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Old 05-16-2019, 12:10 PM   #1
seanile
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Default Low-speed brakes, springing sound, ABS? (1992 240 GL)

hi there! a friend gave me a reasonably well kept 92 240 GL sedan, so i'm getting to know the beast. i've worked on motorcycles, but not cars, so this is all relatively new to me.

i'm going to assume this is an issue with the ABS, but here's the circumstances i'd like help diagnosing:
-low speed stopping, parking lot speeds.
-it doesn't always happen, often when the car is still just warming up, or had been parked for a little bit.
-the brakes, sounds like the front ones, make a deep toned springing twanging sound, as if you were spinning a large coil spring in the wrong direction and the spring's end was skipping.
-when this happens, the pedal sinks a bit toward the floor.
-i haven't noticed the abs light going on, but i have to check that the bulb for that light even works.

possible cause:
-someone sideswiped my car when it was parked and really only contacted the driver's side wheel and bumper. they managed to cause the wheel to turn to the right when they hit my car (they were traveling in the direction i was parked).
-i've been reading about abs sensors being attached to the wheel somewhere, and they if they get loose or dirty, they can malfunction and make the car think the wheel isn't spinning. i've also read somewhere that not all of the wheels have abs sensors?

thoughts? steps i can take?
thanks!


Last edited by seanile; 05-16-2019 at 02:55 PM..
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Old 05-16-2019, 02:20 PM   #2
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From your description I wuold suspect you have a sticky brake caliper. It's sticking and then coming free which affects the brake pedal. It may also be bad rubber brake flex lines that have internally swelled which will let brake fluid through underpressure but can make the caliper stick on and also cause excessive wear on the pads.

The other thing that has springs in it are the rear parking brake shoes. They are a small drum bake inside of the rear rotor which has hardware like return springs in there which if broken or out of position could catch on something.

FYI the ABS has a wheel sensor on each front wheel behind the brake bakinc plate. On the rear the speed sensor in the differential shares the function of speedometer and abs sensing. The sensor is on the back of the diff cover.

I suggest you get a Bentley manual for your car. it has a wealth of information. Also the Haynes manual is good for these cars, too.
DOT4 brake fluid only.
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Old 05-18-2019, 08:15 PM   #3
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Thank you! Great info in there. I took it out for a longer ride today where i was turning it off a bunch to give the system a chance to reassess itself, the ABS light would stay on sometimes, until i turned the car off and restarted it.

Rear ebrake shoes were replaced by a well-reputed shop a couple months ago that i trust was done correctly. He said my cables were in great shape for those as well.

Im going to check the wheel sensors on the front wheels tomorrow.

Ive got a Bentley manual, and was just interested in others’ experiences with a similar issue if any.

Ill take a close look at the brake hoses and bleed them sooner than later in any case!

Anyone else have any additional thoughts?
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Old 05-18-2019, 09:48 PM   #4
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Quote:
Originally Posted by seanile View Post
Ill take a close look at the brake hoses and bleed them sooner than later in any case!
The problem is the brake lines break down and swell internally and frequently it is not visible on the outside. If you at all question them, replace them. It is easy and cheap, especially if you are going to bleed it anyways.
Pay attention to the bleed procedure. These cars dont like it done the wrong way, and they procedure is different from most cars. Get a power bleeder like the motive system and it will make it a much easier one person job. It will also prevent killing the master cylinder by pumping the pedal too far in.

Btw, you can make a power bleeder for about 20-25 bucks out of a pump up garden sprayer, a cheap pressure gauge from harbor freight, a spare master cylinder cap and some brass barbs. Look at the motive system and you will get the idea.
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Old 05-20-2019, 11:23 AM   #5
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thanks, i was planning on following the brake bleed process described here: https://www.brickboard.com/RWD/index...749&show_all=2

do you think thatd be acceptable?


given the ABS light is coming on more often, i'm inclined to think it's one of the sensors rather than a stuck pad though.
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Old 05-22-2019, 04:02 PM   #6
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found this PDF describing ABS faults / ABS Pulses at Low Speeds on brickboard. posting in case others have this issue and find this post.
going to check my sensors this weekend and will report back.

https://www.brickboard.com/FAQ/700-9.../BrakesABS.pdf
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Old 05-22-2019, 04:14 PM   #7
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Sounds to me like the ABS is triggered indeed. When my ABS is active on snow and muddy roads etc. (with my 940 - same unit I believe), I would describe it exactly the same as you (pedal sinking & pulsing and rattling noises).

