angelfj Posted June 13, 2011 Report Share Posted June 13, 2011 (edited) Working on the 3A this past weekend and noticed a small puddle just below the brake light switch. Yes, it was brake fluid. My first reaction was to check the tightness of the switch in the threaded fitting. It seemed tight, but I decided to give it a little tweak. This I did and it appeared to hold pressure when the brake pedal was depressed. However, later in the day, maybe 4 - 5 hours later there was a small drip at the junction between the switch and fitting. At this point I realized that something was rotten in Denmark! I carefully removed the switch and plugged the hole with a suitable bolt and washer - as a temporary measure. The threads on the switch body seemed OK. Then I looked closely at the switch and realized that it was an aftermarket unit. It was supplied by one of the major LBC parts companies over here. I then picked up an original albeit defective switch from the used parts bin. They looked very much alike. Wait a minute. Better measure. WTF! The after market unit was several thousandths longer! Apparently, the new aftermarket switch had bottomed out in the threaded bore and although it seemed tight, it was leaking at the top where it should have sealed against the body of the fitting. The solution was to shorten the threaded portion of the switch and add a copper crush washer. As of this evening the connections are completely dry. Recommendation: If you have a brake switch that leaks, remove it and measure the depth of the bore, "b" and compare this with the length of the threads, "a" on the switch. If the switch is longer than the bore is deep you may get by with only a copper crush washer. We had to shorten the switch AND add a copper crush washer. Good luck! Edited June 13, 2011 by angelfj Quote Link to post Share on other sites
stuart Posted June 13, 2011 Report Share Posted June 13, 2011 Aftermarket parts Huh! I have had problems with some of these switches before though not of excessive thread yet but FWIW I do always fit with copper washer anyway. Stuart. Quote Link to post Share on other sites
Don Elliott Posted June 14, 2011 Report Share Posted June 14, 2011 As the actor with the round glasses in the WW2 uniform on Rowen and Martin's "Laugh-in" used to say, "VEEERRRY Interesting !" Quote Link to post Share on other sites
Andrew Smith Posted June 14, 2011 Report Share Posted June 14, 2011 Make sure you have bought/been given the correct switch - the 3A switch should have a tapered thread, whilst the MG uses switch with a parallel thread which is slightly longer. I had the same problem, and although I ordered the correct part number the lad who picked it from stock just grabbed a brake light switch............ Worth checking. Cheers Andrew Quote Link to post Share on other sites
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