As the title says. Would seem like there's air in the system but would like to know what I can do to check and so forth. The brake pedal is soft, and requires what I feel is an excessive amount of travel compared with what it used to be like.

 

Thanks.

With the engine off and handbrake on, if you push the pedal then a couple of times is it hard high up at the top with no creep ?

Then start the engine, is that when it sinks too low ?

@AnnoyingPentium - I see where @aubrey is coming from.

It'll go hard after a couple of presses when the engine is off since there's no servo assistance. Goes back to the way I've described when driving about. No reaction from the brakes when pedal is pressed a little, then after a little travel they begin to do what they're meant to. If that helps.

 

Still got a reasonable amount of braking performance when I stamp on the pedal, as I tested today on a quiet stretch of roads.

But is it hard high up ?  As if so it would be similar to what my Roomster did when I got air in the ABS Unit. I had to bleed the ABS using VCDS, normal bleeding won't do it and I didn't find a garage that could do that. They all thought I was talking nonsense when I was asking not for a standard brake bleed but it had to be done using the OBD port and a diagnostic machine to bleed the ABS. So I had to do it myself. Immediately after that procedure the brake pedal was back to normal again. Back to the brake pedal activating the brakes high up when driving.

I know I got air in the ABS due to my carelessness on a standard brake bleed, I let the reservoir run dry. Is there any chance air could of got in your ABS unit ?

7 minutes ago, aubrey said:

But is it hard high up ? 

 

I don't completely understand this. If what you mean is that it's soft for the beginning but gets harder after the excess travel?

 

8 minutes ago, aubrey said:

Is there any chance air could of got in your ABS unit ?

 

Erm possibly, if there's an air leak somewhere then perhaps. Otherwise could have been a result of when the rear cylinders were done by the garage. The brakes were very effective after that though.

Hard high up, I mean with the engine off, after a couple of presses, possibly just one press the brake pedal is hard high up. The pedal does not go down much when pressed. And if even pressed hard does not creep down, proving no leaks.

But as soon as the engine is started the pedal drops down a fair way, so from then on the brakes activate a fair way down the pedal. My pedal dropped down over half way to the floor.

That is what I had when I had air in the ABS, as said as soon as I did the ABS bleed procedure. The pedal then just dropped a little when the engine was started and the biting point of the brakes, if that's a valid term, remained at the correct much higher up the pedal location.

If you do do the VCDS ABS Bleed procedure I would recommend you do it with a mate. I did it alone and that made it more tricky with the running back and forth opening and closing both front nipples, then both rear. Having someone do the outside nipple work with another inside working the laptop would be better.

2 minutes ago, aubrey said:

Hard high up, I mean with the engine off, after a couple of presses

 

Aye it's hard high up in that case.

 

3 minutes ago, aubrey said:

But as soon as the engine is started the pedal drops down a fair way, so from then on the brakes activate a fair way down the pedal. My pedal dropped down over half way to the floor.

 

That is what I had when I had air in the ABS, as said as soon as I did the ABS bleed procedure. The pedal then just dropped a little when the engine was started and the biting point of the brakes, if that's a valid term, remained at the correct much higher up the pedal location.

If you do do the VCDS ABS Bleed procedure I would recommend you do it with a mate. I did it alone and that made it more tricky with the running back and forth opening and closing both front nipples, then both rear. Having someone do the outside nipple work with another inside working the laptop would be better.

 

I'll check that tomorrow and then probably leave the bleeding to a garage as I cannot be arsed, frankly.

16 minutes ago, aubrey said:

Hard high up, I mean with the engine off, after a couple of presses, possibly just one press the brake pedal is hard high up. The pedal does not go down much when pressed. And if even pressed hard does not creep down, proving no leaks.

And that proves nothing else but no leaks. The brakes go hard and short travel because you've blown the vacuum out of the servo unit,

16 minutes ago, AnnoyingPentium said:

Then probably leave the bleeding to a garage as I cannot be arsed, frankly.

Remember a normal brake bleed won't do it. To bleed the ABS you have to activate the ABS valves using the diagnostic port. So ensure any garage you ask knows what you are talking about and does that.

I can't remember 100% how I kicked the procedure off now, something like open the ABS Controller, Group 10 and click Go. I had a pressure bleeder attached while doing the VCDS process.

40 minutes ago, KenONeill said:

And that proves nothing else but no leaks. The brakes go hard and short travel because you've blown the vacuum out of the servo unit,

Exactly, yes.    I asked that to rule that out. As I did write exactly about no leaks earlier. It is the combination of all the tests I described. You need to prove the basics first. It also proves/tests for air in the normal brake lines, as air there would cause a lower spongy pedal even with the engine off 

The servo helps but it the activation of the abs when all the power is on, ie engine started I was interested in. 

The pedal will drop a bit when the engine is started. That I believe proves the servo but it doesn't drop a lot. This dropping a lot is when air gets in the abs.

Edited 29 May, 20224 yr by aubrey
Added last bit

Good news... or at least I hope it is. Preliminary tests after doing some heavy braking from 60 to 0 on some quiet roads would suggest the brakes still stop fine.

 

Secondly, I tried pushing the pedal as far as it'll go a few times then yanking the handbrake a couple of times. Seems to have improved overall braking feel and the handbrake holds better as far as I can tell.

 

Think I've had a sticking caliper too as one side was a bit warmer than the other at the front and covered in brake dust compared to the other side which was a bit cleaner. Indicated MPG has went up too.