I would definitely clean the sensors. I had an intermittent ABS light some time ago, cleaned all sensors and it never came back.
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Old 05-22-2019, 04:16 PM   #8
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thank you, that's good to hear. i'm pretty optimistic that's all it'll be
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Old 05-23-2019, 09:16 AM   #9
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Sounds like you're getting pulled in a few different directions.
Here, let me add to your confusion!

I don't think it's ABS. My 92 does the exact same thing you're describing. I park it in the driveway or garage, next day, turn it on, start backing out of the driveway or garage, and on my way down the driveway I hit the brakes, and TWANG weird spring popping noise and my pedal sinks in a bit. But then it never does it on the rest of the trip, until I park it and it sits over night again. And, particularly, it sounds like it is coming from my right rear wheel.

The reason I don't think it's ABS is my 850 has a bad ABS computer so ABS will engage on random stops. So I'm extremely familiar with the feeling of ABS engaging. I've also hit the ABS on the 240 before on a wet highway where some goons slammed their brakes. In my experience, I've never felt ABS do just ONE pulse. It's always a few... to me, I'm guessing a sticky caliper piston that is coming dislodged, but I could be wrong because in the end, I have the same issue as you and have not fixed it (haven't really tried yet). The springing noise could easily be acoustic reverberations in the hydraulic brake fluid. The same thing happens to some water faucets when they choke the water off too quickly, causing this loud knocking noise... it's called water hammer or something like that if you look it up. But it's just acoustic waves from the sudden jolt in the hydraulic fluid reverberating thru the pipes.

Trust your ears, the caliper it sounds like it's coming from is most likely the one to look at.
Also, if it is ABS, one would be able to hear the ABS motor if you're in a quiet setting ( low speed, no music)
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Old 05-23-2019, 09:35 AM   #10
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Temporarily unplug the front ABS sensors (this disabled the ABS on my 88 765). See if the issue changes.
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Old 05-25-2019, 08:22 PM   #11
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reporting back:
as i was driving around during this week, whenever i felt the ABS kicking in, i'd let go of the wheel. by doing that, the wheel would pull to the left because the left front wheel's brake would stay planted and the right front wheels ABS would be pulsing and thus not putting continuous braking pressure. that told me it was ABS, and gave me the specific sensor to check.
i jacked the car up, pulled the wheel sensor and sure enough there was some fuzzy metal bits on the magnet. cleaned those off, put some dielectric grease on the main body cylinder of the sensor (NOT THE SENSOR/MAGNET ITSELF), per the service manual. also did the left one too while i was under there, not as many fuzzy bits, but i'm sure it'd start causing its own trouble eventually.
drove it around a bit, and in the 5 miles i did in the city, no ABS activation!! success, so far.
i will report back if it doesn't hold for the long-term.

Last edited by seanile; 05-25-2019 at 10:39 PM..
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Old 05-30-2019, 11:53 PM   #12
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update:
abs light came on pretty steadily for the few days following that attempted "fix". during that period, i had no problem with the brake shuddering, no symptoms.
the light was not on at all today, and the issue resumed.
this, to me, is another confirmation that the issue is the abs, and that it was, for a lack of better words, "malfunctioning" while the light was on. now that the light is off, the abs is doing what it does best and is working...just not when it should.

next steps to take this weekend are to 1) re-examine the sensor, thoroughly clean the seat of the sensor body so the gap is right, 2) check the condition of the wires from the sensor up to the strut, which is where i've read it travels to (anyone have any more specific landmarks or details i can use to locate it?), 3) check the fuse on the abs module underneath the passenger side carpet just in front of the passenger seat, 4) if i can figure it out, check the condition of the tone wheel/reluctor ring thing (any advice related to that procedure would be very welcome)

also found this thread from the fall with a similar problem: http://forums.turbobricks.com/showth...t=wheel+sensor
linking it here, again, for anyone else's future reference..more info the better.
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Old 06-02-2019, 06:17 PM   #13
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Stopped by a junkyard today. Pulled the ABS module from underneath the passenger seat of a 92 240 wagon, also pulled a wheel sensor. I checked the fuse on the module in my car and that looked good, so I decided to swap the wheel sensor first and see if that would solve it. Pulled mine, put the new/old one in, and that seems to have done it. No braking issues on the short drive I took, and no ABS light on. Now I have a spare module hah
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