norcal928 - Saturday Brake Master Cylinder Replacement and Bleeding
10-12-2008, 11:20 PM
#61
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Mkay seeing as though I'm the one that physically turned the wrench while installed the new MC, we did put that new rubber gasket, and as far as I could see there was no fluid around the gasket area, on the pushrod inside the brake booster or anywhere near there. I don't believe there to be a vac leak, as the pedal is firm without any vacuum at all (engine off), but very soft with the engine running. Sliding the master cylinder over the pushrod was easy enough, and I don't think there's any excessive clearance issues in that area. I believe that adjusting said pushrod would more or less mask the problem, rather than fixing it.
WSM bleed procedure is called out as MC, front circuit, rear circuit, no special procedures.
Dumb question, were the calipers installed with the bleed screws at the top?
Not sure the calipers even CAN be mounted on the wrong sides, but thought I'd ask.
With the power bleeder, did you crank the bleed screws wide open so you saw lots of flow? I found that I would get more bubbles out of the system if I backed out the bleeders almost to the point brake fluid would leak past the threads. You might also try tapping on the caliper as you bleed. If you have an allen socket for the mounting bolts, tap on the bolts with that so you don't ding the finish.
Bill, reverse bleeding might help, but IMHO you should be able to get enough fluid velocity in the lines with the power bleeder to clear the air from them, even if it's mostly downhill. I've bled the brakes on 2-ton trucks this way, where the line goes 3-4 feet almost straight down, and on my Dodge truck where the brake line is coiled near the cylinder. That's also about a 3' drop.
If you could rig a hose from the power bleeder to a bleed valve you might get somewhere but it might end up just making a mess when either the line pops off or the reservoir overflows.
10-12-2008, 11:36 PM
#62
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I can assure you that all bleeder nipples point upwards. I think one of us five would have realized by now, if they were facing the wrong way... 
10-13-2008, 12:19 AM
#63
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So when you put the MC in place against the booster, there was no "springiness" -- that is to say the MC went tight up against the booster with no resistance? If so, that's good.
Dumb question, were the calipers installed with the bleed screws at the top?
Not sure the calipers even CAN be mounted on the wrong sides, but thought I'd ask.
With the power bleeder, did you crank the bleed screws wide open so you saw lots of flow? I found that I would get more bubbles out of the system if I backed out the bleeders almost to the point brake fluid would leak past the threads. You might also try tapping on the caliper as you bleed. If you have an allen socket for the mounting bolts, tap on the bolts with that so you don't ding the finish.
Dumb question, were the calipers installed with the bleed screws at the top?
Not sure the calipers even CAN be mounted on the wrong sides, but thought I'd ask.
With the power bleeder, did you crank the bleed screws wide open so you saw lots of flow? I found that I would get more bubbles out of the system if I backed out the bleeders almost to the point brake fluid would leak past the threads. You might also try tapping on the caliper as you bleed. If you have an allen socket for the mounting bolts, tap on the bolts with that so you don't ding the finish.
The bleed nipples point upwards. Remember, there are no stupid questions, just stupid people. Luckily, none were present on saturday
I only cracked the power bleeders a little bit, basically until the fluid moved reasonably quickly. We did try the tapping on the calipers (and most other components) as well.
10-13-2008, 02:12 AM
#66
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Yes it went in as you described.
The bleed nipples point upwards. Remember, there are no stupid questions, just stupid people. Luckily, none were present on saturday
I only cracked the power bleeders a little bit, basically until the fluid moved reasonably quickly. We did try the tapping on the calipers (and most other components) as well.
The bleed nipples point upwards. Remember, there are no stupid questions, just stupid people. Luckily, none were present on saturday
I only cracked the power bleeders a little bit, basically until the fluid moved reasonably quickly. We did try the tapping on the calipers (and most other components) as well.
I'd recommend opening the screws more... let 'er rip. At the outset, I'd start with a couple quarts of cheap, generic DOT4 until it's working properly, then flush through with the "good" stuff. No point spending a lot of $ on pushing bubbles around.
A pressure gauge, something like this, would at least narrow down which circuit has air. When you saw the ABS operating, which wheels were being modulated by the ABS -- front or rear?
It works a lot better in a narrow tube!
10-13-2008, 02:20 AM
#67
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In the past, on a Range Rover that was having it's first fluid change in about 10 years I'ld guess, I ultimately resorted to completely removing the bleed nipples and pumped the best part of a gallon of cheap fluid through to get the old crud out and then the flow fast enough to bring the bubbles with it. Once that was done let it settle for a couple of days, drove it a bit - yes using the brakes can move the bubbles around to a position where they will float to the top, then bled again with cheap then finally with no bubbles bled through the good stuff.
