sticky brake to soft pedal

[unclebob]

Afternoon all,

My rear driver side brake was sticking, so i had a look at it today. Its on a 55 plate TDI sport 2.0 with bkd engine.

Jacked up took tire off etc. Put bricks in front and behind the three other tires, and handbrake off.

Piston was stuck about half out (pads still have life in them).

Wouldn't budge with a piston winder so i assumed that must have got some crud in the pot itself causing it to stick in place. The dust seal was also not properly sealed at the caliper end, and there was a small rip and the pad end...

Pumped brakes slowly to get piston to come out some more, then managed to use winder to put it back a bit until it loosened up.

Eventually was loose, but because of the state of the cover i bought replacement seal kit. pumped the brakes slowly to get the pot out, lost some brake fluid as expected. (note this was all done while brake line connected to the car!)

New seals came with instructions to soak for 45 min in fluid before installing. So soaked them while i cleaned up around the existing seal and where the dust seal would be reseated.

Put the cylinder seal in, and then put the dust seal over the cylinder, pushing it back away from the pad end. Put the end of the dust seal into opening, then gently pushed the pot into place. Once there was enough space, pushed it further using the winding tool, until it was more then half way in.
Assembled the brake pads and caliper back onto the car.

I bleed that caliper the old fashioned (and maybe wrong way!) - topped up master, left it open - a fair amount of dot 4 went in even though the level was fairly high, as i topped it up, it disappeared into the reservoir. Pumped brake pedal a few times, then opened the nipple. Few spurts of air/dot4. as the pedal went down.
Sealed it up and repeated until just dot4 came out topping up the master a few times in between. The pedal got harder to push in each time as it did when the engine is not running.

Eventually couldn't pump any more, so turned the engine on to soften up the brakes again.

Pumped it a few more times, and turned it off, repeating bleeding again - no air came out just dot4.

Problem i have now is when off, the pedal feels rock solid.
As soon as i turn the car on, the pedal goes hard, then slowly sinks down.

Hand brake is still down at this time. Any ideas what could be causing the slow sink? Wasn't there before i changed the seals...

(i have since read i may have popped the seal on master but hopefully not!)

 

[unclebob]

An update on this...

I took the car for a drive up the road, slammed on brakes to clear abs of any air that may have got in. No change.

Stripped the caliper down to make sure seal didn't kink or get damaged. All good.

Bought eezibleed, air out dot 4 comes out but still spongy brakes.
(Only bled the one I worked on though not all 4.

Any ideas???

 

[unclebob]

Also hand brake stops a lot higher then it did before too- something I was suppose to reset in assembly?

 

[robint]

There is a specific procedure for resetting the handbrake after changing pads and rewinding the pistons so that the screw is correctly set. Cannot remember exactly what it was but involved putting handbrake on a few times. Suspect it is similar on a load of VAG cars so have a quick google.

 

[SNAP-ON]

Sounds like air in system to me . All vag group of cars can be an absolute ass to bleed after rear caliper or hose replacement . Spent hours the other week bleeding an audi tt .
Brake pedal should be hard went engine off and then soft when engine running as you know as servo is being used and most diesels have a sinking pedal when you just sit there with your foot on it .
When you wound the piston in did you wind it back out until the brake is very slightly grabbing ?
When changing pads you should wind piston all the way in , fit new pads then gently wind the piston back out with the tool until you can just about get the caliper back on . This then gives good footbrake and handbrake . If you dont wind piston out and just refit then the brake pedal will be crap as will the handbrake . If u did the proper way then u may have air trapped in system so try (if fitted) bleeding the 2 bleed nipples on the master cylinder itself as this normaly solves the issue .
I would personaly fit a new recon rear caliper as u will have problems with the one u have just played with .

 

[unclebob]

Cheers snap - on. Gonna take the wheels off and bleed the whole system next week now just to make sure no air. I didn't open the piston back out so will do that at the same time.

What kind of problems and would it be because I took it off again? Or more the way it was taken appart/reassembled? (I ask as I still have a second pair of seals so if it's because I refit the piston ill chane the seals again before I bleed the system. Also any pointers as to where I'll find the master cylinder nipples? Please tell me it's not under the storage tank as that looks like a pig to get to...

 

[unclebob]

Btw never had the sinking feel in un this car before today- it's news to me that it's common on other tDi,'s!

