| Author | Message | ||
     richard george yeaman Grand Master Username: richyrich Post Number: 549 Registered: 4-2012 |
Hi, Brake Pressure switches what is their job, and how do they work ( just interested ) Richard.} | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1566 Registered: 6-2006 |
Hi George, The come on when the stored pressure in the accumulator become lower than it should be whilst the engine is running. It has a rubber disc which the fluid pushes on. This disc pushes an insulator which in turn pushes a metal contact. The metal contact earths electrically through th switch body when not being pushed. It goes open circuit once pushed. Typical faults are : The insulator spreads and can not travel freely. Dirt or corrosion on the metal contact keeps the light on either fully or at half brightness. Hope that helps George. I've seen photos of the internals here in the past. | ||
| richard george yeaman Grand Master Username: richyrich Post Number: 551 Registered: 4-2012 |
Thanks Paul I was just curious as they are never mentioned as giving problems is there ever a need to bleed these switches, and how would anyone know that they need to be replaced. Richard | ||
| Christian S. Hansen Grand Master Username: enquiring_mind Post Number: 308 Registered: 4-2015 |
Richard... By chance, earlier this evening I was reading over the brake systems section of the manual, Section G, and they did give a write up on the switches, not so much how they worked, but how to repair them, and there may have been references to how to test for proper function. It was a first time read thru and I was moving rapidly thru the 70 or so pages, looking for something else, but you might give it a reference read to see what is there. Manuals are posted at the forum library of course. Convenient. | ||
| richard george yeaman Grand Master Username: richyrich Post Number: 553 Registered: 4-2012 |
Hi Christian I have read section G in the workshop manual and yes how to repair them is explained and no on how do you know you need to repair them other than you have just had the mother of all crashes !!!! I have posted these questions more for interest and the need for us to pass what knowledge we have on. | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1570 Registered: 6-2006 |
Hi Richard. Symptoms ate: Never coming on even though you've pumped 200 odd times or opened the bleed nipples with engine off. Usually the button that is mowed by the diaphragm seized. Half brightness warning light. Usually crud between the contacts. Light staying on even though pressure available. Usually the moving button seized. If the light takes a long time to go off and a long time to come on. Usually a partially seized button. Don't forget to check the wiring to the switch. If the light is always on pull off the wire. If the light never comes on. Earth the wire. | ||
| richard george yeaman Grand Master Username: richyrich Post Number: 554 Registered: 4-2012 |
Paul thank you or explaining everything you need to know about brake pressure switches in a nutshell. Richard. | ||
| Robert Noel Reddington Grand Master Username: bob_uk Post Number: 1017 Registered: 5-2015 |
Lack of use is often the cause of lights that take a long time to go out. | ||
| Nigel Johnson Prolific User Username: nigel_johnson Post Number: 159 Registered: 12-2008 |
Or no nitrogen in the accumulators. Regards, Nigel. P.S.Geoff's Corniche springs to mind. |
