Bleeding brakes...

[Dead Eye]

Sorry, but I couldn't resist the pun... despite it being done to death...

Anyway, I've put this in general as it is car related, not nothing to do with my Fazers


So, I have just finished the task of replacing the discs and pads on all 4 corners. The rears were very low and almost at metal on metal and the fronts were just old and figured I'd do the whole lot anyway. Having completed the procedure, I bled all 4 corners a few times and the pedal became rock hard - much better than ever before (woohoo I thought)...

But ahah, not so fast the car says, upon starting the engine, the brake pedal falls almost to the floor and the brakes become absolutely useless...

I've never experienced this before and I've actually done the brakes on the same make and model car before as well!

So, off I trot to the internet to do some research... to which I find 101 various answers and counter-arguments, the highlights of which are;

1) Air is still in the system.

2) Calipers / Master Cylinder / Booster are busted

3) ABS system needs to be bled

4) Seals in Master Cylinder have flipped



For each of these things, there is a counter-argument that people have made and so far, in not a single thread I've read has the OP come back with the solution to their woes... fucking bastards...

Now, I could go all night attempting to bleed the brakes, but that seems to have been done by several people with no success. I can't see any bulging on any of the flexi-hoses and there are no leaks on any of the calipers as far as I can tell. I then came across a guide to test the booster, so followed its instructions;

32.  Brake Booster Test
 
 Functional Test:
 
 1. With engine off, depress brake pedal several times; then, depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line, or brake caliper is bad.
 
 2. Start engine with pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or check valve is faulty.
 
 Leak Test:
 
 1. Depress the brake pedal with the engine running, then stop the engine. If the pedal height does not vary, while depressed for 30 seconds, the vacuum booster is fine. If the pedal rises, the booster is faulty.
 
 2. With the engine off, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

My car responded as expected, suggesting that the booster is in full working order.

So, minions of FOC-U, have any of you in your travels experienced said problem and actually managed to solve it? My only real next step is to test each caliper by clamping the flexi-hose (and trying not to destroy it in the process) and spend the next year bleeding the brakes with gallons of DOT4 until the problem magically fixes itself...

[dickturpin]

I had similar problems on a VW not too long ago....sorted by putting more fluid through and lots of bleeding.

[unfazed]

Is you car a Vauxhall by any chance?

[Dead Eye]

Nope, an MG ZS - based on the Rover 45 as I'm sure you all know

[unfazed]

A common problem on the Vauxhalls was the master cyinder seals to flip when the pads were pushed back to quickly or pumping of the pedal to the floor to get pressure up. The pressure going the wrong way can cause the seals to flip

Check to see if it is an issue on the MG as I know very little about them.

[Dead Eye]

I've heard comments like this on some of the threads I've read, one person (talking about the ZT) was adamant that it was near impossible for this to happen given the amount of pressure that can be exerted under breaking. It was also suggested that if the seals were to flip, then you would get no breaking what so ever - I assume this is because the seals would no longer allow for pressure required for the hydraulics to work correctly.

Do you have any idea on the exact symptoms if the seals were to flip?

Having not taken a master cylinder apart, I don't really have a good idea of how the internals work to form my own definitive opinion. For now I guess my best step is to continue trying to bleed the brakes as it is a simple task with little associated cost...

[red98]

Hi liam.......not come across the term "booster" before, but guessing its like a servo, yes I am realy that old  ......a couple of tricks
Ive used before, the first one helped out a foccer on here recently..."back bleeding"...using a pump action oil can.fill with brake fluid and pump the fluid up via the caliper bleed nipple to the master cylinder, pushing any air upwards.the way it wants to go, having isaac on your side here  ...its never failed for me

second one, and I dont know why this works but it does....hold the pedal down over night using a length of timber against the pedal, must be all the way down....used this method on my thou this week, bled the system untill all air pumped through but when I tried the lever, nothing, went straight back to the bar....so pumped the lever several times and used a cable tie to hold it against the bar, left it over night and hey presto....perfect  brakes 

Your gripe about posters not posting the outcome bugs me aswell.....think were all pretty good on here though....so get back out there and give it a go....second one is easy......and dont forget to tell us how you get on   

[Dead Eye]

Having not really come across either before I would assume that booster and servo are interchangeable terms

Would back bleeding not potentially cause the flipped seal problem that others have described on the master cylinder? Some other have also suggested that flooring the pedal can cause the same issue I've actually used the cable tie method on my bikes before with good results

The tech on bikes always seems easier to work with because you can see a lot more of what is going on. Cars are always that little more difficult in everything you try to do... but in any case I'll be leaving it until tomorrow when I should be receiving and adapter for the Eezibleed I bought the other day not realising that it doesn't natively support my car... typical... plus there isn't anyone around to assist me most of the time

Thanks for the advice and comments though

[red98]

Easy bleed are fantastic for cars, been using them for years....which method have you been using up to now, the one way valve jobbie ?

Ive not come across the flipped seal before, but I can see it happening if you let the clyinder run dry and operate the pedal / lever replacing the rubbers in the cylinder is easy but I think kits for cars are not as easy to get hold of as they are for bikes...

[unfazed]

Oops!, Just reread you first post and you seem to be building up some pressure so it is unlikely the seal inversion issue as this would not give any pressure

Are you sure you fitted the anti rattle shims and springs correctly and they are not causing the the brakes to release instead of just stopping the rattling.

The pedal should only be pushed about 3/4 way down only and pumped slowly for pressure build up.

Another option it to try bleeding with the Ignition on or engine running as it may need the ABS motor running to bleed it through correctly
Have you checked if there is any special way of bleeding the  MG with ABS?

