Installing brake switch on 1940 master cylinder

[mcgarrett]

I had a hard time bleeding my master cylinder and and getting all the air out but finally have solid pedal, but have now discovered that my brake light switch is not working . I had silicone fluid in the system previously and have switched back to conventional fluid. I have since learned that silicone isn't too friendly to hydraulic brake switches and I assume that's why my quit working.

Here is my question:
Is it possible to replace it WITHOUT having to bleed again?? I'm trying to avoid the hassle of bleeding again. Would appreciate any and all feedback.

[drolston]

It can be done. Put a helper in the car with a hand on the brake pedal. Remove the bad switch and quickly start the new switch about two threads. Have the helper press the brake pedal lightly by hand until you see some leakage past your loose threads. Keep the light pressure on until you have the new switch down tight. Should be fine after you get the brake fluid off of your hand.

[mcgarrett]

I thought that might work but wanted to get the expertise of others before I tried it. Thanks for your tip!

[51woodie]

I had a problem with the brake switch on my '46, and replaced it with a switch from Harley Davidson, P/N 72023-51E. I cost me C$30.00 with tax, probably $20.00 US. Works well for me.

[51504bat]

Changed the one on my '39 p/u without having to bleed the system afterwards. Unscrewed the defective one and screwed in the new one. Easy peasy.

[Kube]

Sponsored Links (Register now to hide all advertisements)

There's no need to bleed nor have the pedal pushed slowly while replacing this switch. Gravity will allow a bit of fluid to escape while you're doing the R&R.

[russcc]

Any of the hydraulic switches immune to DOT 5, or do you have to use a mechanical ?Thank you Fordbarners

[mcgarrett]

Thanks to all respondents - I think I'll try swapping out the switch without using the buddy system; the theory seems sound.

[FlatheadTed]

X 2 for no buddy system; but check the quality of the threads first ,

[flatheadmurre]

Works fine just being quick.
And any air bubble will find it´s way up into the reservoir.

[corvette8n]

Swapped mine on my '41, I don't think even one drop of fluid came out, took 5 minutes.

[JSeery]

Originally Posted by russcc

Any of the hydraulic switches immune to DOT 5, or do you have to use a mechanical ?Thank you Fordbarners

At one time Harleys used DOT5 so that switch was the recommended one. But some people seem to have issues with them as well. See post #4.

[mcgarrett]

A big thank you to all for the helpful tips. Just installed the brake light switch without a helper and I'm pleased to say I now have brake lights again!!
There's vast knowledge here at Barn!