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MG TD TF 1500 - bleeding TD brakes

OK so another task I have to take on that I haven't done in some time is bleeding the brakes in a TD. I need to replace the brake light switch. Should I just drain the lines or try and save brake fluid while changing out the switch. Does anyone have a step by step for this one? Not looking forward to the mess.

RK Rich

If you don't step on the pedal, very little fluid will be lost when you switch out the switch. That said... if you haven't flushed your brake fluid for a while, now is the time to do it. Replace the switch, and then fill the resivoir and bleed the brakes from furthest from the cylinder to closest. Bleed until the fluid runs clear, and keep the master full.

Dave Braun

Rich - You will either need to get a brake light switch from Ron Francis Wiring (P/N SW-32) or you will need to make and install a relay/arc suppression circuit to go with the cheaper switches available from Moss or NAPA. The cheaper switches will burn out in a short period of time without the relay/arc suppression circuit. Information on making or purchasing the circuit can be found in the article Brake Light Relay in the Other Tech Articles section of my web site at: Cheers - Dave
David DuBois

Dave DuBois,

It will be interesting to see the long-term experience those of us who have switched to LED tail lights have. My pair of LiteZupp Type 1157 LED tail lights draw 0.7 amps, compared to the 4.2 amps drawn by the original Type 1157 incandescent bulbs. At the time I switched to the LiteZupp LEDs, I installed an NOS period brake light switch.

The other modifications to the circuit are arc suppression and a different flasher can (required for the LEDs). With luck, no further maintenance should be required on these components for a very long time.

With the much lower current draw in this circuit, a relay may not be needed.

Larry Shoer

I have had the Moss switch in for over 10 years, switched to LED lights two years ago and no problems so far. Maybe they made better switches years ago, I dont know but mine has held up fine.
Tom Maine (TD8105)

I have had the same luck as Tom with my 10+ year old switch from Nappa. I did "pop" a fuse once, (I added a lot of fusing to my "T") but switch is still working.

Rich, You might want to search the archives for "speedie bleeders". If you haven't flushed the fluid for some time they certainly make it an easier "one-man" job. I love mine.
David Sheward

Well guys. As far as I remember, I have not switched out my brake light switch since at least when I first rebuilt it in 1974. Not sure that I may have just jinxed myself, but I think it is original.
Bruce Cunha

I've been thinking about putting the LED tail lights in the TF but wow..$$$$$$$.

LaVerne, two things motivated my LED upgrade:
- Improved visibility (safety) to trailing vehicles
- A desire to reduce the electrical load on wiring, brake switch, and generator.

Larry Shoer

Tom, did you have to put in a flasher can for things to work properly?


Bobby Galvez


Whether or not the flasher can needs to be replaced is a function of how much current the flasher can requires for operation. My Lucas flasher can operated the LED tail lights, albeit at a faster flash rate, but the dash indicator light flashed once and did not flash again for the cycle. By replacing the flasher can with a Tridon flasher the LED tail lights flashed at a more typical rate and the dash indicator light flashed properly, too.

I'm sure if I added more lights to this circuit (perhaps a third brake light) or a load resistor the original flasher would have worked properly. Since one of my objectives was to reduce the current running through the circuit, I opted to replace the flasher.

Larry Shoer

I got the 1157 (?) halogen replacement bulbs from LBCar Co a few years ago. They are vastly brighter, and work fine with all electrics. I have the early rectangular TD tailights, so not sure if they work in the round lamps. I have changed several brake light swiches over the years without having to bleed. My Lucas swtich about 15 years old failed 6 months ago, am trying Abingdon Spares replacement now. George
George Butz

Thanks for the help guys, this might be my weekend project. My fluid has been in the car for less then 8 years, probably 6, but the car only has 350 miles on it since the restore. My guess is the fluid is probably fine?

Thanks again,

RK Rich

Maybe OK if silicone. If not, change it. Regular fluid is hygroscopic (attracts water). This causes corrosion and will rust the lines and corrode the cylinders, as well as lowers the boiling point.
George Butz

OK as stupid as this question might be... what does boiling point mean?
RK Rich

It's when the brake fluid gets so hot it boils under VERY hard braking, like constant racing conditions. Obviously, this is not s good thing...

I would not leave regular non-silicone fluid in a car for more than 2 years without flushing the system, regardless of mileage. The fluid absorbs moisture from the air just sitting.

Tom Lange
MGT Repair
Bar Harbor, Maine
t lange

This thread was discussed between 14/02/2012 and 19/02/2012

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