Master Cylinder/Booster Issue
11-27-2013, 08:17 AM
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Master Cylinder/Booster Issue
It seems I have an issue with my master cylinder or brake booster that cropped up a week ago when I did a brake bleed. Here's a post for the Norcal forum detailing what originally happened:
And then an update from the next day:
And then the next day:
So I took the car out to the track anyway following all this. The pedal would be mushy for about 3 inches and then firm up decently. At the track I would take a warm up lap doing some stops to get heat into the brakes and tires. About 3/4 of the way thru the lap the pedal firmed up to normal and stayed nice and firm thru the rest of the 20 minute session. I did this for each session (total of 5 or 6 for the day) and each time the pedal would be squishy on the first 1/2 or 3/4 of the warm up lap and then firm up after that. The drive home the pedal was back to being squishy.
I ordered some stainless lines and decided to get them installed last night. Took the S over to a reputable mechanic in the area and had him do the install and bleed for me, just to see If I was doing anything wrong. Once he started the bleed process he notices an air hissing/whooshing noise that happens when pumping the pedal up (prior to opening the bleeder screw). The noise comes when the pedal is pressed, not when it is released and its coming from around the master cylinder booster area. Anyway I had heard this noise before on my previous bleeding sessions, but I've never bled brakes so didn't think anything of it. The mechanic says he's never heard it before on the S and he thinks that either the master cylinder or booster has a leak somewhere. We looked around for a fluid leak but couldn't find anything. He bled the brakes anyway and the noise seemed to get a little better, but the pedal is softer than it was before.
I'd like to try and pin point the problem as much as possible before ordering a bunch of parts or taking anything apart. I see there are a few diagnosis procedures in the 00-03 service manual on pages 19-4 and 19-19 that I will try to run thru to see if that will help.
I'm just wondering if anyone has had a similar issue to this or thinks there may be some things to try before trying to replace either the master cylinder or booster (bench bleed the master cylinder perhaps?).
Thanks for any help and let me know if any additional information is needed.
I was working on the car getting it ready for Thunderhill on Sunday and it looks like I made a mistake somewhere in bleeding the brakes.
Here's a brakedown of the steps I did:
Switched from stock pads to Hawk's on all 4 corners. Before pushing the piston back in on the first corner I drain maybe 1/3 to 1/2 of the brake fluid out of the master cylinder. I then switched all the pads and pushed the pistons back enough so the caliper would fit back over the pads. Bolted everything up and then proceeded with the bleeding.
I tried to follow billman's guide here: https://www.s2ki.com/...eeding-revised/
I did not have the fluid warm and didn't take a spirited drive beforehand. I also didn't have a turkey baster so I used some tubing and siphoned as much fluid out of the MC as I could. I wasn't able to get anything in the front. I then used a paper towel and got pretty much all the fluid and debris out of the back. It was pretty damn clean. I then filled the MC up with the new fluid. Next I proceeded to bleed the passenger front. Old fluid was amber, new fluid was amber, but after 15 minutes I was able to see the fluid coming thru was almost clear (a dark honey color when I first started bleeding). This seemed good and I would say I bled about a cup or so of fluid.
One thing I did was do a sort of lever motion with the tube. I let the fluid build up for about an inch and then I "tipped" the tube down to let the fluid clear out. Perhaps doing this forced an air bubble back into the line?
I then went to the driver front. Same procedure, fluid was clear, capped off and then moved to the driver rear. Same procedure, fluid was clear, capped off moved to the passenger rear. Same procedure, fluid was clear, capped off and then went to top off the MC to the max level. I will say that during the entire process of bleeding the MC level never dropped below half full, probably not even below 3/4 full. I topped it up after doing each corner.
Got in the car and the pedal was squishy. Went driving, pedal is still squishy. The car has brakes and stops, but not until you've gone thru 3/4 of the travel of the pedal.
Here's a brakedown of the steps I did:
Switched from stock pads to Hawk's on all 4 corners. Before pushing the piston back in on the first corner I drain maybe 1/3 to 1/2 of the brake fluid out of the master cylinder. I then switched all the pads and pushed the pistons back enough so the caliper would fit back over the pads. Bolted everything up and then proceeded with the bleeding.
