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Discussion Starter #1
I dont think i need pads..but something scary happened to me the other day. Im on Route 9 rahway, and go to hit my breaks. The pedal goes to the floor and the car slows but i had to really press it down to stop. It continued like that for about 20 minutes,..then all of a sudden its back. Though it doesnt feel as stiff as before. Any ideas guys?
 

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Discussion Starter #5
Thanks DMAX. is this the same shop i was going to have the FCABs done at? You know this happened about a month ago, and ive been driving almost daily and though my brakes arent as tight as when i first got the car,..it does stop the car without much pressure on the pedal..Do you think maybe it was dust? i havent had anyonen look at my pads but i dont think thats the issue here. Just throwing sht out there,..
 

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I wouldn't mess around with this.
If it happened to me I'd have a mess in my pants to clean up.
Take it directly to the shop.
 

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Thanks DMAX. is this the same shop i was going to have the FCABs done at? You know this happened about a month ago, and ive been driving almost daily and though my brakes arent as tight as when i first got the car,..it does stop the car without much pressure on the pedal..Do you think maybe it was dust? i havent had anyonen look at my pads but i dont think thats the issue here. Just throwing sht out there,..
That's the same shop. I can't recommend another!

Anyway, I don't know enough to 'know' what it is, but I know enough to know it's not dust...it sounds like the master cylinder. If you're not losing fluid...doublecheck that, btw, then it sounds like there's a seal in the master cylinder that isn't working. I'm not sure what else it could be, but I'm sure you should be scared enough to see someone reliable...and frankly, I don't think you should come to Union. I think you should find a local, well recommended indy. If you can't find anyone...Union might have to do...but keep your distance from other cars!

It's not pads, it's not dust...it's a real issue and I can tell it's not going to get better.
 

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Brake booster might be going.
I was just talking to my mechanic the other day about the brake booster. You remember the thread where it 'seems' that someone had a hiss from the brake booster line and to eliminate the hiss, he capped off the line to the brake booster?

Anyway, I heard if he didn't have a booster, that the brake would feel very hard...as in, no power assisted braking.

It might fail in other ways too, I suppose, but that's why I tossed master cylinder out...coz it's the only other part I know!
 

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That's a troubling problem. :yikes:

What sort of driving conditions were you in when it happened. Things like speed, road conditions, frequency of braking (i.e. were you in stop-and-go traffic or cruising on the highway) are relevant. Did traction control kick in?

When was the last time the brakes were changed? Brake lines? Brake fluid?

I agree, it's not the typical sign of a bad brake booster (hard pedal that sits high), though I wouldn't overlook the possibility of a mechanical failure in the pedal assembly. A pedal going to the floor usually means hydraulic pressure was lost. That could be the master cylinder going out, the brake fluid boiling, brake fluid leaking, etc. Since the pedal stiffness came back somewhat, I'd say it's most likely the fluid or the master cylinder.

One way to test for a failing master cylinder is to step on the brake pedal hard and to hold it. If it slowly sinks to the floor and there's no loss of fluid from the system, fluid is leaking past the internal seals and the cylinder needs to be replaced.
 

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The only thing more important than going is stopping. If your car does not stop, it fails the first rule of motoring.

I'd not suspect the brake booster as the failure item here. The job of the brake booster is to make it easy to apply the brakes, a booster failure would make the brake pressure go very high, but the pedal travel should remain pretty constant.

I think you have a brake master cylinder that is failing you. When you wait at a traffic light with your foot on the brake pedal, does the pedal sink slowly so that you have to raise your foot and apply the brake again? This too is a symptom of a failing master cylinder.
 

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Discussion Starter #13
Thanks guys. Doesn't sound like a brake booster problem from what you guys are saying. I was driving relatively slow in stop and go traffic. The pedal is def not sitting high. It feels like its actually sitting lower. im going to try the press on the bake test now and will let you know. How much are we talking for a new MC?
 

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Thanks guys. Doesn't sound like a brake booster problem from what you guys are saying. I was driving relatively slow in stop and go traffic. The pedal is def not sitting high. It feels like its actually sitting lower. im going to try the press on the bake test now and will let you know. How much are we talking for a new MC?
About $100 for the part if your car doesn't have DSC; $200 if it does. Add to that labor and fluid.
 

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Ok the pedal does in fact slowly drop..ugh! Need to price a new MC..
And no leaks visible? Reservoir staying constant? It can be hard to tell if there's a change in level when you only have a small leak.
 

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And no leaks visible? Reservoir staying constant? It can be hard to tell if there's a change in level when you only have a small leak.
You can have significant changes in the performance of the system, and no visible leaks anywhere.

The Master Cylinder can develop internal leaks, fluid goes past some O-rings and seals, that makes the pedal drop, and you do not see any fluid loss at all. If there is fluid loss from the brake system, it is normally the wheel cylinders leaking to the outside. You will see fluid around the calipers if this happens. In your BMW, the clutch is hydraulically operated, so there is also the chance that brake fluid can be lost through the clutch slave cylinder. The clutch master cylinder and the brake master cylinders will usually have internal leaks without any loss of fluid, but significant loss of system performance and integrity.
 

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You can have significant changes in the performance of the system, and no visible leaks anywhere.

The Master Cylinder can develop internal leaks, fluid goes past some O-rings and seals, that makes the pedal drop, and you do not see any fluid loss at all. If there is fluid loss from the brake system, it is normally the wheel cylinders leaking to the outside. You will see fluid around the calipers if this happens. In your BMW, the clutch is hydraulically operated, so there is also the chance that brake fluid can be lost through the clutch slave cylinder. The clutch master cylinder and the brake master cylinders will usually have internal leaks without any loss of fluid, but significant loss of system performance and integrity.
Exactly (as I wrote above), and in order to make a positive diagnosis, you have to be sure the fluid isn't going elsewhere. This looks very much like a bad MC if the system is still sealed.
Btw, on these cars, I'd wager it's more likely to have a leak from the flex line at the caliper than the caliper itself.
Also, if you lose brake fluid through the clutch, the feed is cleverly designed to be taken from higher up on the reservoir, so a completely drain of fluid from the clutch hydraulics will not affect brake performance.
 
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