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MG MG Y Type - Brake switch

My brake lights only activate during the middle 50% of brake travel. I assume the problem is the brake switch. Is this switch servicable or should I replace it altogether? I prefer refurbishing original parts whenever possible on this car or I would just buy an aftermarket replacement.
Steve Simmons

The brake light switch on my YT is a constant source of frustration and I have to replace it almost every year. I use silicone fluid and I have been told that silicone brake fluid and pressure switches are somehow incompatible. Don't know the truth of that but I would rather replace the switch than redo the wheel cylinders after they have seized up, which before silicone they did every two or three years. My switches usualy do not quit working entirely, it is that you have to press the pedal with full leg strength. On the TD BB in the archives there are a number of threads about the poor quality of the switches available and some possible alternatives. Terry
Terry O'Brien

All the more reason to rebuild an original? The brakes seem to work fine. If it were a standard switch I'd just say the contacts were dirty.
Steve Simmons

The original Y-type brake switch is a rather tricky mechanical one which lives in the master cylinder housing. It is awkward to service and/or replace and conversions are common. A lot of modern pressure switches are designed to operate relays and the full 12v current is often too much for them. I would probably incorporate a reliable mechanical switch in the pedal area if possible, it is only likely to be seen when the car is on a hoist, etc.
Barry Bahnisch

Terry - Silicon fluid will not hurt the brake light switch. There is a diaphragm between the fluid and the actual switch so the two don't come into contact with one another.

Steve - It sounds like the switch on your YA (B?) is like the one on the TC, a mechanical switch and that it probably needs adjustment.

All - The brake light switch replacements today, whether hydraulic or mechanical are rather wimpy switches, that are prone to being burned out by the current through them or the arc generated when they open on each cycle or both. The fix is to put a relay and arc suppression circuit between the switch and the the actual brake lights. I have designed such a combination of relay and arc suppression circuit that you can incorperate on your cars. for information on building and installing the circuit can be found at: http://www.omgtr.ca/technical/brakelightrelay/brakelightrelay.htm
If you are intimidated by things electrical, I have the relay and arc suppression circuits already built and will supply them to you on request. See the above web site for ordering information.

If you intend to install a relay and arc suppression circuit, it is best to do it at the same time as installing a new switch, since the switch contacts start burning on the first use and can sometimes build up sufficient resistance in a very short time of usage that the switch will not work with the relay.
Good luck - Dave
David DuBois

The original switch is inside (on a YA/T) the brake cylinder assembly in a little box at the back. It is a simple blade operated device - press the pedal and the blade should pass between two brass contact, complete the circuit and bingo, the lights light up.

You need to haul out the floor board over the brake cylinder and check that the brass contacts are not dirty. When I broke a YA a few years ago I was amazed at the amount of dirt that had piled in there!

I imagine the YB would be the same arrangement.

Also, if it is really completely shot there is a hydraulic replacement switch available from the Regalia pages at www.mgytypes.org.

Paul
Paul Barrow

I read in the Ford V-8 Forum where Silicone brake fluid has an effect on brake light switches. The old Fords use the same type as many MGs and they reccommended using one from a Harley Davidson motorcycle.
S.R. Barrow

Brake fluid will only have an effect on switches where there is a diaphram. Assuming you have the original blade activated switch there is no contact with the fluid. The blade closes the switch by mechanical linkage to the pedal travel and piston actuation in the brake master cylinder. There is no direct hydraulic interaction between the OEM switch and the fluid. The same is not true of the After Market switch conversion offered on the Regalia page. The After Market conversion option is a HYDRAULICALLY operated switch.

Paul
Paul Barrow

Silicon fluid will only affect a switch with a diaphragm (ie. hydraulic switch) if the diaphragm leaks and if it leaks, it needs replacement anyway. I have had silicon fluid in our TD (with a hydraulic switch) for over twenty years and have not had a problem with the switch. All the stories about the silicon fluid causing the switches to go bad are old wife's tales (probably started by the brake fluid companies that don't produce silicon fluid). Cheers - Dave
David DuBois

Sounds like I need to find the brake switch in the YB this weekend so I know exactly which type I have. I'll keep y'all posted. Thanks for all the great info!
Steve Simmons

Steve

You might want to check out the use of a motorcycle mechanical switch. Search the MGA Archives for "motorcycle brake switch" for more info. I haven't looked at this in detail but it may be an alternative to a hydraulic switch for the Y.

FWIW

Larry
Larry Hallanger

So long as it's an invisible modification I'm up for about anything. I'll check it out.
Steve Simmons

This thread was discussed between 02/11/2004 and 04/11/2004

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