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Bench Bleed Master Cylinder?
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97 EVC. ?I just had to have a brake specialist replace my entire brake system - calipers, master cylinder, hoses. ?Now the brake pedal is soft and low. ?It is consistently low, meaning that is always goes to the same spot, does not fluctuate. ?The lines were flushed with brake cleaner, then refilled with new DOT4 and pressure bled. ?I'm wondering if it is possible that the master cylinder needs bench bleeding. ?Any experience with this kind of problem? |
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SDF ( aka ;jim lahey' - Scott )
¿ªÔÆÌåÓýIf the MC is producing pressure ..then mostly likely it's bench bleed..or past the need for bench bleeding. bench bleeding is done to get brake fluid into an air-filled MC right out of the box, so it can pump brake fluid. pressure bleeding normally would take care of that - like bypasses the need for bench bleeding. Seems like more bleeding ( and watching for air bubbles during that process? ) is in order. Is there a bit of free play at the top of the brake pedal travel ? important that the pedal and pushrod not be holding MC pistons off of fully seated. if they gave it back to you like that, seems they didn't finish the job really. On 7/8/2015 1:12 PM,
rickardsmith@... [ev_update] wrote:
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Bad Vacuum booster will do that..... On July 8, 2015, at 8:10 PM, "'SDF ( aka ;jim lahey' - Scott ) ' ScottDaniel@... [ev_update]" <ev_update@...> wrote: ?
If the MC is producing pressure ..then
mostly likely it's bench bleed.. On 7/8/2015 1:12 PM,
rickardsmith@... [ev_update] wrote:
? |
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Rick Smith
Brake pedal is low but at a consistent height when engine is on. With engine off, I can pump the pedal and get it to stay higher. Seems like air in the lines after all, but why would I not be able to duplicate the ¡°pump up¡± with the engine on? Also, does not make sense that a bad booster would cause the pedal to be low. I thought the booster was only to augment your foot pressure. Most of the forums agree with this - booster has nothing to do with pedal level or ¡°softness¡±.
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Mark Hollingsworth
I've seen a bad booster cause pedal issues and a 'soft' feel.
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On Jul 9, 2015, at 8:40 AM, "Rick Smith rickardsmith@... [ev_update]" <ev_update@...> wrote: |
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Bad booster will do just what you are saying,? I have replaced them (in the business)? quite a few times on cars which are the same. On July 9, 2015, at 10:41 AM, "Rick Smith rickardsmith@... [ev_update]" <ev_update@...> wrote: ? Brake pedal is low but at a consistent height when engine is on. With engine off, I can pump the pedal and get it to stay higher. Seems like air in the lines after all, but why would I not be able to duplicate the ¡°pump up¡± with the engine on? Also, does not make sense that a bad booster would cause the pedal to be low. I thought the booster was only to augment your foot pressure. Most of the forums agree with this - booster has nothing to do with pedal level or ¡°softness¡±. |
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Rick, is the pedal in two different places while engine off and engine on?? Head scratcher.? Yes, vacuum booster is to augment foot pressure.? Couple of things-? the system still has air in it, and/or there does seem to be a possibility that the ABS module could have air in it.? It has a hydraulic pump in its mechanism, and there does appear to be a bleed procedure for it.?
? If you have bled the system, then the master cylinder is bled during this process. |
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Rick Smith
Agreed. At first did not notice the pumping did any good because we didn't try it. It's now back at the shop, it's been bled several times both manual and pressure bleeding, and the pedal is still very low. Pedal travels almost 3/4 of the way to the floor before it stops. From looking at the Bentley, it's not clear how, or if this could be associated with the ABS pump. Still looking for ideas.
Rick Smith |
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Mark Hollingsworth
Like myself and one other mentioned- I¡¯ve seen this with defective Brake Boosters before.
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Several times. Mark Agreed. At first did not notice the pumping did any good because we didn't try it. It's now back at the shop, it's been bled several times both manual and pressure bleeding, and the pedal is still very low. Pedal travels almost 3/4 of the way to the floor before it stops. From looking at the Bentley, it's not clear how, or if this could be associated with the ABS pump. Still looking for ideas. |
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Only ABS systems I have saw low. pedal was on older cars with only rear abs and drum rear brakes. Saw low pedal from booster a lot more
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On July 11, 2015, at 3:54 PM, "Mark Hollingsworth markh@... [ev_update]" <ev_update@...> wrote:
Like myself and one other mentioned- I¡¯ve seen this with defective Brake Boosters before. Several times. Mark Agreed. At first did not notice the pumping did any good because we didn't try it. It's now back at the shop, it's been bled several times both manual and pressure bleeding, and the pedal is still very low. Pedal travels almost 3/4 of the way to the floor before it stops. From looking at the Bentley, it's not clear how, or if this could be associated with the ABS pump. Still looking for ideas. ------------------------------------ ------------------------------------ To unsubscribe from this group, send a message to mailto:ev_update-unsubscribe@... ------------------------------------ Yahoo Groups Links |
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Unless this condition was present before the brake job I don't see how suddenly you would have a failed brake booster after. Anything is possible but that sounds unlikely.
What brand brake master cyl did you use? If the depth of the "cup" where the push rod from the brake pedal/booster rides is not identical to the master cyl you replaced this could cause this low pedal situation also. Scott mentioned something similar to this in an earlier post. Also it's possible the rear brakes are incorrectly adjusted. Pull off the rear wheels and check the gap between the rotor and the pads. Should be a barely visible gap present. If a big gap is present here this will cause the pedal to travel some distance before engaging the rotor. If it needs adjustment ratchet the caliper piston out using the parking brake cable arm at each caliper while rotating the disc until the pads are just barely touching the disc. If a shop did the brake job they should know this procedure and theoretically already have done it. Best wishes, Justin 2000 EVW 5-spd TDI |
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