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Leading evidence: 'Replace mc, rebuilt calipers, flushed abs multiple times.no error codes' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check abs pump unit' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
I had a similar problem when I changed a rear caliper on my daughter's Corolla.
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Performed · outcome unconfirmed · Original poster
I bench bled the new master and used my power bleeder on all 4 corners.
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Suggestion
If the reservoir is going down, check the abs pump unit.
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Suggestion · Original poster
sounds logical aside from every component being dry and leak free but i will double check hard to see areas.
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Suggestion
You probably already tried this but every time I had the same issue you described, it was either on the track when I boiled my brakes of which bleeding helped but ultimately i had to change my fluid which i started to do after every track event.
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35 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
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symptoms:
-brake pedal slowly sinks a few inches when applying pressure with the engine running
-car stops good
-no fluid loss or external leaks.
-with engine off and no vacuum assist the pedal remains firm while holding pressure on the pedal ( no sinking)
I bled the brakes with no improvement. So i decided to replace the master cylinder and nothing changed. I bench bled the new master and used my power bleeder on all 4 corners.
My next thought was to cap each brake line where it enters the caliper one at a time and see if the problem goes away which would narrow it down to a caliper issue ?
Abossana, sorry to hear about your brakes. You probably already tried this but every time I had the same issue you described, it was either on the track when I boiled my brakes of which bleeding helped but ultimately i had to change my fluid which i started to do after every track event. Or after I changed my brake fluid and I was driving around town and had to pump the brakes a number of times to get the pedal back, of which it did come back.
For sure, it could be other issues/solutions but its typically been one of the two above for me. Hope it helps.
I was thinking along this path as well. Its almost like I am getting too much vacuum assist. One thing I have not done is a clutch slave cylinder bleed. Not sure if air in that circuit could effect the brakes.
I had a similar problem when I changed a rear caliper on my daughter's Corolla. It turned out I did not tighten the brake line to the caliper enough. After bleeding a whole large container of brake fluid the pedal still sunk in a couple of inches. I had my daughter push on the brake pedal while I was looking around the caliper and saw the slightest leak of fluid squeezing past the crush washer. It only leaked under brake pressure, as I could find no leaks prior to her pushing on the pedal. Once tightened and re-bled there was no more sinking pedal.
My bet is you still have air somewhere in the system, possibly drawing it in from a bleeder screw, or perhaps have air trapped in the ABS unit.
I had this recently on my truck. I bled multiple times, zero leaks, etc. Spoke to a buddy, who is an actual tech (everyone is a mechanic, until a real one walks in). Seized slider. Now, I recognize that our brakes don’t have sliders as such but do have pins. For the few mins it takes to check them, pull the wheel, pins, grease and reinstall.
Pulled each pin, cleaned and light grease, No change. Next step is to cap off each caliper one at a time and see if I can narrow it down to a specific caliper.
Any chance you have a brake hardline with a pin hole leak hidden by the plastic under trays ? Happened to me on my C4 . Pedal started getting soft and sinking to the floor . Nothing on the ground or at the calipers . Pulled the under trays and bingo there it was .
Curious. What is the pedal height after it finishes sinking? Is it too low? What happens to the pedal height if you pump it after the sinking stops? Based on no observed leaks, I'm with either the brake booster cause or a vacuum leak from the engine. Maybe check the vacuum line back in the engine compartment. Does the ECU show any weird codes that could be explained by a vacuum leak?
No codes or vacuum leak symptoms.
If I press the brake pedal in a Normal semi fast motion it is firm and normal but if you keep pressing with medium force after stopped the pedal will continue to slowly sink to the bottom of the stroke. From top to bottom it takes about 5 seconds.
if you apply the brakes in a very light and slow motion it doesn�t get firm till close to the bottom.
pedal always returns to top . Pumping is firm at every stroke but will bleed off /sink if keep pressing with a bit of force
Didn't read the whole thread but the seals in your MC are shot. Replace MC, bleed the system and you're good.
ETA: read your first post. Sorry for the waste of bandwidth. Unfortunately I have nothing new to add as to what could cause the problem you describe.
However, I can say that the clutch hydraulics do not affect the brake hydraulics.
Find someone with a PIWIS and bleed your ABS. Durametric won't do it.
Or find a nice dirt road and do a bunch of ABS stops then re-bleed the calipers. Might need to do this a few times.
If the reservoir isn�t going down, that means there isn�t a leak anywhere. Therefore, it�s got to be air somewhere in the system (basic hydraulic principal).
