Brake light pressure switches

[wareaglescott]

Couple questions pertaining to these switches for the brake lights that go into the master cylinder

https://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&model=0792&section=BRKMIS&page=1&bookmark=0&part_number=113-945-515-G-M4&make=POR

1. If you put new switches in does it reduce the brake pedal pressure needed to activate the brake lights? Mine seem to take a big pedal push to come on.

2. Can you change them with the system full of fluid or will a large amount leak out when you unscrew the old one?

3. Would changing introduce air into the system requiring a brake bleed?

Thanks

[RedCoupe]

Yes, you will have to bleed the system. I changed my brake fluid when I changed my switches. Not hard with a pressure bleeder. If your car has brake booster, be sure to have the engine running when you evaluate how hard you need to push to turn on the brake lights.

[Jdub]

Yes, the lights do seem to come on sooner - most folks replace the switches because of this issue. Yes also to full of fluid, and yes there may be some air but you are going to replace and bleed at the same time.

This procedure takes two people. Perform the initial loosening of these tapered thread switches such that they do not leak but can be unscrewed without issue when the time comes. With a container under the first switch (and rag under everything), loosen switch 1 very slowly as the brake pedal is also slowly pressed. Allow the fluid to seep out reasonably freely (control this with your hand/turning) and, when pedal is bottomed, re-tighten switch 1, THEN pedal release up (think vacuum). You will be surprised at what you have purged - black seal particulate typically from the M/C. Now, pedal back at top, repeat this procedure but at pedal bottom, unscrew switch 1 completely, replacing with new switch 1. Repeat with switch 2.

The purpose of this method (there are plenty of other ways) is to first purge all particulate you thought you purged when you last bled the system, directly from the M/C, then to replace with the new switch that, because of your purge, will not immediately have to deal with the grit that cause your old switch to operate poorly.

This has been my experience. Others will have solid info. on this but for sure now that you have the chance purge the stuff right at the M/C for peace of mind. Keep that reservoir full!

[DRACO A5OG]

Use a 2x4 to depress the pedal 2" to keep the reservoir from leaking out.

Prior to get everything ready, tools and or remove fresh air plumbing for easier access.

Break loose then go for it, try dribbling some new brake fluid on the tip of the new switches and quickly replace and torque down, as I recall a 24MM deep socket will work.

As far as bleeding, you may be lucky but I would use a mighty vac, rubber stop from a Hardware store and reduce the fluid levels in the reservoir and hold a 18-20lbs vacuum for 5 minutes to get any little air bubbles out. You musty cap off the over flow as well.

[SCadaddle]

I replaced both of the switches on my SC with nothing other than having my neighbor apply light pressure to the brake pedal as I removed and replaced them one at a time. Maybe a drop or 2 of brake fluid was lost in the process. Didn't have to bleed the system afterwards. An offset box end wrench works well. (The FAE switches are readily available at NAPA if you are in a bind for time)

[wareaglescott]

Thanks for the info everyone. That should take care of me!

[group911@aol.co]

Why not flush the system with fresh fluid while you're in there?
Your calipers will appreciate it.

[Jdub]

Would someone correct my thinking if I am wrong about this?

Twice now I have found blackish grit coming out of the brake switch housings when replacing these switches with new. This is why I advise bleeding at these switch housings when replacing the switches. I keep my brake fluid very clean and do annual brake bleeds. When doing so, I became convinced that this process may not purge the M/C itself.

Is that a fair deduction - that the M/C does not get a thorough purge when bleeding brakes, or is that just wrong? Does bleeding clear the entire channel of the M/C when bleeding the brakes?

Thanks!