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MG MGA - Brake switch threads

Hello people;
I've a new brake light switch that's a dead-ringer for the one offered by Ron Francis Wiring (SW-32), sold by Painless Wiring (#80174) The thread is 1/8 tapered pipe thread w/ 27 threads per inch. I also have a new 4-way fitting that the switch screws into from Moss.
I'm just a bit concerned though; when I manually begin threading the switch into the 4-way fitting, I get less than one revolution before I get resistance. Is this normal? Should I continue screwing until it's snug? Is the use of ptfe pipe thread tape recommended?
Those 4-way fittings aren't cheap and I thought I'd run the above by you before I start screwing that switch down tighter...
I've never uploaded a picture before, so I hope it appears somewhere here.
Thanks!


L.R. deOlazarra

Is this fitting supposed to be NTP or BSP?
Mike
Mike Ellsmore

Something is not right. You should be able to screw the switch in several turns by hand. Yes you can use pipe thread tape.

The brake switch should be 1/8 NPT and the brake lines 3/8-24. Try a 3/8-24 in the brake switch hole, it may have been incorrectly threaded.

If all else fails take the 4 way fitting to the hardware store and try to figure out what the thread size is. Could be that the threads are bunged up and need to cleaned up with a tap.

John
jbackman

I would caution against the use of ptfe pipe thread tape. It is not necessary and if any gets into the brake system, it could clog things up. To make matters worse, when it is wetted with brake fluid, if becomes transparent so you will not be able to locate it in the brake system.

The threads on the hydraulic brake light switches seem to be pretty standard 1/8 - 27 NPT. It is very difficult to tell if the threads in the 4 way pipe fitting in the car is NPT or BPT (28 TPI). It would be quite evident if the fitting had been threaded incorrectly with 24 TPI

I have the same fitting in our TD and MGB and while the switch starts snugging up rather quickly, I have been able to get two to three turns on it, making it quite snug, with no leaks whatsoever (even with DOT 5 silicone fluid in the brake systems).

You may be able to find more information on Barney Gaylord's web site at: http://mgaguru.com/mgtech/ Cheers - Dave
David DuBois

Thanks to all of you for your responses! I went down to the garage and tried a 3/8-24 bolt in the recess for the switch on the 4-way and found that it fit perfectly and screwed in turn after turn with no resistance. I got the same result screwing it into the other 4 female threads on the 4-way. .
So, correct me if I'm wrong, but what I've got is a 4-way that's been correctly threaded to receive the brake pipes, but incorrectly threaded to receive the brake switch, right?
L.R. deOlazarra

Uh-oh. What's the Moss pat number on your new 5-way fitting? Hopefully you have the wrong part and can exchange it. On the flip side, Moss would like to know if you have the correct part number with incorrect threads.
Barney Gaylord

Curiously, my 1500 SPL does not seem to list the switch, though it is shown in the drawing with the fitting & pipes. I was looking because I distinctly recall the switch as sometimes having a copper washer, which means straight threads. Problem with working on all sorts of cars (and MC - Norton has similar switch).

FRM
FR Millmore

Brake switch is in the electrical section of the SPL.
Barney Gaylord

Yes I believe that the original oil switch on the MGA was actually threaded 1/8th parallel thread (requires washer to seal) and not tapered.
I have found if you try and turn a tapered male fitting into a parallel female then you get perhaps 1 turn at best.

I thought there were some original spec MGA brake switches available with parallel threads which would work correctly. Also I think somwehere during production or maybe after market this has changed to tapered fittings as were more modern cars.
Bob Turbo Midget England

Hi there

I have some 4 way brake line splitters. If you look down the hole, you should have nipple in some of them to accept the brake line. Only one will not have it and that will be for the switch. You can always rethread to accept the tapered pipe thread.

Martin
sharpeys

Hi John! (up in Washington)..didn't connect your name at first; thanks for the continued help.
Before I go any further, I need to say I didn't order the part directly from Moss, but from Little British Car Co., which I believe distributes parts from Moss, among others. I got the part number from the Moss catalog and input it in the LBC Co. search box to access the part there.
Barney: the part number is 180-230.
Ironically, I initially ordered the part directly from Moss, but they said it would have to be back-ordered (perhaps because they recognized the thread problem?) Didn't want to wait, so ordered from LBC Co. and cancelled the Moss back-order when the 5-way (right: not 4-way) arrived.
I'll contact both LBC Co. and Moss about the problem asap.
As always, thanks for the help..
L.R. deOlazarra

Back again.
David; I could be wrong, but I think pipe thread tape on the switch threads wouldn't come in contact with brake fluid, since the fluid doesn't get past the diaphragm in the switch.
Nevertheless, thanks for the input in the event that I'd be tempted to use it on the brake line connections!
L.R. deOlazarra

The problem is of course that if you do use a taper thread then it will require some kind of sealant otherwise it will leak. PTFE thread tape is IMO the sensible choice for that application, the only time I understand it should not be used is with Natural gas fittings. Something about contamination and in these cases a special sealer paste is used.
Robert (Bob) Midget Turbo

Curious. My SPL has no dates or issue numbers as most BMC publications did.
It is marked (front page) as AKD599, and the backmost blank page is dated 6/56 - 5000 So very early.
Thing is, the pages are not reliably in logical groups, and the several indices do not correspond to the page numbers.
Therefore, I get to look at the whole thing to find stuff. Not efficient but does remind me of detail long forgot!
Looking once more at the "electrical section", some of which appears twice, still no stop light switch! The "Pipes & Fittings" page which shows the switch sans listing, does not show a gasket.

Went out and looked at Norton (Jan 73)- gasketed so parallel threads switch. I believe I replaced this with one from stock when I got the bike, c1990, but anything I had on hand would have been from a car application. But this switch has spade connectors.

FRM
FR Millmore

David; I don't know what I was thinking...of course ptfe tape on the switch threads could come in contact with the brake fluid, especially since they're tapered. This is what happens at my age. I just love that shriveled feeling I get when I say things that make no sense, put it out there, and then later realize what I'd done.
L.R. deOlazarra

I did some natural gas plumbing with black pipe and Teflon tape during my workshop construction 32 years ago. The place hasn't blown up yet, and the taped joints still don't leak.

There is a trick, or standard procedure, to using Teflon tape in tapered pipe threads. NEVER place tape over the first leading thread of the male connector. Tape on or beyond the first thread is what is exposed inside and can come loose and end up in the fluid system. Keep the tape inside the threads, and none of it can ever get inside the plumbing.

This is similar to the admonition for gasket sealer, never let any of it get inside the box.
Barney Gaylord

And wrap the tape the right way!

FRM
FR Millmore

Yes, very good point. Wrap the tape clockwise (looking at and of pipe) to it does not un-wrap with assembling the threads. Also give it at least 1-1/2 turns to overlap (then pull to break), but less than 2 turns so it doesn't overlap twice.
Barney Gaylord

I knew about wrapping the tape the right way, but was unaware of the more than 1 but less than 2 wraps, and the first thread on tapered threads reference. Thanks for the feedback.
L.R. deOlazarra

This thread was discussed between 04/07/2012 and 05/07/2012

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