Greetings, and some brake advice please!

[grobba]

Hi all, quick one to say hello and hopefully get some assistance from any braking gurus out there!

Having owned a few Audis over the years - Coupe GT5E, 90 20V Sport (best car ever!), A4 Avant Quattro 2.8, and now a A4 Avant Quattro 3.2 FSI S-Line, I've (had to) become reasonably familiar with tinkering and DIY maintenance, although slightly less so as the technology progresses.

My latest endevour was to replace the front disks and pads, which initially appeared to go smoothly enough, the previous disks had worn/corroded 'very' badly on the inside, the outsides were fine.

New disks and pads are Pagid, brakes are 1LA front and 1KW rear.

Having taken the car for a test drive, and driving about town for a few days the brakes were fine and felt like they were bedding in nicely. However, recently had to go for a longer journey, and at 60-70 mph applying the brakes moderately felt like the car was pulling left, not that the steering was getting pulled, but seemed like the car was 'crabbing' a bit.

I've checked the tyres are correctly inflated, and double checked all fasteners are torqued properly, and that there's no contamination on the disks, I was also careful to clean up the contact points between the pads and the carrier, and lubed lightly with copper grease, to ensure a sliding fit. The caliper pistons didn't appear to be stuck when pushing them back in.

I'm confused as the car did not behave this way prior to the new disks and have never seen this on any brake jobs done in the past. The rear disks/pads are also due for a change and have some new disks/pads waiting to be fitted (as soon as I find my rewind tool that's stored very safely somewhere). I wonder if they could be causing an issue somehow, but then again the behaviour only started after fitting the new front disks

Any suggestions would be welcome, and sorry for the rambling introductory post!

Cheers.

[Trevor]

Hi .... and welcome to the Forum

I can only imagine it is binding on one side of the car, enough to pull it in one direction. easiest way to check is the temperature (check with a temp gun to see which side is hotter, if they are the same then not binding)

Did you clean up any slider pins (assuming the caliper is the sliding, single piston type?

Other areas to check would be brake hoses, any restrictions on them (twisted, hose clamp still on, etc)

Let us know how you get on with it

Cheers   Trevor

[grobba]

Thanks for reply Trevor,

I checked the temps. yesterday after returning from the 'longer journey', they were both about 55 DegC +/- a few degrees, they probably cooled down a bit by the time I'd dug out the temp. gun though. I'll try again directly after some braking. I didn't think they were binding, as the car rolls quite easily. The slider pins (with the 7mm hex socket) were cleaned up with fine wet&dry and a little copper grease applied. I'll have a look at the hoses again, although nothing seemed to 'jump out' whilst changing the disks.

I also wonder if the new 'grippier' disks/pads would highlight another issue under braking in the suspension somewhere?

After checking hoses, I think next step is to replace the rears anyway (corroded on inside as well), a bit more bedding in and if still persists get checked on a brake tester, will advise any progress.

Cheers.

 

 

[grobba]

OK - minor update regarding disk temps. after a drive around town and normal braking, checked the disks again - the left one was 80ish DegC the right one 60ish DegC, so bit of a difference after all, although not sure what an acceptable mis-match tolerance would be.. anyways that would indicate perhaps the right caliper getting less hydraulic pressure as the left? is stuck somehow? and/or a blocked hose?

I checked the hoses, visually they are OK, although a bit corroded at the unions on the chassis, lifted the car again and checked by hand for binding, that's OK.

I've read of some people, when pushing the caliper pistons back in, that they open the bleed nipple instead of pushing the fluid back up through the lines, the theory being not to contaminate the system, I just syphoned off the reservoir with syringe as the level went up, didn't really want to open the system up. I'm hoping  there's no crud somehow got into the caliper cylinder, the boots did look OK though.

Cheers.

[Trevor]

The recommended way to retract caliper pistons is to clamp the hose, release the bleed nipple (with a bottle and hose to catch the fluid) and then push/wind the piston in.

Reasons being, you don't push the fluid pressure back into the master cylinder which can have the effect of flipping the seals (used to happen on Vauxhalls a lot) and also you don't end up pushing pressure into the ABS modulator. The hydraulic system is designed for the fluid to be forced to the calipers but not necessarily to have pressure forced back up through the system. 

It sounds as though the caliper is only sticking slightly on the slider mechanism...maybe pull it back off and check and lube up again?