Brake pad/disc replacement gone wrong!

[RyanE1992]

Hey everybody

 

I have just completed a complete service and thermostat replacement with a complete flush through... thank god thats over.

Leaving the easy stuff till last (He says) i was going to replace disc and pads on my vrs mk2 tfsi.

 

First issue torx screw rounded, will probz drill out and if i damage the thread leave it out.

Stupidly, like really really stupidly i went in to get some brekkie this morning and came out with my bro to my car. i asked him to put foot on brakes just while i remove the other screw holding the disc on the other side. forgetting that the caliper has already been removed on passenger side :/

 

You guessed it out popped the piston on passenger side front caliper...

i popped it back in and spent a bit of time carefully getting it perfectly straight and pushed it back in.

I have now introduced loads of air into the caliper. Is this OK to go ahead and bleed? or by popping the piston out could it have caused other issues?

Im not sure how low the brake fluid went down in the resorption as no fluid poured out as such. just what ever got behind the rubber seal. Would you have thought that the level got sooo low in the reservoir that i will now need to bleed clutch and everything else on my car haha?

 

Im going to bleed all the brakes by flushing new fluid through it, however i dont want to do anything wrong here if the reservoir fluid did get too low.

Ive heard about activating abs before bleeding, mainly if there was air sucked into the system. how low does it need to go before air gets sucked into the system?

 

Any advice will be much appreciated. And im sorry for being stupid! hadn't had my coffee :(

[RichieXR2]

As long as the fluid level in the res didn't drop too much you will be ok just to bleed the 4 wheels and most likely the clutch. 

 

Caliper should be fine as long as you didn't nick the seal inside the caliper when putting the piston back in (unlikely). Just make sure the dust cover is seated into the piston properly. 

 

You need to bleed the brakes from the furthest away from the master cylinder so RL,RR,FL,FR. I believe the dealers pump through 250ml through each caliper and 150ml the clutch. 

[Guest]

The clutch will be unaffected.

 

Its feed from the master cylinder reservoir is at the top so once fluid is in the line it's there for good.  Unlike the brakes which are fed from the bottom of the reservoir.

 

If the clutch has never been bled then you might as well spend an extra 20 minutes doing it.

 

If you put everything back together correctly then bleed as normal, the book says LF, RF, LR, RR.

[RyanE1992]

35 minutes ago, RichieXR2 said:

As long as the fluid level in the res didn't drop too much you will be ok just to bleed the 4 wheels and most likely the clutch. 

 

Caliper should be fine as long as you didn't nick the seal inside the caliper when putting the piston back in (unlikely). Just make sure the dust cover is seated into the piston properly. 

 

You need to bleed the brakes from the furthest away from the master cylinder so RL,RR,FL,FR. I believe the dealers pump through 250ml through each caliper and 150ml the clutch. 

 

15 minutes ago, MicMac said:

The clutch will be unaffected.

 

Its feed from the master cylinder reservoir is at the top so once fluid is in the line it's there for good.  Unlike the brakes which are fed from the bottom of the reservoir.

 

If the clutch has never been bled then you might as well spend an extra 20 minutes doing it.

 

If you put everything back together correctly then bleed as normal, the book says LF, RF, LR, RR.

Cheers for your input guys. 

your both saying different so I found this video which also suggests front left first. so may do it that way?

http://www.micksgarage.com/blog/project-gti-how-to-bleed-your-brakes/

 

just for clarification say I do bleed everything how would I know if the abs needs to be run so I can bleed? would abs not work? 

 

also hopefully seal isn't damaged. Couldn't actually see it as dust cover was in the way. fingers crossed it has seated ok. will find out I suppose when I bleed it and see if any fluid seeps out when I put foot on pedal?

 

 

[Guest]

You'll know if you've got air in the ABS pump as you'll have a spongy pedal and ineffective brake performance.

 

The ABS pump will still function as before but will not perform as desired due to compressible air in the system.

 

Hydraulic brake systems rely on being totally air-free from master cylinder, pipework, ABS pump, pipework, calipers. Otherwise a spongy brake pedal feel and lack of braking effect is the result.

 

Unless you were brutal returning the piston in the caliper I doubt you'll have cobbled the seal. More likely you'll have introduced dirt etc to the caliper bore and seal which may cause a fluid leak and accelerated wear.

 

I would have ensured it was cleaned up before reassembly, taking time to remove any corrosion on the piston and removing/cleaning both the piston/dust seals.

 

You may be lucky and get away with it however be prepared to purge the ABS pump via the OBD port to obtain satisfactory braking.

[RichieXR2]

My apologies on bleeding order. 

[Guest]

When doing major work on a caliper I've always used locking grips on the flexible rubber brake line feeding it to isolate it hydraulically from the rest of the system.

 

Not enough to crush them just enough to pinch and stop fluid loss/air entry.

 

When reassembling the caliper loosen the bleed screw to allow easy piston entry then nip up bleed screw, remove grips and bleed as normal.

[Guest]

Re bleeding order.

 

No need to force any used fluid/air any further than it has to to go.

 

Get it out of the system as soon as you can i.e. calipers nearest the master cylinder first.

 

Of course some systems will have a different sequence for optimum bleeding.

[RichieXR2]

Everything I've read/done in the past has said to start at the furthest away caliper/cylinder.  

[maul]

As your car is over 3 years old then losing the old brake fluid  and having to replace it all is actually a good thing. Brake fluid absorbs moisture  if it's old its probably fair to say it has more water contamination in it than you want. That will cause corrosion inside your brake components. And it is also possible under extreme conditions for it to boil and cause your brakes to do some unexpected things. Better to replace it all and not have to worry again for 3 years. Its not like its expensive and if you are doing the discs and pads anyway it makes sense to go that extra little step.