I tried to follow billman's guide here: https://www.s2ki.com/...eeding-revised/
I did not have the fluid warm and didn't take a spirited drive beforehand. I also didn't have a turkey baster so I used some tubing and siphoned as much fluid out of the MC as I could. I wasn't able to get anything in the front. I then used a paper towel and got pretty much all the fluid and debris out of the back. It was pretty damn clean. I then filled the MC up with the new fluid. Next I proceeded to bleed the passenger front. Old fluid was amber, new fluid was amber, but after 15 minutes I was able to see the fluid coming thru was almost clear (a dark honey color when I first started bleeding). This seemed good and I would say I bled about a cup or so of fluid.
One thing I did was do a sort of lever motion with the tube. I let the fluid build up for about an inch and then I "tipped" the tube down to let the fluid clear out. Perhaps doing this forced an air bubble back into the line?
I then went to the driver front. Same procedure, fluid was clear, capped off and then moved to the driver rear. Same procedure, fluid was clear, capped off moved to the passenger rear. Same procedure, fluid was clear, capped off and then went to top off the MC to the max level. I will say that during the entire process of bleeding the MC level never dropped below half full, probably not even below 3/4 full. I topped it up after doing each corner.
Got in the car and the pedal was squishy. Went driving, pedal is still squishy. The car has brakes and stops, but not until you've gone thru 3/4 of the travel of the pedal.
No dice on my brakes. I have a feeling some is broken.
I did 10 ABS stops on gravel and asphalt. Gravity bled once while letting each corner sit for 15 minutes. Took a spin and the brakes were a little better, not much. Had a friend come help and he pumped up the brake pedal and I opened the bleeder for about 2 secs and then closed. Did this ~4-5 times per corner. Brakes are better, but not a whole lot. I have more fluid and will probably try doing it twice more tomorrow AM.
I figure if it hasn't gotten better by now then something might have broken in the process. I did see that two of the screws seemed to leak a little bit when i have them opened, but when closed even with pressure i saw no visible leakage.
I did 10 ABS stops on gravel and asphalt. Gravity bled once while letting each corner sit for 15 minutes. Took a spin and the brakes were a little better, not much. Had a friend come help and he pumped up the brake pedal and I opened the bleeder for about 2 secs and then closed. Did this ~4-5 times per corner. Brakes are better, but not a whole lot. I have more fluid and will probably try doing it twice more tomorrow AM.
I figure if it hasn't gotten better by now then something might have broken in the process. I did see that two of the screws seemed to leak a little bit when i have them opened, but when closed even with pressure i saw no visible leakage.
Well tried bleeding again and the pedal is still mushy. It's quite a bit better than after the first bleed where it practically went to the floor. Oh another thing I noticed while doing the bleed this morning is that the passenger rear seemed to bleed a lot slower than the other three corners. When you are doing the traditional method (as laid out in the service manual) should all corners bleed about the same rate or will others be faster?
I ordered some stainless lines and decided to get them installed last night. Took the S over to a reputable mechanic in the area and had him do the install and bleed for me, just to see If I was doing anything wrong. Once he started the bleed process he notices an air hissing/whooshing noise that happens when pumping the pedal up (prior to opening the bleeder screw). The noise comes when the pedal is pressed, not when it is released and its coming from around the master cylinder booster area. Anyway I had heard this noise before on my previous bleeding sessions, but I've never bled brakes so didn't think anything of it. The mechanic says he's never heard it before on the S and he thinks that either the master cylinder or booster has a leak somewhere. We looked around for a fluid leak but couldn't find anything. He bled the brakes anyway and the noise seemed to get a little better, but the pedal is softer than it was before.
I'd like to try and pin point the problem as much as possible before ordering a bunch of parts or taking anything apart. I see there are a few diagnosis procedures in the 00-03 service manual on pages 19-4 and 19-19 that I will try to run thru to see if that will help.
I'm just wondering if anyone has had a similar issue to this or thinks there may be some things to try before trying to replace either the master cylinder or booster (bench bleed the master cylinder perhaps?).
