Technical General advice on brake bleeding sequence

[LezLezLez65]

Hi, I am having minor difficulty with my 1998 B (and rear brake compensators) but at least it has just passed its MOT (July 2022). My question relates to what in my opinion is a slghtly soft brake pedal. Should I bleed brakes starting at the most distant or longest fluid pipe run and work forwards to the nearest to the master cylinder? Or should I start at the master cylinder and work outwards to the farthest brake caliper - in my case the rear right hand one.
Thanks in advance for your straight forward advice.

 

[The Panda Nut]

I understand you start at the furthest point and work towards the master. Its the way I always do it. For a few £ you can get a Gunsons pressure brake bleed kit that uses pressure from a tyre on teh master cylinder. I have found this very useful in the past, The only issues I have encounytered with soft pedal were air or leaks. If you have a mechanical load valve you may need to raise the suspension to make it think its under load and allow max fluid flow to displace the last of the air. Good luck

 

[StevePD]

Hi, from the tech info I have the bleed sequence for the Barchetta is:
First front left
Then front right
then rear left
Finally rear right.
Fluid Tutela Top (270degC) DOT 4. ISO 4925
I know this is contri to normal sequence as previosly stated but has worked for me with abs brake system..

SteveD

 

[Davefridge]

If you have abs it shouldn't matter. On mine there is one pipe to each wheel from the abs unit under the bonnet.

 

[ernibv]

I was pretty susrprised by this, but that seems to be the b rule from the manual

 

[s130]

Not an expert on ABS braking systems but:

1) Traditional brake bleed pumping will work perfectly OK to flush out and renew 95%+ of old fluid
2) The ABS system has "accumulators" These are reservoirs of fluid within the ABS unit that contain brake fluid
3) The traditional brake fluid pumping may or may not flush these accumulator reservoirs

Now MES and other kit can engage the ABS pumping valves to flush fluid through these reservoirs should you be concerned.

The alternative is to in the wet brake hard to trigger the ABS system which will then pump and flush those internal systems

 

[Pugglt Auld Jock]

It depends whether you're starting with a "dry" master cylinder or just bleeding a system already containing fluid. With a dry cylinder I've always bled the cylinder/caliper nearest the master cylinder first. So on a right hand drive vehicle this is usually the O/S/F. By doing this you quickly eliminate the air from the master cylinder - or half the master cylinder if it's a dual piston cylinder as most are today. This tends to give a good pumping action on the master cylinder. Next bleed one of the rears, doesn't usually matter which as pipe lengths will be similar. Now you should have a master cylinder with no air anywhere in it so you can go on and bleed out the other front and rear. Sometimes, especially with a system where you've started "dry" or where a lot of air may be present due to replacing multiple cylinders and pipes, you will find you get a usable pedal but not a "brilliant" one. This is not al,l that unusual and you'll find it improves if you go round the whole system a second time. Sometimes small air pockets can be difficult to bleed out entirely and you may find that, as long as you've got a good enough pedal for it not to be dangerous - ie it's possible to do an emergency brake satisfactorily - if you drive it around for a couple of days and then do another complete bleed through that small amounts of "fizzy" brake fluid will be expelled and the pedal will get much better.

Remember though that what you are bleeding does not include the fluid inside the ABS unit and usually the only way to bleed this is with a scanner, like MES, which lets you activate the ABS pump and solenoids. Having said this I wouldn't worry about it because I'm pretty sure almost noone does this even when doing a brake fluid change (every 2 years or so?) it would only be done when fitting a new ABS unit or, maybe, if you've allowed air to enter the ABS unit while fitting new pipes etc.

