Mushy brake frustration

[jackedshirt]

'14 Jetta TDI 2.0 Highline


After doing a fluid swap this past summer and following the bentley manual brake bleed procedure, after a few cycles I was able to get super firm brakes.

Fast forward to a few weeks ago, I noticed my economy was turning to **** so inspected the calipers for drag an discovered the front tow were somewhat siezed. Pistons required a lot of elbow grease to push back in with brake clamp kit and they were old so I swapped em out for two new ones.

I've again done the bentley procedure with my pressure bleeder 3 times over the course of the past 3 weeks weeks and I cannot get my brakes as firm as they were and they still feel soft. They are responsive once i get past the halfway depress mark. Is it possible that I was misled on the firmness because the front calipers were somewhat siezed? I don't how firm they are supposed to get with 4 healthy calipers.

here my procedure with pressure bleeder and vw spec brake fluid:

pre bleed front left, front right, rear left, right rear until no air bubbles.

run abs via vcds, open bleeders at front, press brake 10 times, close bleeders.

bleed all 4 over again until no bubbles, (if any)

post bleed all 4 with second person on brake, pushing brake down, opening bleeder, brake depresses more, closing bleeder. 5 times per pedal.

make sure master cylinder isn't overfilled.



Brakes are so firm when ignition is off that you cant even move them. once I turn ignition on, they get mushy. No error codes in vcds.

Any ideas? I dont have any leaks from what I can see, its snowing here and I haven't seen any fresh brake fluid drips in the snow where I park.

 

[Nuje]

What pressure did you have the pressure bleeder at? I'm not sure on the Mk6, but on the Mk7, the manual says pressure needs to be at 2bar (just under 30psi)...which is a lot.

Sounds like you have the procedure nailed down. Only things I'll add:
1. After doing the VCDS procedure, wait a few minutes (like, go grab a coffee, or clean up some tools or whatever) to allow the bubbles to coalesce and move "up".

2. The other thing I've heard/read is that the pedal-pusher in the post-bleed should pump the pedal a couple times then really lay into it - and then hold while bleeder is opened/closed.

I had the same issue after replacing the ABS pump in my Mk7 until I did the latter (convinced my wife to help out...which she did admirably; she hated the mushy pedal, too. )

Good luck.

 

[Jr mason]

I had such mixed results with my Motive pressure bleeder that I converted it to a transmission service unit - the sealed types that can't be filled from a dipstick.

I'd try it again with someone pumping the brakes the old fashioned way. You may be surprised.

 

[jackedshirt]

Ill try those two things, I'm also going to inspect the master cylinder.

I've always kept my pressure bleeder at around 20-22psi. I've seen the 30psi reference before as well but someone said that pressure may compromise an old seal on the master...which could be my case.

 

[jackedshirt]

just an update, rebled everything thrice over (including the two tips above) , pedal feels a bit better but not the same as it was. there was still a little bit air in the lines. I inspected the master and see no leaks, so it boils down to:

bad seal or plunger inside master cylinder?
bad vacuum check valve?

brake doesn't return after holding down after car is shut off nor does it sink after pressing down four times after car is shut off, so i assume my brake booster is ok?

 

[Nuje]

Just throwing out ideas (given that the possible culprits you posit are, while no impossible, at least somewhat unusual)....

Do you know anyone else with the same car - or at least same generation as your car?
Could it be that your recollection of "before" is mis-calibrated? While it feels soft, how "grabby" are the brakes? Maybe drive it for a bit and see if your feel for it adapts? Also maybe it gives time for any possible additional air to bubble together and up (?).

 

[jackedshirt]

Just throwing out ideas (given that the possible culprits you posit are, while no impossible, at least somewhat unusual)....

Do you know anyone else with the same car - or at least same generation as your car?
Could it be that your recollection of "before" is mis-calibrated? While it feels soft, how "grabby" are the brakes? Maybe drive it for a bit and see if your feel for it adapts? Also maybe it gives time for any possible additional air to bubble together and up (?).

iknow someone with a 13' passat, thats it but i'll try.

brakes are very responsive and grabby, but soft and more travel then before the caliper change.

 

[Canary5.0]

I've had this same feeling from my brakes. even after replacing a master cylinder due to loss of brakes when hot. I've had "mushy" brakes for a long time, probably since the first time I changed fluid. had a professional euro shop bleed them this last time and it feels the same it always has. always had good grabbiness too, very weird, like the first bit of travel does little then the brakes come on strong about halfway. I've just learned to deal with it but would love to find a solution

 

[braddies]

There's also the trick of tapping the calipers with a rubber mallet while bleeding to knock free any stuck air bubbles

 

[turbobrick240]

I've had this same feeling from my brakes. even after replacing a master cylinder due to loss of brakes when hot. I've had "mushy" brakes for a long time, probably since the first time I changed fluid. had a professional euro shop bleed them this last time and it feels the same it always has. always had good grabbiness too, very weird, like the first bit of travel does little then the brakes come on strong about halfway. I've just learned to deal with it but would love to find a solution

The solution is simple- get them bled properly. There is air in the system. No bueno. Buy a pressure bleeder and do it yourself in the prescribed order if you can't find a competent shop to do it.

 

[Canary5.0]

The solution is simple- get them bled properly. There is air in the system. No bueno. Buy a pressure bleeder and do it yourself in the prescribed order if you can't find a competent shop to do it.

Shop is/was more than competent. Best Euro shop around imo as well as others. Wouldn't trust anyone else in the area. That being said I know it could still be done incorrectly.
I have a pressure bleeder and that's how I've always changed the fluid. Brakes definitely have full function just not a factory firm feel. It's about time to bleed again so will see how it goes this time.
Can someone confirm for me what pressure I should set the bleeder at for a Mk6? Can't find my notes on if its 1 or 2 bar.

 

[turbobrick240]

~1.5 bar/22 psi should be good. Wouldn't hurt to cycle the ABS pump while bleeding. Or to give a few manual bleed pumps of the pedal. That new master cyl. may have a bit of air trapped in it.

 

[Canary5.0]

cool thanks. Cycle the pump and manual bleed pumps while under pressure from the bleeder? I know the new master was bench bled but again who knows.

 

[turbobrick240]

Yeah, but still close the bleed screw before releasing the brake pedal unless you have tight tubing from the screw into a clean container of fluid and no bubbles in the tubing.

 

[Nuje]

Again - let it sit after churning the ABS pump. It's like turning on a blender for a few seconds so any air in there will get minced and chopping into microbubbles and dispersed everywhere. Give a chance for the micro-bubbles to coalesce.

Can't remember if I posted this earlier in this thread, too, but I couldn't get my brakes to firm up (both a Mk4 and Mk7) until I sent to the good ol' buddy bleeding: Someone pumps and then stands on the brake pedal, other person opens/closes the bleeder screw. Repeat 10x each wheel.