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Bleeding brakes on 300Tdi Disco (non ABS)


freeagent
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I'm having a nightmare bleeding the air out of the brakes on my 300Tdi disco...

I've used the 'search' facility, and have read a few posts on here about it but none were disco specific.

Does anyone have any tips or techniques that they have found successfull? At the moment my pedal goes down about half way with the first pump, but gets a lit stiffer on the second/third pumps..

The truck will pull up ok, but is very spongy and doesn't inspire much confidance...

I've bled all four calipers repeatedly, and get the odd bubble here and there...

Is it worth apying a garage to do it using a power bleed unit? or will they not always produce results that are any better?

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If you take it to a garage and they dont get better results, you can obviously ask them to do it again FOC. They will then advise if another problem may be present. Could be that your fluid needs changing anyway or perhaps your rubbers in the master cylinder are a bit suspect?

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Tony, thanks for the reply..

The fluid is new, and has been changed at least twice over the last 3 years..

The master cylinder was changed on Monday for another known good one, and the symptoms are the same, I can bleed them, but only so far....

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They've been spongy for months, but this got worse when i split the two front hoses to adjust the swivel pin pre-load at the weekend..

I think there has been air in the system for a while, so want to bleed all four corners sucessfully...

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As for bleeding, I still prefer to use the ancient method with 2 people, one operating the brake pedal and the other working on the bleed screws. It works every time on any vehicle, no special tools involved other than the spanner to undo the bleed screws and even a 10 year old kid can be the helper. So this is the method I would recommend.

As for spongy feeling, this could have had other causes (in the first place)

- master cylinder (you replaced that - although I would still have doubt on the "known good" one that you used)

- tired brake hoses (which can swallow under pressure)

- worn brake discs (near or over the limit)

Edit: .. and place the vehicle on level ground, I forgot to say that.

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Just done mine after changing all four rigid pipes to the calipers for MOT.

I bleed using a pressure bleed kit eezi bleed)about £15 to buy and I've used it dozens of times and it never fails, uses the pressure from your spare wheel to force the fluid through.

Problem with the 2 man bleed is where the brake pipe splits at the rear as you bleed one caliper you drag air back in from the other pipe that has not been bled yet ....... does that make sense ?

You cant fail with an eezi bleed kit as all the pipes are pressurised.

If its still spongy after that then you have a leak some where or air can get trapped in the servos, but again pressure bleeding will push this out.

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Ther most effective down dollar way of doing this is to buy a cheap Gunsons easybleed,they used to be about £15.It uses pressure from a car tyre to force the fluid through the system.DO NOT use more than 10-12psi though,it wont bleed any better and you risk bursting the resevoir.Doing it this way is very gentle and is a one man job,you just connect a length of clear hose to each nipple and turn it on like a tap.Just run it till the fluid is clear and turn it off.

The other nice thing about pressure bleeding is that the piston in the master cylinder does not get repeatedly forced into an area of the bore where it does not normally get to.I only say this because old cyls often have rusty patches in them when you take them apart after failure.(Explaining the cost of a new master to a customer after just replacing a couple of rusty brake pipes is best avoided.)

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You are not wrong Ally V8, with either the Gunson kit or flooring the brake peddle. This happened to me on another car and as a result a new master cylinder was required.

It appear'd that everyone in the pub knew about this when bleeding brakes on oldish vehicles, but not me. :(

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Ther most effective down dollar way of doing this is to buy a cheap Gunsons easybleed,they used to be about £15.It uses pressure from a car tyre to force the fluid through the system.DO NOT use more than 10-12psi though,it wont bleed any better and you risk bursting the resevoir.Doing it this way is very gentle and is a one man job,you just connect a length of clear hose to each nipple and turn it on like a tap.Just run it till the fluid is clear and turn it off.

The other nice thing about pressure bleeding is that the piston in the master cylinder does not get repeatedly forced into an area of the bore where it does not normally get to.I only say this because old cyls often have rusty patches in them when you take them apart after failure.(Explaining the cost of a new master to a customer after just replacing a couple of rusty brake pipes is best avoided.)

Our work pressure bleeder runs at 2 bar (29psi) , this is what merc recommend and its been fine on all other makes that i've performed a brake bleed on, always works a treat.

interestingly (a bit OT) merc e and sl-classes use fly by wire brakes, very good! until they go wrong, we have to bleed brakes using a computer, takes about an hour and it can detect any air in the system by itself!

