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Old 09-13-2018, 01:32 PM   #1
unfix8r
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Default Help with a diagnosis? Scary brake pedal shudder at slow speed/ near stopping

Hello fellow Volvo fans!

So I have a 1993 Volvo 245 wagon, automatic with just over 150k miles. She's my daily driver and I think I take pretty good care of her, ie. changing all the fluids regularly, magnets on the drain plug and filter, with lots of upgrades from IPD, and a stainless exhaust. I even flushed the transaxle oil... and I recommend everyone do that... ick!

I love Dorothea, but she's making me nervous lately.

Here's the deal: When I get to the point of stopping, say 5 mph or so, the brake pedal shudders and drops rapidly. Not 100% of the time, just about 35%-40% of the time. I hear a high pitched whine as the car slows to that speed, and then Ka-KUNK, Ka-KUNK!KaKUNK!KaKUNK!! *approximate sound*

With each loud noise, there is pedal drop. The car always stops, but I suspect that the issue has to do with the antilock system somehow, because I had to brake hard last week, and when I did, the wheels locked up, something they aren't supposed to do an an ABS system.

The rotors are newer and straight. (It's not rotor warpage, I know that feeling) The pads are 6 months old, and they are set well. I've flushed the brake fluid twice, in the right order, with a vacuum system. It seemed to help, but then the symptom came back.

To answer some of your questions in advance...

1) the pedal doesn't feel hard to push... it just... gives way with each clunk.
2) the ABS "idiot lamp" icon has not illuminated... (but it could be burned out)...
3) does the brake pedal PULSATE / SHUDDER on application?
4) the pedal does NOT GO TO THE FLOOR or "sink slowly to the floor" if you
hold the pedal firmly w/o lifting?
5) the car doesn't SWERVE SIDE TO SIDE with braking.
6) the STOPPING DISTANCE is pretty regular, if scary with the loss of feel on the pedal.

I cleaned off the ABS sensor with brake cleaner and compressed air. I've dropped it at two shops, they said they cant' replicate the issue. It's making me nervous.

There's a self service shop nearby that I can use with any tools necessary, and I'm open to all diagnoses.

One of my fears it that I had my son help with the car, and he put power steering fluid in the brake reservoir, but that was years ago, and I got it all out. Just trying to share ideas.

I have been researching whether it's the brake booster, the ABS sensors, or what, but I'm at a crossroads here of what to do next, and fear it's becoming unsafe.

I'm not giving up on old Dorothea, she never gives up on me.

Last edited by unfix8r; 09-13-2018 at 01:34 PM.. Reason: missplellings
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Old 09-13-2018, 06:50 PM   #2
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Find a way to disable the ABS temporarily. Pull a fuse or relay for the ABS. If the problem is still there after that, it's not the ABS. A defective brake master cylinder can cause the pedal not going down if you keep the pedal pressed and not let up to press again (symptom number 4).
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Last edited by lummert; 09-13-2018 at 06:56 PM..
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Old 09-13-2018, 10:30 PM   #3
dl242gt
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How are the front suspension bushings? Worn bushings can make for weird shudders. Check the tightness of the front crossmember bolts. Also worn struts and upper mounts can make for weird stuff like a shudder under braking. Loose wheel bearings? Bad lower ball joint? Even the steering ball joint ends and tie rods can do weird stuff.

I'm not ruling out something with your brakes either. But other stuff being bad can misdirect you sometimes.
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Old 09-14-2018, 04:12 PM   #4
unfix8r
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Default So I replaced the tie rods and ball joint, as well, didn't change anything.

I actually lied when I said it whined and then clunked.... it does a big Clunk, then a whine, and then two or three more shudders, and when I say that I mean the pedal drops.

I didn't want to disable the ABS this morning as the fuse for ABS is also the brake lights. I'll try in a non populated area this evening.
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Old 09-14-2018, 04:43 PM   #5
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I'm pretty sure the fuse for the ABS on a 93 245 is one of the large fuses on the battery positive terminal. The brake lights fuse should be in the fuse box near the door.
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Old 09-26-2018, 02:18 PM   #6
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So I went out of town, and came back. I popped of the fuse on the ABS, the big 40amp fuse, and while the idiot light on the dash came on, the braking was smooth and predictable. What should I check next? I'm not against having a 3rd shop look at it, but I'm losing faith in professionals.
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Old 09-26-2018, 02:46 PM   #7
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Have you measured the resistance of the ABS sensors? I had similar symptoms in a 745 because a bad ABS sensor. Your symptoms seem quite similar, apart from the fact that mine never locked the brakes up. Started with random pedal shudder and slightly poorer distance when braking at low speeds, but no warning light in the dash or fault codes. Neither did the pedal go to the floor. After a while I got a warning light as well and the car just shuddered at almost every low speed braking. Think I had some kind of not too describin fault code at that point too. I measured both front sensors and the other didn't react to spinning the wheel. Swapped the sensor and the problem was gone.
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Old 09-26-2018, 04:08 PM   #8
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Hope you get it sorted with a new sensor somewhere. Since your speedometer is fine it's probably one of the front sensors. There are only three wheel speed sensors used on abs with a 240 series. Two fronts and one rear shared with the speedo.
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Old 09-26-2018, 07:15 PM   #9
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Quote:
Originally Posted by Acke View Post
Have you measured the resistance of the ABS sensors? I had similar symptoms in a 745 because a bad ABS sensor. Your symptoms seem quite similar, apart from the fact that mine never locked the brakes up. Started with random pedal shudder and slightly poorer distance when braking at low speeds, but no warning light in the dash or fault codes. Neither did the pedal go to the floor. After a while I got a warning light as well and the car just shuddered at almost every low speed braking. Think I had some kind of not too describin fault code at that point too. I measured both front sensors and the other didn't react to spinning the wheel. Swapped the sensor and the problem was gone.
I think that may be my next step. I cleaned the sensor, (looked like a black porcupine) and reinstalled, but I think you are right. I doubt its the tone ring, there's no moving parts and it looked clean.

You sound like you had the same issue, so I'm going to go with your recommendation next. IPD?
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Old 09-26-2018, 07:16 PM   #10
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The speedo is pretty dead on, and Although I run Virgo wheels, they are still r15's, which comme within a couple percent of the stock radius. But there's no jumping of the needle at all... super smooth. I'll check the rear sensor, but I suspect it's the front. Maybe I'll end up doing both.
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Old 09-26-2018, 10:48 PM   #11
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There is an inline connector for each sensor in the engine compartment. Disconnect there and check the resistance at that connector.
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Old 09-27-2018, 02:46 PM   #12
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Quote:
Originally Posted by dl242gt View Post
There is an inline connector for each sensor in the engine compartment. Disconnect there and check the resistance at that connector.
This. If it's broken the IPD bosch replacements are probably really good. I bought cheaper ones (A.B.S branded) and they've worked great so far.
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Old 10-05-2018, 07:18 PM   #13
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When looking at the speedometer, just look at it when the ABS is kicking in. I had a similar problem, and while the speedo worked fine through most of the speed range, the signal dropped off around 8mph. In the cabin, this looked like the speedo working fine, then as I hit 8mph it would bounce a little or just drop off entirely. If you have a multimeter, you can connect it to both terminals of a speed sensor in ACV and spin the wheels, if one has significantly lower voltage (in mV) start with that sensor.

The front sensors are prone to getting gummed up with brake dust and crap, if you pull them and clean them, maybe the tone rings too, you might get lucky.
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