Soft pedal after brake change

[a22nec]

Hey, I just changed the front brakes, discs and pads, and bled the entire system with a pressure bleeder.

I took 200ml of each brake and the only side that there was air and quite a lot for some reason, was the right rear.

As soon I turned on the engine I felt the brake pedal soft and sinking more than normal leading to the feeling that it's not going to stop.

I've read that the brake pads and discs take an amount of bedding in to come to it's full performance but something is wrong.

Just a few weeks ago I changed the brakes on another car (smaller ones also) and the situation is the opposite, light touch of the pedal and the car stops immediately far too aggressive to my liking.

What could be causing this? Air in the system? It was my first time using a pressure bleeder, I pumped to 1 bar so nothing crazy, the fluid reservoir was completely filled that it start spilling as soon as I removed the cap so I guess there was no chance of it pulling air on the lines ?

Any clue ?

Thanks.

 

[RUM4MO]

The recommendation from VW Group is to remove 200ml from each front wheel brake and 300ml from each rear brake.

What I tend to do is after removing as much old fluid from the reservoir as I can with the sieve/strainer in place and refilling with fresh new fluid, is, starting at the rear wheels, from the longest pipe run remove maybe as much as 450ml the idea being to end up with nothing but new fluid in the reservoir and that first long pipe, then remove 300ml from the other rear wheel, and 200ml from each front wheel - as you can see the total fluid volume removed is more than 1.0ltr, which might be annoying.

Other than repeating the fluid change while making sure that the pressure bleeder tank never runs out of fluid, maybe you need to be patient and allow the new friction materials and discs "bed in" - though doing that will depend on just how "bad" you think the brakes now are. What type of brakes are on the rear and have you taken them apart to clean them up while replacing the front brakes, if so, then if you have drum brakes at the rear, you might need to force them to adjust to their "best" settings - does the handbrake lever move as much or the same as it did before you took the rear brakes apart, if indeed you did work on the rear brakes.

Edit:- using a pressure bleeder set to 1.0Bar is normally a very safe and efficient way to change brake fluid, and provides very little chance of introducing air into the systems.
I'm not trying to be insulting, but you are closing the bleed valves before removing the pressure and/or the pipe from the bleed valve you are working on/at.

 

[a22nec]

The manual for the Ibiza says 250ml for each side and 100ml for the clutch but since I had only 1 liter, I did 200ml on all 4 sides, 100ml for the clutch and left 100ml on the pressure bleeder as a precaution to not suck up air. In the end I didn't bleed the clutch as I couldn't bother to take the air filter and battery. lol

This is the sequence I followed.

Rear right, Rear left, front right, front left.

The brakes on the rear are ferodo eco friction, I did remove them, cleaned and reapplied copper grease where the pad ears slide on the brake carrier. Handbrake feels the same.

I used 1bar because in the manual it says that above 1 bar there's a switch valve for the esp that closes and does not let a more thorough bleed.

about the bleeding I'm closing the bleed nipple first then remove the pipe/tubing while there's still pressure on the bleeder.

 

[RUM4MO]

So you have done everything correctly, with the VW Polo 2015 and Audi S4 2011 I have official workshop manuals for they both quote "300ml for rears" and "200 for fronts" but I'd think that the volume your manual said should be okay for Ibiza/Polo/Fabia. I'm a bit lazy and tend to ignore the clutch fluid.

 

[a22nec]

Can you show me a print or something ? I've looked for the polo and don't find the quantities.

For the Ibiza 6j i got this from etka.

Table of work sequence and brake fluid quantities
N01-10692
Work sequence: Brake fluid quantity which must flow out of wheel cylinders or brake callipers:
Slave cylinder 0.1 litres
Rear right 0.25 litres
Rear left 0.25 litres
front right 0.25 litres
front left 0.25 litres

 

[RUM4MO]

This is what I have, it was found on a VW Group motoring forum and I'm sure that the copies of the official workshop manuals use the same information:-

Both you and I and I'd think most other people, start at the rear of the car, maybe VW Group wrote it this way to make the task slightly quicker - ie time is money! Plus the above information will be for LHD cars, like you have.

Edit:- I don't think that the quantity of brake fluid you removed has any effect on how these brakes now seem to feel.

 

[a22nec]

Interesting, I would have thought the polo was exactly the same as the Ibiza.

I wish I tried the brakes before bleeding that way I would have known if it was my mistake.
I guess I will have to buy another liter of dot 4 and bleed again.

If anyone has experience with this pressure bleeders, is there a trick to take the cap off from the reservoir without making a mess ? Even without pressure it's completely overfilled and as soon as I start unscrewing it, the fluid starts coming out and dripping to the engine bay.

 

[RUM4MO]

I have always started using the pressure bleeder by removing as much of the old fluid first and refilling to near the top with fresh fluid, then connect the pressure bleeder's filled bottle to the reservoir, then apply the pressure source.
As the level in the pressure bleeder bottle drops down to be quite low, I remove the pressure source and refill the bleeder bottle. At the end of the bleeding process, you need to plan to have emptied the bleeder bottle and so that means while working on the last wheel's brakes, you end up removing fluid from the reservoir - as the bleeder bottle has been emptied of fluid. If you have done that so that the level in the reservoir is down to below the MAX level, then when you remove the pressure source the level should still be below the MAX level, so very little fluid gets spilt when you remove the bleeder.

