MGB & GT Forum

I've read all the posts on the topic above. Here's my problem. I've purchased a B that had a very good brake pedal for the first week or so of ownership. I noticed a stream of brake fluid on the floor and now have half the pedal I had originally. The rear half of the BMC is dry and there seems to be some weeping around the warning light switch. Is my shuttle valve bad or is it the switch which needs attention? I cannot see any problem with the rear brakes. No signs of fluid. Can the shuttle valve be repaired in place?

Thanks

Your master is going bad

You can't loose enough fluid in a week from the pdwa to affect half pedal.
Install a 3/8 24 unf bolt 1/2 inch long with a copper or nylon washer.
Then don't drive it till you replace the master and flex lines and inspect /replace rear slaves.
Brakes are good to have in ample supply.

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The previous owner had replace the master a few years ago. I'd have thought it would have lasted longer? If the rear of the BMC is dry I guess it makes sense there's a problem to the back. I really don't understand the master going bad and the fluid leaving from only the rear half. It's been my experience if it gives it up you have no or a mushy feeling pedal and maybe some internal leaking.

It could be going out the slaves. Peel them back and look.

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LNDRVR4X4.COM
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1957 Series 1 Land Rover electric VEHICLE CONVERSION

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VIETNAM 1969-1972

I sympathise with your sentiment, but the early double MC is an unpredictable bastard. Guess how I know

I once managed to get new seals in such a device following Porter's recipe from his book (slightly modified), but it was a PITA job. JT even has a video on YouTube with a failed attempt.
In the past these MC's were horribly expensive, but in recent years I've seen quite low prices for aftermarket new ones. Thanks to the Chinese renewal is cheaper than ever

The shuttle valve and the brake warning system are something else and not integrated in this first double MC type, like it became in the later one. The switch was always a bit finicky, but even if the switch and shuttle valve both are at fault it will hardly give a spongy brake pedal. This HAS to come from the MC, a rear brake cylinder or a caliper up front. In a car that stood still for a number of years, there is a high probability of rust in one of the rear brake cylinders, which leads to damage on the seal and loss of fluid. I would always check the condition of the rearbrake cylinders, by taking the drums off and check for fluid loss. Cars being sold have often not been used frequently before and most probably will also not have received new brake fluid in their system every 2 years

All the best with your B though, you will solve this one way or the other




Edited 1 time(s). Last edit at 2016-05-24 03:15 AM by Donthuis.

I'd find out where all that fluid had leaked out from before drawing any conclusions.

In relation to the car where exactly on the floor was it ?

Pool under drivers front. Inner fender Looks like it had ran down inner fender under the junction of all the lines at the shuttle valve. MC looks dry.

This reads as if the seals in the shuttle hve gone bad. Not so daunting to change however you will need to bleed the brakes. I suggest that you promptly wash the brake fluid from thr inner fender, this fluid eats paint quite well.
You can get a kit of seals from teh usual vendors

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Bad seals in the shuttle typically don't show up with that kind of fluid loss.

I'd check the lines around the PDWA for holes or loose connections. That's a lot of fluid to lose.

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"Speed costs........how fast you want to spend?"

What model year? (it makes a BIG difference). Please put model year in your profile.

I had a rebuilt MC last 10 years which I thought was not acceptable and I really did not like doing that particular job over and over again so I sent my original to Apple Hydraulics in Chicago. They will put a silicon bronze sleeve in and they are better than the original. Leaking around the brake sensor manifold is common. Most will tell you to remove the sensor and plug the hole but that is not entirely safe because if the piston in the manifold is leaking the fluid may go between the cylinders defeating the purpose of the dual cylinder system. You can get a rebuild kit from Moss for the manifold. Then after you rebuild it you can plug the hole because the brake sensors were silly and useless.

Simon X2.
Shuttle errors seldomly lead to significant fluid losses, just weeping at the center where the switch is sitting

The model year (1973) is in the title. Have good and bad news. The warning switch had been over tightened and was leaking at the base.(Good news) I tried removing it and it broke off leaving plastic threads in the brass shuttle valve threads. (Bad News) EZ outs will not remove the remains of the switch. I'm about to start digging them out and hope I don't screw up the threads in the shuttle valve. Anyone got any other suggestions?

Donnie, too bad the switch snapped off, it was probably brittle with age. However, the switch does not figure into the sealing of the body of the valve. If the seals on the plunger are shot then it will leak through the switch.

The fix is to remove the whole thing, take it apart, replace the O-rings on the plunger, and reinstall. Or, put the bolt in place of the switch after you've dug all the plastic out of the threads.

Already gave you the specs of the bolt. And contrary to some belief the valve doesn't create or maintain the dual circuits. It is and always shall be just a warning device not a failsafe dual circuit protector.
Lose one of either circuits and your braking is compromised, your foot is heading to the floorboard, if working the silly lamp will light up. You won't notice it because hopefully when you stomped on the brakes and realized you weren't stopping and your foot was going places never gone before you have taken the needed measures to avoid the object's fast upcoming

Want a true dual circuit system? The desighn has been posted several times for the simple to install modification..

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LNDRVR4X4.COM
Home of Project "INCARN8'


1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
FIXITUPCHAP INCORPORATED

RD3 Radar/ Electronic Warfare Technician
VIETNAM 1969-1972