That sinking feeling.

[John Hurworth]

986 s 2003 100 k approaching traffic lights and braking with pedal resistance felt to half travel then as more pressure applied, the brake pedal slowly travelled to the floor pan. Rebuilt master cylinder with new seals which has improved ability to lock brakes when pedal pumped but pressure reducing over time and pedal drops to the floor, slowly in the end. No ABS fault recorded using a foxwell 510. Looking at the abs schematic diagram of hardware how does brake fluid get back to the reservoir or master cylinder to releave pressure at the slave cylinders?  Unable to instigate an ABS bleed function on the foxwell 510, even after update. Could be many things including master cylinder after rebuild and or poor bleeding after rebuild. No fault on ABS so reluctant to start accusing abs module or pump. If ABS ecu down could this be why I cannot find an ABS auto bleed function on the foxwell.  

Can you block off the master cylinder ports with plugs to test the rebuild and if so what do u use for the plugs?  Any assistance appreciated. Need a logical approach.

[JoeyH]

Hi John.

Having rebuilt master cylinders before I can tell you it's not always a success.

The rebuild is based on the assumption that it's only the rubber that degrades.

After doing two which both failed within a matter of either hours or weeks I spoke too a company that refurbs cylinders and several trusted mechanics.

They explained that inside the bore can suffer from micro- scores that allow fluid to leak past the seals under pressure  creating exactly the situation I experienced on two consecutive Alfa 916 master cylinders...internal leaks.

The solution is new cylinder or a SS insert or sheath inside the existing bore.

I replaced the refurbished cylinder with a new one ( no easy feat on a 916) and the problem was resolved.

It's such a pig the second car has been on the drive 6 months "awaiting" doing.

 Re the insert vs new cylinder Both solutions  will outlive the car and the new cylinder will be a cheaper option.

I would and did choose that option.

So I strongly suspect your ABS system is fine but your refurbished cylinder is not.

I'm afraid there are no diagnostic steps to assert this is the case but other than a coincidental ABS failure at exactly the same time you refurbished your master (highly unlikely)  it's highly likely your refurb hasn't been successful.

In my experience when dealing with any automotive issue it's always best to start with the last job completed when looking at a "new problem" 

 

Best of luck.

 

Joe

[John Hurworth]

Hi Joe,

Thanks for the useful feedback.  Will replace master cylinder with new to remove this from the list. All makes sense and unable to sensibly bench test. The bores looked good but suspect not under a microscope. Having read a couple of similar articles the master replacement does not solve the problem in all cases but with no abs fault codes registered is the more likely culprit. 

Unit is stamped with Lucas in the casting and Porsche quoted £419 for the part which would take several days to turn up from Germany.  Lots of OE parts on the market including TRW, Bosch, Bremba around the £100 mark. 

Again, thanks for the feedback. Hopefully, one step back,  five forward.

Regards

 

John

[JoeyH]

Very much doubt ABS is the issue.

If it is though the brembo,TRW options are the same quality.

Keep us posted and good luck...!

 

 

[John Hurworth]

Thanks, will do.

Regards