advice though.

Chris, get yourself the manuals, you can't possibly hope to do any work on these cars without them, and the people on this BBS will always assume you have them and will give references to them. The Bentley book is best, but Haynes got me through my first 2 years of B ownership. They're not expensive compared to the petrol we put in every day.

ttfn & good luck,
--
Olly
Oliver Stephenson

Olly. Have been down with a cold for the last two weeks, hence, I did not capitalize properly. Simple Green is a "biodegradable" cleaning solvent available here in the US. It is not as good a degreaser, in my experience, as Castrol Super Clean, STP Grease Eater, brake cleaner, etc. but is much easier on the paint, hands and lungs. Hence, it makes a good solvent to start with. If it will not do the job, you can go to one of the stronger ones.

As to Black Adder, have not seen it for years. Recently, my wife found a four episode or five episode VCR at the local library, dealing with the WW I scenario. (There was also a second set of Black Adder episodes dealing with early Brit exploration shown here in the US.) Unfortunately, the local Public Broadcasting System intermixed the episodes and broadcast them out of order. When seen in order, them made a very surprisingly powerful statement. Les
Les Bengtson

Did you place clamps on all hoses? or inadvertently knock one off?

Things rarely go "pop" in the night --

I'd suggest you double check hoses, clamps, connections etc.
glg gimbut

Gotcha Les, I was just wondering if there was another substance that was simply known by its colour, like blue is. Y'all know what I mean, right? :o)

Taraa,
--
Olly
Oliver Stephenson

A pipe from carb to engine is nothing to do with braking. The brakes problem is purely coincidental. If there is no fluid on the floor and the level is correct in the reservoir the master cylinder seals have gone, Pure and Simple.
Paul Hunt

This thread was discussed between 31/03/2003 and 01/04/2003

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