# MKIV Golf TDI - Brakes not stopping



## TheGreek (Aug 20, 2008)

I saw a mention in another thread that the brake master cylinder is the same one used for the clutch...i never knew they did this...

so, i put in a new rear caliper...bled my brakes...when i was done, i had a decent pedal, but not awesome...i topped off the fluid and took it for a test drive...the pedal went all the way to the floor and didn't stop hardly at all..after pumping the brakes it was better for that stop, but then had to do it again for the next stop...since all the calipers are fairly new and i didn't see any fluid leaking i was thinking it was the master cylinder that had to be bad?! but, my clutch is perfect...so now i am second guessing that...any ideas?

thanks guys and gals! kosta


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## BsickPassat (May 10, 2010)

the brake booster the connects to the vacuum pump has a tendency to harden & crack, causing a leak


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## TheGreek (Aug 20, 2008)

BsickPassat said:


> the brake booster the connects to the vacuum pump has a tendency to harden & crack, causing a leak


The actual brake booster or the line connecting them?

how do I check for this? would that explain the light pedal?


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## KG18t (Aug 9, 2006)

If the vacuum line was trashed, the pedal would be stiff and it'd be difficult to press. More likely - master cylinder. When bleeding the brakes - did you use a pressure bleeder or manually? Two possibilities for trashing the MC arise from this - either you punch the pedal to the floor and it trashes the seals, or you used too much pressure and trashed the seals.

Just to quote myself, because I feel like I've said this a lot lately:



KG18t said:


> {press the pedal} after the car is off - a few pumps and then the pedal gets harder - this is normal. When the car is running, it builds up vacuum in the booster which assists the pedal press. After it's off, the vacuum is sustained for a while, using the brake drains the boost... so to speak.
> 
> You said "to the floor" in your first post. Did the pedal actually go all the way to the floor? Or did you just have to stand on it?
> 
> ...


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## TheGreek (Aug 20, 2008)

KG18t said:


> If the vacuum line was trashed, the pedal would be stiff and it'd be difficult to press. More likely - master cylinder. When bleeding the brakes - did you use a pressure bleeder or manually? Two possibilities for trashing the MC arise from this - either you punch the pedal to the floor and it trashes the seals, or you used too much pressure and trashed the seals.
> 
> Just to quote myself, because I feel like I've said this a lot lately:


I did it manually...I did the pump/hold/open/close method, and i did a hose on it with the hose in a jar of brake fluid...both times i appeared all air was gone...

if the MC was bad, wouldn't the clutch fail too if they use the same MC?


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## KG18t (Aug 9, 2006)

Sorry, forgot to correct that from your first post - the clutch and brakes use the same fluid and reservoir - but the clutch has its own master and slave... otherwise, well, you'd have a hard time using the clutch and/or the brakes.

After starting the car, press the brake with a normal pressure - does it hold for a second and then start falling?


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## TheGreek (Aug 20, 2008)

KG18t said:


> Sorry, forgot to correct that from your first post - the clutch and brakes use the same fluid and reservoir - but the clutch has its own master and slave... otherwise, well, you'd have a hard time using the clutch and/or the brakes.
> 
> After starting the car, press the brake with a normal pressure - does it hold for a second and then start falling?


Gotcha! I will try this tonight and report back! I really appreciate it. I am in a bind and need the car for a trip this weekend, but can't seem to nail it down. THANKS IN ADVANCE!


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## radlynx (Jan 4, 2007)

try to bleed the fluid with the car running. whatever air is on the line needs to be removed. otherwise, you will get the spongy feeling.



TheGreek said:


> Gotcha! I will try this tonight and report back! I really appreciate it. I am in a bind and need the car for a trip this weekend, but can't seem to nail it down. THANKS IN ADVANCE!


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## KG18t (Aug 9, 2006)

radlynx said:


> try to bleed the fluid with the car running.


Not relevant.


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## TheGreek (Aug 20, 2008)

KG18t said:


> Not relevant.


I always bleed with it running to get the vacuum booster helping...but yea, not sure it matters?!


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## radlynx (Jan 4, 2007)

what i think is air got into the line when he replaced the caliper. air always stays in the highest point of the line. so, with the car running while bleeding it, it will put more pressure to the line that takes the air out of it, thus removing the spongy feeling when braking. maybe, it's a different issue, could be a master cylinder. just my .02 cent that is worth a try. what are you going to loose?



