A3 brake pedal sinks, help please.

[bunyoch]

" I personally don't like the pressure breeders." ------- Hoot ?

Ma sowel, ma sowel -- its ma Bluidy A3 brakes wur tryin tae soart oot nae some o thae artificial insemination o coos -- oar sim ither sculdugary wi hoarses oan a stud ferm ---

Aye an the cyclin the abs wi the vag com ---we had the fluid jist pishin oot o thae nipples intae buckets Aye we had the enchine rinnin ; we had the enchine nae rinnin ; we had the pedal risin frae the flair as if Etna hersell wis pushin it up --- AN still phuque awe brakes et the end !

Andy is mutterin aboot a wee thing lik a 2 litre Trident fur flushin the airs oot BUT Masell am thinkin mair lik --http://www.pump.co.uk/booster-sets-c25/pressure-vessels-c31/afv-500-litre-vertical-accumulator-pressure-vessel-p150

Maybees we wull jist blast the hale brute intae oarbit an blame anither bit o space debris oan bits fallin aff the Space Station ( we wull remove the badges an plates aff it afore attemptin the bleedin jist in case , an naebuddy wull be any the wiser ! )

[Kieron20V]

Sounds to me like the valve in the servo is knackered and its actually pulling the pedal to the floor, not just sinking.

[andy10v]

Sounds to me like the valve in the servo is knackered and its actually pulling the pedal to the floor, not just sinking.

Would it be able to pull the pedal to the floor though if there was no air in the lines?

How does/can valve fail? (I have never taken a servo apart)

[andy10v]

Bled today with a pressure bleeder at 2 bar, rotated the rear calipers to get the bleed nipple at the top, bled ABS pump, still slowly sinks. I cant make up my mind if its sinking slower, in which case I might just need to bleed more?

I have not bled the clutch with the pressure bleeder yet, garage is unbearable after running diesel.

How fast is the fluid supposed to come out with a pressure bleeder? Do people normally open the bleed nipple and let it run or pump the brake pedal?

[Monkeymagic]

In my experience most modern cars with abs if you maintain pressure on the brake pedal it will slowly sink. Does the initial bite point remain constant any build up with repeated pressing?
As for pressure bleeder you.do not need to pump pedal.

[andy10v]

Apparently the A3 MK 60 needs less than 1 bar or closes a valve

When using filling and bleeding appliance, e.g. VAS 5234 or V.A.G 1869 A, to replenish brake fluid care must be taken to ensure that filling pressure does not exceed 1 bar.

In the event of a filling pressure greater than 1 bar, a hydraulically actuated switching valve for the EDL control system prevents full flushing of the areas of the hydraulic unit specific to EDL. Proper bleeding is then no longer guaranteed.

The brake fluid pressure at the filling and bleeding appliance must therefore be reduced to 1 bar.

Also odd bleed sequence?

Bleeding brake system using brake filling and bleeding appliance VAS 5234 or V.A.G 1869 A


Sequence of operations

‒ Connect up brake filling and bleeding appliance VAS 5234 or
V.A.G 1869 A.
‒ Detach protective cap at bleed screw of brake caliper and attach bleed hose of bleeder bottle to bleed screw.

Bleeding sequence

1 - Front left brake caliper
2 - Front right brake caliper
3 - Rear left brake caliper
4 - Rear right brake caliper

‒ With bleeder bottle hose attached, leave bleed screw open until the brake fluid which emerges is clear and free from bubbles.
‒ Press brake pedal 5 times to assist bleeding process.
‒ Tighten bleed screw to 10 Nm, detach bleed hose and attach protective cap to bleed screw.
‒ Repeat bleeding procedure in stated sequence at other brake calipers.
‒ Making allowance for pad wear, fill brake fluid reservoir as far as max. mark and screw on cap.
‒ Start engine and check both brake pedal travel and pressure.
‒ In the event of excessive pedal travel, check brake system for leaks/repeat bleeding procedure.

On completion of bleeding, perform test drive involving at least one ABS control operation at all four wheels.

After bleeding brake system, zero position compensation must be performed for brake pressure sender -1- -G201.

Has anybody had to to zero the brake pressure sender?

I have heard of people going out to activate the ABS but thought that was due to a lack of software to activate the ABS?

Bleeding brake system without brake filling and bleeding appliance

Note:

Make sure brake fluid reservoir is always full.

