Challenge for the new year: Troubleshoot brakes, smoothen ride
01-07-2008, 11:08 PM
#16
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If there's debris in the caliper, it's sometimes possible to get it out by removing the caliper and invertiing it so the bleed srews are down. Completely remove the screws one at a time, starting with the inner. Flush as normal with the power bleeder. with both cavities flushed, replace the calipers in normal position and bleed the air out the top as you would normally.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
If these steps don't give you the correct resultas, you'll need to rebuild or replace the calipers.
Rebuilding calipers were a matter of maintenance at one point in auto/motorcycle history; before the throw away/replace with new era.
Nicole.....if your calipers are OEM have them rebuilt with fresh gaskets and consequently fresh fluid, pads and/or rotors.
The vibe issue is perhaps in the tube, gbox, half shafts and wheels/tyres..........look at them all rather than just one potential.
Best of luck.
01-07-2008, 11:17 PM
#17
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my car rides smoother after i get the tires warmed up as it sits for long periods as well. I do notice this and it goes away after about 25 miles or so.
That said I would check the rear wheels off the ground for roundness as well as the fronts.
Also the tires you have may possibly have a belt coming loose from hitting a big pothole or a curb, check the tires and wheels after you have driven the car for a while otherwise it will give you false info.
Also consider the shocks on your car then may be in need of replacement if so i would recommend the stock springs and a new set of Bilstien shocks.
The brakes from what you say sound like it could be time to remove all of the calipers and replace the seals and clean the pistons.
Also pay attention to the fitment of the pads in the calipers, since the rear pads dont move much they are more suseptible of having the pads binding in the calipers, and the pistons may fill with dirt as Dr Bob has said.
This is due to long periods of using the same brake fluid.
One caveat if your brakes pistons are corroded in the calipers then i would recommend that you do either of these things one rebuild the master cylinder or replace it.
If you opt to not replace it then when the bleeding process starts use a pressure bleeder......do not press the pedal more than it normally travels as you run the risk of pressing the master cylinder seals into parts of the bore that the seals dont normally contact as a result the seals hit debris /rusted areas of the bore and thus will begin to leak internally, I have seen this more than a few times when working on a older car that had original parts and the brakes were good when it came in and a few months later the master had to be replaced.
Also to consider do you use any kind of tire shine sprays on the tires, or do you wash the car and park it?
It could be possible that your rotors are either getting the tire spray on them or the pads still being wet after the wash, begin to rust the rotors and thus cause high spots to develop, since the pads are covering the rusted parts of the rotors you wont really notice this untill you press the brake pedal to stop the car, Goodluck Nicole, Stan
That said I would check the rear wheels off the ground for roundness as well as the fronts.
Also the tires you have may possibly have a belt coming loose from hitting a big pothole or a curb, check the tires and wheels after you have driven the car for a while otherwise it will give you false info.
Also consider the shocks on your car then may be in need of replacement if so i would recommend the stock springs and a new set of Bilstien shocks.
The brakes from what you say sound like it could be time to remove all of the calipers and replace the seals and clean the pistons.
Also pay attention to the fitment of the pads in the calipers, since the rear pads dont move much they are more suseptible of having the pads binding in the calipers, and the pistons may fill with dirt as Dr Bob has said.
This is due to long periods of using the same brake fluid.
One caveat if your brakes pistons are corroded in the calipers then i would recommend that you do either of these things one rebuild the master cylinder or replace it.
If you opt to not replace it then when the bleeding process starts use a pressure bleeder......do not press the pedal more than it normally travels as you run the risk of pressing the master cylinder seals into parts of the bore that the seals dont normally contact as a result the seals hit debris /rusted areas of the bore and thus will begin to leak internally, I have seen this more than a few times when working on a older car that had original parts and the brakes were good when it came in and a few months later the master had to be replaced.
Also to consider do you use any kind of tire shine sprays on the tires, or do you wash the car and park it?
It could be possible that your rotors are either getting the tire spray on them or the pads still being wet after the wash, begin to rust the rotors and thus cause high spots to develop, since the pads are covering the rusted parts of the rotors you wont really notice this untill you press the brake pedal to stop the car, Goodluck Nicole, Stan
Last edited by Mrmerlin; 01-07-2008 at 11:36 PM.
01-08-2008, 12:00 AM
#18
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One thing no one has mentioned, that I've seen several times now on the rear brakes, is warping of the "H"-shaped pad guides.