If you start by bleeding the cylinder/caliper furthest away from the master cylinder sometimes, especially when a brake apportioning valve is present on the rear axle - which might tend to restrict flow (and, if you've got the car up on stands you may have to jack the rear axle up a bit to open this apportioning valve to allow fluid to flow to the rear) the air in the line will compress when you push the pedal down and expand when you release the pedal creating a sort of "push me pull you" action with any fluid being pumped into the line being returned to the master cylinder when you let the pedal up again. If you've been bleeding through and getting some sort of a pedal but not good enough to live with, it can be useful to clamp off one flex hose at a time and try pressing the pedal. If the pedal goes hard when one flex is clamped then you can say to yourself, Ok this is the one where the air is and bleed just that one out until you get a good pedal. Of course it may be that there's air all over the place and you can isolate that down by clamping off all the flexes and trying the pedal. If it's hard with all pipes clamped then the m/cylinder is bled Ok so try releasing just one clamp. If it's still good then there's no air there so try another clamp, doing this one clamp at a time until you get one that goes soft pedal, that's the one to bleed. Keep doing this till the pedal comes good. Sometimes you just get a "rogue" which frustrates all attempts. I remember a wee Simca many years ago which we got a good bleed on the fronts but couldn't get the rears to clear. In the end we got it to bleed out by almost standing it on it's nose with it's back wheels on the ramp and leaving it like that for a few hours to encourage air in the system to find it's way to the rear and finally we got a good bleed on it. We had that car in the garage for some 3 days with nearly all of us having a go at bleeding it periodically before we finally got it sorted.

Edit. I'm a firm believer in not fully depressing the brake pedal when bleeding by pumping the brake pedal in order to stop the pedal rubbers entering part of the cylinder bore not normally used. Put a wooden block, or similar, under the pedal to restrict it's stroke.

 

[Pugglt Auld Jock]

I was pretty susrprised by this, but that seems to be the b rule from the manual

I'm largely in agreement with that manual bleeding procedure but with the proviso that you limit the stroke of the pedal as I said above. Also, sometimes, it helps the master cylinder to draw fresh fluid from the reservoir on the return stroke if you close the cylinder/caliper bleed nipple at the bottom for every bleeding stroke and then open again before the next depression of the pedal. Stops any air being drawn back in round the bleed nipple threads too. So it's:
1) Open bleed nipple.
2) depress brake pedal.
3) with pedal held down close bleed nipple - just "nipped up" is enough.
4) release/raise brake pedal.
5) with pedal fully up open bleed nipple and repeat.
Of course be sure at all times that there's sufficient fluid in the reservoir to prevent the master cylinder drawing in air.
Pressure bleeding with something like the Gunson equipment - which, considering how little it costs is actually pretty good - eliminates the possibility of air being drawn back into the system and also keeps the reservoir topped up. You do need to be very careful to fit the reservoir adapter cap properly otherwise it'll leak big time! guess how I know that! Here's a link to the Gunson tool, which is sold at half that price in Halfords and even less in special offers on line - other contenders exist (see ebay): https://www.gunson.co.uk/product/G4062/Eezibleed-Kit

 

[ernibv]

I don't want to sound like to much of an old fart, but it's refreshing to hear discussions on basic car mechanics

 

[s130]

I don't want to sound like to much of an old fart, but it's refreshing to hear discussions on basic car mechanics

Indeed and begs the "horror" stories we have all had.

As for bleeding brakes on my old long ago 600D (I was 17 going on 18 and this was one of my 1st car DIY jobs) I had to replace the rear rusty brake pipes for an MOT failure. In those days I did not posses a brake pipe union spanner and the unions were all seized. I was certainly not going to cut one of my precious ring spanners so I cut the rusty brake pipe to slip on two ring spanners. Really chuffed I was.

It took for ages to bleed the brakes and M & D called me in for dinner before I was done. Next day I finally got the brakes bled, firm pedal, etc. and went for a test drive. Brakes were fine but I could hear a rattle under the car.

Upon examination I found that one of the ring spanners was still around the brake pipe! It had obviously slipped down the pipe well away from the union which I did up with open ended spanners.

I was temped to just tape the spanner in a position up out of the way but decided to split the union and remove it. Fortunately the brakes bled OK this time round.

I learnt a lot on those two days about:

1) Preparation and plan of attack, tools required
2) Tool tally - bit like a surgeon have the tools laid out as best as you can so you can use and replace and then check afterwards
3) If you drop a tool, nut, bolt, etc. stop what you are doing and retrieve said item even if it take forever (until found it could be disastrous)
4) Check and double check every aspect of the job and tool tally when done

Sadly as we get more experienced we often tend to be less attentive / regimented.

