No brake lights - maybe obscure master cylinder part

850forum · Post by **850forum** » 30 Dec 2020, 05:45

Need help figuring out what's going on, cannot drive it at all without brake lights coming on when I hit the brake !
Mechanic has found these two parts to be defective, not sure which is affecting the brake lights.

on a German site:

https://www.skandix.de/en/spare-parts/e ... l/1027160/
PN 1027160
Sensor, Pedalweg Bremse (sensor, brake pedal travel)
This goes on the BOOSTER, not the master cylinder. Mechanic says it senses pressure.
Its NOT the electical switch on the brake pedal that lights the brake lights.
Priced at 96 Euros plus postage.

SKANDIX Shop Volvo Ersatzteile: Sensor, Pedalweg Bremse 271892 (1027160)
So these must be 3rd party parts (ersatz).

https://www.skandix.de/en/spare-parts/e ... l/1027160/
Cap, Brake fluid reservoir brake fluid

The above seems to be the same part the mechanic specifies but the German site has a different (more up to date?) PN than the site the mechanic gave me: darcarsVolvoParts:

PN 9122562
Cover. Master Cylinder.
Mechanic says this is actually built in to the cap, or the cap is integral to it, so it would be part of item 5 on the upper exploded diagram on the page labeled "Master Cylinder. -1995. -1993. The diagram drawing ID on page lower right says 5277859s.

The lower diagram labels the knurled cap portion as 12 and an electrical connector going into the cap assembly as 13 ( PN 9162107 Housing AWD Control Module Hydraulic Pump Master Cylinder 2 Pole 2WD Servo...) .

The cap screws into the Fluid Reservoir.

see
viewtopic.php?f=1&t=96123&p=563775#p563775

cxf · Post by **cxf** » 30 Dec 2020, 13:05

How do you know that the problem isn't the brake light switch down by the pedal? On my '96 I've lost my brake lights a number of times and I have always taken out the switch assembly, filed down the contacts and reinstalled and adjusted and was good to go.

850forum · Post by **850forum** » 30 Dec 2020, 14:34

The mechanic would (should) have found that. With New Years, can't get them to put a voltmeter on the switch until Saturday.

The Skandix place won't accept my order - won't take my email. Called on the phone, got an English speaker who said she would take care of it, but not yet. They might be off for New Year's already, dunno.

cxf · Post by **cxf** » 30 Dec 2020, 15:06

I would look up removing the switch from pedal and cleaning up the contacts. It's a little awkward removing it being upside down in the driver's footwell but very doable. Is this mechanic a Volvo guy or a general mechanic?

850forum · Post by **850forum** » 30 Dec 2020, 17:22

Volvo mechanic at a private garage. Too bloody cold to get upside down myself. He's diagnosing why my ABS light is staying on.

Post by **BEJinFbk** » 30 Dec 2020, 17:37

If what you're saying is that you have no brake lights
showing at the back of the car when you press the
brake pedal, then start at the switch at the pedal.

Be sure that it has power and it's adjusted properly.

The sensor at the vacuum booster does not affect them.

And the float switch in the brake fluid reservoir cap only
illuminates a light in the dash telling you to check fluid level.

Are you confident with the abilities of this technician?

850forum · Post by **850forum** » 30 Dec 2020, 18:43

Well if those two parts are not involved at all, the mechanic would have had no reason to suspect the brake lights were not working while working on the ABS light.

If there's a photo of where its located & where to put a voltmeter, if it doesn't start to rain I might be able to crawl under there. Hard on my back in the winter.

This isn't a lot of help:
viewtopic.php?f=1&t=94786&hilit=brake+light+switch

And if the solution is to buy a new switch, I won't be able to get one until after the weekend anyway, so may as well let the mechanic strain his back.

"I have always taken out the switch assembly, filed down the contacts and reinstalled and adjusted and was good to go."
I suppose I could yank it out and do that; what exactly & why are you "filing down" - taking off corrosion, or adjusting their length substantially?

How does one adjust it - must it be tightened in its bracket so that... what, the switch is just barely open when the brake is not depressed? Is that state easily visible at the brak pedal or do you need to run back & look at the tail lights as you move it mm by mm ?

Does it slip or stretch so that maybe adjusting its position is all that's needed - no filing?

If it was summer I'd figure it out. But not in the dead of winter.
OTOH I'd like to fix it if possible so we can go out & look at the Christmas lights before people stop lighting them up.

850forum · Post by **850forum** » 30 Dec 2020, 18:56

so this is pretty clear. All these switches basically the same mode of function? Don't need a Volvo part, just any brake switch from Pep Boys etc?

850forum · Post by **850forum** » 30 Dec 2020, 19:26

OK its working now, I adusted the "push-pull" click action. From "always on" one more click to turn it off.
Can't figure out how to remove it from the bracket, not a quarter twist like in the above video.

So why did it stop? The click adjustment got bumped some how, or should I take it apart & clean the contacts inside?
Or maybe the white plunger sticks sometimes, so I should clean & lubricate it?

And the kick panel seems to droop a bit in the rear left. I see a white bracket on the right that it slides into, didn't notice the same on the left.

850forum · Post by **850forum** » 01 Jan 2021, 06:37

how to remove the switch - totally non intuitive, unusual design. When replacing switch, the pedal moving into its "neutral" position will make the switch self-adjust:

I should remove it to make sure it adjusts correctly.