Nicole, when you and Bill did the rear pads did they slide smoothly in and out of the caliper bore? On each end of the bore there's an H-shaped piece of spring steel bolted to the caliper body with an Allen-head button screw. Over time pad material and other debris gets between the guide and the caliper body. In much the same way that a tree root can move a house, the debris will over time bend the guide so that the pad will not move freely and thus get stuck in the bore. Also, pad material can build up on the face of the guide and prevent the pad from moving. But, that's easily cleaned with a wire brush. Replacing the guide is possible (a repair kit is available) but it's a bit more involved.
So, pull the rear wheels, unbolt the rear calipers and make sure that the pads slide freely along the two required axes (e.g. in and out of the caliper and in and out with respect to the rotor.) If they do not move freely, clean the guides with a wire brush. If the guides are warped then you'll have to replace them.
IIRC, The WSM calls for anti-seize on the edge of the pads where they contact the guide.
Nicole, when you and Bill did the rear pads did they slide smoothly in and out of the caliper bore? On each end of the bore there's an H-shaped piece of spring steel bolted to the caliper body with an Allen-head button screw. Over time pad material and other debris gets between the guide and the caliper body. In much the same way that a tree root can move a house, the debris will over time bend the guide so that the pad will not move freely and thus get stuck in the bore. Also, pad material can build up on the face of the guide and prevent the pad from moving. But, that's easily cleaned with a wire brush. Replacing the guide is possible (a repair kit is available) but it's a bit more involved.
So, pull the rear wheels, unbolt the rear calipers and make sure that the pads slide freely along the two required axes (e.g. in and out of the caliper and in and out with respect to the rotor.) If they do not move freely, clean the guides with a wire brush. If the guides are warped then you'll have to replace them.
IIRC, The WSM calls for anti-seize on the edge of the pads where they contact the guide.
01-08-2008, 01:49 AM
#19
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Several months ago we measured the run-out on Nicole's rotors, and it was within spec. The tires weren't too round, however. I don't recall if we checked the wheels for run-out. I think we did. Maybe Nicole remembers.
The shocks are relatively new and the behavior she reports isn't what I would expect from bad shocks. There are no apparent leaks.
I don't recall the pads on Nicole's brakes wearing that unevenly. I do agree that uneven wear, which I have in my car, is a sign of sticky calipers and indicates a need to overhaul the calipers. I hope that if I noticed it, I commented that the calipers should be overhauled at some point. I just don't remember. I have some recollection that I was able to move all the pistons with equal ease, so I may have minimized the uneven wear. My pads have always worn unevenly (outside much more than inside), but I have had no braking problems at all. Anyway, point taken that it could account for the brake issues she reports.
I don't remember if and when we flushed the brakes. We did do the pads and made sure all the hardware was clean and serviceable. And as Dave C mentioned, we put some antiseize on the pad contact points with the guides. Nicole's squeaking problem is annoying. I don't have any anti-vibration inserts and have had essentially no squeaking with stock pads and rotors.
Anyway, Nicole, let's rebuild the calipers if the pads are wearing unevenly. Order the seal/boot kits. That would involve a brake flush as part of the job, so that question will be answered as well. I did not like the run-out on your rear tires. We could swap my wheels and tires onto your car and see if it makes any difference. Now that I am retired, we can do this literally anytime. And start a service log if you haven't so we can remember what we did.
The shocks are relatively new and the behavior she reports isn't what I would expect from bad shocks. There are no apparent leaks.
I don't recall the pads on Nicole's brakes wearing that unevenly. I do agree that uneven wear, which I have in my car, is a sign of sticky calipers and indicates a need to overhaul the calipers. I hope that if I noticed it, I commented that the calipers should be overhauled at some point. I just don't remember. I have some recollection that I was able to move all the pistons with equal ease, so I may have minimized the uneven wear. My pads have always worn unevenly (outside much more than inside), but I have had no braking problems at all. Anyway, point taken that it could account for the brake issues she reports.
I don't remember if and when we flushed the brakes. We did do the pads and made sure all the hardware was clean and serviceable. And as Dave C mentioned, we put some antiseize on the pad contact points with the guides. Nicole's squeaking problem is annoying. I don't have any anti-vibration inserts and have had essentially no squeaking with stock pads and rotors.
Anyway, Nicole, let's rebuild the calipers if the pads are wearing unevenly. Order the seal/boot kits. That would involve a brake flush as part of the job, so that question will be answered as well. I did not like the run-out on your rear tires. We could swap my wheels and tires onto your car and see if it makes any difference. Now that I am retired, we can do this literally anytime. And start a service log if you haven't so we can remember what we did.
Last edited by Bill Ball; 01-08-2008 at 02:07 AM.