Worse still as you get into your retirement years you pick a tool up, use it, put it down and then can't find it again

 

[Pugglt Auld Jock]

It took for ages to bleed the brakes and M & D called me in for dinner before I was done. Next day I finally got the brakes bled, firm pedal, etc. and went for a test drive. Brakes were fine but I could hear a rattle under the car.

Upon examination I found that one of the ring spanners was still around the brake pipe! It had obviously slipped down the pipe well away from the union which I did up with open ended spanners.

I was temped to just tape the spanner in a position up out of the way but decided to split the union and remove it. Fortunately the brakes bled OK this time round.

I learnt a lot on those two days about:

1) Preparation and plan of attack, tools required
2) Tool tally - bit like a surgeon have the tools laid out as best as you can so you can use and replace and then check afterwards
3) If you drop a tool, nut, bolt, etc. stop what you are doing and retrieve said item even if it take forever (until found it could be disastrous)
4) Check and double check every aspect of the job and tool tally when done

Sadly as we get more experienced we often tend to be less attentive / regimented.

Worse still as you get into your retirement years you pick a tool up, use it, put it down and then can't find it again

Your spanner story made me think of my Dad and an incident which occurred when I was in my teens. He was a "professional" man with little knowledge of cars so all the maintenance was done by the garage. He always had something unusual and at that time he had a triple carb 3.8 Jag saloon - for it's time an indecently quick motor. He did not trust it to our local garage down in the Scottish borders so it would be taken up to Rossleigh, the Jag main dealer, in Edinburgh, a good half hour plus away. In this instance it had been delivered back to the house and Dad had just been into town to his office in it. On his return he said "something seriously wrong with the car son. The engine's not running smoothly and there's a tinkly noise" I was already driving bangers round the fields and trying to repair them when they broke down and he let me open the bonnet and have a look - with him hovering closely over me just in case I broke something! - this car had the old XK engine with twin OH cams and spark plugs running in the "valley" between them. There was a spanner rattling about in the V tinkling away and occasionally shorting a plug HT. The spanner went into my sorry excuse for a tool kit and the problem was solved. I think it was this incident which persuaded my Dad that I was not going to be a "professional" man as it was shortly after this that he came in and told me he'd entered me for an apprenticeship with Rolls Royce! - which I failed to get and later started studying for my City and Guilds. The rest is history!

I love your 1,2,3,4 plan of attack, When young I would often put a spanner down on the scuttle or other nearby place and never forget where I'd put it, To my knowledge I've only ever lost a small screwdriver doing this, and it was a very good and much used, so much missed, tool. Now, I daren't do that as I'd never find it again. I've spent days searching for tools or small parts that I've put down whilst I deal with something else and can't find again. All tools either go back in/on the tool box or get laid on the ground where it's easy to see them later.

Isn't it strange how dropped small parts often find the most obscure places to "hide" We were putting a new door mirror on my boy's Astra the other day and the inner trim, which has to be removed to access the torx screws which hold it on (why torx screws?) This trim panel is secured by 3 "pop" type nylon studs, one of which decided it didn't want to stay on the trim panel and dropped off at just the right moment so it could disappear down a quite small slot into the interior of the door. Door card had to come off to retrieve it!

Regarding your last statement, I'm afraid I'm doing this more and more these days and, of course, unlike when I was young with just a cantilever toolbox half full of tools, I've now got a lovely big cabinet and top box to say nothing of all the other "stuff" so the potential to loose things is almost infinite. I can "loose" a spanner within a minute of having just used it. I found a Stanley knife which I'd not seen for close to 2 years the other day. Normally it would "live" in the 2nd drawer down on the left of the top box but I found it in the cantilever box which has some plumbing tools in it - there's just no hope for me!

 

[ernibv]

In 1974 the cantilever tool-box lived in the trunk of my '64 MGB

 

[pablopablo]

I was pretty susrprised by this, but that seems to be the b rule from the manual

Wow, me too! I bet the vast majority of us have been doing it the regular way.

 

[LezLezLez65]

Just a short thank you to you all for your reply and comments to my inquiry. I will now study your details and decide how best to proceed with my 1998 B which has 2 brake compensators and too soft a brake pedal. I do support the observation that if there are 4 separate fluid lines from the master cylinder, sequence might not matter too much!
Thanks again.