TheGreek said:


> I always bleed with it running to get the vacuum booster helping...but yea, not sure it matters?!


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## TheGreek (Aug 20, 2008)

So I went out to check the brakes...and the battery is dead!? it's on the charger now...

I did press them with the engine off...they went down pretty far...with a second pump they firmed up...a third pump was about the same spot...held it there firmly and it didn't seem to get soft at all

thoughts? is there a part with the vacuum to inspect? i don't see fluid anywhere


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## KG18t (Aug 9, 2006)

Ok, well, that tells you the booster is fine. It holds vacuum for a bit after the car shuts off, if there's no fresh vacuum supply, the pedal will stiffen up. IF the mc is trashed - I don't know if the seals are far gone enough for you to press past them without a vacuum boost. If you can stand on it with the car off and the pedal goes down though (probably take quite a bit of force), replace the MC assuming you don't see any leaks at any of the calipers.


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## radlynx (Jan 4, 2007)

can you try the hand brake a couple of times, pull and release? using the hand brakes will push the piston on the proper spot, thus giving you only the right amount of space between the rotor and pads when released. 



TheGreek said:


> So I went out to check the brakes...and the battery is dead!? it's on the charger now...
> 
> I did press them with the engine off...they went down pretty far...with a second pump they firmed up...a third pump was about the same spot...held it there firmly and it didn't seem to get soft at all
> 
> thoughts? is there a part with the vacuum to inspect? i don't see fluid anywhere


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## radlynx (Jan 4, 2007)

I'm referring to the back caliper for these.



radlynx said:


> can you try the hand brake a couple of times, pull and release? using the hand brakes will push the piston on the proper spot, thus giving you only the right amount of space between the rotor and pads when released.


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## TheGreek (Aug 20, 2008)

radlynx said:


> I'm referring to the back caliper for these.


This is something I actually replaced...maybe I should have included that...

So, I replaced both brake cables...I did pull it and release it several times so I think it is in the right spot. 

Car should be charged up now...going to check it out!


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## TheGreek (Aug 20, 2008)

okay...it's alive again!

So, I went out...car off...pedal went down pretty far...3 pumps and it was firm again...

car on...same thing...but if i held it on the 3rd pump it would slowly go back to the floor

then i turned it off...3 pumps...firm pedal...held it down...no changes...started the car while holding it firmly...pedal went to the floor again once the car was started

does that help? anything else you want me to do to help diagnose it?


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## radlynx (Jan 4, 2007)

Looks like you need to replace your master cylinder. if the engine is running and you pressed the pedal and hold it, it should not go down anymore. the rubber inside it seems to be leaking fluid back to the fluid container. what's your current mileage?



TheGreek said:


> okay...it's alive again!
> 
> So, I went out...car off...pedal went down pretty far...3 pumps and it was firm again...
> 
> ...


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## radlynx (Jan 4, 2007)

You can actually replace the rubber inside it if you want to save on money instead of replacing the whole master cylinder.


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## TheGreek (Aug 20, 2008)

crap...this is not what i was hoping!

any writeups on how to do just the rubber part? i will start doing some searching


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## radlynx (Jan 4, 2007)

check this out. http://www.youtube.com/watch?v=HPXBDuRgxG0




radlynx said:


> You can actually replace the rubber inside it if you want to save on money instead of replacing the whole master cylinder.


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## radlynx (Jan 4, 2007)

try the bench bleed first and see what happens.



radlynx said:


> check this out. http://www.youtube.com/watch?v=HPXBDuRgxG0


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## TheGreek (Aug 20, 2008)

i have bench bled a MC on my jeep...but it was when i was replacing...it is possible to do this with it still in the golf?

also, what if i took it somewhere with a pressure system...would that get any trapped air out?


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## TheGreek (Aug 20, 2008)

radlynx said:


> what's your current mileage?


it's a 2001 tdi with about 130K on it


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## KG18t (Aug 9, 2006)

I'm sure they exist, but I've not seen rebuild kits for mk4 MCs. When you get a new one, or rebuild the old one, bench it. If you're going to pay someone - might as well get a pressure bleeder yourself:

http://www.ecstuning.com/Volkswagen-337_20AE--1.8T/Braking/Tools/

Wondrous things, they are. Just don't over-pressure it.


