Identifying where the issue is

[cxite]

Hi folks

Appreciate this has potentially been covered previously in other threads, all of which I have read but have to no avail.

The story, recently acquired this car, A4 B6 1.9TDi, and I have the dreaded brake issue. First occurred when it was raining pulling up to a junction, first pump of the brakes, all ok, second pump, the pedal went rock solid and no matter how much pressure I put on the pedal I could only get say 10% of the usual braking power.

First port of call is the plenium chamber and water getting into the servo, doesn't seem to be blocked, even took the battery out and shoved a hose into the tray and the water drained away immediately so have ruled this one. Some suggest that there is a vacuum leak but have followed the usual procedures as described below and all work as intended.

Procedure as above, turn car off, pump brakes 2-3 times until solid, turn car on, brake pedal falls maybe an inch or two and slowly reduces in pressure thereafter. Second test as above, pump brakes with engine off until the pedal goes hard, the pedal stays hard until you turn the car back on.

I can replicate the issue by pumping the brakes, with the engine running, maybe 4-5 times, the pedal goes rock hard and the very slowly softens up again.

So my question really is, taking into account the above, is there anything blatantly obvious that i am missing or could anyone provide any further tests to carry out? I don't want to go replacing servos and pumps willy nilly.

Thanks in advance for your help.

[zollaf]

check the connection where the big vacuum pipe goes into the pump as this can have a loose fit and leak air. a bit of silicon around it will act as a temp repair if this is the case.

[cxite]

Will try this one tomorrow and report back, had noticed the hose to this little plastic pipe was loose so put a new jubilee clip on it but hadn't thought of the silicon method, thanks!

[soobusdriver]

Hi, could you take a pic while you're there, just for reference to locate the area for others with the same problem?
Good Luck!
Cheers

[nevo]

Putting silicon on is only a temporary solution,all the vac lines should be checked and secured correctly,also check they're in good condition and not collapsing internally.

[cxite]

Hi, could you take a pic while you're there, just for reference to locate the area for others with the same problem?
Good Luck!
Cheers

So here are the pictures at my temporary repair to see if this solves the issue, will let you know the outcome after the drive home!

28076 28077 28078

[zollaf]

thats the kiddy. its the union that goes into the pump. did this on a customers car last year and it made a big difference.

[cxite]

Unfortunately this hasn't solved the problem, next item to check I guess is the pipes collapsing on themselves as nevo said above. Will report back once I know more =)

[nevo]

Check the big pipe that goes to the servo for cracking,since its intermittent could be the vac pump itself or the servo,obviously you don't want to chuck money at it so just bear it in mind for now.have you got a vac gauge to check the performance of the pump.

[cxite]

I'll be sure to check that hose, have questioned the materials it made from (some brittle plastic/rubber composite) but I can source a vac gauge easily enough, what pressure should it be producing?

[nevo]

Don't know the exact spec but I would have thought about 20"hg,having thought about it,if it was the vac pump you would have had turbo problems,so i'm more inclined to the servo or the pipe.

[cxite]

You raise a good point and I can confirm I have no lack of boost from the turbo, surprisingly pokey for a 1.9! So im with you on the servo or pipes theory, is there anyway to check the servo without replacing it? Re the pipes, would I not also encounter turbo issues as they are all connected to the same vacuum system?

Also, just a quick thanks for all the help so far, it really is appreciated, been banging my head against a brick wall for a couple of weeks over this now!

[cxite]

Right well VAC tested today and getting a steady 23hg, direct from pump and from the pipe that goes directly to the servo, so I would say its ruled that out.

Would air in the brake system cause these same symptoms as wondering if it's worth bleeding them?

[nevo]

Won't be air, you would be pumping it,hard pedal is loss of servo assistance,those of us old enough to remember pre servo days will remember how hard the braking was,anyway there are issues with servo internal corrosion on these cars do a search and see what comes up,also check up near the pedal connecting rod if its drawing air in there.