01-08-2008, 02:17 AM
#20
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As far as I remember, the inner pads had a bit more meat left than the outer ones.
I have some recollection that I was able to move all the pistons with equal ease, so I may have minimized teh uneven wear. My pads have always worn unevenly (outside much more than inside), but I have had no braking problems. Anyway, point taken that it could account for the brake issues she reports.
Anders has experienced the violent vibration when braking hard on our way to Buttonwillow - how many years ago was that??? That's how long I have been annoyed by this off and on, and whatever we did in the meantime has not made it go away. Again, it's not always noticeable, and I have not been able to determine a clear pattern of when it happens. But I do notice it way too often to ignore it.
While it's merely annoying on a slow approach to a stop light, it is outright frightening when you have to brake hard from high speed and the whole car shakes and vibrates. I'm not convinced I get optimal braking power that way, which would be very important to me, aside from not scaring my passengers.
Anyway, Nicole, let's rebuild the calipers if the pads are wearing unevenly. Order the seal/boot kits. That would involve a brake flush as part of the job, so that question will be answered as well. I did not like the run-out on you rear tires. We could swap my wheels and tires onto your car and see if it makes any difference.
For rebuilding the two calipers, I suspect I would need the following:
2 x 951 352 919 11 (item 8 on the illustration)
2 x 951 352 919 10 (item 8 on the illustration)
Correct?
Should I also order need new pads and silencers? There is a lot of "meat" left on the existing factory pads, but as I said, they squeak.
Per Dave's suggestion, would I need number 12 and 12a?
What else should I order?
Either way, when we do this I'd like to disassemble them one day and touch up the peeling paint, before we put them together again. Just so the whole thing looks nice and clean again.
01-08-2008, 03:12 AM
#21
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One other variable is bedding of new pads. Porsche's bedding procedure is pretty aggressive. I don't follow it religiously, but poor bedding can account for noise and uneveness during braking. I think we took any glaze off your pads last time we looked at them and chamfered the edges, which should reduce squeaking, and we talked about bedding, but I'm not sure what you did.
I don't think we'll need pads. Check with your supplier about the seal kits. I can't quite decipher the PET in this regard at this hour. Each caliper has 4 pistons.
After you get the parts, let me know and I'll help you remove the calipers if you want for painting and we can do the rebuild the next day after they dry.
I don't think we'll need pads. Check with your supplier about the seal kits. I can't quite decipher the PET in this regard at this hour. Each caliper has 4 pistons.
After you get the parts, let me know and I'll help you remove the calipers if you want for painting and we can do the rebuild the next day after they dry.
Last edited by Bill Ball; 01-08-2008 at 03:42 AM.
01-08-2008, 09:11 AM
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01-08-2008, 12:58 PM
#23
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There's "stupid stuff" that can cause brake issues you describe. Start with the rotors. We sometimes spend a bit of time detailing rotors, but don't do such a careful job detailing and cleaning the mounting surfaces on the hats and hubs. Any debris on or deformation of the hub multiplies the runout at the friction faces of the rotors. Verify the runout on the rotors as they are mounted on the car, using a dial indicator mounted to the suspension. S-l-o-w-l-y rotate the rotor and record the minimum and maximum lateral readings. Verify against WSM spec (which I don't have handy where I am right now).
Verfiy that the thickness of the rotor is consistent all the way around. Use a micrometer to measure in at least four spots spaced equally around the rotor. A rotor that's not consistent will generally cause a pulsing pedal rather than a vibration up to hard braking under Anders' foot.
Either of these conditions can be caused by poor setup when resurfacing, and cured by using a good setup and resurfacing.
Put new pads in. Use good pads. In my very limited experience, the factory pads were dirty but did an OK job stopping the car. The accumulation of brake dust was tough on the wheels, and built up in the caliper a lot. For street and the occasional fun drive at US speeds, stay away from competition pads and work with a better street pad. I've had a set of PBR's on the car for close to 50k now and only lately have they started to tell me it's time for replacement soon. This is with some groaning as I come to a complete stop with gentle pedal; they still look fine and nowhere near the pad sensors, but soon it will be time for new.
As far as caliper rebuilding. this is a great idea if they are leaking or sticking. I know Bill knows how to do them with all the scooter experience, but generally I recommend that DIY'rs stay away. Why? because they inevitably end up shooting a piston or two across the room, bouncing it off the wall or the floor a few times, and denting it. There are ways to capture the pistons of course, and you need to be gentle with the air pressure. Also, cleanliness is next to long life, you need some assembly lube, and you can't use any sharp or metallic tools in the bores or on the pistons for fear of scratching the metal and ruining the sealing faces and grooves. Most folks only learn about this stuff from their own bad experience.
