Brake fluid?

[veteran]

Once again, there is no vacuum created, either in the device or at any of the nipples. If there were vacuum created at the nipples, you'd get air being drawn into the system via those nipples. They are better described as positive pressure bleeders, positive inward pressure into the braking system, such that if you then undo a bleed nipple, the fluid will be automatically forced out. The positive pressure exerted by the device replaces your foot pressing the brake pedal. Hence, they are a one-person tool, or one that doesn't require you to keep returning to the brake pedal and pumping the brakes.

IMHO, they have a flaw in that, as I've pointed out, they initially trap a long column of air inside the outlet tube that runs between the tank and the car's reservoir, and that air, or at least some of it, gets forced into the car's system in due course, it breaking up into lots and lots of micro and sometimes bigger bubbles in the car's brakepipes. That's the very thing you're trying to avoid, it seems to me. It then takes an awful lot more bleeding to then get it all out of the system again. So although pressure bleeders are okay for a one-person job and they obviously get the job done of doing a complete fluid replacement, it's at the expense of probably ending up with more air in the car's system than you had to begin with, and therefore spongy brakes. But, as I pointed out earlier, with the right design of bleeder, you can avoid an awful lot of that column of air getting forced in by utilising the technique I described earlier. Potentially, you've then far less air to bleed out. Note that the Laser's metallic valve on the end of its outlet tubing is normally a stop-end, but when you mate it with the reservoir adaptor the stop-end stops and you get flow-through.

I had had quite high hopes for the Laser bleeder but my view now is that it's best to avoid pressured setups and instead to do the job the old-fashioned way, without all that gubbins. Often the old ways are the best ways. But each to his own, as they say.

You can often get a good result by just using a simple inline one-way valve at the nipple drawoff; they're sold all over Amazon and eBay these days for less than a tenner. I see that ciclo has bought one as a standby. With that simple one-way valve you can avoid a second person doing the pedal-pumping. Otherwise, just let the nipple output pass straight into a jar, with the end of the drawoff tubing kept below some fluid in the jar, so that no air can get sucked back in. A word or two on those inline valves, however: the one I've got in my arsenal is one I bought and used many years ago and is well made. There are now many copies sold but of poorer quality. Often now, they don't seal too well in the backward direction and sometimes you can't actually take the valve apart to inspect/clean it. Mine hasn't that problem. The inline valve consists of a lightweight aluminium tube with a spring and a light ball bearing inside, the latter fitting on to a shaped seating.

[wolfie]

Once again, there is no vacuum created, either in the device or at any of the nipples. If there were vacuum created at the nipples, you'd get air being drawn into the system via those nipples. They are better described as positive pressure bleeders, positive inward pressure into the braking system, such that if you then undo a bleed nipple, the fluid will be automatically forced out. The positive pressure exerted by the device replaces your foot pressing the brake pedal. Hence, they are a one-person tool, or one that doesn't require you to keep returning to the brake pedal and pumping the brakes.

Sorry but you are not correct, unless you are limiting your explanation to only "positive pressure bleeding" The small hand vacuum pumps and the larger pneumatic garage type bleeders operate by creating a vacuum. In effect it's no different than applying pressure to the reservoir side, which is what happens with the positive pressure bleeders.

At the nipple, there is simply a pressure differential. With the vacuum pressure bleeders it is not unknown to see air bubbles exit the system via the beed lines. That is as you say, air sneaking in past the bleed nipples. But as there is a vacuum on the other side of the nipple any air is pushed towards there and not into the braking system. The braking system sees 14.7psi at the reservoir, with respect to the bleed nipple so fluid is in effect pushed in towards the bleed nipple by atmospheric pressure. The vacuum is generated outside in the brake bleeder, you simply attach it to the nipple as normal. In some explanations people advise smearing the base of the bleed nipples to stop air sneaking in. Either method is described as pressure bleeding.

Not the most detailed explanation, but it illustrates how it works. (I'll see if I can find a more detailed video)

[veteran]

I am correct in describing the Laser 5642 and its smaller brother as a positive pressure bleeder. It's positive in the sense that fluid is driven through and out of the car's system from positive pressure applied by the device at the car's reservoir. I took the trouble to discuss the matter and confirm a few things with LaserTools themselves before I made the purchase. You may well have come across another system that instead sucks the fluid out of each nipple in turn at the far end by creating a negative pressure (a 'vacuum' if you like) at the nipple output, but that isn't what I've been describing. I reckon you're confusing two types that are on the market. Anyway, you'll have to make your own decision as to which bleeder and technique to use when you get around to actually doing the job. Let us all know how it works out. I am still of the view that the old-fashioned technique(s) are better and less troublesome in the end.

BTW, the reason for various manufacturers advising putting grease, eg. copper grease, around the threads of the nipple is to help prevent the nipple seizing in place over time and then the nipple possibly sheering when you undo it at the next bleeding time. If the presence of some such grease on the threads happens to prevent a little air from entering the system and going back up the nipple as it were, then that's just coincidental, I think. But with a positive pressure bleeder in use, the pressure at the nipple outlet will be just on the positive side still (until the moment you undo the nipple) and, in theory, should prevent outside air from getting in. I always find it tricky to gauge by how much to loosen the nipple. You have to unscrew it enough to get it off its internal seating so that fluid can flow easily out, but if you undo it that little bit too much, air can creep in down the threads so to speak. I guess you're familiar with that annoyance of old? The outward stream of fluid will tend to sweep it out again, though.

