MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Brake pressure warning valve

I have a late midget 1500 with the brass brake pressure differential warning actuator (PDWA).
I noticed that there was a leak from the electrical switch. I read in the archive that this indicates that the 'O' rings inside the brass 5 way connector need to be replaced. I purchased the service kit from Moss and removed the connector, then I removed the switch which broke off leaving about 1/4 inch of plastic at the bottom of the bore.
I eventually managed to remove the remains of the plastic switch (Not easy is it).
I then removed the cast iron end fitting.
In the archive people have stated that it is easy to change the 'O' rings without giving any details of how this is done.
After removing the cast iron end cap the shuttle shaft seems to be almost welded into position.
I have tried to pull it out with pliers and used compressed air. Before I get brutal with it I just need to make sure that I'm not missing something.
I would hate to write it off in ignorance as replacements are either NLA or ridiculously expensive.
Grateful for your advise.
PS
Apologies, just noticed that this has turned into a novel !




s baker

not sure I understand.... do you have a photo?, those 5 ways are almost always on ebay for under $40

IIRC...just unscrew the switch with the 2 wires, pull out of the 5 way brass body and the O ring is at the bottom of the switch with the 2 wires.

Prop...Well Im "Fairly" sure thats how its done
Prop

Hello Prop,
The idea of the 'O' rings is to stop brake fluid getting behind the electrical switch. The switch should only leak brake fluid if the 'O' rings have failed. The 'O' rings are fitted onto the shaft sticking out of the 5 way. I assumed that you would just pull the shaft out and fit new 'O' rings then refit but it won't come out !
Maybe the shaft is just siezed in and needs brute force to remove. Just wanted to make sure I'm not missing something before I use brute force and possibly damage it.


s baker

Prop -

Nope, the 2 O-rings in question are actually fitted to a shuttle inside the valve unit. A leak in one of the brake systems will cause a loss of pressure on that side, so that application of the pedal will force the shuttle toward the weak side and turn on the warning light. When the O-rings perish - as mine have - brake fluid gets past them into the space between the seals, and leaks out through a vent slot in the switch threads. In my case, I ordered the repair kit, took one look at the location and accessibility (NOT) of the valve, and replaced the switch with a bolt and a copper washer. ;-)

So I've never disassembled mine, and as such, I can't advise on how to get the shuttle out if it's stuck. RE: the photo posted above... is that the end of the shuttle sticking out the near end of the valve assembly? Can you get some vice-grips on it? (Oops, just re-read your post. So much for that idea.)

Best of luck doing a job I really ought to do myself - and keep us posted -

-:G:-
Gryf Ketcherside

Prop -

Nope, the 2 O-rings in question are actually fitted to a shuttle inside the valve unit. A leak in one of the brake systems will cause a loss of pressure on that side, which will force the shuttle toward the weak side and turn on the warning light. When the O-rings perish - as mine have - brake fluid gets past them into the space where the switch actuator lives, and leaks out through a vent slot in the switch threads. In my case, I ordered the repair kit, took one look at the location and accessibility (NOT) of the valve, and replaced the switch with a bolt and a copper washer. ;-)

So I've never disassembled mine, and as such, I can't advise on how to get the shuttle out if it's stuck. RE: the photo posted above... is that the end of the shuttle sticking out the near end of the valve assembly? Can you get some vice-grips on it?

Best of luck doing a job I really ought to do myself - and keep us posted -

-:G:-
Gryf Ketcherside

Unfortantly its been ALONG time scence I did mine...Or had one in the system...went a differant direction, So I cant remember what is involved, I think mine took some work to remove also because of corrosian...but should just pull out

Im certianly not the person to ask at this point... but yes a bolt and copper washer is an easy fix also...just no warning light and perhaps an issue of limp home mode
Prop

I am soaking assemly in penetrating oil until the weekend, then will try again to release shaft. I'll let you know how it goes.
Steve
s baker


Had a go at removing the shuttle last night and it came out. Wobbled it around for a bit, put it in vice and forced it back into the housing just a fraction to break stiction then I was able to put the end of the shuttle in the vice and it slowly pulled out. The shaft and 'O' rings look to be in pretty good condition. The 'O' rings looked OK and were soft.
Not sure why it was so difficult to remove except that car has been off the road for about 5 years so shuttle has not had to move during this period.
Will rebuild and fit this weekend. If it still leaks now I will just put a bolt in like Gryf.
Photograph shows housing, shuttle and end cap but not the two 'C' washers and spring.


s baker

Thanks for the picture, Steve. Now I know what to look for if I ever actually rebuild mine!

If you get a chance, can you please shoot a close-up with the O-rings fitted? Thanks!

Cheers,

-:G:-
Gryf Ketcherside

As previously stated, I replaced 'O' rings using Moss service kit and then tried to fit new switch at the weekend. However, rather than just fit the switch I thought that I would take some measurements.
The depth of the 5 way boss down to the 'cam' on the shuttle measured 15,8 mm.
The old switch free length measure 18,4 mm.
The new switch free length measured 14,0 mm.
This means that the plunger of the new switch would not even make contact with the 'cam' on the shuttle. If fitted the brake failure warning light would have been illuminated permanently.
Maybe this is why so many people have had trouble getting it to switch off !
Have now decided to just fit a bolt and if I come across the correct switch at some point in the furure maybe have another go at fitting it.
s baker

Moss sent you the wrong part? NO!! It cant be true, your lieing, theres no way! Thats got to be a 1st. Ive never even heard of moss sending out look alike parts... Surly NOT them.


LOL. I wouldnt worry about getting the wrong parts from moss, Its when you get the correct parts from Moss on the 1st try you need to cower down in fear, cause something is wrong in the universe if that happens.

most likely the switch is for another car like a B, or a mini...throw a dart at a board to find out, or use a magic 8 ball, if you send it back enough times they will get it right ... eventually

Prop
Prop

This thread was discussed between 26/04/2010 and 04/05/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.