MK4 Brake issues.

Hi, I am having spongy pedal problems with my Mk 4 (2000 GT TDI AJM engine code). It’s taken a while for me to realise but I am now thinking the problem goes back about 6 months.
I felt my brakes weren’t as good as they should have been, I didn’t think the discs and pads were that bad but told myself I was being a cheap-skate and decided to do them. So all new genuine VW discs and pads later and a fluid change, I am happy again but not for long, so I decide to bleed them again only this time I manage to run the reservoir dry and have to do a full Vag-com ABS bleed which I am not sure about as the commands from my 20IE system are a bit misleading but with the help of Ross-tech and information on forums I manage to get the hang of it and I am fairly sure I am doing it right now and have the correct sequence which was also an issue.
So to date I have done the following; I have completely changed my fluid for Dot 5.1 which exceeds VW recommended specs. I have gone through the bleed sequence in the Haynes manual, both the pre-bleed (for cars where the fluid has been run dry) and the normal bleed sequence, I have done the Vag-com ABS bleed on 3 occasions although I could only guarantee getting it right last time and the usual sequential bleeding, usually using a pressure bleeder (Gunsons easy bleed).
This takes me up to about four weeks ago when I knew the brakes were getting worse and on the advice of my MOT tester I did a gravity bleed which I had never heard of before (but did read something on here from one of the gurus), which didn’t actually help much so I followed it with a sequence bleed and the pedal was better for about two weeks. By this time I had been asking some questions on forums and someone gave me the Elsawin procedure for brake bleeding, which is similar to Bentley, (which I have) but includes the use of (VW specialist tool) a 'brake pedal actuator'. I am still unsure if I did this correctly, Wallace specialist tool (a piece of wood and a hammer, wedged between the seat and pedal but how much to depress?) to depress the pedal, then I bled the 2 master cylinder bleed screws (as by this stage I am suspecting a problem there) a sequential bleed as follows; Right rear, Left rear, Right front, Left front, Clutch. Left I take to be o/s/f and beating in mind my car os Right hand drive so master cylinder on the opposite side to US cars.
So the pedal is better again but nothing to write home about and I may be paranoid by now but after 3-4 days I think it is softening again
So if anyone has any ideas what might be going on I would be very grateful, you guys have been very good to me in the past and I seem to have exhausted the knowledge on the other site (better not say any names but no-ones talking to me now anyway) and I am pretty well out of my depth. Any ideas appreciated, Wallace.

Anyone any ideas? I don't mind criticism, if I've screwed up just tell me!

Bentley's -

WARNING - Use only new approved brake fluid that complies with MVSS 116 DOT 4. Do not use silicone based brake fluid (DOT 5). Even the smallest traces can cause corrosion in the brake system.

PDiesoiler said:

Bentley's -

WARNING - Use only new approved brake fluid that complies with MVSS 116 DOT 4. Do not use silicone based brake fluid (DOT 5). Even the smallest traces can cause corrosion in the brake system.

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DOT 5.1 is compatible with DOT4. It's confusing, but it's not silicone based like DOT5.

Check the brake hoses for damage and softness.

Sometimes air can be stubborn and it will take a helper to operate the brake pedal in addition to the pressure bleeder (at 14.5 PSI). The extra fluid motion will assist in pushing out any trapped air.

There are (at least) two possible ways to use the ABS pump to bleed the brakes with VCDS.

You might try doing the OUTPUT TEST and having the bleeder port open during the individual wheel locking portion of the test - this is with all 4 wheels for many systems (one at a time). As well as during the Basic Settings test when the front bleeders are opened.

Or perhaps you have already done both?

Hi, Thanks for the replies. I am sure the 5.1 fluid is OK like some people said it seems to exceed the VW specs. I did wonder about the flexi pipes right enough as they are 10 years old now, will have a check at those with an assistant to depress the pedal. What I don't understand is if that is the problem, why would bleeding help at all?
I read through all the stuff on the site here last night and I seem to have done everything OK with the embarrasing exception of running the MC dry, can I say this was only a tiny amount, I opened a bleed nipple and heard a gurgle, closed it straight away and checked to find the fluid low in the reservoir, I actually thought I may have got away with it, Hah!
I have only done the Vag-Com bleed one way as per the recommendation on the Ross-Tech site, didn't know there were options, so I may need to look at that.
No-one has mentioned the brake pedal depression during bleeding, it's not mentioned on Bentley, although it is mentioned in other procedures relating to brakes ie not normal bleeding. I did wonder if this was bum information from another forum and nothing is mentioned in procedures in the How-to section on here, anyone any ideas?

jcrews said:

DOT 5.1 is compatible with DOT4. It's confusing, but it's not silicone based like DOT5.