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I no longer allow Merc stuff in my workshop,used to look after a few G-Wagens.Now its just Land Rover stuff and watching a 300TDI Disco M/Cyl res swell up when you go over 20 psi is a bit of a worry - I dont like brake fluid at the best of times ! 10psi is plenty - esp if you try doing the brakes on a 1949 S1,any more and it stops dead.

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Pictures of some 'tools' for DIY brake bleeding...

1. Is ok but gets messy when the jam jar falls over and you need a little helper (cipx2)...

2. Is ok has a ball bearing valve thingy on the end but again gets messy when the jam jar falls over, I've used this for years a one man system, no little helper required...

3. The Gunsons kit, new and still in the box which will get used some time soon, I found the kit on ebay for £13 something a deal I think.

post-5809-1238694183_thumb.jpg

post-5809-1238694200_thumb.jpg

post-5809-1238694217_thumb.jpg

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You lot may laugh, but I bleed Defenders and Discos without any gear except an 11mm spanner and a water hose. Reach in, put the spanner on the nipple and loosen it. After a few seconds close it. Do all four and then use the hose pipe to get rid of the spilt brake fluid.

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No laughing from me side. I'm waiting for someone to say something about what kind of water traps and oil filters should the compressor used to inflate the tyres must have so the brake fluid doesn't get contaminated etc ... to have some :D

Although true and I might agree with something in AllyV8's p.o.v (explaining to customers), I will always prefer to run the piston all the way with the risk of damaging the seals on the piston.

I prefer to inflict further damage, if the case might be, this way finding that there's something wrong on the inside, and replace the whole thing than finding that later, in the middle of nowhere

If there's rust in there, sooner or later some tiny fragments of rust will dislodge from the vibrations when braking - those vibrations the manufacturers try to keep in the ultrasonic spectrum so that our delicate ears don't get upset by the squeaky sound.

Those tiny fragments will work their way down to where the piston normally sits at rest (because most of the master cylinders are tilted back) and will act like as a grinding paste on the following piston travels.

Well, each to his liking. I've bled my 98 Disco this way about 3 times, last time more than 1 year ago, it's still on the original master cylinder and I never had a problem with no damage on it.

Problem with the 2 man bleed is where the brake pipe splits at the rear as you bleed one caliper you drag air back in from the other pipe that has not been bled yet ....... does that make sense ?

It doesn't make sense as it doesn't happen :). Get 3 small diameter clear hoses (about the same inside diameter as the brake lines), join them with a T piece and test with water so see for yourself. It's a matter of superficial tension, fluid properties and the amount of depression the master cylinder can make.

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No laughing from me side. I'm waiting for someone to say something about what kind of water traps and oil filters should the compressor used to inflate the tyres must have so the brake fluid doesn't get contaminated etc ... to have some :D

Although true and I might agree with something in AllyV8's p.o.v (explaining to customers), I will always prefer to run the piston all the way with the risk of damaging the seals on the piston.

I prefer to inflict further damage, if the case might be, this way finding that there's something wrong on the inside, and replace the whole thing than finding that later, in the middle of nowhere

If there's rust in there, sooner or later some tiny fragments of rust will dislodge from the vibrations when braking - those vibrations the manufacturers try to keep in the ultrasonic spectrum so that our delicate ears don't get upset by the squeaky sound.

Those tiny fragments will work their way down to where the piston normally sits at rest (because most of the master cylinders are tilted back) and will act like as a grinding paste on the following piston travels.

Well, each to his liking. I've bled my 98 Disco this way about 3 times, last time more than 1 year ago, it's still on the original master cylinder and I never had a problem with no damage on it.

It doesn't make sense as it doesn't happen :). Get 3 small diameter clear hoses (about the same inside diameter as the brake lines), join them with a T piece and test with water so see for yourself. It's a matter of superficial tension, fluid properties and the amount of depression the master cylinder can make.

Its easy to mock,but what you do in your own back yard on your own car is different to running a garage.To try to maintain a decent reputation and avoid conflict with customers can be a difficult thing to do.With your own car if the M/cyl failed 2 days after bleeding you could see this as fair wear and tear and be a part of "Bigger picture" maintainance.But if I bleed the brakes on a customers LP RR and the same thing happens - what then,last time I had to price up one of those it was over a grand,not something I would like to swallow.Many owners cant really afford to run their cars properly in todays financial climate so any garages with any sense do whatever they can to make sure this type of situation never happens.The days of "Fix it and send me the bill" are long gone,unfortunately its now more of a blame and claim culture.So I'll carry on gently pressure bleeding and having a quiet life.
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It doesn't make sense as it doesn't happen :). Get 3 small diameter clear hoses (about the same inside diameter as the brake lines), join them with a T piece and test with water so see for yourself. It's a matter of superficial tension, fluid properties and the amount of depression the master cylinder can make.