[wolfie]

I think you just missed earlier discussions in the thread and limited your view to only the positive pressure device you have first hand experience with, not the wider subject. There are indeed many alternatives on the market in all shapes and sizes. Some cheap, flimsy and not worth the effort, to those that are too costly for most DIY/weekender pockets. Personally, mainly due to my budget I was either considering the tried and trusted Gunson-Eezibeed or possibly a MityVac 8000- hand pumped version. But having read RUM4MO's comment on issues he had using one, and your comments on the reservoir not being filled to the brim at the end of the process. I probably lean towards a £20 Eezibleed. For myself it would only come out of the box every couple of years, so spending much more is unnecessary for my needs. Also every man and his dog sells them.

From what I've used and read, the key to getting these bleeders to work effectively is ensuring that they are leak free and hold pressure for the duration of their use.

[ciclo]

Here's a YouTube Video. It's using a pressure bleeder like yours, on a Golf. It's a basic fluid swap with no additional information regarding energising the ABS pump. I've not yet looked for the correct method via ErWin, etc.

https://www.youtube.com/watch?v=EkmKGptc4rM

Very instructive without a doubt.

Having now used a Laser 5642, I'd say that a key piece of advice that's lacking from the instructions is that you need to prevent the initial air column in the exit tubing from being pushed into the car's system as you proceed. Otherwise a lot of it you'll have to bleed out, along with the old fluid, and that could potentially take a long time and a lot of new fluid! In order to limit the amount of air that's initially trapped in the tubing what you need to do before starting the pump-up proper is to fit the adaptor on to the metallic valve and then hold it over the reservoir's opening as you gently work the pump, in order to expel that air and replace it almost fully with the fluid. Then at the last moment you screw the adaptor, with valve still attached, on to the reservoir. It's possible to do that because the valve-to-adaptor connection is rotatable whilst remaining airtight. Well, at least that's the case with the Laser 5642. This technique should ensure that the minimum of air gets pushed into the system.

Thanks for the advice based on your experience (tool), the guy in the video that I am not able to find now did this step such you describe it.

You can often get a good result by just using a simple inline one-way valve at the nipple drawoff; they're sold all over Amazon and eBay these days for less than a tenner. I see that ciclo has bought one as a standby.

Exactly, I bought a one-way valve to have a plan B in case something goes wrong with the bleeding pump method, and what better way than to return to traditional methods.

[ciclo]

According to ElsaWin the brake fluid change order for 6R is the same as indicated in the video for Golf GTI.
1- Front left
2- Front right
3- Rear left
4- Rear right
5- Clutch

For bleeding it is different:
1- Front left (wrong, see correction below)
2- Rear left (wrong, see correction below)
3- Front right
4- Rear right
5- Clutch

---
Correction:
erWin POLO 6R


Notes:
- for brake fluid change order for 6R it's OK.
- erWin does not specify differences between RHD and LHD in the order for 6R. (in other vehicles it is specified)

[veteran]

Yeh, now that's something that's been puzzling me a bit, ciclo. I'm sure I've seen before, elsewhere in these forums, different sequences suggested, depending on whether it's a change or a bleed. But can't think why it should need to be any different.

Before doing my change the other day, I read some VW official workshop instructions I have, and the order in which it recommended opening the nipples and 'doing the business' was:

Front Right
Front Left
Rear Right
Rear Left.

So, near to what your ElsaWin sequence recommends. The above was, however, for when VW workshops use their own specialised bit of kit for doing a change.

My gut feeling is that, when doing a bleed of any sort on the Polo brakes it's best to start with the rear nipples and finish with the front ones. I think that's what I'll do if I have cause to tweak the lines between now and the next change. I think I'd then drag less of the old contaminated fluid all the way to the fronts. But then you'll be bleeding the fronts next anyway - so does it really matter the order in which you do it? Seems to me it's 'six of one, half-a-dozen of the other'.

[Dink]

Does bleeding/changing fluid change with what side the steering wheel is on. I know that certain gti parts only fit RHD cars due to master cylinder being in the way on LHD cars.

Just a thought that it might go from closest to furthest from master cylinder?

[RUM4MO]

Does bleeding/changing fluid change with what side the steering wheel is on. I know that certain gti parts only fit RHD cars due to master cylinder being in the way on LHD cars.

Just a thought that it might go from closest to furthest from master cylinder?

Yes Dink, that is what most people aim for either closest to furthest or in my and some other's way of doing this job, furthest to nearest - the master cylinder now almost always moves to be on the side of the steering wheel, crazy cheap ways used in the past by car makers like VW Group, used relay shafts and linkage which could be problematic by increasing braking pedal effort required of having the relay shaft under the carpet on the passenger side leading to a passenger being able to press down on the carpet and restrict the free movement of the shaft - not, I think in the case of VW Group cars but maybe on some Citroens!

[RUM4MO]

I like the mention of a turkey baster in that video, I also use a turkey baster for quickly removing as much of the previous fluid as possible.

[veteran]

Dink wrote: Just a thought that it might go from closest to furthest from master cylinder?

If that's the case, then so far I've been doing it correctly. But was Dink talking about bleeding, or changing?

[Dink]

Well both.

If someone is describing a technique for a LHD then right and left would be swapped for RHD car.

[ciclo]

Please read correction if you are interested. viewtopic.php?f=56&t=73523&p=559421#p559389

[RUM4MO]

I think that a bit of over thinking is going on here, VW Group will write these official workshop manuals in a way that either fits in with their already established procedures, ie "copy and paste" and/or in a way that minimises labour time to keep productivity up in workshops, and costs down to owners.

[ciclo]

Even it's written in the document/manual itself in each page:
... 'Volkswagen AG does not guarantee or accept any liability with respect to the correctness of information in this document'...

However, 99.95% of the times are corrects...