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Discussion Starter · #21 ·
Another thought, if you are bleeding with a high-mileage m/c and you haven't flushed the fluid regularly, it's a bit risky pushing the pedal all the way to the floor. Moisture accumulated in the m/c over the years can corrode the part of the bore not swept by the u-cup seals during normal braking. Now you push the seals way past their normal travel and they scrape over the corroded area.

Malcolm
I think this is the reason I need to change the MC in the first place :(
 

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That's too bad. Some guys put a 2x4 under the pedal to limit travel when bleeding.

I work on older vehicles and when you dismantle a m/c, you can often clearly see where a drop of water has been sitting in the bottom of the bore and pitted the bore. Because it's usually outside the area swept by the seals, honing the bore and putting in new seals often works if it's a hard-to-get m/c.

Malcolm
 

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Discussion Starter · #23 ·
Bled the system last night following nightkrawler's TIS instructions to the letter. Big improvement. It's still far from perfect, but better than I've ever felt it.
 

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Which is why you need to manually open the correct solenoids and flush fluid thru them. Backwards forwards I don't care, but these mushy pedals are a ABS solenoid problem not much different than the vanos solenoid problems. That said if you now just drive the car and get on the brakes hard enough to engage the ABS a few times, after 1000 km the brakes will be firmer.
 

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I was thinking more about this thread and the problem of soft pedal and was wondering how they bleed cars during production. Go drive a new BMW, or really any new car, and you'll see that the brake pedal is very firm. Most new cars have very sensitive brake pedals, while here we are complaining about soft pedals. At the factory I am sure that they have to bleed in a short period of time with minimal to no fluid waste, and they are starting with a system full of air. Anyone here works/worked in a car factory and can chime in? I think that they probably fill the brake system the same way they fill the cooling system, using vacuum. There are many videos out there on vacuum filling cooling system, so if you are not familiar with that, please watch. On some cars getting air out of a cooling system is a major pain, and vacuum filling solves that quickly. For the brake system I think they do the same thing, and I don't mean vacuum suction at each caliper one at a time. No time for that in production. I think they probably apply vacuum to the master cylinder reservoir and suck all the air out of the entire hydraulic system at once. This would include the clutch system as well because it is connected to the master cylinder fluid reservoir. They probably cycle the ABS solenoids while the vacuum source is connected to the brake reservoir which then pumps all the air out of the ABS unit. They then introduce brake fluid into the reservoir and it fills the entire system (brake and clutch), and they never even have to touch any bleeders. This would be fast, efficient (can be done by a single person), and not wasteful (no fluid discarded). Curious if anyone has tried something like that.
 

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Anyone here works/worked in a car factory and can chime in? I think that they probably fill the brake system the same way they fill the cooling system, using vacuum.
Yes I have (mechanical engineer and I worked on E70/E71 production in Spartanburg) and you're right, that's exactly how it's done. Full system vacuum and then fluid fill. Power steering fluid was also done this way. And while I don't know for sure, I'm confident that you're also correct that the ABS solenoids would just be cycled on/off during this process. Replicating that in your garage though would be a pretty big job. . .
 

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austrianvespaguy, thanks for confirming that this is how it is done. I suspected that in production bleeding one wheel at a time would be too slow and error prone. Also, if there is any moisture in the system, the vacuum will help remove it just like it does in an A/C system.

I actually don't think that it is that difficult to replicate this system at home. I haven't done it yet, but I will try. Basically you need a screw on attachment for the master cylinder (the vacuum should help hold it in), the same as one uses for pressure bleeders. From there it connects to a t fitting. Each side of the T goes to a ball valve. One ball valve controls vacuum (need a vacuum pump obviously, but I have one for the A/C system so will adapt) and the other ball valve goes to a hose which is inserted into fresh brake fluid. Exactly like a vacuum coolant filling system. Then when the system is under vacuum, use an appropriate software to open and close various valves in the ABS unit. Since the goal is to pump out all the air, I think the sequence of ABS valve opening and closing may not be critical, although I may be wrong. I just need to figure out what software I can use to cycle the ABS solenoids.
 

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As an aside, all E39s (all V8 examples fwiw) I have experience with over the past 20 years have had soft and squishy brake pedal responses even when fully and perfectly bled. I ordered and bought a 2002 540i/6MT new and then bought an M5 near new (12k miles) in 2004 and have done brake jobs on and driven many other E39 M5s over the years. The one thing that dramatically changed how the pedal felt was installing a Stoptech front BBK. Now the pedal was much firmer and better responding. Years later I swapped back to the OEM front brakes, and that E39 squish returned. Conversely, the S62 swapped 540iT we installed my BBK on now obtained a nice firm pedal.

The net is that you really can't compare the feel/travel/squish on the E39 to other newer designs and try to find a solution in further bleeding if the system is fully and properly bled. If you really want a nice firm pedal and significant reduction in squish/travel/etc, that Stoptech BBK did wonders for the car.
 
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