MG Sports Cars

I'v been trouble-shooting the fact that my front disks keep locking up, I've tried all the usual suspects so now I'm taking look at this. Mine is the one located on the driver's side inner fender not the on that's part of the master cylinder assembly.
I unscrewed the switch assembly expecting to see a plunger but there wasn't one. Also the hole was full of fluid when I had read that it would be dry in there.
What's the story behind this?



Edited 1 time(s). Last edit at 09/04/2015 10:14AM by limey222.

[www.youtube.com]

I'm more than a little concerned about the explanation of the operation of the "shuttle valve" on YouTube.
First and foremost. If the valve is leaking.
You must fix it!
Threading a bolt into the hole to seal it is beyond belief.
To recommend that repair is irresponsible to the extreme.
All that you have accomplished is to turn your brake system back into
the very dangerous single line system.
Clearly this gentleman does not understand the function of this valve.
It's main purpose is to shut off brake fluid flow to the damaged circuit.
This ensures that the remaining resources can be directed towards the functioning circuit.
The warning system is a secondary function. It merely indicates a failure, that clearly, you can feel in the pedal.
It's purely a federal requirement designed to prevent stupid people from doing even dumber things.
As they say "if we could remove all the warning labels, the problem would cure itself".
Making your braking system the most high performance system on your vehicle should be your first priority.
If you can't stop you have no business going.

Fred

JT tends towards controversy that way. There are other examples including his recommendations for setting spindle bearing clearances as I recall but so far every one of his videos I've watched include a basic cluelessness of the underlying engineering objectives. It's more that he gives the impression that there is only one way to do things, it's his way, and it's the right way. That might be OK if he was in fact right but like anyone else, sometimes he is not. It would also help if he really knew his subject, but again from appearances, often he is missing critical information. Like this video, it reminds me of a country back yard shade tree mechanic who has found a way to get the car running again, and right or wrong, that's the way to do it, regardless of other considerations. But maybe I'm being overly critical.

To give him credit, John has apparently been a powerful figure in certain MG circles, particularly in his own geographic area, has promoted the sport rather tirelessly, has hosted an annual gathering which has grown quite large, and has provided goods and services to a wide spectrum of MG owners, and for that he deserves full credit. He has also evidently published a large number of videos on how to do common tasks and I'm quite sure that for the most part they have benefitted vast numbers of owners who needed answers and guidance. It's unfortunate that most of the ones I've seen have been flawed, but at least they are there and for the most part seem to do more good than harm, or at the very least allow for a temporary or emergency repair.

That's the category this one should be in probably, emergency repair and then only in specific conditions. Well, he did say "if it is leaking" and I suppose we are to assume the braking system is otherwise performing correctly and the indicator light is not on, meaning the shuttle is centered. However that also means at least one of the shuttle seals are bad so the risk of compromising the dual circuit system is obvious. The worst of it is that he did not fully explain the operation of the shuttle valve in what is an essential safety system where there is a very great possibility of creating a condition that can endanger the vehicle's occupants. One may assume that this could be because he did not fully understand said operation, and until Fred's explanation, I'll admit I did not either. I had no idea it could shut off one master side of the dual cylinder but this is a great idea as it retains the fluid in the reservoir in the condition of a leak, obviously safer than simply draining it down to the divider wall in the reservoir when there is one. (Aren't redundancies wonderful things?) Still, the proper fix is to replace the shuttle seals. I think he did mention that.

I'm quite sure someone will defend JT here, he has a lot of followers. And that's a good thing too.

Jim

Quote:

It's main purpose is to shut off brake fluid flow to the damaged circuit.
...
The warning system is a secondary function.

Fred,

Usually, I take your word as gospel, but I must disagree with you this time.

The sole "purpose" of the valve is to operate a warning light. In order to do this safely, it also must provide isolation between circuits. Take out the warning light function, and the valve serves no purpose/function at all. To get the warning function, an additional failure point was introduced.

I don't have one on my car. The two circuits are totally isolated from each other using hard lines, no isolation valve needed.

Don't know if its relevant but you may get brakes locking on and not working at all if you use silicone brake fluid in these dual line systems. I had this problem and changed all the master cylinder seals twice before going back to the single line system which works perfectly with the same silicone fluid.
I have been told since that the seals can harden a little and it causes a problem with the servo.

Not that, I use DOT4 but thanks for the suggestion.

I fly to the UK tomorrow for our 25th Wedding anniversary, a vacation and to visit family. I have arranged to pick up a reconditioned valve from a supplier while I'm there, hopefully it will cure the problem so I can actually drive the car for a few weeks before the Oregon rains set in for the winter. The whole conversion took much longer than anticipated and I missed all of the good weather and the All British Car meet this weekend. Actually it waste darn hot a lot of the time this years to drive a roadster during the heat of the day.
We had record number of days over 94 degrees. Can you say climate change?



Edited 1 time(s). Last edit at 09/06/2015 02:07PM by limey222.