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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old August 9th, 2019, 13:18   #1
sisyphus
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Default sketchy brakes, booster?

So I think my brake booster is shot; the pedal goes just about to the floor and pumping doesn't do anything. I hooked a mityvac up to it and running at idle I see 27 in/hg but when I step on the brake it dives down to nothing.
Is this a hard job? Are brake boosters even available anymore? This is for my 99.5.
thanks
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Old August 9th, 2019, 17:25   #2
Mongler98
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so you got it backwards.
if the booster was bad, you would have extreemly stiff brakes.
Your fluid is suspect. its an easy job if all the bleeder screws will move.
Suck all the fluid from the res, fill with some dot 3 or 4, go the the passenger rear then driver rear, passenger front and last driver front, and bleed them the old school way with someone pressing the brake pedal, but with a 2x4 under it, DO NOT LET IT TRAVEL all the way, if it has already then screw it, it dont matter now. shortens the life of the master due to crud back where it normally does not travel.
get all the air out.
you might have a leak, but bleeding will tell all.
fluid is only good for 2 years MAX, and it helps if you do it once a year, fluid is cheep.
stay away from vac bleeders, they never do a good job, the VW res is nice because it can use a pressure bleeder. that is a great way to do it and makes it a 1 man show.
you might need to cycle the ABS with VCDS if its REALLY nasty dirty and definatly if you get air in it.

not a hard job
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Old August 9th, 2019, 17:30   #3
Genesis
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The Motive Pressure Bleeder system is the jazz for this. Buy one and if you have multiple brands of vehicles you can buy just the caps for the other ones after the first. It's one of those tools that once you have one you'll wonder why you didn't buy it 20 years earlier.

Just don't put fluid in it (they recommend doing that -- bad idea.) Suck out as much of the old as you can, replace with new, attach bleeder and put some pressure in it (~10psi), do right rear, check and refill master if necessary, do left rear, etc. If a stick do not forget the clutch slave! Be CAREFUL with the bleeder on the clutch slave -- it's PLASTIC and WILL break if you crank on it.
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Old August 9th, 2019, 19:28   #4
Mongler98
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if the res is really dirty, it can be removed easily and cleaned with MORE brake fluid ONLY, dont use solvents.
either 1 or more of 3 things is going on, brake fluid is bad, its leaking or empty, or you dropped a brake pad
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Old August 9th, 2019, 21:46   #5
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Quote:
Originally Posted by Genesis View Post
The Motive Pressure Bleeder system is the jazz for this. Buy one and if you have multiple brands of vehicles you can buy just the caps for the other ones after the first. It's one of those tools that once you have one you'll wonder why you didn't buy it 20 years earlier.

Just don't put fluid in it (they recommend doing that -- bad idea.) Suck out as much of the old as you can, replace with new, attach bleeder and put some pressure in it (~10psi), do right rear, check and refill master if necessary, do left rear, etc. If a stick do not forget the clutch slave! Be CAREFUL with the bleeder on the clutch slave -- it's PLASTIC and WILL break if you crank on it.
Pressure bleeding is the cats pajamas for sure...no matter how clearly you speak or the words you use, the pedal man never can get it right...I blame smart phones...now I don't have to worry about that now

Word to the wise, don't leave fluid in it and keep the cap adapter very close by, mine went missing for a while

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Old August 10th, 2019, 03:46   #6
Genesis
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Yep -- don't put fluid in the bleeder AT ALL.

Just suck out the old fluid from the master (an epoxy syringe works fine for this; you can buy them at a boating or hardware store) until nearly dry, replace fluid with new to right near the top, attach bleeder and pressurize. Just make sure when bleeding that the master never runs dry (which means, most of the time, topping off the master after each wheel.)

I had to replace the hard lines on my '02 Suburban (Chevy used uncoated steel and routed it in a way that required lifting the body partly off the frame to get to them -- and of course where you can't see them is where they failed) and that meant the system was basically completely dry. The Motive made refilling and bleeding the whole system a job that took about 15 minutes..... I change the brake fluid in all my vehicles every 2 years and have for the last 20+ years now -- since adopting that as "standard" I've yet to have to replace a caliper, master, etc. VW specs 2 year intervals but many other vehicles have no specified brake fluid replacement -- that's insanity as the fluid picks up moisture from the air over time and corrodes everything from the inside out.

I've seen a booster go "insane" and do what the OP is reporting but I'd check first for the possibility of air in the system. How does the brake pedal and system behave with the car off? You should be able to stop the car with manual foot power; is the pedal good and firm with the engine not running?

Last edited by Genesis; August 10th, 2019 at 03:56.
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Old August 10th, 2019, 08:44   #7
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Genesis, why are you saying to NOT put fluid in when doing the Motive? I mean going against the manufacturers instructions and telling others to do it as well without explanation is a little disconcerting. I've used fluid in mine and just curious how making it harder to use (depressurizing it, checking fluid level in the MC, filling, and the pressurizing it again) is better for the car. Thanks!
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Old August 10th, 2019, 09:09   #8
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Because then you have to clean it and make VERY SURE it's absolutely, 100% dry and clean before using it again.

