Hi nice people,
This is my first post here. I have a '07
Boxster
987 2.7 and from the day I bought it, it had strong vibrations under braking and a very long pedal travel- I replaced all 4 brake discs and the vibrations were gone, the indy replaced the brake fluid and noticed a ton of air in the rear lines. After that, normal pedal travel and no vibrations until ~5k km later, the vibrations under braking on the rear came back and one disc had a darker spot, plus some intermittent dragging noise right after releasing the brakes and a slight increase of the pedal travel.
I thought I messed up the discs due to overheating or defect and replaced them again together with the pads to another brand, same story, at the beginning fine, after ~4k km at high speed I start noticing a vibration on the rear axis, the pedal travel increased noticeably on the first press, if you press a second time, the travel and feel is normal. The intermittent dragging noise after braking is there for a few seconds.
With this a hit the wall and don't know what to do:
I checked if the hub was bent, and it was fine (unless my measuring tools and setup were wrong), but I see the mark of the picture, don't know it happened. Could this small irregularity be enough to generate the problem?
I hear a clunking noise on potholes from the rear, maybe a bushing has something to do with those vibrations under braking, but does not explain the dragging noise after braking.
At very high speeds (+200kmh) there are no vibrations on the car, only when braking and increases with the speed, which tells me it shouldn't be the hub.
I have two sets of wheels and it happens with both, I discard a bent rim.
Maybe is a seized brake caliper, but I feel the pistons move freely and since the dragging noise disappear after a few meters, it tells me they move okay.
I don't want to continue replacing parts without a better idea what it can be. I should start sanding down the irregularity in the hub, but want to check if someone had a similar issue or have any other idea.
Cheers and thanks for reading.
Hi Mr. Kroket… looks like you are doing a lot of DIY work on your car. Great way to know it much better!
anyway on to your issue, have you recently checked:
1. the master cylinder if it holds the pressures (no mention if the cause of the air in the system was identified)
2. The brake seals and pistons serviced? (Sometimes may need some seals replaced/pistons greased).
3. You also did not mention what pads you have or if they are stock/aftermarket.
4. Are you using the brake shims on your car or are those removed?
Something seems to point to irregular wear or action since it has recurred around the same mileage. on my last brake service for
987.2
I used Zimmerman rotors and those were nice.
Hi, thanks for your reply. Yes! I try to do everything myself when I can on my cars.
1. It does hold the pressure, but maybe is a very small leak.
2. Never serviced, only cleaned them on the surface, the car has 80k km but I guess with almost 20yo would be time to do it.
3. First I tried with TRW pads and discs, and I replaced them with ATE pads and discs.
4. On the rear calipers didn't have the shims as far as I remember, so currenlty is without them. Can they affect?
I should start with grinding this small damage in the hub, I will try in the next few days and post an update.
I would certainly remove any high spots on the hub. You could use a
dremel
or a flat cross-cut metal file. You're better with a depression than a raised area obviously - but I don't think that's the issue.
It sort of sounded as if the excess pedal travel happens about the same time as you experience the shudder under braking?
Usually shudder like this is uneven pad deposits on the rotor, usually caused by overheating the brakes, and staying on the pedal at a stop while the rotors are too hot. It burns some of the pad composite into the rotor causing a hard spot, which then causes shudder when braking.
I think rebuilding the calipers might be a good first step.
The reason I asked about the pedal travel is - the shudder caused by the uneven friction can push the pistons back into the caliper a bit, which then have to be extended the correct amount under the first brake application. Pretty much the symptoms you're mentioning.
If you aren't riding the brakes, or using them at the track - the noise you mention - along with the other symptoms to me would indicate a caliper with a piston that starts hanging up when the pad is worn a certain amount - accounting for the repeat at a certain mileage - and that hanging piston causes continuous pad rubbing on the rotor, which causes it to overheat even when you aren't using the brakes. Caliper pistons are actually pulled back into their bore a tiny amount by the square profile seal on the piston. It cocks a bit under extension (braking) and then pulls back when the hydraulic pressure is gone, pulling the piston back a tiny bit away from the pad. If the piston has a flaw in it at a certain point the seat may not work as designed in pulling the piston back. In that case, the pads rubs, you have noise
I'm going to make the WAG that a caliper rebuild or replacement will solve the issue. I've BTDT on a Toyota Supra I owned.. after the second set of pads/rotors I figured it out. Replaced the one caliper and that was the end to the problem.
Your symptoms (and a great job of describing them!) all point to the caliper being the problem.
Let us know how it works out - and when you have a bit of time, please post an intro with some pics of your car in our New Member Intro forum..
Good luck!
