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Aerated brake fluid


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I'm troubleshooting recent braking issues in my 1994 S4 (anti-lock light and only 3 pushes to activate pump).  I like to think I understand the system fairly well, but I figured I better check with the experts.

 

Every time I depressurize the system (40 pumps), the rear portion of the fluid reservoir is murky (milky looking) indicating, I presume, that it has air in it.  I can only imagine the air getting in through a failing diaphragm in the accumulator.  Is that accurate?  Or is there another way?  I'm not losing any fluid and the brakes feel fine while driving. 

 

I bled the whole system, got it up to 5 pushes to activate pump, but 2 days later I was back down to 3 and the dreaded anti-lock light.  I thought I'd ask before committing to another accumulator (this one is only 5-6 years old).

 

Thanks, Richard.

 

 

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The milkiness worried me s well initially. A pressure gauge is very handy for working out whether it is the accumulator or switch playing up.

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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The system seems to have completely given up the ghost now, with pump on and anti-lock warning flashing on the first press.  

 

I'm going to do the bleed sequence once more and then order in one of those Wabco Range Rover accumulators.

 

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Just to let you know. i ordered one of those wabco range rover accumulators. While it does look like it will fit, only two threads on the accumulator reach the pump. Not very good. i brought mine to a machine shop and they machined the shoulder into it so all the threads would reach. 

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1 hour ago, tmusc said:

Just to let you know. i ordered one of those wabco range rover accumulators. While it does look like it will fit, only two threads on the accumulator reach the pump. Not very good. i brought mine to a machine shop and they machined the shoulder into it so all the threads would reach. 

Thanks for the heads-up.  I could see it happening, as the tee fitting I was planning to use to put a pressure gauge into the system had that same issue.  The pump threads are recessed fairly deep, so my fitting wasn't going to make more than a thread or two either.

 

As I had both accumulator and pressure switch out, I decided to try "cleaning" the pressure switch, though the process seems dodgy at best.  On re-install it appears all is well.  I am getting 6 presses of the brake pedal to activate the pump, which is fine.  I am test driving today to see if it holds true on the road, but have no reason to suspect it won't.

 

Oddly enough, the tip about trying to clean the switch was posted by Mark T-C, who previously maintained this same car.  So this is the second time cleaning this particular switch.  I think he cleaned it 4 or 5 years ago, so if I can get that again I'd be rather satisfied! 

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This is what the WABCO accumulator looked like after it was machined to accomodate the deep threads. As you can see there wasnt much left of the nut part on the accumulator.

IMG_20160423_105552.jpg

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  • 2 months later...

This thread looks the same as the one on the pressure switch, i.e. M14 with an odd seal arrangement.

Could you do the same as I did with that   ...

Take a M14 bulkhead adaptor screw it into the housing gently until it bottoms, then cut it off to give some clearance and then screw it up with a copper washer, and then screw on a female/female M14 adaptor with a copper washer so that you are then left with a standard M14 female fitting which shoud take the WABCO accumulator?

Both adaptors are available from hydraulicmegastore.com

The M14 bulkhead adaptor is https://hydraulicmegastore.com/product/metric-male-x-metric-male-bulkhead-with-locknut/ 

The M14 female/female adaptor is https://hydraulicmegastore.com/product/metric-fixed-female-to-metric-fixed-female-equal-1-5mm-pitch/

Image 1.png

Image 2.png

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Be careful with modifying this part.  I recently had an issue with my PMIII last year and have the factory GM accumulator pressure gauge set up.  Apparently the pressure accumulator on my car was one as described above where the threads were different - installed by the DPO.  I threaded it on not paying attention as I figured they were "all the same" but did make sure it was tight.  I placed the accumulator in a car wash bucket as I was afraid there might be a slight fluid leak during the test.  Pressurized the system with key on and was watching the gauge pressure up ...1000..1500..2000...2500...2600 and a huge bang that left my ears ringing as the accumulator had either unthreaded itself or was not holding enough threads but it shattered the bucket into 50 pieces and shot brake fluid all over the garage including my face. Luckily I had the bucket on the garage floor but I felt the force of the impact on my shin. felt like someone hit it with a baseball bat. I pushed the car out of the garage and washed the car within a minute of this happening three times for fear of permanent paint damage which fortunately there was none. Then washed my hair /face :shock: Fortunately my eyes closed when this happened so I did not get brake fluid in my eyes.  Shin hurt for three weeks after the event (might have had a fracture but it did not hurt "that bad" and finally went away).

Respect the pressure this system generates. It is scary sh#t when these things launch like a rocket and if it were to happen in the car you will guaranteed have fiberglass damage from a launch impact. I'd recommend getting an accumulator with the proper threads if possible from the beginning.

 

Edited by Paul93Lotus
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