Sometimes in a 2 person job, the person in the car does not follow the pedal down when the pressure is released at the nipple
Pump the pedal slowly until it goes hard, open the nipple close it and release the pedal.
Order is left back, right back, left front, right front,

[Dead Eye]

The method I used was the two-person method with my mum sat in the car...

I more or less followed the instructions you posted; with the exception that the bleed nipple is opened before pushing the brake pedal - so Open Nipple, Push Pedal, Close Nipple, Release Pedal - this is what I have always done, on both cars and bikes.

With the order, I did Rear Left, Rear Right, Front Right, Front Left - assumed I should do the rear calipers first as it just made sense.

I did a little digging on the MG ZS forum I'm a part of, but I don't think they as active as this forum is, so most topics are just basic questions such as choosing the right discs etc

But I'll try bleeding them again tomorrow and I may try bleeding with the engine running - not sure if that is wise though haha


Wish me luck...

[chaz]

you could try to make sure the pistons are pushed right back int the calipers and use wedges to hold them while you bleed them not sure on the rears as some have to be wound in? the thinking behind this is there's less spaces to get air trapped, I did this on the bike when I renewed the fluid but didn't need bleeding as I didn't get any air in.

[unfazed]

That may be your problem.
You have to have pressure before opening the nipples. Pump it 4 or 5 times until it goes hard, then hold it, open the nipple slowly to release fluid slowly, follow the pedal down, close the nipple quickly before the pedal goes all the way down, repeat procedure on all wheels.

What Chaz says is correct, but not really necessary here since you did not open anything other than the bleed nipples.

[Dead Eye]

After looking for the past few days for my Haynes manual, its only now that I've managed to find it at long last...

It describes the same method; my pumping the brakes until there is pressure and then opening the bleed nipple. It has a different order of bleeding though; Left Front, Right Rear, Right Front, Left Rear - I always assumed you should do the calipers furthest from the MC, but it seems a lot of cars these days have the opposite (from what I've read so far...)

Hopefully I won't have the same issue tomorrow as I'll be aiming to use the Eezibleed rather than the 2-person method Just have to hope and pray that the adapter arrives at a sensible time...

[unfazed]

Order may have something to do with the ABS system on the MG.

Definitely a new one on me.

[dickturpin]

be careful of the pressure used on easibleed...I have heard of them splitting the plastic reservoir on some older cars.

[Dead Eye]

Yeah, I figured I'd use a lower pressure to start with the ensure I don't go full retard and completely break the car...

The stupid thing is that I've had to get a universal adapter which most people say is crap because it uses some stupid flimsy elastic to hold it on to the reservoir - so my plan will be the use of straps and clamps, without too much pressure hopefully

[Dead Eye]

Well the universal adapter was just as useless as the people on Amazon said it was, so that was an expensive waste of money. Strapped it down with two straps in addition to the one it comes with and used a G-Clamp and it still threw about 300ml of brake fluid all over my engine bay at about 8psi ...  so that wasted my time this afternoon.

Ended up waiting until my mum got back and put her on second-person duty in the car but this time tried it the way that unfazed described. Seemed easier and although next to no air came out (a few tiny bubbles maybe) the brakes are now usable 

Whilst the engine is off, there is no discernible difference in the pedal stiffness. Whilst the engine is running it still doesn't quite feel right to my mind, but the brakes at least work. I'm going to give it a few weeks and bed the brakes in and see what I make of it.


So I guess so far the answer to this topic is; bleed the brakes more...

[unfazed]

Good to hear you can stop again. Pump the brake pedal 5 or 6 times and hold the pressure on it then with the pedal still pressed start the engine, it should drop a little, if it drops any bit all is well.

When you change discs and pads everything sits flat and the pedal does not need to be pushed as far to apply the brakes.
Wear in the brakes occurs slowly over time and you just got used to the way the pedal travelled more with the worn Pads and discs.

Once the pads and discs bed in all should be well.

The discs come with a fine layer of grease to keep them looking good while in storage, you did clean this grease from the discs before fitting with either brake cleaner, thinners or surgical spirit or something like that??????

[Dead Eye]

If anything, there is slightly more pedal travel than there was before - I wouldn't be worried about less travel :P

Some brake cleaner was used... but I wasn't specifically cleaning the discs. I expect that to "burn" off soon enough

[unfazed]

If anything, there is slightly more pedal travel than there was before - I wouldn't be worried about less travel :P

Some brake cleaner was used... but I wasn't specifically cleaning the discs. I expect that to "burn" off soon enough

If you have more then you need to adjust the handbrake more, press the pedal as hard as possible and with it held operate the handbrake a few times pull it up well. With the handbrake up release the pedal and try again This might put it over the next notch of adjustment and reduce the pedal travel.
After a few 100 miles do it again as the pads will have "settled"

[Dead Eye]

I've never heard of that before - I assumed the handbrake was on its own auto-adjustment. The handbrake itself hasn't been adjusted and operates just as well as it did before, so there's one plus side...

Just went out for a nice evening cruise and the pads are definitely beginning to bed in - brakes are beginning to feel more normal. I'll check out the handbrake adjustment method you've described to see if it makes any difference - the pedal travel has always felt a little different compared to other cars I've driven

[unfazed]

With rear disc brakes the handbrake operates the Caliper piston with a screw type system, which is why you have to wind the piston back on the screw system when replacing the pads, unlike the front where the pistons can be pushed back 

As the pads wear the piston is pushed out and operating the handbrake sets the automatic adjuster to take up the slack

[davidkent]

I bleed my brakes with the engine running... Done several cars on the 2 man method with the engine running, especially if it has ABS etc..

And As above with the handbrake off also...

[RobG UK]

Doh