If the reservoir is going down, check the abs pump unit. I had this problem. There�s a plug on the bottom of the unit that blows out and leaks. The fluid sits at the bottom of the area (under the plastic cowlings) where the abs pump/plumbing is located and won�t exit the bottom of the car� it will eat the paint down there though, so check it soon! Good luck
I left the plastic cover after replacing the master cylinder to monitor the area for leaks. Everything is dry as a bone. I�ll look into the ABS bleeding operation
New development�. I originally selected the wrong ABS version on the durametric . The ABS 5.7 version is correct and I have the following fault code. When I activate the pump I get a click on the module. Not sure if this is my problem but it seems like a possible culprit. No ABS light was ever activated on the dash.
The saga continues..... installed the new ABS pump assembly and now I cant get the air out of it. It turns out the Durametric has the menu to cycle the ABS pump for bleeding but it doesn't work. After much research this is a knows issue with the software. So its very likely that my original was just fine but needs to be bled. It seems the only true known way is to have the dealer do it with the Porsche software. I have seen some opinions that it can be accomplished by activating the ABS multiple times while driving then re-bleed but i cant even get enough braking power to lock up the wheels at this point after the module swap, even after multiple bleed attempts with zero air bubbles left. Does anyone have real world experience with a scan tool that will activate the ABS bleed function on a 986/996 generation car ?
with a standard brake bleed i have never had this issue with or without PSM. This issue only seems to happen if a large amount of air is introduced between the ABS unit and master cylinder. A few likely culprits are: New master cylinder, new ABS unit or bleeding the brakes and letting the fluid get too low and sucking air into the system.
It just dawned on me that I had a similar issue on my e30 back when it was my daily driver. Gosh, 1994 or so?? The pedal would sink so I replaced/updated the master cylinder to an e32 7 series master cylinder for good measure.
I have brand new 996 master cylinder if you'd like to try it rather than buy a new one to test. If it solves the problem, keep it and send me a few bucks. If it doesn't solve the problem, just send it back.
I know PIWIS will do it. I have not used any of the other testers such as foxwell or icarsoft. The actual instructions are to bleed the brakes at the wheels like usual. Then turn on the pump and bleed the right front again while working the pedal. I have read on here somewhere that someone jumpered the return pump motor to the battery to activate it with good results.
Couple other thoughts. Run a piece of vinyl tube from the bleeder screw back to the brake fluid reservoir and use a speedi-bleeder check valve bleeder screw. Then you can pump the brake pedal hard and fast without running out of fluid. Do one front and one rear bleeder screw at the same time. Sometimes that hard and fast pedal action forces bubbles that are stuck by surface tension to get moving. I use this trick bleeding the Teves 02 electrohydraulic ABS on my VR Corrados.
Pressure bleed from the calipers back to the master. Same reasoning.
Crack the pipes from the master where they attach to the ABS valve block and use the pedal to make sure the master is fully bled too. Messy but it works.
I brought home a high dollar obd2 scanner from a coworker. I�m going to try using that. I also ordered the Foxwell unit which will arrive tomorrow so I will report back. Foxwell claims it will work but I haven�t heard any real world evidence in this generation car. It works on the 981 generation for sure.
I have already attempted jumping 12 V to the pump motor and it runs but it does no good unless you activate each individual electromagnetic valve within the unit. I believe there is 12. Basically need to activate each individual valve so you can clean out the air in the fluid paths. If none of the scanners work I will probably figure out a way to manually energize each individual electromagnet and manually cycle through each pin on the connector plug until I get this figured out. I won�t give up that easy 😂
I had the exact same thing with my 01. Replaced MC, Rebuilt calipers, Flushed ABS multiple times.No error codes. I ended up finding a used ABS unit and replaced it and the problem disappeared. Good Luck!
JIm
UPDATE !
Problem solved finally. The new abs module fixed it. I was never able to bleed the module by means of a scanner. The foxwell and durametric does not allow abs system to be activated for a bleed cycle. I was finally able to get enough pedal to lock up the brakes in the rain and activate the ABS multiple times. After a few times doing that and bleeding each caliper I was able get the remaining air out of the new abs module. Quite the adventure and learning process.
I can’t stand dealers and I was very worried that was my next stop. I would have likely bypassed the abs module before paying them their ridiculous rates.
Good to hear you solved it!
I am wondering if activating the ABS by braking hard (or on low grip surface) would have solved your issue with the original ABS unit too.
Had you tried that?
I did try but I wasn�t as aggressive on the abs braking with the original unit. It�s Very possible that with more cycles it may have purged itself. The �new� unit was only $40 on eBay vs $5,000 for a new one so I can�t complain.