 

Make of that what yous will.

3 hours ago, AnnoyingPentium said:

I tried pushing the pedal as far as it'll go a few times then yanking the handbrake a couple of times.

Yep; fast, easy and cheap way to adjust the rear brakes.

5 minutes ago, KenONeill said:

Yep; fast, easy and cheap way to adjust the rear brakes.

 

I believe it was you that posted it on another thread I had seen. It seems to have worked but I've not been back out with the car yet.

3 minutes ago, AnnoyingPentium said:

I believe it was you that posted it on another thread I had seen.

I've posted it multiple times yes, and use it myself.

I think I have the same fault with our Mk 4 Golf in that the initial biting point on the brake pedal is lower than before. 
Maybe 6 years ago I had the rear callipers replaced at a local place and the pedal bite came back lower. 
I took it to VW for a brake bleed and it came back perfect. I will have described the low pedal to them on booking in. 
 

last year I had to change one of the rear callipers again due to handbrake problems and I know air did get into the system so I sent it to VW for a bleed but did not mention the low pedal and so it came back the same. I was baffled but this thread is making sense. I’m going to VW to ask them about this again this morning for a VCDS bleed rather than the ordinary bleed just to refresh the fluid every two years and see what they say. 

2 hours ago, prt57 said:

VCDS bleed

As part of a fluid change? If so, then the VCDS bleed is the only way to guarantee you change the fluid in the ABS valve block.

59 minutes ago, KenONeill said:

As part of a fluid change? If so, then the VCDS bleed is the only way to guarantee you change the fluid in the ABS valve block.

Yes, I suppose so. What I think I’m understanding from this is that the fluid in the ABS is not flushed out as part of a normal fluid flush and it needs VCDS to open valves in the unit. 
 

On a similar theme, the fluid leading to the clutch slave cylinder is not flushed out either unless you ask as part of the brake flush. 
last year I had the clutch changed in my Fabia and I watched as the fluid was flushed through to the bleeder block and it came out a very dark brown. Probably never been done in the previous 16 years. 

6 hours ago, prt57 said:

I’m going to VW to ask them about this again this morning for a VCDS bleed

VW would use their proprietary ODIS system. Not all ABS Units need OBD bleeding. Your Golf by age probably does though.

As long as they do the ABS Bleed Procedure then that's it. Something that is always done on ABS Unit replacement, as a new unit would always be dry on installation.

The problem is in your head, not the ABS block, if there's no trapped air in the system then you don't need to bleed it, once you have a solid pedal with new fluid then it's job done.

Air can't get into the ABS block unless you allow the reservoir to run dry during bleeding.

So it's nonsense and there's nothing to worry about. 

1 minute ago, sepulchrave said:

Air can't get into the ABS block unless you allow the reservoir to run dry during bleeding.

That's exactly what I did. I was doing a normal brake bleed and while going round the wheels the pressure bleeder fell over, and its tube came out of the fluid. The first I knew was air being forced out a rear brake nipple and not fluid. So I'd managed to push air the whole way through.

I agree to get air in the ABS you would of had to done something similar.

I'd be surprised if just changing a wheel caliper would do that unless you let the brake system gravity drip a long time and empty itself.

I normally put a piece of cling film over the reservoir and screw the lid back on to create a vacuum lock to stop dripping when I'm changing flexible hoses/calipers etc.

But totally agree you would of had to of done something to get air in the ABS, as it's not an easy thing to do.

Despite all the internet shrieking I use and have always used an ancient round bar clamp designed specifically for hydraulic hoses, this prevents any loss of fluid or ingress of air while removing calipers etc.

 

As for changing the minute amount of fluid trapped in the ABS block, who cares, if you've changed 99.5% of the brake fluid then that's plenty good enough, rather like engine oil you'll never get the whole lot anyway.

1 hour ago, sepulchrave said:

Despite all the internet shrieking I use and have always used an ancient round bar clamp designed specifically for hydraulic hoses, this prevents any loss of fluid or ingress of air while removing calipers etc.

I still have the all stainless steel one (including the pivot hand rivets) that I made as an apprentice, it is always carried in the car and has got me out of trouble many times to isolate one wheel when a brake cylinder has failed usually when collecting a new acquisition.

 

In hindsight I should never have stamped my name on it just in case one day the worse happens!

4 hours ago, sepulchrave said:

Despite all the internet shrieking I use and have always used an ancient round bar clamp designed specifically for hydraulic hoses, this prevents any loss of fluid or ingress of air while removing calipers etc.

 

As for changing the minute amount of fluid trapped in the ABS block, who cares, if you've changed 99.5% of the brake fluid then that's plenty good enough, rather like engine oil you'll never get the whole lot anyway.

I use the hose compressor but on my Golf the flexible hoses at the back of the car had aluminium internal strengthening tubes so the hose compressor I used would not stop the fluid escaping and then dented the internal aluminium piping as well so needing the rear brake line to be replaced so lots of time to lose fluid. 

1 minute ago, prt57 said:

I use the hose compressor but on my Golf the flexible hoses at the back of the car had aluminium internal strengthening tubes so the hose compressor I used would not stop the fluid escaping and then dented the internal aluminium piping as well so needing the rear brake line to be replaced so lots of time to lose fluid. 

 

How can it be flexible if it has a solid core, it doesn't make any sense.

Flexible hydraulic hoses have a braided core that can be steel or nylon depending on the pressure rating, I've never heard of alloy braiding though.