I finally got round to replacing my accumulator sphere today.
My pump was activating every time I pressed the brake pedal, indicating that it was holding basically no pressure.

I had to remove the pump assembly, & did my best to bleed the fluid on the low pressure inlet when reconnecting the hose, by using the flowing fluid from the feed pipe to 'fill' the flexible line before reattaching.
Once replaced, upon the first startup, the pump sounded quieter than before, & ran for a constant 40-50'ish seconds, whilst gradually reducing in speed, then wound down completely & stopped.

Is this expected, & indicative of a successful 'charge' of the accumulator? Mine has never worked properly so I'm hoping this sounds like normal operation.

Does anyone know of a good summary of how the Teves ABS system should operate, including quirks of operation & bleeding etc? I think i've seen some very good posts on here before but I can't find them now.

 

Asdrewq,

As you've probably realised, the Teves system is very complex. It has a number of important elements:

- It doesn't have a "Master Cylinder". Well it does, but the master cylinder is merely a very small chamber at the front end of the "Actuation Unit" and releases fluid to the front circuits only
- The Actuation Unit is the heart of the system and controls fluid output ultimately to the wheels but via the ABS valve block
- The ABS valve block provides abs control of the fluid via series of solenoid valves.
- The Actuation Unit takes a combination of fluid inputs from both the reservoir and from the high-pressure circuit
- The high-pressure circuit takes a fluid feed from the reservoir, runs it through a pump controlled by a pressure relief valve, and charges the Accumulator]
- The Accumulator then feeds high-pressure fluid back to the Actuation providing boost-assisted pressure for the front circuits, plus boost pressure for the rear circuits
- The rear wheel circuits receive ONLY boost pressure. The brake pedal does NOT push fluid to the rear brakes. This is why the bleeding process is quite different to a conventional brake system.

As regards the timing of your pump running; you need to fully discharge the system first. Turn off the ignition, then press the brake pedal at least 30 times. The pedal should get increasingly hard as the boost pressure is dissipated. Then take your foot off the brake and turn on the ignition. Now time how long the pump runs.

One of the challenges of diagnosing where a failed unit exists in the high-pressure circuit, is because it could be a failing pump, a defective PRV or a failing accumulator. It's dangerous to just guess that it's the accumulator.

If you've got a specific question, just post back and I'm sure someone can advise.

Cheers

Paul

 

Thanks Paul. I've done a bit more testing this evening & have a couple of questions:

- From the system being fully discharged, the pump runs for 42 seconds - Is this within the spec?
- Once pressurised, I get around 5 pedal presses before the pump reactivates, & runs for around 7 seconds - as above, is this within spec?
- The system pressure appears to dissipate whilst left overnight, enough for the pump to need run again for around 20-30s after around 12hours - is this normal?

- while pumping the pedal with the ignition off to discharge the pressure, I felt a strange & inconsistent sensation in the pedal, almost like for some random pedal presses it depressed slightly further, then firmed back up. I also noticed that once it's discharged & the pedal is firm, there is a fair bit more initial 'freeplay' on the brake pedal, compared with when it's pressurised. Does this sound normal?

 

Asdrewq,

A few thoughts:

- From fully discharged, a charge time of 42 sec is not unreasonable. I've seen quicker but not much.
- 5 presses from full before some form of reactivation is also reasonable as is a 7 second topup charge
- A chargeup from overnight is almost inevitable. My car always does some form of topup. The challenge is that you almost definitely had your foot on the brake just before turn off so you were already discharging some pressure.

- The only slightly vague one is your comment about higher initial freeplay after full discharge. I'll think further on that one and test it on my car later this week,

Cheers

Paul