What's the fluid properties got to do with it ?

I teach fliud power (hydraulics) to aircraft engineers and i can assure you that in a split system there is no way other than luck you will dispell all the air without simultaneous bleeding.

It may appear to be air free but aeration ( tiny particles of air suspended in the fluid) will not be removed. This will eventually manifest itself as 'sponginess' or slow operation to give it its technical term.

keeping the fluid under a constant pressure is the only way to ensure complete de-aeration. And even this is not fool proof.

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He, he ... the hydraulics and aviation bits remind me of another hydraulic brake specialist working in the aviation bussiness that had issues trobleshooting a (what I consider a simple) D2 brake problem not long ago on this forum ... :D

What do you mean by "What's the fluid properties got to do with it", Mr Hydraulics Teacher?!

You mean none of the properties of a fluid has something to do with the miscibility between that fluid and another? You mean there's no property of a fluid that tells you something about how that fluid wets the surface of a solid? You mean there would be no difference if, in the said 3 hoses configuration, you want to replace the air with another gas, water, brake fluid or mercury?

Come on Mr. Hydraulics Teacher, you must be familiar with those fluid properties.

Mr. Teacher, there are some things you didn't take into account:

1. the history of the trade (automotive, not aviation), what we're talking about in the trade and the tricks of the trade

2. the big picture

1. The trade:

- this method (separate bleeding) was the only method applied for decades and it worked just fine until mass production, optimizing repair times, advanced ABS systems etc

- we're not talking about bleeding a 50 m long half inch thick hydraulic line of a plane, we're talking about a 1m hydraulic line on a car

- there is a trick you can do at the last bleed of a ramified pipe to ensure the last mixed air/fluid bit, although slight chances to be the case, is pushed back past the T and will be expelled when bleeding the other pipe (I'll let you discover it, it's not hard).

2.The big picture:

- although there are some miscibility phenomena where the pipe splits (T piece), this will take place for a limited amount of bleed cycles; that's because of two things:

a.) the pipes are small enough and the replacing fluid is viscous enough (brake fluid in our case) so there's no vertical fluid separation in the pipe

b.) the brake fluid will 'dislodge' (carry away down the pipe to be bled) a limited amount of air; if the air is taken down the pipe to be bled , the missing air must be replaced with something (brake fluid), you can't have vacuum in the pipe (the one not bled yet); let's say you'll have a couple cubic cm of air dislodged (which will be replaced with brake fluid so in the last bleed cycles there will be no air close enough to the junction) and will be all the air that will mix with brake fluid further down the line and in the caliper.

There are two other aspects of the big pictures:

- the amount of air still on the bled pipe

- the amuont of air in the rest of the brake system due to the wetting quality of the brake fluid and the inside surface roughness.

You will always have air in the system, no matter the method used for bleeding, no matter what you do. What's important is how much air is in the system, if it's in an acceptable quantity. 'Cause if you have so much air that you get a 2 cm longer pedal travel it's not good. But 2mm would be considered perfect.

AllyV8, I said I understood your personal p.o.v from where you're standing in the first place, didn't I?

How things should be done in a garage or what is says in a Workshop Manual it's not always the best approach for a DIY-er. We're not talking about how to run a garage but it's nice you gave an explanation for the readers here, potential clients of yours.

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He, he ... the hydraulics and aviation bits remind me of another hydraulic brake specialist working in the aviation bussiness that had issues trobleshooting a (what I consider a simple) D2 brake problem not long ago on this forum ... :D

What do you mean by "What's the fluid properties got to do with it", Mr Hydraulics Teacher?!

You mean none of the properties of a fluid has something to do with the miscibility between that fluid and another? You mean there's no property of a fluid that tells you something about how that fluid wets the surface of a solid? You mean there would be no difference if, in the said 3 hoses configuration, you want to replace the air with another gas, water, brake fluid or mercury?

Come on Mr. Hydraulics Teacher, you must be familiar with those fluid properties.

