Uneven rear caliper wear ('04 FWD Passat)

[SirWired]

I recently experienced grinding on my RR brake. Took it apart yesterday and the outer pad was fine, but the inner was down to the backing plate. (The LR caliper was fine; nice even wear on both pads.)

The car has 147k now, these pads have been on since 30k, I think. (I drive like a granny and have an M/T... I'm still on the original fronts!)

The slide pins look good as new, slid smoothly, still had grease, and uncompromised boots. The carrier does not have any visible issues where the tabs slide. The brakes were not dragging (I notice, since they were making such a racket.)

I went ahead and changed the pads/rotors. (AA house parts (Platinum Ceramic pads, house rotors); I needed the car up and running quickly... in retrospect I should have assumed I would need to do a brake job no matter what the problem was and mail-ordered better stuff, but I digress.) But obviously I don't want to grind through my new pads/rotors in a hurry, so it would be good to figure out what the problem was/is.

Any ideas? The only thing I can think of is to just assume it's got something to do with the slide pins and throw a rebuilt carrier at it. (The carrier includes and houses the slide pins.)

 

[Falken]

I am not sure, but if the guides slide well but you have inner pad wear, verify the operation of the handbrake, maybe something is dragging slightly?

I have to excuse myself as I never really paid attention to how a VW Handbrake operates on a rear disc to diagnose it.

 

[SirWired]

The B5 Passat handbrake simply extends the piston slightly, just like pushing the brake pedal. (It is cable-actuated, and the cable pulls on a lever on top of the caliper. This goes some mechanism that runs on magic to extend the piston.)

It's one of those rear calipers that requires turning the piston while pushing it in order to retract it for a pad change.

 

[Nick1994]

Rear brakes are usually an issue with the A4 VW chassis. Usually the parking brake cables stick.

My 2004 VW Beetle TDI (DSG) has 175k miles on original front brakes, still have 3/4 pad left.

 

[cat843]

Flex brake hoses can be internally constricting but look fine.

 

[SirWired]

But wouldn't a stuck mechanism or plugged hose case both the inner AND outer pad to wear (and cause brake dragging on that wheel)? There's nothing special about the forces applied by those things vs. just pressing on the pedal (other than happening all the time.)

 

[CT8]

Sometimes you may have to keep on fixing it untill you get it right.

 

[silveravant]

Easy way to check if the emergency brake mechanism is dragging is to check the disk for heat after driving. I could tell when my Jetta emergency brake was dragging just by walking past. I've had really good luck with Centric calipers. The last ones were powder coated black. Work well, look good,

 

[Trav]

Its the parking brake mechanism hanging, sometimes its the cables other times its the caliper itself, I change quite a few of both.

There is a small rubber boot on the cable that deteriorates and lets water run down the cable core. Disconnect the cable from the caliper and have someone pull pull up on the brake handle and release it, the cable should move freely by hand if not change it.
If its free the caliper is hanging, either way the thing will burn through the new brakes quickly.

When I change the cables on these I saturate the entire inside with gearope from Kano labs, the stuff is amazing in this application, it flow down the inside then thickens. Put 2 small zip ties around the boot ends and its good for many years.
If the caliper is mechanism is sticking just replace it with a reman from AA, at least they give a lifetime warranty on them.

GEAROPE Gear and Cable Lubricant from Kano.

http://www.kanolabs.com/indLub.html

 

[KGMtech]

if you did not use the special caliper piston tool to retract the piston, you've messed up. VW / Audi of that vintage use a parking brake design that does require a special tool to replace pads at rear.

 

[spk2000]

When I worked at the brake company we purposely made inner pads thicker by about 2-4mm as it was know inners wear faster than outers. I never understood why but only knew it happened.

 

[SirWired]

Again, if it was the p-brake hanging (or the piston getting stuck), why would that cause uneven wear? I could understand if it wore out BOTH pads on one side vs. the other, but why just one pad on one side? On the other side, both pads were worn evenly.

And yes, I used the correct tool to retract the piston.

 

[supton]

I don't know if the Passat is like my '04 Jetta, but my Jetta did have problems with rear pads. Too easy for rust to build up and causing things to not slide. Got to the point where I'd just take everything apart spring/fall and regrease, either 2x per year or every 5k even.

On my Jetta I think the rear calipers were a weak design, prone to corrosion. Each time I did brakes I'd find one piston hard to turn in. Wound up replacing calipers each time rear pads were due.

Odd that RR has the issue. I'd expect worse on driver side, as it likely sees more wet weather.

 

[Tegger]

Originally Posted By: SirWired
why just one pad on one side?

When the INNER pad wears most on a floating-caliper brake, it means one of tthree things:
1) the caliper is unable to move on its sliders
2) the OUTER PAD is unable to move on its mount bracket
3) the piston is sticking in its bore

Point 1:
You seem to have addressed point one.

-------------------

Point 2:
BOTH pads should require EQUAL effort to remove from the mount bracket. And that effort should be ZERO.

You should be able to use only light fingertip effort to remove the pads; the pads ought to want to fall out by themselves unless restrained by anti-rattle springs (I'm not familiar with the specific VW setup).

If you had to pry or do anything more strenuous than opposing any anti-rattle springs, then that pad is seized.

-------------------

Point 3:
If the piston is sticking, this is usually accompanied by high-heat at that wheel, a burning odor, and sometimes even smoke.

Sticky pistons are normally caused by rust on the piston. The piston will be just fine until it is turned back into the bore at a pad change. After that is when it starts sticking.

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