Brake light switch

[Jefftav]

I need to change my BL switch and I was told to hold the pedal down for 5mins and keep it held down whilst unscrewing the switch from the junction beside the radiator. Just I would have thought it should be the opposite as holding the pedal down will push fluid out when I unscrew the switch.

Can anyone keep me right with this? Thanks in advance, Jeff

[Dean]

I'm inclined to agree with your observation. The switch works off pressure, therefore pushing the pedal down to put the brake lights on and unscrewing will result in brake fluid in your face.

Im thinking, boil a kettle of water and keep to hand. Take your brake master cylinder cap off and put some clingfilm over the hole, then screw on the top to create a vacuum in the brake system. Undo the brake light switch... carefully with a rag around to capture any leakage. replace with new oil pressure switch, pour boiled water over any spilt brake fluid on body work and wipe clean. Remove cling film from master cylinder. If there is leakage you may have to bleed the brakes again.

Never tried it, but it's the way I'd attempt it.

[alanworland]

Just changed mine (it packed up after 58 years!)
I just unscrewed it with a bit of rag around the fitting, hardly anything come out - I filled the new switch with brake fluid (I use silicone) and screwed it in - didn't even have to bleed it!
I did find the new switch although having a tapered thread 'bottomed out' before screwing tight - I fitted a soft copper washer which sealed the switch against the top of the fitting.
Make sure you hold the fitting whilst unscrewing the switch otherwise you will end up bending the brake pipes!

[mike.perry]

If you have a spare foot available you can push very gently on the brake pedal as you tighten the switch, just to push any air out that might have got into the end of the pipe

[alanworland]

I found that the fluid just 'hovered' at the top of the fitting and as the switch was screwed in it just displaced the excess! Brill!

[Dean]

That's good to know Alan, thanks.

[bmcecosse]

Oh - I thought the kettle of water was for a nice cup of tea..........while the system self-bled !