"brake" light in gauge cluster

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633INGA

"brake" light in gauge cluster

Post by 633INGA »

Quick question - Does the "brake" light in the cluster measure pressure or level of brake fluid? Mine stays off for the first 10 miles of my commute each morning but then comes on and stays on the rest of the way. On the way home it comes on then blinks intermittently with no rhyme or reason. The reason I ask is the level is where it should be and The MC is less than a month old. Oh and this is a Non-ABS car. Thanks in advance

Keith
83' 633 CSI
Chris Wright

Re: "brake" light in gauge cluster

Post by Chris Wright »

633INGA wrote:Quick question - Does the "brake" light in the cluster measure pressure or level of brake fluid?
In a word, Yes! (and no, it is not a Yogyizim)

There are 3 "Brake" warning lights:

1) - The one in the check panel to the left of the cluster tests the stop light bulbs.
2) - The "Brake Lining" light in the cluster monitors the brake pad thickness.
3) - And the "Brake" light in the cluster monitors 3 separate things (See page 120 of your ETM):
  • a) The brake fluid level (switch on brake reservoir cap, closes on low fluid level).
    b) The brake accumulator pressure (switch on side of regulator, closes below 319psi).
    c) The minimum hydraulic system pressure (switch on top of regulator, closes below 22psi Steering pump pressure).

    - These switches are wired in parallel, and any one of them closing turns on the "Brake" warning light.
To troubleshoot the problem, unplug the brown (ground) wire on one of the switches listed under item 3 above and see if the problem goes away. If not, plug it back in and go to the next one until you find the culprit (be careful with the plugs on the brake reservoir cap, they can come loose and pull out.

It could be a bad pressure switch, they are known to leak internally and go bad. See if one is leaking around the spade lug. IIRC, they are around $25 at AutoHaus

If the problem is with the brake accumulator pressure switch on side of regulator, the accumulator may be going bad. See here to troubleshoot it:

Brake Bomb / Accumulator:
viewtopic.php?t=9492&
Lost only part of it's charge: viewtopic.php?t=6770&

Of course there could be a short on one of the wires going to the switches.
Last edited by Chris Wright on Thu Sep 27, 2012 4:50 pm, edited 2 times in total.
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Ed Lyerly
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Location: North Carolina, USA

Post by Ed Lyerly »

I had a similar problem ...... turned out to be a fauty brake pad sensor.
---------------------
1985 M635 #1998 (gone but not forgotten)
1994 850CSi (also gone but not forgotten)
1985 M635 #589
633INGA

Post by 633INGA »

great response Chris, Thanks. I had seen a similiar writeup from you on this very same subject but the car is question was a late 80's car. I wasnt sure if my 83 was covered under the same troubleshooting. Thanks again for the reply.
E24ureka

Post by E24ureka »

Are you sure that your hand brake handle is all the down when released or that the switch there may be faulty? The 'brake' light also monitors this function.
dws
Yuros
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Re: "brake" light in gauge cluster

Post by Yuros »

Resurrecting this post as I'm trying to elminate the red "Brake" light. Using the tips above I traced it down to a pressure switch on the side of the brake accumulator. I am wondering is this DIY job to replace? I assume I should release the pressure from the system by pumping the brakes before removing this switch? Appreciate any tips on replacing that switch. Thank you!
1987_ 635CSi_5 spd
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JCS
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Re: "brake" light in gauge cluster

Post by JCS »

The part just unscrews,
I use white Teflon plumbers tape, before installing back onto the accumulator, wrap the tape, 3 revolutions.
Jay
'88 M6, Red/Tan
My NEW Website https://www.jaysbmwparts.com/
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RossDinan6
Posts: 295
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Location: SW FL, USA

Re: "brake" light in gauge cluster

Post by RossDinan6 »

Bringing this back from the dead.

The brake switches do not require any sort of thread sealant. They seal with a copper crush washer. Tapes and sealants can cause contamination issues in the system.

That said, There is a reason for this bubbling back to the surface. I need to check the system pressure to diagnose an intermittent brake light. Does anyone know the specifics threads on the brake pressure switches? I pulled the top one and measured an OD of 11.75x1.5, which I haven't been able to match up with any hydraulic fittings. ID looked to be 10mm. I need to adapt to -4 JIC for my gauge.

