Tdi brakes better wwhen cold

[fARQUARE]

Hello, my afn is ticking over fine apart from one small issue - the brakes feel more positive and have more initial bite when the engine is cold.
I'm suspecting the vacuum line to the servo might have perished and collapses when hot, has anyone else ever had similar issues?

The pedal certainly feels a bit more wooden when up to temp but when cold there is a really positive initial bite

 

[Oranoco]

Pad compound and or brake fluid that has absorbed too much moisture would be my first thoughts. Vacume to brake servo is generally a hard pipe that won't perish and if it did fail you'd lose the servo assistance and have a horredously heavy/wooden pedal all the time

 

[aragorn]

Maybe the vacuum pump itself is dying?

 

[fARQUARE]

But the vacuum pump controls the boost for the turbo and also the egr too, as i'm not throwing any codes and performance is great wouldn't I see other issues if the pump was on the way out?

I wouldn't rule out fluid but again I cant get my head around why the initial bite is better when cold. All disks and pads are less than 6 months oold so I can rule that out.

One issue I read about on tdi club was a broken rear box link pipe heating the brake lines under the rear bench. I fixed this pipe at the weekend as the liink pipe had slowly fallen apart, I guess i'll see if that repair has had any effect.

 

[fARQUARE]

just to bring this thread back from the dead, the car has 2 brake issues which may or may not be related.

firstly, when covering the brake pedal just as you take up the "slack" in the pedal there is a click coming from the f/o/s caliper, i've had the front disks and pads off 2-3 times but can't see anything obviously out of place. Best guess is the pad moving slightly in the caliper till it hits it's natural stop against the carrier but can't be sure.

second and more worrying in the last 2 days the pedal does not seem to be holding initial bite. I'll be slowing down gradually and the pedal travels more or less to the floor. If i come off the brake and re-apply the pedal bites and does not loose pressure. If i'm sitting stationary and i pump the pedal a few times with the engine running there is no loss in pedal but if i depres once and slowly i can get it almost to the floor.

All disks and pads are less than 2 months old, as are rear brake lines, 1 rear caliper and handbrake cables. I had to get the garage to re-bleed a few days after fitting as the car had similar symptoms, does it sound like there is still air in the system?

thanks in advance

 

[aragorn]

the pumping pedal thing could be sticking sliders on one of the calipers

the missus car did something similar a few months back, removed and regreased and the issue went away.

 

[fARQUARE]

Daft question but are the sliders the 6mm chrome pins that bolt into the carrier?

Did I read a thread about copper grease not being the correct tool for this particular job?

 

[aragorn]

well i'd used copper grease, and it turned into a weird sticky gummy mess, which is what caused my issues.

I had a sachet of some silicone grease stuff that came with some polybushes, so used that and immediately you could feel the difference, the caliper slid REALLY easily on the sliders by hand, rather than the usual dragging feeling that was present before.

I suspect in reality that isnt the right stuff either, but it worked for me. Copper grease would probably work, but i'd imagine you'll need to service it at least annually, cleaning all the old grease away, and applying new fresh stuff.

 

[murran]

if when you can slowly press the brake nearly down to the floor. but if you can quickly press it and it'll hold where it should. then its very likely the brake master cylinder is on its way.

the servo meerly helps you press the pedal to increase your own effort on the fluid. theres a straight mechanical link from the pedal to the master cylinder. the servo cant effect dictate pedal height.

the caliper sliders aslong as theyre free and greased (with anything) theyre fine.
the carrier surfaces? the ones the pad edges rest on, are they smooth without too much rusts or grooves?

 

[fARQUARE]

Brakes bled today, spongyness gone and noise gone too! Excellent

 

[fARQUARE]

Spongyness came back the next day. New master cylinder fitted.
So far so good