Mr. Teacher, there are some things you didn't take into account:

1. the history of the trade (automotive, not aviation), what we're talking about in the trade and the tricks of the trade

2. the big picture

1. The trade:

- this method (separate bleeding) was the only method applied for decades and it worked just fine until mass production, optimizing repair times, advanced ABS systems etc

- we're not talking about bleeding a 50 m long half inch thick hydraulic line of a plane, we're talking about a 1m hydraulic line on a car

- there is a trick you can do at the last bleed of a ramified pipe to ensure the last mixed air/fluid bit, although slight chances to be the case, is pushed back past the T and will be expelled when bleeding the other pipe (I'll let you discover it, it's not hard).

2.The big picture:

- although there are some miscibility phenomena where the pipe splits (T piece), this will take place for a limited amount of bleed cycles; that's because of two things:

a.) the pipes are small enough and the replacing fluid is viscous enough (brake fluid in our case) so there's no vertical fluid separation in the pipe

b.) the brake fluid will 'dislodge' (carry away down the pipe to be bled) a limited amount of air; if the air is taken down the pipe to be bled , the missing air must be replaced with something (brake fluid), you can't have vacuum in the pipe (the one not bled yet); let's say you'll have a couple cubic cm of air dislodged (which will be replaced with brake fluid so in the last bleed cycles there will be no air close enough to the junction) and will be all the air that will mix with brake fluid further down the line and in the caliper.

There are two other aspects of the big pictures:

- the amount of air still on the bled pipe

- the amuont of air in the rest of the brake system due to the wetting quality of the brake fluid and the inside surface roughness.

You will always have air in the system, no matter the method used for bleeding, no matter what you do. What's important is how much air is in the system, if it's in an acceptable quantity. 'Cause if you have so much air that you get a 2 cm longer pedal travel it's not good. But 2mm would be considered perfect.

What we were actually talking about was the best method for the original poster to bleed his brakes, not a history of the 'you wanna do it this way brigade' I and many others it seems agree that pressure bleeding will be the best chance of a solution to the issue.

Point 1. Miscibility regarding liquids is not relevant as we are only using one type ' automotive hydraulic fluid (liquid as fluids are also gases). As you 'must' know air and brake liquid are imiscible hence the need to bleed !

Point 2. Aircraft hydraulic lines are nothing like 1/2 inch in thickness but as you are a car 'Mechanic' and I am an aircraft 'Engineer' I will forgive this minor lack of knowledge. And you would not find a 50m long run of pipe as the problem of maintaining a laminar flow becomes more difficult to control over longer runs of stainless steel pipe as used on aircraft, as a more turbulent flow will tend to release the entrained air (caused by the liquid and air being imiscible) giving a less sensitive output force.

Point 3. The big picture. The big picture is that he has tried to bleed the old way using a number of bleed cycles, so maybe he should use the single cycle method of pressure bleeding ! Yes you will probably get a laminar flow but its more consistent when applying a force to the fluid reducing the chance of air remaining. as that pressure will be felt equal at right angles and without loss throughout the system.

Now if the 2 split pipes were the same length then you may not encounter any problems, indeed you may not encounter problems full stop, due to the, as you say, small scale hydraulic system we are dealing with. However liquid will always take the easiest route out !

Now as a spend most of my time explaining Brahms and Pascals to future engineers I really don't want to get in to a Fluid power/dynamics lesson as you seem to want to, I try to explain in simple terms, but theres always a smart alec isn't there ? I can sit and quote theories and mathmatical terms all day but it wont help the chap bleed his brakes now will it ?

Use the Eezi bleed mate it works, and i did it at 20 psi from my spare tyre as the instructions on the box tell you to. Cracked each bleed nipple once and top job, took 15 mins.

Sorry to the other readers for this boring post that is of no real help.

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OK chaps I don't mind you two blinding each other with rocket science and quantum physics but if it degenerates into a name calling session I'll stomp on it so please keep it nice and friendly ;)

BM

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All I asked was how best to bleed 'em at home.....

I wouldn't mind but I'm a bloody Engineer anyway, so certainly don't need a lesson in fluid dynamics.

Don't be a spoil sport i'm enjoying it, it makes a change, although "no understand" as i'm only an electrical engineer... O yes what was your thread about " bleedin brakes on a 300Tdi" or is that bleeding, have you done them yet ? as i'm not too far from Northfleet just the other side of Southfleet you might say, so if you need help.

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Dont worry I'm done with it.

Try one of these chaps they are ace. Pull it out! Not Cheap but are less hit and miss than the easi-ish bleed (watch the pressure on that one). Get a good compressor hanging on it and its the best remedy. This is supposed to be our hobby not our chores!! kit up and enjoy

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