Excessive brake pedal travel

[Chris]

Wish I'd bought a vacuum bleeder 20 years ago. It is without doubt the easiest brake bleeding method I have every used. I'd have saved hours and litres of fluid too. I think that where it scores is that air is easier to suck out than fluid. Science fact, I believe. And therefore it pulls very little fluid though at all to get rid of the air. It also means I don't have to drag the Missus out onto the drive in her curlers and shout 'Up - are you up?' And 'down, is it down?' And 'right pump it hard for me and see how it feels?'

 

[Bat21]

Wish I'd bought a vacuum bleeder 20 years ago....

I bought one of those last year..... a pile of pants it is too. It seemed to prefer to 'suck' air in around the bleed nipple once slackened off rather than pull it out of the caliper.

This new pressure one I have is much easier and efficient.

Everyone has their favourite method I guess.

 

[Towpack]

I know zero about motorbikes...well except that as a passenger on a Hyabusa (is that spelt right?) I nearly needed new underpants after a 'quick run a around the block'!!

And yes the ABS sensors are used to detect wheel slip when the brake pedal is not being pressed, I mentioned the Land Rover TD5 recently and the system is ABS brakes and TC. I have a fair amount of experience with these systems and the pressure bleeder will not work. and neither does the manual pedal push method. The TD5 TC use is quite crude in this application, the amount of revolutions the spinning wheel has to reach before the brakes are applied is quite high, this results in quite a 'lurchy' progress across poor surfaces. The later versions have a more gentle application of wheel braking which results in the valves not being subjected to such high and sudden pressures.

The brake callipers use laptop/software to be bled, kneel by wheel spanner in hand, press button on laptop and open the nipple, software decides when the brakes are bled, it is only when you have bled the ABS module with a laptop from the TD5 drivers seat, retracted brake pistons on Audi's with a computer to get the pads in, how accurate your 'very old design' comment is.

regards

Dave

The modern systems may perform better but a laptop to bleed the brakes! WTF! Now I've heard it all. Definitely a big plus for the older systems and the DIY mechanic. My road bike also has TC but it's quite complex and was regarded as an industry leading, innovative system when it was launched in 2012. Not only detects wheelspin reactively but can also predict potential wheelspin before it happens. Don't ask me how, it's all controlled by a little black box. I digress.

 

[Towpack]

I bought one of those last year..... a pile of pants it is too. It seemed to prefer to 'suck' air in around the bleed nipple once slackened off rather than pull it out of the caliper.

This new pressure one I have is much easier and efficient.

Everyone has their favourites method I guess.

That looks similar to the Gunsons Easibleed setup but better IMO as it holds more fluid and you don't need a separate air source for pressure. Interesting to note that is says it uses a pressure range suitable for use with ABS.

 

[IRLGW]

This is the best bleedin brake system I have seen to date

 

[Dave2000]

Vacuum/pressure/laptop/foot, the problem with all of them is that none are any longer truly universal and different vehicles need different approaches, also people get different results depending on products used.

The vac system can draw in air around the nipple threads but is a 'cleaner' method than the pressure system, but then you have to top the fluid reservoir whereas the pressure system needs no topping, and you could do a full fluid change in 10 mins without thinking about topping the reservoir. The foot system needs two people although I have used a jack handle to hold the pedal down and gone back and forth and of course computers for replacing pads/bleeding and so forth.

Many of the later systems simply will not bleed up in the normal way god knows I have tried, I have one client who had a mechanic replace pretty much his entire braking system in an effort to get a decent pedal, all to no avail. He too had never heard of a computer to do the job. The answer is to get out the 'lappy', less than 10 minutes later and he nearly put his missus through the screen when he first used the brakes after being bled 'electronically'. Crazy electronics in cars nowadays, they have introduced more problems than the manufacturers claim the alleviate. They do have their place but when they go wrong, get out your cheque book!

regards

Dave

 

[Chris]

It matters not if the vac system draws air in around the nipple as long as it suck it out of the brakes. You don't need to stop and top up because it pulls so little fluid out. I drained the entire system on mine. Totally, bone dry. I filled up the res, opened the nipples until I saw a bit of fluid weeping out (remember I don't have ABS), topped up again and bled the system in a oner and it didn't even need topping up again.

