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Bleeding Brakes

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Bleeding Brakes

I Need to change the Brake Pads on my car and was thinking of doing this over the weekend, it's a job I have done a few times before on other cars but the last couple of times the brakes felt very  '  spongy'. This would indicate air had somehow got into the brake system but I can't understand how that could have happened, however a few car internet sites recommend that you release the bleed nipple on the wheel you are working on with a tube terminating in a jar of break fluid so when you push the piston back to make room for the new pads the fluid is forced out through the bleed nipple and not all the way back to the main chamber ?
Has anyone who has done this job before got any ideas or tips before I embark on this project.
The Local garage want £100 for the job including VAT. The Pads and brake fluid have cost me a quarter of that.
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Re: Bleeding Brakes

Whenever I've changed brake pads / shoes on cars it has just been a matter of keeping an eye on the fluid level in the reservoir to avoid spills.
If the brakes feel spongy then a full bleed of the system may be required bearing in mind special procedures for ABS systems.
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Re: Bleeding Brakes

Changing brake pads should not normally require any bleeding of the system. When the pistons in the callipers are withdrawn the fluid in the master cylinder will rise slightly. Do one pad at a time to minimise this effect. A word of caution, brakes used to be a relatively simple job however brakes on modern cars are more complicated. For example my previous car, Audi A4, required a special tool to withdraw the pistons on the rear brakes. My current car Audi A6 need new rear pads and it seem the car need to be connected to a computer to withdraw the piston to fit new pads.
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Re: Bleeding Brakes

Never really had to worry about it to be honest. When changing the pads you're only moving the piston back so the fluid should simply run back up the pipe slowly into the reservoir.. in theory. Having said that, whenever my mates do it they always insist that you have to pump the brake pedal afterwards. I've never done this and found that as soon as you start the car the brake system does all it needs to anyway however my car is a bit of a freak and probably does its own thing differently to most anyway (it's french, rare and nothing is normal on it).
That said, I did have to do a rear caliper replacement recently for the MOT. That was a slight pita as I didn't have a windback tool so had to get creative. The cable was also a pita too but I got there eventually. When it came to the fluid, I didn't even bother with the jar method as I didn't have any pipe so I just got the SO to pump the pedal slowly and gently with the valve open, closed it before the pedal came back up, opened it for the pedal down etc until there was no bubbling. Failing that though, as you said you can use a jar with fluid in the bottom covering the end of the pipe and just pump the pedal a few times so that the air is forced out and surfaces without getting back up the pipe. Be sure to check the fluid level in the reservoir after and top up from the jar as needed.
I've never opened the bleed nipple just to move the piston back though.. seems odd to me although I did once see the reservoir squirting fluid out of the pressure release hole  Cheesy
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MJN
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Re: Bleeding Brakes

I'd recommended a one-man bleeding kit e.g. this Draper one as they're cheap as chips and make bleeding a doddle. When was the last time your fluid was entirely replaced? It should be done every few years and so now might be an ideal opportunity to do it.
As the others have mentioned, simply fitting new shoes/pads shouldn't require you to bleed the brakes afterwards. However, it is worthwhile doing not only to maintain optimum operation but also to help prevent the bleed nipples from seizing up.
Mathew
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Re: Bleeding Brakes

And, please remember that brake fluid can be quite nasty stuff - read the warnings and take care.
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Re: Bleeding Brakes

As mentioned, by others... you should only need to force the pads away from the disk..(judicial and careful use of large screwdriver)  (or tyre lever) (don`t scratch the disc)  to give enough room for the new pad(s) to be installed.... no air should get in the system, as the fluid is being forced back up to the reservoir... keep checking to make sure that it is at correct level and not overflowing...
I reckon the job should take a competent mechanic about 30 mins to 1 hour max, at £20--£25 per hour... plus the parts... so £100 is a bit OTT....
Do you have any "mobile mechanics" in your area?
Check on Google, for a forum on the make/model of your car, and see if there is some helpful advice going on there...
MJN
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Re: Bleeding Brakes

Quote from: Oddball
My current car Audi A6 need new rear pads and it seem the car need to be connected to a computer to withdraw the piston to fit new pads.

That'll be due to the electro-magnetic handbrake. The computer is merely to release the brake to allow the piston to be retracted.
Any other system, i.e. with a cable operated handbrake, is serviced in the conventional manner.
Mathew
MJN
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Re: Bleeding Brakes

Quote from: shutter
[...] at £20--£25 per hour

Crikey, where do you live?! You could double that around here at least!
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Re: Bleeding Brakes

Thanks for the feedback.
Strat, you mention special procedures for ABS ? This particular car has ABS and it's rear pads I am changing. What specific procedures do you need to do ?
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Re: Bleeding Brakes

Basically disconnecting the battery before starting work on the braking system and leave it until all work is finished before reconnecting.
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MJN
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Re: Bleeding Brakes

Some ABS systems have a specific bleeding procedure for the ABS pump, however for what it's worth the service manual for my Hyundai Coupe explicitly states that no special measures are necessary and hence presumably this could well be the norm. It's the manufacturers call on what, if anything, needs to be done so a Google search for your make/model might be worthwhile. It could well be necessary to use a scan tool to open the valves up to allow it to be bled independently. As long as you're not depleting the fluid from the system, and thus introducing air to the pump, then you shouldn't have any issue though.
I am curious as to why the battery needs to be disconnected though? Assuming you're not working with the ignition on then the ABS circuit should be dead. Perhaps on some cars this is not the case - is it a particular vehicle you had in mind Strat?
Mathew
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Re: Bleeding Brakes

Nothing in the Haynes workshop manual about a specific procedure other than removing the key from the ignition.
I Have watched a number of you tube videos and apart from one instance where mention is made of removing the fuses for the ABS whilst the work is being undertaken no other mention is made of this.
Not sure why you would need to disconnect the battery as no electrical components are being touched and the only work to be done in the engine bay is to remove the old fluid with a syringe and replace it with new whilst taking full precautions not to spill any on anything.
I Note the new pads did not include new clips or shims so hopefully the old ones can be cleaned up ok.
Only other conflicting advice regarding bleeding the Brakes is where you start ie nearest to the master cylinder or the furthest point from it ?
MJN
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Re: Bleeding Brakes

The disagreement about where to start is likely down to the advice originating when brake systems were clunky single circuit affairs and starting with the furthest would expel the most air on the first go. However with modern dual circuit systems, with much less volume, it arguably doesn't matter which you start with - unless of course the manufacturer has specified it in order to accomodate whatever particular nuances their design has.
Mathew
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Re: Bleeding Brakes

+1 on the Draper one-man-system, used it on my Mondeo for quite a few years now, it has a one way valve in the hose to allow the fluid out but no air in, I think I paid about £6 for it from the local car shop.