brickers,

i have searched a good bit and have not been able to find an exploded view of the brake junction block swith on my 89 240 sedan. this is the switch that gives the "BRAKE FAILURE" light.

here is what I know about mine. it has a white nylon plug about 1/2 inch in diameter extending from the junction block. this plug has a connector in top to which the wiring harness plugs.

the threads are very fine and are a bear to work with.

when i removed the plug, i observed that it has a rubber washer about the size of a wedding ring on it. (no brake fluid leaks observed)

once the plug was removed, there is a spring, slightly larger that a pen spring and a brass pin about the size of a 22 shell. one end of the pin has a little nipple.

the spring and brass pin came out easily. it seems that the nipple of the brass pin fits into another nylon part. that part appears to be screwed into the same set of threads that held the nylon plug. it looks like it has a flat head screw slot in it. i assume it screws out but I have not gone that far. i was concerned that i might not get it out.

does anyone know what lies under the second plug (the one with the flat head screw slot)?

one source said that older models had to be reset but that newer models did not have to be reset. from what I see, there is no resetting necessary on my unit.

it seems that the design of the switch has changed over the years and the cheap manual i have did not keep up with it.

any help will be appreciated as i caused a "BRAKE FAILURE" during a recent brake bleeding and have been to chicken to go any further into the switch until i hear from someone who has been there.

thanks

Well, I've been in as far as you have, but no farther. I got a 'BRAKE FAILURE' light one day that would not go away. Against other's better judgement, I replaced my switch. It has been suggested that it is often better to simply replace the whole junction block, rather than fiddle with the finicky switch. I ordered a switch rebuild kit, it came with the nylon outer screw-in 'shell', o-ring, pin and spring. My switch had become contaminated by dirty road spray (NOT brake fluid from inside the block.) It was a bit of a bear to get the thing out, but once out, I cleaned the hole out, dried it well, and put the new parts in. Working that nylon piece in took another dose of patience. Once the whole unit was back together again, it worked fine.
--
Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)

gt6,

thanks for the info. did you have to move the piston to get the light to go out? i guess that i am suprised that new switch parts alone would do the trick. i could understand if the nipple was broken off the brass pin but other that that i'm confused. my fear is that the piston in the junction is gunked up and that it need to be brought back into the center position somehow. any comments? thanks.

2OldVolvos

If the bit inside is free and not gummed up then it is supposed to reset once you have sorted out the rest of the system - ie eqalised the pressure in the two brake circuits. Usually it resets with a bit of help by some sharp pumping of the pedal.
You can sometimes force it to reset by lowering the pressure on the circuit that was previously the higher one, eg by pushing a piston back into the caliper and then giving a sharp jab on the pedal. The pressure in the circuit with the retracted piston will momentarily be lower, while the other circuit will have full pressure. This 'might' cause the sliding valve to recentralise.
Check that the two circuits really are working though. Commonly I find after any brake work on an old system the brake master cylinder seals give up, particularly if you have given some extra long strokes during bleeding. If there is internal leakage in the master cylinder the 2 circuits will not have equal pressures, so the octopus thing will not recentralise.