Thanks for any help and let me know if any additional information is needed.
11-27-2013, 03:55 PM
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yea you could be getting green fade from the pads if you did not bed them in. If you brake pads don't get properly broken in (bedded) they can produce gas or liquids that lubricate the pad and make you have to use double the force to stop.
And If a brake booster fails it makes the brake pedal hard as a rock
And If a brake booster fails it makes the brake pedal hard as a rock
11-27-2013, 04:12 PM
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Can you take pics if both rear calipers? I just need a pic of the two fingers that squeeze on the outer pad.
At a decent angle if you can, kinda like if you were trying to look between the pad and caliper
At a decent angle if you can, kinda like if you were trying to look between the pad and caliper
03-17-2014, 03:10 PM
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Mac,
I didn't get photos of the rear fingers and didn't seem to notice anything wrong with them when I worked on the car yesterday. I do think I solved the problem though.
First I switched back from the racing pads to stock and found that I had put the front pads on backwards. By backwards I mean that I put what should've been the inner pad on the outside and the outside pad on the inner. I'm not sure if this is a big deal, but there is a little bump on the inner pads the the outer pads do not have. Anyway I switched pads and went for a drive and there was improvement on the pedal, but it was still going pretty low and mushy.
I then followed Rob's MC bleed guide on his website, bleeding through the ABS on the 4 lines. ( I did this in the car and brake fluid get's everywhere so be careful if you ever try it) Then did a bleed at the calipers through all 4 corners, starting RF then LF, LR, RR. Went for a drive and the brakes are the best they've been since I F'd them up. I'm still not quite sure if they are back to normal. I want to drive someone else's S with stock brakes to compare, but I think I'm good.
I also took a video while doing the MC bleed to capture a whooshing/hissing noise. This sound similar to what I had mentioned about while bleeding the brakes. Not sure if this is just normal noise or something has a bad seal. When I tried to pinpoint where it was coming from it almost seemed like it was coming from the ABS unit:
[media]http://www.youtube.com/watch?v=l6GeAXNvVjc[/media]
I didn't get photos of the rear fingers and didn't seem to notice anything wrong with them when I worked on the car yesterday. I do think I solved the problem though.
First I switched back from the racing pads to stock and found that I had put the front pads on backwards. By backwards I mean that I put what should've been the inner pad on the outside and the outside pad on the inner. I'm not sure if this is a big deal, but there is a little bump on the inner pads the the outer pads do not have. Anyway I switched pads and went for a drive and there was improvement on the pedal, but it was still going pretty low and mushy.
I then followed Rob's MC bleed guide on his website, bleeding through the ABS on the 4 lines. ( I did this in the car and brake fluid get's everywhere so be careful if you ever try it) Then did a bleed at the calipers through all 4 corners, starting RF then LF, LR, RR. Went for a drive and the brakes are the best they've been since I F'd them up. I'm still not quite sure if they are back to normal. I want to drive someone else's S with stock brakes to compare, but I think I'm good.
I also took a video while doing the MC bleed to capture a whooshing/hissing noise. This sound similar to what I had mentioned about while bleeding the brakes. Not sure if this is just normal noise or something has a bad seal. When I tried to pinpoint where it was coming from it almost seemed like it was coming from the ABS unit:
[media]http://www.youtube.com/watch?v=l6GeAXNvVjc[/media]
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03-18-2014, 11:55 AM
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Oh I also made another mistake when installing the pads first time around. I put grease on the face of the pad, but didn't put the stock metal shim over the grease and so grease came in contact with the piston, which probably isn't good. Here's what the front pad's were like after one day at Thunderhill:
Here's the stock pad's going back on, this time with the metal shim. Grease is between pad face and metal shim.
Perhaps the grease being on the piston contributed to it feeling soft? I wonder if this is something where I should clean the piston/caliper or if it's fine?
Here's the stock pad's going back on, this time with the metal shim. Grease is between pad face and metal shim.
Perhaps the grease being on the piston contributed to it feeling soft? I wonder if this is something where I should clean the piston/caliper or if it's fine?
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