Rear tire problems, like out of round, out of balance, belt shift, bruising, and excessive runout are most easily diagnosed by installing a known good set, looking to see if the problem goes away.
Verfiy that the thickness of the rotor is consistent all the way around. Use a micrometer to measure in at least four spots spaced equally around the rotor. A rotor that's not consistent will generally cause a pulsing pedal rather than a vibration up to hard braking under Anders' foot.
Either of these conditions can be caused by poor setup when resurfacing, and cured by using a good setup and resurfacing.
Put new pads in. Use good pads. In my very limited experience, the factory pads were dirty but did an OK job stopping the car. The accumulation of brake dust was tough on the wheels, and built up in the caliper a lot. For street and the occasional fun drive at US speeds, stay away from competition pads and work with a better street pad. I've had a set of PBR's on the car for close to 50k now and only lately have they started to tell me it's time for replacement soon. This is with some groaning as I come to a complete stop with gentle pedal; they still look fine and nowhere near the pad sensors, but soon it will be time for new.
As far as caliper rebuilding. this is a great idea if they are leaking or sticking. I know Bill knows how to do them with all the scooter experience, but generally I recommend that DIY'rs stay away. Why? because they inevitably end up shooting a piston or two across the room, bouncing it off the wall or the floor a few times, and denting it. There are ways to capture the pistons of course, and you need to be gentle with the air pressure. Also, cleanliness is next to long life, you need some assembly lube, and you can't use any sharp or metallic tools in the bores or on the pistons for fear of scratching the metal and ruining the sealing faces and grooves. Most folks only learn about this stuff from their own bad experience.
Rear tire problems, like out of round, out of balance, belt shift, bruising, and excessive runout are most easily diagnosed by installing a known good set, looking to see if the problem goes away.
01-08-2008, 01:47 PM
#24
In my case, three of the four pistons came right out with moderate air pressure using a simple rubber nub on the air gun, and I was able to control them so they didn't even touch the wood block I was using as a safeguard. But the fourth required me to come up with a brake line fitting screwed into the caliper to be air-tight. 20,30,40psi it didn't budge. Then at 60psi POW! Smacked against the wood block with real force. This one had the worst accumulation of gunk and was definitely one of my brake problems.Rebuilding calipers is really a pretty easy, if messy job, and much cheaper than buying new ones. Just be careful.
01-08-2008, 03:37 PM
#26
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Appreciate the further comments and suggestions.
We checked the rotors pretty thoroughly with calipers and dial gauge.
As dr. bob said, I have lots of experience with caliper rebuilds on my scooters. Some of the ones I have had were notorious for corroding if you didn't ride them for a while. And I learned quickly how to remove the pistons safely, even with compressed air, and not turning them into missles.
Anders is undoubtedly right.
We checked the rotors pretty thoroughly with calipers and dial gauge.
As dr. bob said, I have lots of experience with caliper rebuilds on my scooters. Some of the ones I have had were notorious for corroding if you didn't ride them for a while. And I learned quickly how to remove the pistons safely, even with compressed air, and not turning them into missles.
Anders is undoubtedly right.
01-08-2008, 07:22 PM
#27
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Well, I ordered the rebuild kit and the H-Shaped thingies today. Will pick-up on Friday. Maybe I can even drive the car there.... providing it stops raining in the meantime.
01-08-2008, 07:43 PM
#29
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Nicole
Didn't you have a problem with the rear rims being bent last year? Maybe the wheels are internally flawed and won't hold a proper balance? Maybe a "road force" balance will reveal something that a standard spin balance won't...
It seems the problem is related to a wheel issue...which could cause everything you describe.....I'd loan you my rear old rear wheels, but they already are on loan to someone else......
Didn't you have a problem with the rear rims being bent last year? Maybe the wheels are internally flawed and won't hold a proper balance? Maybe a "road force" balance will reveal something that a standard spin balance won't...
It seems the problem is related to a wheel issue...which could cause everything you describe.....I'd loan you my rear old rear wheels, but they already are on loan to someone else......
01-08-2008, 07:55 PM
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Hi Brian:
I'm not sure how the two would be connected. I'm not saying they are not, but I've had my wheels straightened, had two sets of tires, and the brake issue did not change. But I would love to borrow a straight set of wheels and see what happens.
I'm not sure how the two would be connected. I'm not saying they are not, but I've had my wheels straightened, had two sets of tires, and the brake issue did not change. But I would love to borrow a straight set of wheels and see what happens.