Thanks for any help.
Ross
'84 633 Dinan turbo
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JCS
Posts: 999
Joined: Wed Sep 22, 2010 11:06 pm
Location: Santa Ana, California, USA

Re: "brake" light in gauge cluster

Post by JCS »

RossDinan6 wrote: Sun Nov 28, 2021 5:49 pm Bringing this back from the dead.

The brake switches do not require any sort of thread sealant. They seal with a copper crush washer. Tapes and sealants can cause contamination issues in the system.

That said, There is a reason for this bubbling back to the surface. I need to check the system pressure to diagnose an intermittent brake light. Does anyone know the specifics threads on the brake pressure switches? I pulled the top one and measured an OD of 11.75x1.5, which I haven't been able to match up with any hydraulic fittings. ID looked to be 10mm. I need to adapt to -4 JIC for my gauge.

Thanks for any help.
Ross,
And you are worried about contamination from Teflon tape, in a 35 year old car. Apparently you have never flushed a hydraulic system before.
You should see the junk I see when I rebuild a brake booster and other Hydraulic parts. Or when a 30 year old filter at the bottom of the canister. As it dissolves into sawdust and is circulating throughout the system.
Replace the switches. Before the become NLA.

The reason I told that guy about Teflon tape was for the accumulator as it uses an o-ring,
if you are curious about o-rings read my old website page 6 on any link.
Jay
Jay
'88 M6, Red/Tan
My NEW Website https://www.jaysbmwparts.com/
User avatar
RossDinan6
Posts: 295
Joined: Mon Jan 29, 2007 2:35 am
Location: SW FL, USA

Re: "brake" light in gauge cluster

Post by RossDinan6 »

I made my statement based on hydraulic systems considerably more complicated than this one. All of them build up crap over the years. I'll continue to do all I can to keep them spotlessly clean while working on them and do all I can to prevent issues caused while working on them.

So, back to my question: What is the thread size for the pressure switches?
Ross
'84 633 Dinan turbo
KINGJOHN808
Posts: 127
Joined: Sat Feb 16, 2019 2:27 am
Location: Ewa Kai

Re: "brake" light in gauge cluster

Post by KINGJOHN808 »

Chris Wright wrote: Thu Sep 27, 2012 4:36 pm
633INGA wrote:Quick question - Does the "brake" light in the cluster measure pressure or level of brake fluid?
In a word, Yes! (and no, it is not a Yogyizim)

There are 3 "Brake" warning lights:

1) - The one in the check panel to the left of the cluster tests the stop light bulbs.
2) - The "Brake Lining" light in the cluster monitors the brake pad thickness.
3) - And the "Brake" light in the cluster monitors 3 separate things (See page 120 of your ETM):
  • a) The brake fluid level (switch on brake reservoir cap, closes on low fluid level).
    b) The brake accumulator pressure (switch on side of regulator, closes below 319psi).
    c) The minimum hydraulic system pressure (switch on top of regulator, closes below 22psi Steering pump pressure).

    - These switches are wired in parallel, and any one of them closing turns on the "Brake" warning light.
To troubleshoot the problem, unplug the brown (ground) wire on one of the switches listed under item 3 above and see if the problem goes away. If not, plug it back in and go to the next one until you find the culprit (be careful with the plugs on the brake reservoir cap, they can come loose and pull out.

It could be a bad pressure switch, they are known to leak internally and go bad. See if one is leaking around the spade lug. IIRC, they are around $25 at AutoHaus

If the problem is with the brake accumulator pressure switch on side of regulator, the accumulator may be going bad. See here to troubleshoot it:

Brake Bomb / Accumulator:
http://bigcoupe.com/phpBB2/viewtopic.php?t=9492&
Lost only part of it's charge: http://bigcoupe.com/phpBB2/viewtopic.php?t=6770&

Of course there could be a short on one of the wires going to the switches.
Great post and fix. Had similar issue, turned out to be the brake reservoir cap having issues. Was not picking up that the fluid was full, always “low”. Replaced, cap and “brake light” issue went away
Ewa Kai, Hawai’i
1984 633CSi
1983 633CSi (wreckers)

“Aloha and have a great day!”
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