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## radlynx (Jan 4, 2007)

Yes you can, you don't have to remove it if you don't want to and it will be a mess. brake fluid is very corrosive to paint. if you took it somewhere, you might as well replace the rubber inside. you can look around if you can find a master cylinder repair kit.



TheGreek said:


> i have bench bled a MC on my jeep...but it was when i was replacing...it is possible to do this with it still in the golf?
> 
> also, what if i took it somewhere with a pressure system...would that get any trapped air out?


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## TheGreek (Aug 20, 2008)

Is this the grommet that you are talking about? there is a $64 master cylinder on there...seems like i might as well just replace it all...

power bleeding kit is affordable! i think i will get that first...that video makes sense on how if you pedal bleed it will have the pedal go further than normal operation and there is corrosive crap down in the end that the seal could rub and then ruin it's sealing power...maybe that is what happened

http://www.napaonline.com/Catalog/R...ty=1&Ntt=&N=599001+102001+50074+2074015+26352


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## KG18t (Aug 9, 2006)

Nope, not the grommet - that's to seal the reservoir to the MC. ECS has MCs as well. http://www.ecstuning.com/Volkswagen-Golf_IV--TDI/Braking/Master_Cylinder/ Not cheaper thought. Make sure you get the appropriate one for with ESP or without.


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## TheGreek (Aug 20, 2008)

So are you pretty sure it is the MC? or is there anything else I can do to test this to be sure? 

I like the pressure bleeder kit...i think i will get that!


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## KG18t (Aug 9, 2006)

Rather sure. Either way, the pressure bleeder's a highly useful thing to have around.


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## radlynx (Jan 4, 2007)

Usually what fails in the master cylinder are the rubber inside. to make it easier for you, just replace the master cylinder and be done with it. i'm 200% sure it's the MC.



TheGreek said:


> So are you pretty sure it is the MC? or is there anything else I can do to test this to be sure?
> 
> I like the pressure bleeder kit...i think i will get that!


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## TheGreek (Aug 20, 2008)

thank you guys! i will work on that!


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## TheGreek (Aug 20, 2008)

finally a nice weather day...going to tackle this today...

questions for you...

both of you were pretty damn sure it is the MC...but i don't understand why it is the MC if it holds pressure with the car off? to me that would see that it is the brake booster or something else in teh brake system that is changed when the car is on...then i got to thinking about it...maybe when the car is on it produces more pressure and since it is producing more that is what causes the MC to fail...as in, my foot pressure with car off isn't enough to cause the MC to fail...but with the help of the MC, it fails...is that what you guys were thinking? just trying to understand it all...thanks again!


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## radlynx (Jan 4, 2007)

exactly. with the engine off, it will not produce more pressure.



TheGreek said:


> finally a nice weather day...going to tackle this today...
> 
> questions for you...
> 
> both of you were pretty damn sure it is the MC...but i don't understand why it is the MC if it holds pressure with the car off? to me that would see that it is the brake booster or something else in teh brake system that is changed when the car is on...then i got to thinking about it...maybe when the car is on it produces more pressure and since it is producing more that is what causes the MC to fail...as in, my foot pressure with car off isn't enough to cause the MC to fail...but with the help of the MC, it fails...is that what you guys were thinking? just trying to understand it all...thanks again!


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## TheGreek (Aug 20, 2008)

radlynx said:


> exactly. with the engine off, it will not produce more pressure.


okay...new MC is in...

it still has the same symptoms as before....it will slowly ease to the floor when the car is on...

however, it at least holds enough pressure that the car stops...so....i can stop again, but it still doesn't seem 100% and that slowly dropping to the floor still bothers me...


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## radlynx (Jan 4, 2007)

Did you bleed it or bench bleed the MC and all the wheels?



TheGreek said:


> okay...new MC is in...
> 
> it still has the same symptoms as before....it will slowly ease to the floor when the car is on...
> 
> however, it at least holds enough pressure that the car stops...so....i can stop again, but it still doesn't seem 100% and that slowly dropping to the floor still bothers me...


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