Brake light switch problems

[nwxh]

Ok, I've given up trying to get it off. All approaches failed.

The union has come off easily, so I'll replace the whole union. (which I probably should have done from the start).

I've never done bleeding before. Should I jack the car and take the wheel off to do it (for each wheel), or can I just slip behind?

What else should I replace at the same time (apart from brake fluid)? The brake pipes are new, but I should probably replace the front once as a precaution.

(I will use the gravity/jam jar method.)

[bmcecosse]

No need to change anything if it's all 'new'. Don't jack the car up - you want the bleed nipples lower than the master cylinder.

[nwxh]

I mean, just in case my failed attempts damaged the brake lines (they still have pressure and no leaks visible).

Do I jack up and remove wheel, or do all the bleeding with wheels in place and car flat?

[chesney]

Leave the wheels in place.

[bmcecosse]

Car flat.

[nwxh]

That sounds better than I feared.

If the lines were slightly bent by the twisting, will the pressure solve it or could they one day completely break?

[bmcecosse]

Pressure won't solve anything.......if the pipes are twisted they should be renewed....

[nwxh]

I'll inspect tomorrow, but I think just on the one from the MC to the union is pinched.

[nwxh]

So I'm attempting to screw in the new switch into the new union. It goes in nicely about halfway along the length of the switch thread, then becomes very stiff.

Is this just a manufacturing tolerances problem with one of the parts? How tight should I screw it?

[bmcecosse]

Is it the correct thread ? There are several different threads out there. Don't force it!

[nwxh]

No idea, both the threads on the union and switch have gone black and it becomes stiffer after 4 turns. The union is "as per original". The brake light switch is from the URL, NPTF.

I'll get one of the unfortunately known not to last long ones from the same supplier for now.

[bmcecosse]

NPTF is definitely not correct. Where did you get that?

[nwxh]

You suggested the following part based on a recommendation of another member:
http://www.autoelectricalspares.co.uk/l ... -158-p.asp

So I can only assume the member jammed it in and won't get it out easily?

[kennatt]

Has no one tried a micro switch under the pedal instead? Save all the faffing about with crappy replacement switches

I once had an MGB (same switch system) with a failed switch,brake light on all the time. So as a temp repair,disconnected wires and fitted a micro switch on shaft of the pedal,as per moderns,just bodged it on ,with the intention of sorting it later. after three years it was still on when I sold the car to my friend,who left it on for another 4 years One massive advantage is that as soon as you touch the pedal ,even the weight of your foot ,moves it enough to put the light on. Whereas with the pressure switch it needs the pedal to become firm ,so allthough not a problem there is a slight delay( handy for shifting boy racers off your tail without slowing down probably the best advantage )
Don't see how you could do it on a minor,with the shaft arrangement as it is,but may be something could be rigged under the cover near to the pivot. Or drill a hole through the pedal and fit one with the switch just protruding so your foot activated it. Probably not worth the trouble though.

[nwxh]

People have definitely done it. I would not want to do it except as a backup, even if it is more reliable, because it'd be harder to get away with having not working brake lights if you didn't use the "right" parts.

[katy]

Methinks that the thread on the switch should be either 1/8" BSP (British Standard Pipe) 28 tpi, or 1/8" NPT (National Pipe Taper) 27 tpi. Can you measure the old one?

Edit. Forgot to mention, being that it's pipe thread, it's a tapered thread, so it will tighten up as it goes in but the switch won't "bottom" as a nut would on a bolt.

[bmcecosse]

It's certainly not going to be National Pipe Thread in the UK - although there's not much difference at that size, if the original really is BSPT. Compare the two against a backlight to check the thread pitch. I certainly can't agvise you to just screw it in and hope for the best.....

[nwxh]

The other one I ordered came in the post. The threads are different, but the one I got today still gets tighter after 5 turns but can be turned further.

I will hand tighten it using the union with the switch held still.

(The old one is still jammed, so cannot measure. )

[bmcecosse]

Certainly sounds more realistic....

[nwxh]

Ok screwed in, about three threads didn't go in, but I assume that's fine being a tapered thread? (I'd have thought it would be designed to have 1-2 threads remaining when tight to allow for tollerances.)

Now to have fun with brake fluid...