I borrowed a pressure bleeder that strapped onto the MC and it was the biggest ****** @@@@ of a device it's eve been my misfortune to ever bugger about with. Pop round with your truck and I'll bleed your brakes before the kettle's had time to boil. It LOOKS like its pulling in air only because it pulls so little fluid out. For me it's up there with some of the best bits of kit in my armoury. The simple proof is in the brakes after going round only once.

This isn't a question about favourite ways, it's about what actually works. If it hasn't worked for some of you I am surprised. But from drained to fully bled in minutes with only one person, no top up and only a tablespoon of fluid pulled out, I can't better it.

 

[frank rabbets]

" Bone dry" might be the clue here Chris. If you have partial fluid and air pockets you need to draw fluid through followed by the air pockets. Just seeing the fluid appear might not be enough. I have just drained my system to strip the callipers and just had to go round once before I had a hard pedal. Then once more to double check and no air came out.

TP you took the strokes off my keypad. WTF laptop for brakes.

 

[IRLGW]

Dudes I have a really simple system where I get a piece of clear medical tubing and squeeze it really tight over the nipple and ring spanner, then wedge the end of it somewhere high up. I then lightly pump the pedal until the fluid starts to rise and you can see any bubbles escaping. It is also good because you can see when the fluid becomes clear. any recoil in the system will only draws the head of fluid back in.

The internal Diameter is probably only about 2mm so even if you fill a few inches it wont empty the reservoir. I usually just crack the the minimum amount to let the fluid out which is usually only half a turn. You do need a small container handy to catch the fluid thats in the tube when you remove it but you can usually squeeze it together enough to keep the fluid in until its removed. I have really good brakes on my truck using just this method.

If your brakes are still spongy after even normal bleeding with the traditional method then it more likely to be stick calipers. I have pumped the pedal to the floor in the past and have suffered the inverted rubbers sydnrome on my Accord once but it sorted itself after about a week.

Having said this, I think the design of the pipework has a lot to be responsible for and I would think the pressure filling or vacuum filling might be a better way to go in some cases. The clutch pipe on a defender runs up to the top of the bulkhead, across for about 300mm before dropping down and so is higher than the pedal box. If the system gets drained when the slave is disconnected to change a clutch say air gets trapped up there. It is still possible for fluie to get through along the channel but the air remains so it is not possible to bleed the traditional way (although it will eventually move the air over a period of time) I had to use a pressure bleeder in that case.

here is an interesting system....https://www.carthrottle.com/post/this-simple-vacuum-brake-could-be-the-future-of-making-cars-stop/

 

[Dave2000]

Chris, IMO the air does not travel ‘through’ the fluid, regardless of the method whether push or pull the fluid must move to bring the air with it, the result is the amount of fluid used to move a bubble would be the same, a good shove on the pedal would IMO move the bubble along the tubing and eventually out of the system.
　
Re IRLGWs comment about air being trapped in a pipe reflects my experience, I think if the air is sitting at the top of a loop (air rising in fluid) then it is entirely possible that the fluid will drawn or pushed slowly ‘under’ the bubble, I have seen this using the gravity method on clutches. It would have to be a very small bubble or a collection of the same for this to happen, I would also guess this is why some people bleed the brakes and still have a poor pedal, leave it over night and the small bubbles merge into one large bubble, they bleed again and the brakes are great, the larger bubble being pulled/pushed along the tubing.

This may also offer an explanation to BAT 21’s problem, a very small leak letting in a very small amount of air, remember when you release the brake pedal there is a ‘negative’ applied to the fluid. Tiny air bubbles enter the system from (enter component here), then they collect over a number of days and form one large bubble, the result is the low pedal. A few pumps possibly push the air back out of the place it came, the pedal returns to normal, park up ad infinitum.


regards

Dave

 

[StarCruiser]

If it's any help, the Smart was looking like it needed bleeding so I asked the question of a pro. He said (the Smart has ABS BTW) to put pressure bleeder on the MC tank, run the engine and bleed rear left, rear right, front left, front right. With someone operating the brake pedal as well. Drive it for a week then do the same again. He also added that the only sure fire way he had found was a very expensive machine he had.

I know this doesn't apply to your truck, just added it here in case it helps anyone with ABS.

 

[Dave2000]

True the ABS does add a complication to the system when it comes to getting the air out. When thinking about these things I look back the factory during assembly, and taking the SMART as an example, the factory would not assemble bleed, sell the car and ask the customer to come back a week later. They obviously have a system that enables quick and reliable bleeding, we simply need to find out what was used on whatever car we are working on at the time.

regards

Dave

 

[StarCruiser]

Forgot to add that he also said to do the pedal down and up AS WELL. Edited above.

