"Spongy" brakes....pads to blame?

[jonathanc]

Well recently I've "upgraded" the front and rear discs + pads for my Audi A8.

 

I have this annoying brake pad worn warning light came on and also the braking feels spongy, even after doing 100 miles. The garage has already fully bled the whole system. According to the mechanic he says the vented,grooved and drilled discs I've got on the front are to be blamed. (Rears are EBC jobbies and OEM pads)

 

I've also heard I should get better pads like EBC for the front discs as they are the performance type. I've bought the cheapest 30 quid pad for them.

 

So, question is : Will changing the pads solve my problems?

[Rob]

Did they purge the ABS unit? Is this an Audi garage, or if not do they have VAG-COM software and interface?

I can't see pads making the brakes feel spongy unless the pads are, well, made of sponge.

 

Do the upgrade pads have the electronic wear indicators built in that OEM audi ones would have? If not then the ECU is expecting some resistance across the system (so to speak) and being unconnected will register as a fail.

[jonathanc]

Did they purge the ABS unit? Is this an Audi garage, or if not do they have VAG-COM software and interface?

I can't see pads making the brakes feel spongy unless the pads are, well, made of sponge.

 

Do the upgrade pads have the electronic wear indicators built in that OEM audi ones would have? If not then the ECU is expecting some resistance across the system (so to speak) and being unconnected will register as a fail.

 

Good question. It's not the Audi garage but the guy said he had the VAG COM OBD2 unit although I suspect that's the same one I had from eBay as well. I don't think you can purge the abs unit can u? Erase codes?

 

I am not sure if the upgrade pads have the wear indicator to be honest. I've bought the cheapest one but its compatible for my car. How do I make sure if they do? edit: I guess I should order from Audi then. Hopefully can find on eBay else its stealership I guess)

 

However you've been a brilliant help mate! I've never thought of it this way before. I might do some research to see if I can purge the Abs system. Does that make the brakes spongy? It's not really responsive at all although when braking (really) hard I can feel the ABS slightly working.

[Terminator]

Not all "upgrades" are that in reality. Spongy peddle is down to air in systems, as it will compress and expands. As brakes are the last thing saving you and some other road use from impact, buying the cheapest is not the best idea, OME spec would be the lowest that should be considered.

[jonathanc]

Not all "upgrades" are that in reality. Spongy peddle is down to air in systems, as it will compress and expands. As brakes are the last thing saving you and some other road use from impact, buying the cheapest is not the best idea, OME spec would be the lowest that should be considered.

 

Thats the first thing we've suspected mate. He bled the whole thing out just to make sure and apparently shouldn't be any air.

 

I might start to hunt for some OEM pads for the mean time although I am really curious about the ABS unit theory. Never really heard of this one before.

[Chris Wilson]

Neither pads nor discs are compressible, look elsewhere. Hose, anti squeal shims deformed, air in ABS unit, air master cylinder, seized caliper or caliper sliders, worn hub bearings.

[Rob]

Pads with wear indicators will have a plug hanging out the back of them, this plugs into the plug hanging near the strut arm.

If they have nothing, the garage will have zip tied the car-end plug somewhere....or...if they are feckwits, they will have snipped off the wires. Lets hope its not the latter.

[jonathanc]

Neither pads nor discs are compressible, look elsewhere. Hose, anti squeal shims deformed, air in ABS unit, air master cylinder, seized caliper or caliper sliders, worn hub bearings.

 

Will do. It does stick abit when I try to rotate the disc using my hands but not too much. The guy used an automated system to bleed the brake fluid and according to him its virtually impossible to get air in, at least only negligible amount.

 

I will relay what you said to him and see what he says.

 

@Rob: When you said purge ABS unit did you mean electronically or physically purging the unit itself?

[Chris Wilson]

Sounds like the caliper sliders are seized, assuming the car has sliding calipers. If someone presses the brakes on and off hard someone else should see the caliper flexing if something's stuck.

[jonathanc]

I've found this using Google :

 

IIRC there is a procedure to bleed the brakes using the vag-com.

You put the car up on jacks,

connect the vag-com.

Select ABS

then one of the options on the ABS screen gives you the testing / bleeding procedure.

 

You need 2 people, one to operate the vag and the brake pedal the other to bleed the brakes as required by the

vag display.

 

The software takes you through the whole process telling you when to apply brake pressure and what bleed screws

to open and close.

 

IIRC it's just the front bleed screws used.

 

someone else on a gti-vr6 website or something,

 

Then cycle the pump using the VAG-COM software. To do this, choose “ABS Brakes” from the main menu.

 

Then select “Test Output” and follow the on-screen instructions.

 

The computer will cycle the pump, and then test each of the valve positions, one corner at a time.

 

After this is done, you should have good brake feel again.

 

I’ve heard that running the pump for more than 30 seconds or so could lead to the pump overheating

and susbsequent damage, so accomplish this procedure reasonably quickly.

 

from Ross tech themselves,

 

Procedure for Bleeding the ABS Brake Pump on VW Golf, GTI, Jetta, and Audi TT:

 

[select]

[03 - ABS Brakes]

[basic Settings - 04]

Group 001

[Go!]

 

My mechanic has no idea what this is and I reckon the VAG com tools we have also doesn't seem to have that function. I've asked him countless times about air in system and seizing calipers but according to him he is adamant that's not the case.

 

I think I would have to bring the car down to the dealership then.... need good brakes for the winter!

 

edit: just spoke to him again and he says according to him the brakes feel normal before they are servos? Not very sure myself but there's no braking feel at all until more than halfway down. Even then you have to really give it the beans to stop the car...

[Rob]

I would take it to the dealers then. He's not clued up on VAG if he doesn't recognise that stuff.

 

It's not difficult to get into VAG but once in, if you make any mistakes it can get messy and cause problems months later. Maybe you're better off spending your wad elsewhere.

[jonathanc]

I would take it to the dealers then. He's not clued up on VAG if he doesn't recognise that stuff.

 

It's not difficult to get into VAG but once in, if you make any mistakes it can get messy and cause problems months later. Maybe you're better off spending your wad elsewhere.

 

I do have a nifty VAG COM that reads error codes and resets service intervals. It could reset some minor errors too but I guess that's as much as it goes.

 

That's the pain of buying cars like this sometimes. Yes, they depreciate a lot so price might be cheap but once something goes wrong it gets really expensive lol.

 

Sent off some enquiries to my local (ish) Audi dealers and now bending down and preparing for the onslaught.