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Good to know, thx jcrews...Thats a relief for the OP...sounds like he knew that too.

I think it was Mogolf in a post somewhere that recommended pump brake pedal 10 times, hold then firmly pull hand brake, release and repeat 10 times.

This gives my pedal a bit more confidence. I do it on a pretty regular basis. Helps take up mechanical slack from brake wear and cable stretch.

That's interesting about the pumping of the pedal 10 times etc as part of the ABS bleed procedure includes something similar. I was confused at this point as I thought the bleed screws should be open and did it this way on one occasion but the amont of fluid used is quite a lot. I then did it with the bleed screws closed, which is how I now think it should be but I wasn't sure whet I was trying to achieve.
Tonight I noticed something, incidentally I am pretty sure my brakes are fading by the day. When the engine is switched off if I pump the pedal up till it's hard then release, then press and hold it stays form for a couple of seconds then I get a slight hiss and it drops about half an inch the holds firm again, is this normal? or does it perhaps shed any light on what the problem may be? Otherwise I haven't tried anything else yet, I was away from home at the weekend and minus 7 outside last night, probably poke around at the weekend again, any suggestions what I should poke first would be good.
Cheers Guys for the help.

jcrews said:

Check the brake hoses for damage and softness.

Sometimes air can be stubborn and it will take a helper to operate the brake pedal in addition to the pressure bleeder (at 14.5 PSI). The extra fluid motion will assist in pushing out any trapped air.

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^^^ +1.

Wallace, I got your message, sorry to hear about the woes.

Once you've admitted air, it can be very difficult to get things back to normal. Here are a few thoughts:

You are not leaking fluid, right?

I really don't have any experience with DOT5.1 and would never fool with it. The DOT4 and DOT4 Super are the only ones recommended by VAG regardless of any "meets or exceeds" claims you may have read.

You must pressurize the reservoir to 14.5psi as noted here.

I believe that two persons are required to perform the VAGCOM bleeding procedure and you'll end up going thru a LOT of fluid. However, if there is air in the tiny passages of the ABS pump, it will be very difficult to remove. I think VAGCOM is the only way to purge the air. (I do hear of others taking the car out on a dirt/wet road and forcing the ABS pump to operate to get the fluid cycling thru. I don't know if this will work on a VW.)

Check for any "bubbles" in your rubber brake lines. They do fail over time.

As already mentioned, you can do an "extreme" bleeding session with the aid of a helper. Pressurize the bleeder to 1 bar and tap on the rubber lines while a helper is pushing the pumping the pedal inside the car...you'll move a lot of fluid doing this and may get any air bubbles out of the system. Be certain you place some sort of "stop" behind the brake pedal so it is NOT depressed to the floor!!!

You could have a defective/worn master cylinder.


I've had a similar situation with my Mk4 car and it probably took me several weeks and much bleeding to restore things to normal. I did not let my reservoir run dry, but I did install new brake lines

Thanks Dieseldorf, loads of good advice in there, I am pretty sure there are no fluid leaks, what size of stop do I need under the pedal? Is it possible that although after previous bleeds the brakes have felt better, they have still not been as good as they should have been and therefore there has still been air in there? What I don't understand is how over the next coiple of weeks they would get worse as this suggests to me more air being introduced into the system? Some other advice I had was to use "Gravity bleeding", I didn't have much sucess with that, do you think it is worth it? If you don't get a chance to answer any of this by the weekend don't worry as I have plenty info to be going on with but I would be interested in your comments. I will get myself a vat of DOT4, have a go anyway at the weekend and post up my results.

the gravity bleed will not yield results.

I supposed you'd want something 5cm thick or so ...you do NOT want the brake pedal to be able to push all the way against the floor when you have a bleeder open.

Ok thanks for that, I was given this; http://uk-mkivs.net/forums/t/268832.aspx but I am not sure it's relevant to my car, it doesn't match Bentley and I wasn't sure about the VW brake depressing tool, never seen this before and didn't know how much to depress the pedal etc. Digressing a bit I know, what I really need to do is do some work on the car and report back. I think the procedure originates from Elsawin. I keep getting conflicting opinions about the DOT 5.1 fluid too, some people saying yes it's fine, others no replace with Dot 4?