 

[StarCruiser]

The thing is Dave, the factory can afford to build the most quick efficient system for filling and bleeding the brake lines from both ends if need be and tilt the whole thing at 60 degrees if it needs to. We probably won't be able to exactly mimic it but will surely as you say be able to do something that works. Unfortunately these days everything is computerised. The Smart could exercise and test the brakes from the Merc Star system and calculate the brake force.

It's now got a really springy pedal so 'I have a need to bleed' [emoji6]

 

[Chris]

I agree Dave. Just as well it wasn't me who said the air would travel through the fluid. The vacuum effect of the unit is VERY low. It only just sticks to your tongue actually. When the air collects in the chamber of the caliper, it pulls that air out but not lots of fluid. It will only start to pull fluid once all of the air has been removed. It doesn't pull a bubble all the way from the reservoir. That's just not realistic.

I am unsubscribing from this thread now because I am wasting my breath. The unit works fabulously well. If it didn't then at least 4 cars in my possession would be in a hedge bottom by now. If people don't like the idea fine. If you haven't tried one then shut up. if you have and it didn't work, that's a shame. Mine does, like a charm. I tried two pressure ones and they failed in every aspect other than they bounced well when I flung them at the garage wall. Traditional pedal bleeding works perfectly but needs two people and can and does shag up old seals.

Personally I think the positive pressure idea is the best, but I haven't found one that worked on any Cruiser I have owned. I even tried to make a top on the lathe to get a seal and that didn't work. Stupid fiddly little straps round the MC drove me nuts too. So vacuum it is.

 

[Bat21]

I bought a vacuum bleeder last year..... a pile of pants it is too. It seemed to prefer to 'suck' air in around the bleed nipple once slackened off rather than pull it out of the caliper.

This new pressure one I have is much easier and efficient.

Everyone has their favourite method I guess.

.... I borrowed a pressure bleeder that strapped onto the MC and it was the biggest ****** @@@@ of a device it's eve been my misfortune to ever bugger about with....
This isn't a question about favourite ways, it's about what actually works. If it hasn't worked for some of you I am surprised. But from drained to fully bled in minutes with only one person, no top up and only a tablespoon of fluid pulled out, I can't better it.

Pressure bleeder was quick, efficient, no mess and the job was done in a few minutes.

.... This isn't a question about favourite ways, it's about what actually works.

.... Everyone has their favourite method I guess.

At least we agree on this one

 

[Chris]

Sorry I have unsubscribed from this thread and as such can't see your reply.

Oh, just a minute ..

 

[frank rabbets]

I can't see how a small leak (enter component) would not cause brake fluid to come out and witness. Also when the car is parked there is a small amount of positive pressure due to the height of the reservoir compared with the rest of the system so I don't see how air can get in.

"Better to have lost in love than never to have loved at all" so your unsubscribing is just life Chris. But I do agree I wouldn't risk subscribing at all re:- Facebook. lol.

Any road up having an intermittent brake problem is a real pisser whatever.

 

[Dave2000]

Chris stay cool, everyone has had some success with all systems you are not alone with the vac and you can bet someone loves it and some hate it as they do pressure systems, and hey I want you doing your 'moderator thing' so earn your keep!!

Frank, I am not sure about positive pressure. If the positive pressure was a constant (parked or otherwise) the brakes would bind all the time creating drag? When the pedal is released the pads retract, part of this is due to the rubbers deforming and the rest as the piston returns to rest i.e. pulling back on the fluid, as you know you never tighten the nipple on an up stroke for this very reason, and the amount of air needed to make a pedal spongy is very small indeed so.....................?

There is a possibility that the air is getting in through a very tiny leak but not big enough to leak fluid unless, the brake pedal was pushed and perhaps held over a period of time, perhaps start engine, wedge pedal down and switch off and leave overnight?

Awkward this one mate,

regards

Dave

 

[Chris]

I'm quite cool. I just get annoyed when your opinion or experience is rubbished, you get misquoted and simple answers get blown out of all proportion with ridiculously over blown technical responses which don't answer the original question. Other than that don't worry, I am completely cool.

This was originally a question about soft brakes and MC seals.