Planet-9 Porsche Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
243 Posts
Discussion Starter #1
Hello everyone, i've a strange issue with my brake pedal.
Last week my struts were replaced (i installed the bilstein B6 in place of the stock items).
When i had the car back, the brake pedal felt strange, in certain conditions the first half of the travel was useless.
Took the car back, made a brake bleeding (without putting the brake line in pressure - only a classic mode bleeding), almost no improvement.
Took it back again, done another bleeding, this time following porsche procedure: 2 bar pressure, rear right/rear left/front right/front left. Done it twice. Didn't do the secondary circuit bleeding.
Anyway the mechanic who installed the struts assured me he didn't disconnect the calipers...
The situation improved, the pedal is definitively harder, but sometimes it becomes longer again. After pressing it twice, it becomes normal again.
The feeling is like brake pads not being close to the disc, and i need to "pump" one time to have the correct pedal travel.
It seems that this problem happens after i take narrow corners/roundabouts. The first braking after the pedal become longer. If i press it twice it's ok.

Any guess???
 

·
Premium Member
Joined
·
2,524 Posts
Sounds like air in the system. Think I read somewhere that once you got it in the system a secondary circuit bleed can help.
 

·
Registered
Joined
·
243 Posts
Discussion Starter #3
so i'll need to go to the dealer...

another thing: is it normal that the rear left quarter (let's say the rear wheelarch area) is much hotter than the right side? To be honest i've never noticed such a big difference as tonight!
 

·
Premium Member
Joined
·
2,524 Posts
I believe that software such as Durametric can also do the secondary circuit. I imagine there are others. You could try an independent shop in your area. They may have it. Or you could try another normal bleed. I've just read that bleeding the secondary circuit by activating the ABS pump has helped in cases that normal bleeding hasn't. No direct experience. Really does sound like air in the system when you have to pump it up to get a firm pedal.

Anything I'd say on the temperature difference in the rear quarters over the wheels would be speculative at best. I've never even checked mine. It could be anything from a sticky caliper, an exhaust leak, parking with the right side in the shade, to nothing more than the 987 not having an engine bay cooling intake on the left. Maybe someone else would have a better idea. I just don't know.
 

·
Registered
Joined
·
292 Posts
If it is taking one push to set the pad, perhaps you have a rotor not quite on correctly or a badly warped rotor. A rotor askew can push the pads back into the caliper when rotating (called knock-back) and then it takes one pedal press to re-engage the pads with the rotor. It seems unlikely a strut change could do it, unless MAYBE they dropped the car off a jack onto the rotor or something? Try a hard stop or two (hard enough to engage ABS) and see if that makes any difference. Does the long pedal travel occur after a longer stint without pushing them...like first braking after being on the highway? That COULD be pad knock-back.
 

·
Registered
Joined
·
243 Posts
Discussion Starter #6
No it does not require a long stint. One corner is enough, i just need to rotate the steering wheel.
Later i'm gonna check if discs and calipers are correctly installed anyway.
Can anyone try to run a maybe stupid test? Engine on, a couple if pushes to the pedal, rotate the steering wheel all on one side, then on the other, and on the center again. Press the pedal again. What happens?
 

·
Registered
Joined
·
243 Posts
Discussion Starter #7
Ok i removed all the wheels, pads and i checked the rotors.
The surface is not perfect (trackdays...) but they rotate quite good. The worst has approximately 0.1 mm of runout on the outer face, measured close to the edge.
I found a quite alarming thing, the external pad of the rear right side was split in three parts. See pic here https://goo.gl/photos/5mq7CSrgk7v36ELi7
That's a brembo pad.

For now i installed two old stock pads...

Anyway, all the other stuffs were good.

Tested the car, same problem.
It just take a short turn left or right of the steering wheel to create a longer pedal.

Does anyone know how power steering and power brake are linked?
 

·
Registered
Joined
·
292 Posts
If a turn seems to induce the pedal travel, perhaps you have a wheel bearing issue. The rotors are fixed, so fi the rotors are moving in/out, then that would cause the pads to move and could lead to first-application pedal travel. It certainly SOUNDS like something is moving and creating the travel.

After a few track days, I also was getting the first-application travel and went and replaced my rotors. I had some light cracking (less than .5 mm deep) on the rears, but I don't think this was it. I had some pedal pulsations as well which I felt could be causing the pad knock back. I would check for in/out play and see if anything is amiss. I can't quite picture what the shop could have done to cause it. Hmm.....
 

·
Registered
Joined
·
243 Posts
Discussion Starter #9
That sounds strange. I mean, the front discs were not even removed, while probably the rear ones were.
What i might try to do is lift the car, rotate the steering wheel and then check if i see any pad getting far away from the rotors.

With the steering centered i really didn't see anything loose, there was no play on the rotors or calipers.

