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Old 05-16-2019, 12:10 PM   #1
seanile's Avatar
Join Date: Feb 2019
Location: Boston
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?

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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Join Date: Jun 2002
Location: S NJ, a suburb of Phila.

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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Join Date: Feb 2019
Location: Boston

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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Join Date: Aug 2008
Location: gangcouver

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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Join Date: Feb 2019
Location: Boston

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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