‒ Detach protective cap at bleed screw of brake caliper and attach bleed hose of bleeder bottle to bleed screw.

Bleeding sequence

‒ Build up pressure in brake system by pumping with pedal.

Note:

Press brake pedal slowly to avoid formation of bubbles.

‒ Once pressure has built up, keep brake pedal depressed.
‒ Open bleed screw with hose of bleeder bottle attached until pressure has been dissipated (pedal sags).
‒ Keep pedal depressed and close bleed screw.

‒ Release brake pedal and wait approx. 2 seconds to allow brake fluid to flow in from brake fluid reservoir.
‒ Repeat procedure until brake fluid emerging is clear and free from bubbles.
‒ Tighten bleed screw to 10 Nm, detach bleed hose and attach protective cap to bleed screw.
‒ Repeat bleeding procedure in stated sequence at other brake calipers.

Notes:

◆ If one chamber of brake fluid reservoir is completely empty (e.g. on account of leaks in brake system), brake system must be pre-bled => Page 47-44.
◆ On right-hand drive vehicles, brake master cylinder must additionally be bled. Bleeding sequence => Page 47-49

‒ Making allowance for pad wear, fill brake fluid reservoir as far as max. mark and screw on cap.

‒ Start engine and check both brake pedal travel and pressure.
‒ In the event of excessive pedal travel, check brake system for leaks/repeat bleeding procedure.

[andy10v]

In my experience most modern cars with abs if you maintain pressure on the brake pedal it will slowly sink. Does the initial bite point remain constant any build up with repeated pressing?
As for pressure bleeder you.do not need to pump pedal.

Ok, thanks.

I will check if the bite point is the same or pumps up, if it pumps up it normally means air in the system to me?

[Monkeymagic]

A little run would be worth it. I have never reset the 201. I do.loads of hydraulic blocks for g201 failure.
I have only.had one that would not allow me to clear the fault.but that was cured by another bleeding

[4WheelDrifter]

I had this when I first bled the brakes on my A3.
I solved it by bleeding the brakes with the engine running, using the good old fashioned method. Bleed the caliper furthest from the master cylinder and work towards it. No pressure bleeders, no VCDS.
It worked every time since.

HTH.

[Monkeymagic]

I agree excessive travel with no resistance and then a build up with each pedal stroke would indicate air in the system.
However if the pedal feels fine but steadily sinks with constant pressure then this is common on many modern cars. I have seen this on many a mk4 golf with the braking system being in top condition.
Is this a car you are familiar with? One you know etc?

[Monkeymagic]

I also.agree with the above. I've always found the pressure bleeders make a mess. The only difference being to.bleed the mc

[andy10v]

I had this when I first bled the brakes on my A3.
I solved it by bleeding the brakes with the engine running, using the good old fashioned method. Bleed the caliper furthest from the master cylinder and work towards it. No pressure bleeders, no VCDS.
It worked every time since.

HTH.

Thanks, will turn the car around so it exhausts out the garage and capture somebody to press the pedal.

[andy10v]

I agree excessive travel with no resistance and then a build up with each pedal stroke would indicate air in the system.
However if the pedal feels fine but steadily sinks with constant pressure then this is common on many modern cars. I have seen this on many a mk4 golf with the braking system being in top condition.
Is this a car you are familiar with? One you know etc?

That is weird, I would have thought once the piston in the master cylinder goes past the reservoir feed it would be a closed system? Or is it to do with the ABS internals?

The bite is normal, just sinks too noticeably to feel normal, eg you would notice it if you came to a stop and sat with your foot on the brake at a junction etc.

Its my dads car, I dont drive it normally. Failed MOT on corroded rear brake lines, so popped on new ones and just expected a straightforward bleed

[andy10v]

Tried again tonight.

Pressure bled at 12psi in order Audi suggested, no change, bled clutch as well.

Bled manually with the engine running, no change.

With the engine off the pedal is solid and does not change if pumped.

With the engine on the first pedal stroke is long, appears to pump up if pressed repeatedly.

When using the pressure bleeder the fluid flow from the rear calipers is MUCH slower than the front. When you push the brake pedal quickly with the rear bleed nipple open there is a SSSSSHHHHHHH noise from the brake hardline under the car, if you push slowly there is no noise.

[Monkeymagic]

The rears will bleed much slower than the front. Just a thought try replacing rear flexis if they were clamped.