I do have some pulsation on the pedal and noise, due to some material transfer from pads to rotors, but it was there also before replacing the struts. I can't quite understand what has changed.
I'm not sure if air in the brake lines can do something like that...
 

·
Premium Member
Joined
·
2,524 Posts
Air wouldn't cause pedal pulsation. Takes material transfer, warp rotor, bad wheel bearing etc to cause that. A wheel bearing will usually have other symptoms like a bit of shimmy in the steering wheel, at least when they get really bad. The shimmy tends to go away when the brakes are applied.

If I understood what you did correctly a rotor runout of 0.1 mm is ok. Particularly for used hardware. Doubt you'd do that good with a bad wheel bearing either. The material transfer you noted seems the most likely cause for pedal pulsation.

I don't know what to suggest beyond air in the system. Another thing you might try short of a dealer is just an old fashioned bleed. Have an assistant pump up the pedal and hold. Open the bleed screw and close before the flow stops. Do both inner and outer bleed screws. Sometimes the much higher line pressure will get trapped air when the 2 bar pressure bleed won't. Don't know what else to suggest.

In answer to the other questions there isn't a link between power steering and brakes. Try braking on a straight after waiting a bit and see if your pedal doesn't do the same thing. If it only happens when the steering is turned I'd check the wheel bearings again. Wouldn't hurt to go over all the nuts and bolts to make sure nothing was left loose also.

Forgot. Best guess on the cracked pad would be PSM applying the brake. Get the pad hot enough and the adhesive lets go. Or the caliper is sticking.

Good luck.
 

·
Registered
Joined
·
109 Posts
As a follow up to Bofus' comment, based on your symptoms that a turn creates long pedal travel, then something is causing pad knock back when you turn. Both the rotor (indirectly) and the caliper (directly) bolt to the wheel carrier and it's hard to see how there could be sideways movement between the rotor versus caliper but that seems the only way knock back could happen with a turn. I'd check to make sure ALL connections for the new struts are absolutely tight.

You may be able to check for knock back by turning to create the condition and then use a thin feeler gauge to check for any clearance between pads and rotors. (Of course, you would need to use only the parking brake after the turn.) And I'd start at the wheel where the pad was destroyed.

Good luck!
 

Attachments

·
Registered
Joined
·
243 Posts
Discussion Starter #12
Thanks for all the suggestions.
Yes it seems like something is moving in the corners, but it's quite strange.
If we have to consider any part changing position the rear should be out of the equation probably.
All the calipers are correctly bolted for what i've seen.
The bad pad was on the rear.

What i might try to do is really lift the car and observe if there's something moving while turning the steering wheel.

One more thing: while they made the first bleeding at the shop, i've seen one front caliper moving considerably while applying pressure. Didn't see the other. According to the guy making the bleed, that movement was normal.
Should i believe him?
It was like the caliper (or its support) was not stiff enough to support the pressure applied...
 

·
Premium Member
Joined
·
2,524 Posts
Can't say I've ever looked but the calipers are multi-piston fixed design and should not move visibly. Did any of the others move?
 

·
Registered
Joined
·
1,034 Posts
I agree with Les, the calipers should never move. Something is not right with your suspension or hub. I would suggest jacking the car up and see what is moving.
 

·
Registered
Joined
·
243 Posts
Discussion Starter #15
Tomorrow i agreed with a tyre shop close to my workplace - which i know very well considering how many tyres i replace - to jack the car up and let me give a proper look to suspensions and brakes while steering. I'd be relieved to find something visible and clear...
I called also a porsche dealer in milan, he invited me to go there on thursday or friday to test the car and decide what to do.

The movement seen on the caliper was a sort of "torsion" caused by the pressure. I imagine that a certain degree of torsion could be admitted, especially while the rotors are not rotating, but i don't know how much...

Didn't see the other 3, the bleeding was already done unfortunately
 

·
Registered
Joined
·
243 Posts
Discussion Starter #16
Update: i went to the tyre shop and checked for any moving part. Nothing, the pads don't knock back while turning.
According to a young mechanic working there there still is air in the system. He believes the bleeding was not done correctly. He made me notice that, when the pedal has the correct stiffness, if i press and keep it pressed with enough force it would slowly go down. So air in the system or something worse like a leak in the booster or master cylinder.
We also have seen that the two rear calipers need a rebuild. The rubber seals are hardedend and split... Dont't know if this could allow air to enter in the system, but it's surely not something happened in the last days.
Tomorrow we'll try another bleeding of thr primary circuit, hoping to see bubbles coming out...
 

·
Registered
Joined
·
243 Posts
Discussion Starter #17
Another bleeding done. Nothing changed.
Tomorrow i'll go to the dealer to discuss this problem. I believe they'll suggest for sure the bleeding of the secondary circuit.

Which are the symptoms of problems on the booster or pump?
 
1 - 17 of 17 Posts
Top