07-30-2017, 02:53 PM
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#41
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Registered User
Join Date: Feb 2017
Location: New Mexico
Posts: 42
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Quote:
Originally Posted by lskolnick
I just resolved this exact problem today. Master cylinder replaced twice before determining it was a bad ABS pump. $50 on eBay and some labour, and she's all fixed up. Make sure you get the correct part number. There are several over the years. Just match your existing pump.
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It's odd that there really hasn't been any threads about a bad ABS causing this issue. I did a ton of searching and only found an offhand comment in a 987 thread. So, I figured it was quite rare. Then you post you had the same problem recently and Mueltone has PMed me that he think he has the same issue. So...there are more ABS problems out there than I expected.
I wonder if the ABS units are rebuildable? I worry a bit that my replacement unit is that same age and will start to do the same thing in the near future.
__________________
V.H. Whitley
Owner of Waaay too many vehicles
Non Porsche :1959 International B120, 1960 International B120, 2015 BMW M3
Porsche: 1997 986, 2001 986S, 1968 911L, 1968 911S, 2005 911, 1984 928, 2008 Cayenne S.
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07-31-2017, 05:18 AM
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#42
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Project Addicted
Join Date: Aug 2015
Location: Eastern Shore, MD
Posts: 623
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That's a long, frustrating but good result!!!
__________________
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Jon
1966 912, 1976 911
1986 944, 2000 Boxster
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07-31-2017, 10:51 AM
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#43
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Registered User
Join Date: Dec 2009
Location: Orange County, CA
Posts: 1,848
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Congratulations for finding the root cause, and thank you for posting your results!
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10-07-2018, 04:39 PM
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#44
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Registered User
Join Date: Feb 2007
Location: Australia
Posts: 217
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Booster Issue
I had pretty much the same symptoms & it was the booster.
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10-10-2020, 02:55 AM
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#45
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Registered User
Join Date: May 2019
Location: Deephaven, MN
Posts: 21
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Rotmilky, thanks for your detailed outline of the progression! I also have an 01 986S that is exhibiting the same problem. It happened during a recent track day, where we were working the vehicle (and ABS) to its limits most of the day. I'm running race compound slicks with stock pads so the forces (and pressures) in the braking system were at a maximum. Based on your journey, I'm actually going to start with a used ABS pump and see if that corrects the problem. I'll make a point of reporting back my results and hope somebody else can benefit from the insights.
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10-18-2020, 04:45 PM
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#46
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Registered User
Join Date: May 2019
Location: Deephaven, MN
Posts: 21
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ABS replacement worked.
Just wanted to close out on my issue above. Thanks to eBay and $75 I replaced the ABS unit with an identical part number, i.e. had the same stamped part number and was from the same model year vehicle ('01 986 S).
After replacing the ABS unit and a brake fluid flush to all four corners, the brakes feel like new. No sponginess and they do not slowly compress after the initial contact.
When it failed, I was running stock pads but with race class slick tires (Toyo Proxes RR), and intentionally pushing the brakes to threshold several times on every lap (including occasional ABS activation). I suspect I was pushing the ABS to its limits. It would have had max pressure and coefficient of frictions of the tires was beyond what the engineers tested for 20 years ago.
Hope this helps the next guy...
(BTW, as most of you know, the brakes on the 986 and 996 are virtually identical other than tuning)
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09-12-2021, 04:39 AM
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#47
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Registered User
Join Date: Sep 2019
Location: Toronto
Posts: 20
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wow great detective work. looking at the clues... and resourcefully finding a reasonably cheap fix... (three mc later!) and hope you did the work your self vs rack up tons of labor... looking at similar problem now...
brakes locked up while driving, glowing red hot formula 1 style...
called tow truck, while it was on its way, brakes released (we talking so hot, the brake wear indicator wire caught on fire), and drove home...
drove around the block next day, no problem then the lockup situation happened again.
enough such that the rear tires would lock and skid
tried to bleed the system, and not able to push fluid through the rear brakes, not with motive push bleeder, foot pumping or vacuum tools... even started the car to run vacuum to the booster for more pressure
removed the rear calipers, inspected, appear okay and reinstalled and still cannot bleed the system, fluid will not flow
suspect: master cylinder, abs control unit
plan: disconnect abs unit, consider to bypass and bleed system to determine where is the fluid being stopped from flowing
perhaps look for spare abs unit and hope to find one on ebay
my 2000 986S has 65,000 miles on it... sucks!!
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