I have a second hand 2004 model Skoda Superb. I recently noticed that after long trips and when the car temp is on the higher side braking is not very effective. Today after one such long trip around 150kms and a bit of traffic I noticed lesser brakes. I reached my office and had a friend in the car so had to leave the A/c running for about half an hour. On my return and while backing out the car I experienced total brake failure and had to stop the car using hand brakes. I noticed the ambient temp was at around 47 deg cel. Stopped the car and let it cool for about a hour took the car out for a test drive and I was able to stop the car without the help of the hand brakes though I had to press the pedal till the end.

Can any one help me out here is there any quick fix. Any idea as to why this is happening? Brake pads are as good as new and brake fluid is full. Any suggestions will be greatly appreciated.

The brake servo can corrode and fail to pull a vacuum. Worth looking for corrosion on it.

Thank you for your quick reply fred bloggs. Is the brake servo a Black round box with steel fixture atop looks like a pump? If that is the one then yes the paint has come off at one particular point just below the brake fluid container and there is some rust where the paint has peeled off.

It's possible that if the brake fluid hasn't been changed for a long time, then you may have boiled the brake fluid and a vapour lock has occurred. The brake fluid will absorb water moisture over time and this will lower the fluid boiling temperature. A quick boiling point check on the fluid can be made on the car to confirm that the brake fluid is O.K. Your garage should be able to do this.

47 deg C ambient temperature is very high and will cause high humidity when it cools down at night. This high night time humidity could adversly affect the brake fluid over time.

I couldn't cope with this high temp. - might make my blood boil ! (lol).

Edited 1 September, 201114 yr by vwcabriolet1971

Thank you vwcabriolet1971. Like mentioned in one of the earlier topic discussions elsewhere, I did the press brake pedal with engine switched off test it worked according to how it should, hard by the first few pumps and when I started the engine the pedal moved freely till the end(not exactly till the end). So I guess the servo is still in good condition.

Now back to vwcabriolet1971, I guess its been a long time since the brake fluid has been changed. In summers we get temp up to 55 deg cel. and it is summer now. My car had a few problems with the cooling and heating department. Had rectified all that and the car was working fine until this happened. Now during the initial period before I had rectified all the problems with the cooling & heating department the temp had risen to almost the red line a few times. Every time this occurred I would let the car cool off and then start again. The other day when I had total brake failure I checked the brake fluid compartment to see if there was fluid well!! yes it was almost brimming to the cap. I thought there might be a block at the filter like thingy and I used my finger to try and clear it. To my surprise the fluid almost burnt my finger and there was no block but a spring operated button(kinnda). So in short I guess your explanation can be the problem. So what do you think I should do. The dealer is bad so I never take the car to them, the mechanics here are funny they don't know stuff about Skoda. However, I found one guy but he is lazy to check out whats wrong. Took the car to him today, he just got into the car pressed the brake pedal a few times and said you have to change the servo pump. I asked him to check if there was enough brake fluid he said it was full. I told him I'll get back to him once I have sourced the brake servo.

Can I change the brake fluid myself. Is it a very difficult job or is it best I leave it to the mechanic. If it is a DIY job can you guide me through the process or some sorts. I greatly appreciate your valuable time, thank you again.

If you want to change the brake fluid yourself, I'd get a copy of the Haynes workshop manual 4279 for the Passat. You'll be able to get it online from Amazon if it's not sold where you are.

But surely there must be a VW workshop somewhere near you who can do this - for a mechanic it's a basic job.

cheers

Edited 2 September, 201114 yr by sidewaze samm

If you don't positively know that the brake fluid has been changed in the last 2 years, get that done first. I'd take it to a VAG garage, since they will know the correct bleeding procedure, and there are at least 2 "gotchas" in bleeding a VAG car with ABS, one of which requires VCDS to resolve, and the other of which breaks the master cylinder.

Perfect brakes at last!!!

Cheers to vwcabriolet1971, I followed your advise. Went to the mechanic told him to change the brake fluid. It was rather a simple job but requires two guys. One to replenish the fluid and remove the nut at the wheel and the other to pump the pedal. Guess what initially he told me to change the Pump but I insisted to change the fluid before replacing any thing. Like you said there was a vapour lock, according to the mechanic it was at the front left wheel side. Thank you once again and everyone that replied to my post.

If you don't positively know that the brake fluid has been changed in the last 2 years, get that done first. I'd take it to a VAG garage, since they will know the correct bleeding procedure, and there are at least 2 "gotchas" in bleeding a VAG car with ABS, one of which requires VCDS to resolve, and the other of which breaks the master cylinder.

Interestingly enough it doesn't break the master cylinder, I actually found out what happens this week whilst on a course.

The EDL system that is fitted to our cars with ABS uses a separate circuit and solenoid valve within the abs block. This solenoid shuts off at pressures over 1 bar and won't open, as pedal pressure is over one bar air stays in that section and gives a spongy pedal. This is why ABS bleeds must be carried out with a pressure bleeder with a pressure no greater than 1 bar.

If pressures over 1 bar are problematic, it is probably safest to use vacuum bleedd then rather than pressure bleed.

If you have oil extractor you can normally reuse this and suck brake fluid. I use this and an old Gunson pressure kit bottle to replenish reservoir. Works very well, and has additional advantage of reducing spills at the brake and clutch nipples.

Interestingly enough it doesn't break the master cylinder, I actually found out what happens this week whilst on a course.

The EDL system that is fitted to our cars with ABS uses a separate circuit and solenoid valve within the abs block. This solenoid shuts off at pressures over 1 bar and won't open, as pedal pressure is over one bar air stays in that section and gives a spongy pedal. This is why ABS bleeds must be carried out with a pressure bleeder with a pressure no greater than 1 bar.

Can this be overcome by following the VCDS bleed procedure to run the abs pump?

Interestingly enough it doesn't break the master cylinder, I actually found out what happens this week whilst on a course.

The EDL system that is fitted to our cars with ABS uses a separate circuit and solenoid valve within the abs block. This solenoid shuts off at pressures over 1 bar and won't open, as pedal pressure is over one bar air stays in that section and gives a spongy pedal. This is why ABS bleeds must be carried out with a pressure bleeder with a pressure no greater than 1 bar.

Always happy to learn from a master like yourself. I'd been told previously that the over-pressure/over-stroke applied could invert the master cylinder seals, and the only way out of that one was a new or re-built cylinder.

If pressures over 1 bar are problematic, it is probably safest to use vacuum bleedd then rather than pressure bleed.

If you have oil extractor you can normally reuse this and suck brake fluid. I use this and an old Gunson pressure kit bottle to replenish reservoir. Works very well, and has additional advantage of reducing spills at the brake and clutch nipples.

See above; you are aware that you're arguing with a VW Master Technician who actually merits and deserves the title "Master"?

From physics point of view, brake vacuum bleed is the same as pressure bleed, except you cannot exceed 1 bar pressure difference (of the atmosphere). That and lack of spillages are 2 reasons why it is safer than pressure bleed.

VW has procedure for vacuum bleeding the cars, check their own manuals (Elsa), especially Audi ones.

Also, I do not think you can cycle the "öld" ABS unit in Mk1 Superb via VCDS, only in newer Mk2.

Edited 6 September, 201114 yr by dieselV6