Hard brake pedal, new booster, stumped.

[machinebaby]

Hi all,


I have a 2003 ALH MKIV Jetta Wagon, 220K miles. Bought it 18 months ago with light mods including larger injection nozzles. Has developed an exhaust leak that I haven't addressed yet.

I have done some searching but still stumped, please help.

I had a bad leak in my booster, making a hissing sound that stopped when pedal depressed. I actually still had normal braking capabilities despite the bad leak. I replaced the booster and sure enough it was torn.

After replacing the booster, I developed hard braking, limp, and A CEL. I have no vag com or code reader.

I checked the main hose from the pump, but it looks fine. One note, when putting the hose into the new booster, the sealing grommet pushed through and dropped into the booster. I bought a new grommet and properly installed the hose using the new grommet, but the one that fell into the booster is still in there. Not sure if that makes a difference but there you go.

There was oil coming from the pump so I removed, cleaned, and rebuilt it with the reseal kit from RXTech.

Still hard braking, limp, and CEL.

I checked the one way valve, it was faulty so I replaced it. No help.

The lines were brittle so I got a line replacement kit with german hoses and replaced all the vacuum lines. I snapped off the nipple on the reservoir during that process, so I replaced the reservoir too. Still hard braking, limp, and CEL.

I had new MAF, N18, and N75 on hand so I put them in, no change.

I would like to do a full vacuum check of the system but I haven't been able to fine a newbie-friendly step by step on that, can someone point me to one please?

Anything else I am not thinking of?

I am going to try to borrow a code reader today, and will post results when I get them.

Thanks in advance.

 

[csstevej]

Did you replace that hard plastic line between the booster and the vacuum pump?
They are notorious for breaking on the inside of the bend where you cannot see it.
I replaced mine with a section of 3/8 ID heater hose for a couple of bucks over 12 years ago.

Not sure if dropping grommet in will affect brakes....probably not.

Can you measure the amount of vacuum coming off the pump? Could be a bad vacuum pump or severe leak. I believe it should be around 20 “ of vacuum.

Really need a reader to at least see what code you have.

 

[KrashDH]

Can you measure the amount of vacuum coming off the pump? Could be a bad vacuum pump or severe leak. I believe it should be around 20 “ of vacuum.

Really need a reader to at least see what code you have.

Yup, you need to do this now.

I chased hard pedal and limp mode for a couple weeks. End result was the vac pump could not produce the required amount of vacuum for the system.

Replaced and all was good again.

 

[BobnOH]

^All good.
Might ask what the replacement part is and where did it come from.

 

[machinebaby]

Thanks all

I did not replace that hard line because it looks so shiny and new, not obvious cracks.

I'll get the reader and see what it says.

 

[KrashDH]

^All good.
Might ask what the replacement part is and where did it come from.

Bought a new pump from Cascade German. I have in my notes what kind it was, can't remember off the top of my head

 

[wonneber]

I would want to get the missing grommet out of the booster.
Don't know if it would wear through the booster diaphragm or not but I would not want to find out the hard way.

 

[machinebaby]

Hi all,
First thanks for the replies. Very much appreciated.
Also, sorry for the lag. COVID etc has made work insane
OK, so I have codes:
VCDS 17964-Charge Pressure Control
P1556-35-10 Negative Deviation-Intermittent
But also, I finally learned how to use my mity-vac-like device.
Turns out that while the vacuum pump is putting out 25+ psi, the brake booster is holding 0 psi.
I do very much dislike the idea of removing and replacing the brake booster, so before I do that can anyone shed light on a possible problem I am not thinking about that may be fixable without swapping it?
Second, did I mess up some how or did I install a faulty booster? I cant really see how it is something I did wrong in the installation, but...is there something I may have done wrong in the installation?
Thank you.

 

[wonneber]

Look close at the hard vacuum line going to the booster?
I've read it cracks in a spot that's hard to see.

If you pull that line out of the booster is there vacuum getting to it with the car running?
Thumb over the end should tell.

 

[[486]]

my hard line cracked long ago, replaced with 11/32" rubber line the parts store had in stock

new booster might be bad, new is an acronym for "never even worked" after all

 

[machinebaby]

just occurred to me a may have messed up the o ring on the master. cant think of anything else. the hard line is new too. no leaks there. it holds 25+ psi but when I connect it to the booster the needle never even moves.

guess I gotta pop the master off and see. rebleed the brakes. live and learn. ugh. thanks for the help ill let you know if that was it.

 

[swetbak]

Reviving this thread since it's a very similar situation. Just changed brake booster and now have hard pedal with poor breaking. Only diff is I don't have any CEL's or codes in VCDS. Double checked my vacuum lines and I have plenty of vacuum at the booster. Like the OP I'm hoping it isn't a bad booster and have to do this again. Hopefully he'll chime back in with his solution.

 

[swetbak]

I reviewed my installation instructions twice and all the booster tests online point to the booster. Reluctantly ordered a new one.

 

[swetbak]

I'm wondering if I could have put the master cylinder on incorrectly. Does something line up from inside the booster to the master? I just lined up the two studs and put the nuts on.

 

[swetbak]

Mystery solved! First though, there is a rod in the booster, but probably not possible to install the master incorrectly.
During disassembly to redo the booster I discovered that I never tightened the two nuts holding the master