Seems my dual braking switch is dead. This is the little grounding switch that screws into the dual braking block just below the master cylinder and let's you know if something is amiss. Anyone got a useable unit or know where I can buy one?

Actually, i have another question. Whenever I bleed brakes or otherwise disrupt the system, I first remove this switch so that the system can reset when everything is equalized. Been doing this on umpteen Volvos since forever. But I recently replaced the master cylinder, which was seeping (I'd rebuilt it some years ago, but I had a new master cylinder in my extensive parts inventory and figured, what the heck, I'm nearly 70, what are they going to do, bury it with me?) and darn if I didn't forget to remove the switch during the change.

What exactly happens in that case? Does the piston in the dual braking block deflect if there is a pressure loss to it's north? I'm a little concerned because when I pulled the switch to test it.... no continuity when the plunger is depressed... and then screwed it back in, I didn't feel any resistance at all. So i'm wondering if the piston is still off center. If someone can school me on this situation and tell me how to tell the status of the piston in there I'd be grateful.

Removing that switch during brake service that requires bleeding is SOP to prevent damage to the plastic tip.

FYI, on the later style of switch used on the 240, removal of the switch is NOT required.

You have the operation of the switch backwards as the switch makes continuity when the plunger is NOT depressed.

BTW, there are actually 2 pistons inside the distribution block and they look like baseball bats with a groove for an o-ring near the head. The way this system works is the pistons are situated inside the block with the ends that resemble the handle of a baseball bat back to back which creates the ridge that the plastic tip of the switch is supposed to sit on when the system is bleed and balanced.

When the system is unbalanced, the pair of pistons will slide to the side without pressure and the plastic tip of the switch drops down and should pass a ground to the warning light which then turns on the light when everything is working/connected correctly.

When the plastic tip get shorten by repeating bleeding while still installed shortens the tip and then it won't push into the switch high enough to break the ground contact, so the light should stay on all the time when the key is on.

And new switches are available and I usually have at least 1 in stock.



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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502