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Car Forum / BMW Cars / December 2005Bleeding brakes
I am bleeding my brakes this weekend and I have three questions (328i 98 E36). First I have heard two different things about where to start, one the closest to the cylinder and two the driver side rear…So which do I bleed first? Second, I want to bleed the clutch, it’s my understanding that the brake reservoir is the same one the clutch uses?? Were is the bleed point one the clutch? You don't need to bleed the clutch. Brakes are bled to keep the boiling point of the fluid from dropping due to water absorption. Usual advice is to begin bleeding farthest from resevoir, though I cannot see why it matters. start at the pass rear, not sure of all the physics involved, but its always worked for me.... > start at the pass rear, not sure of all the physics involved, but its > always worked for me.... It does not matter where you start as long as you don't let the reservoir get low and suck in air.  Signature-Fred W > > start at the pass rear, not sure of all the physics involved, but its > > always worked for me.... > It does not matter where you start as long as you don't let the > reservoir get low and suck in air. Convention says to start at the one furthest away from the master cylinder - which would normally be the nearside rear. Then progressively to the nearest. Signature*No husband has ever been shot while doing the dishes * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. I would stronly disagree with the statement that the clutch does not need bleeding. While it is true that the boiling point of the brake fluid drops due to moisure absorbtion, an equally important reason that these systems require periodic bleeding is to get rid of the water that has been absorbed by the fluid so that the internal components of the system don't corrode. With that in mind, you should use the whole container of fluid because you are really replacing all of the fluid that's in the lines and cylinders. It's a good idea to suck all the old fluid out of the reservoirs with a basting bulb and replace it with new before you start pumping so that you know it's all new fluid that you are pushing down the lines. > You don't need to bleed the clutch. Brakes are bled to keep the boiling > point of the fluid from dropping due to water absorption. > > Usual advice is to begin bleeding farthest from resevoir, though I > cannot see why it matters. I disagree, there is a definate reason to start from the rear, something about how the sediment (be it air or water can settle, Ive bled from the front to back and not been able to get the same solid pedal as rear to front.) Also of note is the ABS, I remeber that to get a solid pedal on my e36, I had to turn the car on, then have someone pump while I bled, if I did it without the abs system being active I got a slightly spongy feel, not tremendous, and it still stopped, but it was considerably more "solid" when done with the car on. >I disagree, there is a definate reason to start from the rear, >something about how the sediment (be it air or water can settle, Ive [quoted text clipped - 5 lines] >not tremendous, and it still stopped, but it was considerably more >"solid" when done with the car on. Bleed brakes to get rid of air in the lines, that's why you start at the farthest point from the master. > I disagree, there is a definate reason to start from the rear, > something about how the sediment (be it air or water can settle, Ive [quoted text clipped - 5 lines] > not tremendous, and it still stopped, but it was considerably more > "solid" when done with the car on. You only get a non-solid pedal feel if you have air in the system. We were not talking about bleeding for trapped air, we were talking about changing the brake fluid because it was old. If you bleed your brakes then and get a soft pedal you screwed up. Signature-Fred W It's a complicated topic. A good article is at http://www.findarticles.com/p/articles/mi_m3102/is_9_123/ai_n6221217. > It's a complicated topic. A good article is at > http://www.findarticles.com/p/articles/mi_m3102/is_9_123/ai_n6221217. Wow. Excellent article. I defer to the information therein. Apparently, there can be corrosion without oxygen in the sealed system. I stand corrected. Signature-Fred W >> It's a complicated topic. A good article is at >> http://www.findarticles.com/p/articles/mi_m3102/is_9_123/ai_n6221217. > >Wow. Excellent article. I defer to the information therein. >Apparently, there can be corrosion without oxygen in the sealed system. > I stand corrected. Very interesting indeed... > I would stronly disagree with the statement that the clutch does not need > bleeding. While it is true that the boiling point of the brake fluid drops [quoted text clipped - 6 lines] > basting bulb and replace it with new before you start pumping so that you > know it's all new fluid that you are pushing down the lines. Yes and no. Yes, you should bleed the clutch lines, and yes it's because you want to remove all the moisture from the system, but no, it's not because it's going to corrode inside the sealed system if you don't. It's just so the fluid boiling temp does not become reduced. There will never be enough water absorbed by the hydraulic brake fluid to precipitate corrosion, *unless* you are using the DOT5 fluid (which you should not be on any BMW I am aware of). Unlike DOT 3 & 4 fluid which is glycol based and therefore hygroscopic (absorbs water) DOT 5 is silicone-based. It will not absorb water. While you might think that is a good thing it means any water in the system will remain separate. Also, since the system is sealed there will (should) be no oxygen (air) which is needed to create corrosion. Signature-Fred W > Also, since the system is sealed there will (should) be no oxygen (air) > which is needed to create corrosion. It can't be totally sealed otherwise fluid from the reservoir wouldn't top up the master cylinder as the pads wear. There is a small breather at the filler cap. If the system is full when you come to replace pads, forcing the pistons back will push fluid out of the reservoir even with the cap on. Signature*Two wrongs are only the beginning * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >Yes and no. Yes, you should bleed the clutch lines, and yes it's >because you want to remove all the moisture from the system, but no, [quoted text clipped - 12 lines] >Also, since the system is sealed there will (should) be no oxygen (air) >which is needed to create corrosion. That's very interesting. I've often thought about that - after all, the internals of the brake system, even with some "absorbed water" is still very "oily"... I don't suppose you'd have any collaborating links? Thanks for everyones help.... Th only problem I had was once I finshed I brought the old fliud to Autozone. Well, autoZone won't take brake fluid, so I had to run around town tring to find a place that would. >I am bleeding my brakes this weekend and I have three questions (328i 98 E36). >First I have heard two different things about where to start, one the closest >to the cylinder and two the driver side rear…So which do I bleed first? >Second, I want to bleed the clutch, it’s my understanding that the brake >reservoir is the same one the clutch uses?? Were is the bleed point one the >clutch? |
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