I have NEVER put fluid in mine. There's simply no reason to do it; the fluid in the M/C is sufficient to do one wheel and, on a truck or other vehicle with a large reservoir (you can SEE the level in all modern vehicles) frequently two.

The risk of contaminating the system is MUCH higher if you put fluid in the unit -- not so much the first time you use it out of the box, but on every successive use. It's trivially easy to depressurize it (just crack the cap on the Motive -- NOT on the master) and the pressure is released, then remove the cap, put in some more fluid, repeat.

The rule I have for brake fluid is that fluid that leaves a NEWLY OPENED container from the store goes into the system and then never goes anywhere else except the trash. So anything that gets bled out goes into the junk can (and taken to Hazmat recycling, which they do here free.) Anything I suck out with the syringe from the master when starting, ditto. If I put fluid in the Motive then I have to be sure that the unit is equally clean to the brand new container I just bought, and there's no way for me to do that nor to clean it after use with a solvent that won't risk contaminating the system on a subsequent use -- so I don't.
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Old August 10th, 2019, 12:31   #9
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yea, never added fluid to mine either. completely pointless and counterproductive. also you know how F'n big that tool is? you would need to dump well more than 1 L into it to do the job and you will suck in air, it will settle out of the res but you are putting tiny air bubbles into the system and if they get bled into the line, well, thats not correct is it?

i never toss any fluids in a bottle, i always flush the rest of it until its all gone. but yea, no reason to store it.
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Old August 10th, 2019, 12:45   #10
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Quote:
Originally Posted by Mongler98 View Post
yea, never added fluid to mine either. completely pointless and counterproductive. also you know how F'n big that tool is? you would need to dump well more than 1 L into it to do the job and you will suck in air, it will settle out of the res but you are putting tiny air bubbles into the system and if they get bled into the line, well, thats not correct is it?

i never toss any fluids in a bottle, i always flush the rest of it until its all gone. but yea, no reason to store it.
That's why I got the small one and I used fluid in mine and wasted a ton of fluid, it attacked the tygon tube...I got the schwaben one that doesn't allow the pump to come out...if I find myself bleeding all 3 cars at the same time...maybe I'll add fluid again but in hindsight it does seem a little lazy to not just depressurize and too off and avoid any possibility of air and contamination from fluid in the tank and some may say it's not important or why invest so much effort in these cars, better procedures lead to better results and less worrying about or problems with systems down the road

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Old August 14th, 2019, 11:49   #11
sisyphus
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Ah, cool. Thanks for all the responses. This makes sense now, since I recently had the local mechanic replace a rear caliper for me since I didn't have the time. I guess he never bothered to bleed the system.
Next time I'll take it to the sober guy.
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Old August 14th, 2019, 12:24   #12
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Uh, yeah. Bongs and working on cars, not so good.
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Old August 14th, 2019, 13:25   #13
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hope you didnt pay him! you get what you pay for! yada yada yada .....

you need to bleed the entire system any time you touch one part like that, also he probably F'ed up and drained it and put air in the ABS, your going to need VCDS and a cable to cycle it if so.
SMH
never get reman parts. i have found parts that even from bosch that fail right out of the box, bits of grit in them that bind the piston from the sandblasting of used parts.
its supper easy to rebuild them, just takes time.
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Old August 14th, 2019, 13:30   #14
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Quote:
Originally Posted by Mongler98 View Post
you need to bleed the entire system any time you touch one part like that.
This is not true. Unless you are talking about something else other than the caliper that was replaced on the OP's car.
I did a full bleed of the system last summer.
A couple weeks ago, I needed to re-build a caliper on the front passenger side. Whether you're replacing a caliper or you go the rebuild route, the procedure for removing and installing is the same.
You just need to re bleed that line that is being worked as long as you don't run the master completely dry of fluid.
I will agree though if you haven't done it in a couple years, mine as well do all 4 corners
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Old August 14th, 2019, 14:54   #15
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I said you need to, not that you must. sorry i should explain better.
brake fluid should be changed any time you have access to the system, fluid is cheep, and its a good idea to bleed it when you can. in a hurry, yea sure, totally can just bleed the one line you worked on BUT you DO get uneven brake wear IF the current fluid is a bit old, more than 1 year. its not much but it does happen. had this happen a few times when i needed to fix it on the side of the road or on a trip, car pulled to the bled side. but that was because the fluid was OLD, like 4 years old and once at highway speeds the heat was enough to cause some minor boiling and thus the pull to the left (side i worked on) and on my escape that for the 3rd time since i have owned it, one of the bleeder screws sheared off on the front caliper, I HATE SHADE TREE MECHANICS, so its been running for the last year now with old fluid since i have bled the system, i do it every 1.5 years. and now the pads on that caliper are much less worn down, by about 20% and i have never had issues with this as i properly grease the pins and so on!

Last edited by Mongler98; August 14th, 2019 at 14:58.
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