PS It's worth noting that opening the bleed nipples more than about two turns does nothing to increase flow rate as the restriction to flow is the holes in the side of the nipples. Only completely remvoing the nipples gets you more flow rate.
Last edited by jon928se; 10-13-2008 at 02:23 AM. Reason: forgot something
10-13-2008, 02:32 AM
#68
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Yeah, Dave, I probably will always remember that other (not so) "stupid" question.
I could not distinguish any pulling or uneven ABS application.
When Nicole originally reported that the rear brakes were hot while the fronts were not, I had thought there must be some way to check pressures, but I did not know of any such pressure gauges, so thanks for that link. I think we're beyond that now, as the front rotors definitely get HOT and hotter than the rears. We can probably get some approximate information from slowly applying the brakes with the wheels off the ground and seeing which ones lock first.
I could not distinguish any pulling or uneven ABS application.
When Nicole originally reported that the rear brakes were hot while the fronts were not, I had thought there must be some way to check pressures, but I did not know of any such pressure gauges, so thanks for that link. I think we're beyond that now, as the front rotors definitely get HOT and hotter than the rears. We can probably get some approximate information from slowly applying the brakes with the wheels off the ground and seeing which ones lock first.
10-13-2008, 07:21 PM
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I know in some state's that require a yearly inspection, the inspection stations have a way of measuring the braking percentage of each wheel. Would using something like that help to determine if there is air and where in the system is?
10-14-2008, 01:28 AM
#72
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Yeah, Dave, I probably will always remember that other (not so) "stupid" question.
I could not distinguish any pulling or uneven ABS application.
When Nicole originally reported that the rear brakes were hot while the fronts were not, I had thought there must be some way to check pressures, but I did not know of any such pressure gauges, so thanks for that link. I think we're beyond that now, as the front rotors definitely get HOT and hotter than the rears. We can probably get some approximate information from slowly applying the brakes with the wheels off the ground and seeing which ones lock first.
I could not distinguish any pulling or uneven ABS application.
When Nicole originally reported that the rear brakes were hot while the fronts were not, I had thought there must be some way to check pressures, but I did not know of any such pressure gauges, so thanks for that link. I think we're beyond that now, as the front rotors definitely get HOT and hotter than the rears. We can probably get some approximate information from slowly applying the brakes with the wheels off the ground and seeing which ones lock first.
So the car has 16 bleed valves, right? What was the bleeding sequence that you used? Then when you found the pedal issue, what steps did you take?
10-14-2008, 01:48 AM
#73
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Hi Dave:
https://rennlist.com/forums/928-forum/426524-a-few-brake-caliper-refinishing-questions.html, starting at Post #39
https://rennlist.com/forums/928-forum/426524-a-few-brake-caliper-refinishing-questions.html, starting at Post #39
10-14-2008, 02:31 AM
#74
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OK, the only thing that stands out for me is "used 1/4 quart of fluid".
Seriously, get 2-3 quarts of cheap stuff, put the stock bleed screws on, and bleed at ~10psi with the bleed screws backed out for maximum flow.
Also, with a new MC there is no risk bleeding with the pedal, since you don't have to worry about rust spots and the seal. You can get a lot more pressure this way, therefore a lot more velocity. Hook up the power bleeder then with the bleed screws closed, jam the pedal down hard then quickly open the bleeder. Close the bleeder once the pedal hits bottom, let off the pedal, open the bleeder and let it flow for a moment, then close. Repeat. Even though the higher pressure will make the bubbles much smaller and prone to hide in crevices, the high velocity and the "shock" of sudden flow may help dislodge some bubbles.
Seriously, get 2-3 quarts of cheap stuff, put the stock bleed screws on, and bleed at ~10psi with the bleed screws backed out for maximum flow.
Also, with a new MC there is no risk bleeding with the pedal, since you don't have to worry about rust spots and the seal. You can get a lot more pressure this way, therefore a lot more velocity. Hook up the power bleeder then with the bleed screws closed, jam the pedal down hard then quickly open the bleeder. Close the bleeder once the pedal hits bottom, let off the pedal, open the bleeder and let it flow for a moment, then close. Repeat. Even though the higher pressure will make the bubbles much smaller and prone to hide in crevices, the high velocity and the "shock" of sudden flow may help dislodge some bubbles.