Edit:- on the subject that Ibiza = Polo well as far as maintenance is concerned, not always, the individual VW Group car marques do seem, at times to write up their own methods, where that shocked me was when I used my VW Polo workshop manual as a torque reference when working on the age Ibiza front suspension. At some points, where one marque gives a single torque figure, the other can end up giving a much lower torque figure and an additional angular turning angle - and both cars use the same parts!

I ended up roughly in the same situation as you and wished that I had made sure what the brakes felt like before cleaning up the brakes and changing the fluid, it was on my 2011 Audi S4 and it has an electric handbrake, I think that I had forgotten to reset the electric handbrake correctly - anyway, I reversed that car out of my garage before checking the brakes and when I pressed the footbrake there was just too much travel and the pedal was not as firm as it should have been, the electric handbrake saved me though! I re-ran the electric handbrake resetting procedure and went for drive, the brakes improved again, but once you have experienced that, you really do question if everything is okay. Put it this way, that has never ever happened to me in the past even with that car, so when I cleaned up the brakes and replaced the fluid on my older daughter's 2019 Leon Cupra, I made sure that I knew what the brake travel and pedal feel was BEFORE starting work on its brakes and made sure I pressed the brake pedal after refitting the brake parts on each wheel, ie so that the pistons/pads were out to their normal positions.

Actually, I used my Gunsons pressure bleeder as I always have done over the years, when changing the fluid on my 2011 Audi S4, but because I ended up getting annoyed by the air and fluid leaks on that, a new kit of parts, the next car I replaced the fluid on was my wife's 2015 VW Polo and by that time I had bought a vacuum bleeder that has an auto top-up bottle, and again when I replaced the fluid on this 2019 Leon Cupra, I also used that vacuum bleeder, the only reason being, I has annoyed with the pressurised fluid spills considered that there was no air in these systems, so was happy enough to use this simple vacuum bleeder although even when trying to stop them sucking air in via the bleed valve threads you usually fil slightly so see small air bubbles in the pipe that draws out the old fluid.

 

[a22nec]

I didn't remove old fluid first but the fluid level was visible on top of that filter (brownish color not black), I connected the pressure bleeder and pumped until 1 bar. I've already thought that I should have primed the pressure bleeder hose before to reduce the air inside the reservoir but since the air goes always to the top due to gravity I don't think it could push it into the brake lines.

I've always bleed the brakes although not many times by 2 person method or 1 person and the pedal always felt the same, note that it's the first time swapping the front brakes (up until now I've only swapped the rears), this time I used the pressure bleeder as I've seen it's the best method and this issue happens. I question myself if it's really the bleeding or it's the brake pads and discs combo.

I've researched extensively before and didn't find any complaints but maybe I'm the lucky one as usual.

I used TRW Dtec pads (ceramic low dust) with drilled discs,
This brake pads supposedly have a special coating that reduces the need for bedding in and better than normal initial braking performance but I'm not feeling confidence with this brakes at all.
There's also like 5mm at the inner and outer edge of the disc not being used although I can see the brake pad on top of it.

 

[RUM4MO]

The way the standard selection of brake parts gets chosen by car manufacturers does seem to end up meaning that the inner and outer areas of the disc do not get used (Edited) on some cars, or when using some aftermarket brake parts.

The air space in the top of the brake reservoir and any other air initially in the brake fluid supply will get reduced by the incoming fluid compressing it - then new fluid will come into the top of the reservoir and so just add to make fluid is already in there, so I don't think that there is any need to be able to "remove" any air before opening the brake bleed valves, ie as long as the top-up bottle keeps adding in enough new fluid to the reservoir, then none of that air will end up going into the fluid system, though I'd also like to be able to release all the trapped air as well - but I can't while using the usual DIYer pressure bleeder kits, but that is okay.

 

[a22nec]

The way the standard selection of brake parts gets chosen by car manufacturers does seem to end up meaning that the inner and outer areas of the disc do not get used (Edited) on some cars, or when using some aftermarket brake parts.

The air space in the top of the brake reservoir and any other air initially in the brake fluid supply will get reduced by the incoming fluid compressing it - then new fluid will come into the top of the reservoir and so just add to make fluid is already in there, so I don't think that there is any need to be able to "remove" any air before opening the brake bleed valves, ie as long as the top-up bottle keeps adding in enough new fluid to the reservoir, then none of that air will end up going into the fluid system, though I'd also like to be able to release all the trapped air as well - but I can't while using the usual DIYer pressure bleeder kits, but that is okay.

Yes but I compared and measured both brake pads and they are the same so they should use the same area of the disc. As I said before the brake pad is on top of the area that is not being used, it just doesn't touch yet maybe in the next kilometres it will hopefully.

I drove it today and it is a bit better but I still need to press more to get the same amount of braking.


Right side

Left side

 

[RUM4MO]

You can see from the profile of the previous disc, that the previous pads and calliper position, matched the disc intended swept area well enough, maybe there is a slight taper on the inner and outer edges of your new pads, and that things will improve once these pads have worn down/in a bit more.

The difference or loss of "width" of the swept area is not "huge", but like you, I'd expect that the correct replacement discs and pads would end up with the same swept disc area.

 

[a22nec]

Yes it is not huge but it looks ugly and it will look even worse when further down the line the disc starts wearing to the point of showing a lip.

The caliper pins are not the problem because I lubed them with silicone grease and they moved really really easy compared to before.

 

[RUM4MO]

I always service the brakes every 12 months or at worst every 24 months, to avoid anything seizing up.