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sealing brake light switch
rodgling - 21/4/15 at 07:53 AM

My brake light pressure switch doesn't appear to have a V-shaped bit at the bottom to seal into the union, so presumably my options for sealing are:

a) rely on threads to seal (don't think it is a tapered thread, it's 3/8 UNF) - doubt this will work
b) use thread lock
c) use PTFE tape
d) use a copper washer (but the union doesn't have a nice flat machined face to seal against?)

what is the "right" option?

rodgling - 21/4/15 at 04:00 PM

No one? In that case I reckon the best option will be a dab of thread lock, will give this a try.

owelly - 21/4/15 at 04:17 PM

Do't use threadlock! If you ever need to remove it, it will just shear off. Use two wraps of PTFE or thread sealer.

motorcycle_mayhem - 21/4/15 at 05:58 PM

From your post, I'll infer two assumptions:

1. Your brake light switch is a 3/8" fitting, male, but without male conical.
2. Your housing (T-piece) is a regular 3/8" female

OK, if there isn't a land on the T-piece for a copper washer, you need to stop now, get a beer. Forget PTFE, threadlock, epoxy, or anything else of a similar ilk.

I would purchase an adapter to get that brake light switch looking like a male conical.
Check the Goodrich catalogue while consuming another beer, order adapter

Problem solved.

rodgling - 21/4/15 at 06:22 PM

quote:
Originally posted by motorcycle_mayhem
From your post, I'll infer two assumptions:

1. Your brake light switch is a 3/8" fitting, male, but without male conical.
2. Your housing (T-piece) is a regular 3/8" female

OK, if there isn't a land on the T-piece for a copper washer, you need to stop now, get a beer. Forget PTFE, threadlock, epoxy, or anything else of a similar ilk.

I would purchase an adapter to get that brake light switch looking like a male conical.
Check the Goodrich catalogue while consuming another beer, order adapter

Problem solved.


Correct on your assumptions. On closer inspection a copper washer might actually work OK, the union is more precisely finished than I'd realised. Perhaps this is the answer. The adaptor sounds like a good idea... but then I need to seal the switch into the adapter...

owelly - 21/4/15 at 07:33 PM

Only rely on a copper washer of you can run the switch into the fitting by hand until it touches the shoulder.

rusty nuts - 22/4/15 at 05:36 PM

If this is for your BMW based car why use Imperial fittings instead of metric? IIRC all imperial brake light switches used copper washers?

rodgling - 22/4/15 at 06:54 PM

quote:
Originally posted by rusty nuts
If this is for your BMW based car why use Imperial fittings instead of metric? IIRC all imperial brake light switches used copper washers?


It's currently on metric. Long, annoying reason for changing the union over:

I've always had issues with a squishy brake pedal which I think is probably due to the brake pressure switch trapping air. So to solve this I decided to use a 5-way union at the front, for master cylinder, left front, right front, switch, and bleed nipple with the nipple at the top and switch at the bottom. Unfortunately these seem to only be available in imperial, so I've had to get a new switch and replace three perfectly good hoses. Bit of a waste, but it should make the system really easy to bleed. I could use two unions and keep M10 stuff but that seems like a messy way to do it.

The new brake switch screws into the union and bottoms out with a bit under 1 mm clearance for a washer, this looks about right to seal with a washer to me.