Hi Folks, apologies for not getting back on sooner but I have had no time to fiddle witht he car and actually ended up putting it off the road last week. At the weekend there however I got some time, did the full Vag-Com ABS procedure with an assistant, also some pedal depressions, 5cm thick piece of wood under the pedal, tapping the flexi pipes, which incidentally seem problem free (no bubbles etc), then did a full pressure bleed. The bad news is it hasn't helped.
More and more I am thinking it must be the master cylinder and on that vein my thoughts are that basically everything I have done since about September last year (DIscs/Pads front and rear, fluid change/Bleeding) has only marginally or temporarily improved things, i am thinking because it has just steadily been getting worse. As far as not depressing the pedal to the floor, I am sure it has been virtually to the floor before, if not through bleeding then through how low the pedal has got it normal vehicle operation.
So I priced a Cylinder today, No-one seems to do a repair kit which I wondered about as the car has only done 70,000 and I have had it since it was 2 years old, so I don't think I would get a better second hand one. New it's £152.00 from VW and somewhere between £65 and £75 from an independent parts supplier (there would be discount on both these prices), so how easy a job is it to do, is there anything I need to look out for and would a genuine part be best? Repair kits, possible/good idea?
Basically as usual any advice greatly appreciated as I am out of my depth now, not the first time and always dug my way out, slowly but out and continually learning none the less. Cheers

You do know the parking brake adjustment affects the brake pedal travel? The pivot arm should rest at least 1mm but not more than 3mm from its stop at the rear caliper with hand brake off (at rest). When I did this to mine it firmed up the pedal nicely. One click of the hand brake now holds the car from rolling. That hissing noise seems suspicious though.

Pretty sure the parking brake is Ok, generally holds on 2 clicks, maybe 3 on a hill, haven't measured it recently but I doubt I could get much adjustment.
I noticed the hissing sound when we were bleeding too, even without servo assistance it's there, press the pedal till it's reasonably firm, then you get the sound and it drops about half an inch, by that time your well down, top face of brake pedal below the level of the same on the accelerator/gas pedal, which is not far off the floor.
Someone said to me that if the M/C was gone the pedal would drop to the floor, I am not sure how far down they meant, on the road I would imagine sudden pedal to the floor would be pretty scary and I wonder if maybe the design for safety reasons would mean, not all the way down but maybe soft pedal and almost to the floor but with some brake pressure maybe just enough to stop, if that's the case then I am almost there.

I seem to be talking to myself here but anyway, here goes; OK I bled it all again tonight, M/C first then the rest and I have a pedal again woo hoo! How long for I don't know but there are some signs of possible M/C leakage. On the inner wing there's some oily dirt I don't remember seeing before and around the mounting nuts to the servo the paint is slightly bubbled like a paint reaction or what brake fluid used to do to your body work if someone poured it over the car. So outlook could be a M/C soon but for now just pleased I can drive it again.

530 views. You are not talking to yourself.

Ah well, that's something, don't suppose you have any ideas about my brakes?

Wallace, If I had anything to add, I would not hesitate. Since I could not add anything, I just watch for the resolution; I figure I might learn something. I did not want to burn up the bandwidth with no additional intelligence. But I did not want you to quit posting the saga either.

OK Cheers for your interest, I guess I am just getting to tne outer reaches of most people's experience, makes me feel a bit better anyway as I am not the only one.

Interested to know how you are getting on with your brakes as my Toledo has a similar issue with soft pedal.

If at idle I sit with my foot on the pedal it will gradually depress if I keeep a little pressure on it.

Have you checked hard vacuum line the provides vacuum to the master cylinder booster tank? They get brittle and crack and provide lousy, spongey, bleeding off braking.

rackaracka said:

Have you checked hard vacuum line the provides vacuum to the master cylinder booster tank? They get brittle and crack and provide lousy, spongey, bleeding off braking.

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Not yet but I'll have a look. Thanks for the info.

rackaracka said:

Have you checked hard vacuum line the provides vacuum to the master cylinder booster tank? They get brittle and crack and provide lousy, spongey, bleeding off braking.

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Checked this and it all looks fine

ToledoTDi said:

Checked this and it all looks fine

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Sorry for the misdirection. Did you actually remove the hard pipe? I've found them looking good and split in half when removed from the car. They do get hard with age / heat.

Hi Guys, sorry, not been on for a while. I did get this resolved but have been moving house too so very little time. It turned out to be the Master Cylinder, I sispecetd it for a while and one or two people mentioned it but no-one really said categorically that's what it was, so I dithered a bit before making a decision that I was just going to change it. I am guessing there is a fair bit of protection built into them nowodays, so that you just don't get to a set of lghts and the pedal goes to the floor. Did the job, not completely problem free (that's another story) but got there in the end and that's about 2 months ago now and I am finally convinced all is Ok.Cheers for all your advice and assistance, much appreciated,Wallace.