 

[SNAP-ON]

Ok now you have explained it clearer it sounds to me that u have incorrectly set up the rear caliper by not winding the piston out . This WILL give a crap/soft pedal due to the piston is pumping out to much as you apply the footbrake and this in turn gives a crap handbrake . No need to restrip the caliper it just needs setting up properly .
Start by removing caliper from carrier with the 2 bolts and wind the piston in fully . Now with the pads still in the carrier slowly wind the piston out a small amount at a time and each time just refit the caliper back onto the carrier until you can just about get it on and you can just about turn the wheel . This in turn gives a solid pedal and good handbrake . A good way to visualy see if its set up good is to remove the wheel and using your hand push the handbrake lever on the caliper closed and see how far it moves until you cant turn the wheel by hand . A good set up will be very minimal movement on the caliper lever . If you can move the lever almost half way its set up wrong and piston needs winding out further which in turn will give less lever travel . Hope this helps .

 

[unclebob]

Thanks snap-on. Will unwind first and see what that gives me before moving on to bleeding if still soft. Your input is very much appreciated as from what I'm reading on other threads makes me think taking it to a mechanic will most probably give me nothing better then I have unless they deal with vag cars!

 

[unclebob]

Progress:

I wound the piston all the way back, with the bleed nipple open. Two tiny but significant bubbles came out of the caliper.

I measured the thickness of pads and disc, wound the piston out to just before this amount and put it in ( tight fit!). Tested as per snap-on ' s directions and hand break back to normal. Breaking improved but still sinking.

With engine running:
First press: pedal grabs, stops halfway and car slows/stop. Keeping the pedal pressed it then starts to sink. Release pedal and then reapply same but pedal doesn't sink as much. Release and apply third time and no noticeable sink. I'm guessing air bubble still somewhere? Going ot order fresh dot 4 and flush the whole lot out. Anyone know approx how much the system holds? Also still not able to identify bleed nipples for master cylinder :s

 

[SNAP-ON]

Glad u have had progress ,and i am a vehicle technician lol . Sounds to me like trapped air in the system normaly between rear hose by axle and caliper . Can be a bummer to get air out had same issues with golfs and tourans . Good way to tell is as u have already said drive car and apply footbrake then off and back on and it will feel better almost like you can pump it up .
Not sure if altea or leon have the master cylinder bleed nipples as not looked yet but if so there will be 2 and an absolute bum to get to and bleed . There normaly both on same side and 7 or 8mm .
Another thing you can try to rule out if trapped air is to clamp that side rear flexi brake hose by axle not caliper and give it a drive . If good pedal then air trapped after that hose .
You may end up having to stick vagcom on it to allow you to bleed system but this is normaly only the case after the abs pump is replaced . Hope this helps

 

[unclebob]

Thanks for the reply.

Going to order a fresh 5 of dot and flush the whole lot as much as I can using pressure flush system. Hopefully will clear out any trapped air in pipework and hopefully it's not stuck in the cylinder somewhere.

Looking online at replacement masters can't see any nipples just feed /return so I guess I'd need to loosen those to bleed he cylinder itself.

Job for later in the week

 

[unclebob]

So bled the whole system- 2 and a bit litres came out of not clean fluid, compared that coming out to going in to check if it was flushed.

Back became a two man job even with the eezibleed as at best there was a few drops every 10 seconds from the back. Ended up turning the engine and pumping the pedal gently half way repeatedly.


The fronts worked without engine running or pumping of pedal.

Feels better but still got that sinking feeling the first press... will see how we go over the next few days but much improved. Not sure if it was bad dot4 the first time, a bubble or something else but seems to be much better. Still not found nipples on master so not done anything at that end just the 4 wheels...


Any ideas re the sinking pedal? Pops back up straight away as normal just sinks when held

 

[robint]

Just a thought - had a similar problem years ago on a MG Midget where the back brakes where behaving oddly - that was an internally collapsed rubber hose - no visible damage externally. Meant that fluid could (just) get to the back brakes with pedal force but there was not enough return pressure to free the brakes - was similarly difficult to bleed. May be worth disconnecting a hose or two to see where fluid comes from easily, just in case you have a similar problem.

 

[unclebob]

Brakes seem free now after cleaned up the piston and put a new dust cover on but may give it a go if still not sure it its back to right!