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My son was driving his '90 240 with 220K miles when he says the brakes suddenly stopped working. He said they felt "odd" at one stop and at the next red light the pedal went to the metal. Fortunately, he was able to stop with the e brake. When I went to check it, the brake pedal felt nice and firm, but as soon as I started the motor, the pedal sunk to the floor. I removed and sealed off the vacuum hose to the booster and was able to drive home (with the expected hard/poor braking). There is vacuum at the check valve, and the check valve seems OK (air flows towards the manifold, but not the other way.)
I assume the problem is a bad booster, but I've never heard of any failing this way. I thought that when they failed, they simply stopped giving a boost, and you could still rely on the brakes working. Before I plunk down the $$$ (and put all the effort into removing those 4 nuts), is there an alternative diagnosis?
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The one critical observation is that the pedal went to the floor. It's simple physics (well, simple hydraulics). No matter what the condition of anything else, the only thing that would let the pedal reach the floor is that the master cylinder has an internal leak.
This is indeed sometimes intermittant -- but a seal between the piston and the passages to the reservior is "acting up", allowing fluid that should be compressed in the cylinder to, instead, leak past the seal and return. Thus, the reservoir stays full while the piston is allowed to advance to its stop because there's no build up of pressure to halt its advance. Change the master cylinder ASAP.
Of course, it could be a fluid leak somewhere , but I assume you looked for it, and it would show by a loss of fluid in the reservior which I also assume you checked when you were poking around the check valve for the booster. And sometimes a really "soft" flex line would swell and soften the pedal, but not enough for it to drop to the floor.
And you're right, a bad booster would harden the pedal, not let it drop that much (although it will have to move a little more). And also, you're right again that a bad booster is very rare -- but a failed master cylinder is at the other end of the probability scale (fairly common when the mileage is up there).
Good luck.
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Thanks, everyone, for helping me think through this. You've convinced me that it can't be the booster. Air in the lines/inadequate bleeding makes sense, but I find it unlikely. Not because I'm an expert bleeder (and I did bench-bleed the m/c), but because the problem existed before I replaced the m/c. Similarly, I find it unlikely that it's a bad m/c because the odds of the new one having the same problem as the old one seems remote. (Though neither are impossible!)
I like the idea of a swollen brake hose. That could explain why the brakes work OK with the booster disconnected--maybe not enough pressure to cause a "ballooning" in a line. It might also explain the sudden onset--maybe one hose isn't actually ruptured, but suddenly developed an aneurysm, so to speak. I'd think that would cause enough of a pressure imbalance to cause the brake warning light to go off, but still worth exploring.
I wish I hadn't been so tired/rushed when I replaced the m/c the other night and had thought to look at the hoses carefully. So that's what I'm headed to do now....
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Just finishing replacing the master cylinder--and no change in the symptoms. Grrr.
Bled the system and had a nice firm pedal. But as soon as I started the motor, the brake pedal sunk, almost to the floor. Turn off the motor, pump a couple times, and the pedal is firm again.
So now what???? I'm thinking of going back to my original plan of replacing the vacuum booster. But I am perplexed that even though the pedal sinks, the brakes do work, and they're clearly boosted.
Any other theories before I plunk down the $100 and attack those four tricky nuts?
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I don't think it is the booster. If the pedal is dropping to the floor with booster assist, then isn't the booster working?
Depress the pedal gently as at a stop light and see if it slowly sinks. If it does then it's probably the MC or a leak.
Open up the old Master Cylinder and check for a damaged seal. (Remove triangle wire with plunger depressed with a Phillips screwdriver, release plunger gently to avoid it flying out.)
--
1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.
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The gentle application pressure and sinking to the floor test is about a definitive as you can get.
Just a soft pedal that sinks more initially or more than you like but hits kind of a hard stopping point before the floor usually indicates that there is still air in the system.
Even if pressure bled, I have a had two cars now that had residual air in the system after a MC replacement in spite of bench-bleeding the MC before installation. I am guessing that during pressure bleeding I forced some air down from the MC connections to the junction block where it got kind of hung up.
On the 240 with problem, driving it for a few weeks and then bleeding again solved the problem. On the Saturn, time healed the wound as I believe these bubble traveled back up to the MC and purged at a later time.
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Hello,
Does your 1990 240 have ABS(Antilock Brake System)?
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
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More oddness: I did the test described in the FAQ of holding the pedal steady (after releasing all vacuum) and then starting the motor. The pedal is supposed to drop a little--but it drops a LOT. That's what I noticed when I first checked the car. But what I just realized is that in my tests in the garage, the brakes did work and obviously had boost--it was just that the pedal was near the floor. My son said that was what happened to him at first, but then it went to the point of not braking at all. Does that offer any hints about what's wrong?
BTW, the second part of the test is to hold the pedal steady and then turn off the motor; if the pedal tries to rise, there's a problem. When I tried that, it did NOT rise.
I wish I understood how brake boosters work--maybe then these symptoms would make sense.
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The booster only makes it easier to apply brakes. It has nothing to do with how far the pedal goes down.
Get a master cylinder... and get one yesterday!
--
-Matt I ♥ my ♂
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Hello,
Sound more like a bad brake master cylinder than a bad brake booster.
How old is the brake master?
Look for brake fluid seepage at the back of the brake master.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
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Thanks, Planetman and MatB--so you both suspect the m/c. It was replaced in 2001, at 108K miles--meaning that the replacement is as old as the original when it failed. I like your idea, because it's certainly cheaper, easier and quicker (probably actually in stock locally, unlike the booster).
BUT, inquiring minds want to know--if the m/c is the culprit, why was I able to drive the car home OK with the vacuum booster disconnected? Wouldn't the m/c show the same symptom with or without the booster connected?
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Hello,
What is probably happening is that without the brake booster vacuum assist, it is a lot harder to over power the sealing capabilities of the failing brake master cylinder piston seals.
And while the brake master cylinder piston seals are not bypassing, you will have some brakes.
You have to remember that a correctly working brake booster multiplies you pedal effort.
--
Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
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Thanks, Eric, that makes sense. Looks like I know what I'll be doing tomorrow night!
P.S. Now live in Golden, CO but grew up right on the Torrance/Gardena line. Where's your shop located?
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Golden eh? Still have a 1800 too?
Got friends in Golden that we plan to visit before long... not for a few weeks, as we'll be heading to the west coast next week (in the ES, of course).
Feel free to drop me an email if you need anything semi-locally. Forcefieldmatt-at-gmail
--
-Matt I ♥ my ♂
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posted by
someone claiming to be mr volvo
on
Fri Sep 21 06:39 CST 2012 [ RELATED]
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One time I had a stuck rear caliper it was bending the disk the length of motion
was enough to send the petal to the floor. may not be your problem but it was odd
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