Caliper Issues at Speed?
06-09-2022, 01:23 PM
#1
Racer
Thread Starter
Caliper Issues at Speed?
A friend has a special edition 987 in Lava Orange. It has somewhere north of 87k miles. She says the car shimmies at speeds over 80 and was told the front calipers need replacing. What issues with the calipers would cause a shimmy at speed that requires them to be replaced? Also, can calipers from a 981 be installed and what would be necessary for the conversion? Or are they a direct bolt on replacement for the 987 calipers? Are the hanger bolts in the same location? Spacing the same?
06-09-2022, 01:42 PM
#3
Rennlist Member
A friend has a special edition 987 in Lava Orange. It has somewhere north of 87k miles. She says the car shimmies at speeds over 80 and was told the front calipers need replacing. What issues with the calipers would cause a shimmy at speed that requires them to be replaced? Also, can calipers from a 981 be installed and what would be necessary for the conversion? Or are they a direct bolt on replacement for the 987 calipers? Are the hanger bolts in the same location? Spacing the same?
06-09-2022, 01:47 PM
#4
Drifting
Caliper rebuild kits are available. Ceramic puck/piston can crack but it's rare.
https://racingbrake.com/cayman-boxst...7-981-982-718/
With the right tools it is an easy DIY.
https://racingbrake.com/cayman-boxst...7-981-982-718/
With the right tools it is an easy DIY.
06-09-2022, 01:49 PM
#5
Racer
Thread Starter
That's what I kind of suspected - piston/s hanging or seals gone bad. Do you know if 981 calipers would fit a 987?
06-09-2022, 02:03 PM
#6
Rennlist Member
I would go after the tires long before I suspected the calipers. The imbalance forces in the tires increase with the square of the speed. I have a shop that does a Road Force balance, which can shush out issues that a regular balance does not identify. I would also check lateral runout of the wheel. My tire shop does that as a matter of course. Can you swap out front tires with her, as a test?
There might be an issue with the brake discs. Based on track events, there is a scenario where we get a sudden red flag and have to pull over and stop with hot brakes. The disc is locally shielded from heat disipation in the area under the brake discs. Rumor has it that this can have bad effects such as warping of the disc, although I think cracking is a more likely result. There is also a phenomena where the brake pad material is built up unevenly on the disc. This is a second order effect but the point is small imbalances can become noticable as the speed of the wheel rotation increases. I find the Cayman steering on my 2 cars, an 06 and an 07, can be "jiggly" under the best of circumstances. Porsche certainly leaned on the side of good driver feedback, at the expense of damping out minor vibrations.
There might be an issue with the brake discs. Based on track events, there is a scenario where we get a sudden red flag and have to pull over and stop with hot brakes. The disc is locally shielded from heat disipation in the area under the brake discs. Rumor has it that this can have bad effects such as warping of the disc, although I think cracking is a more likely result. There is also a phenomena where the brake pad material is built up unevenly on the disc. This is a second order effect but the point is small imbalances can become noticable as the speed of the wheel rotation increases. I find the Cayman steering on my 2 cars, an 06 and an 07, can be "jiggly" under the best of circumstances. Porsche certainly leaned on the side of good driver feedback, at the expense of damping out minor vibrations.
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PhillyNate (06-09-2022)
06-09-2022, 03:11 PM
#7
Rennlist Member
IMHO, im not a big fan of changing brake configurations on cars with ABS, especially swapping just one end of the car. ABS is programed with a lot of assumptions about how the car is expected to react and perform.
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ekam (06-09-2022)
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06-09-2022, 03:47 PM
#8
Racer
Thread Starter
I would go after the tires long before I suspected the calipers. The imbalance forces in the tires increase with the square of the speed. I have a shop that does a Road Force balance, which can shush out issues that a regular balance does not identify. I would also check lateral runout of the wheel. My tire shop does that as a matter of course. Can you swap out front tires with her, as a test?
There might be an issue with the brake discs. Based on track events, there is a scenario where we get a sudden red flag and have to pull over and stop with hot brakes. The disc is locally shielded from heat disipation in the area under the brake discs. Rumor has it that this can have bad effects such as warping of the disc, although I think cracking is a more likely result. There is also a phenomena where the brake pad material is built up unevenly on the disc. This is a second order effect but the point is small imbalances can become noticable as the speed of the wheel rotation increases. I find the Cayman steering on my 2 cars, an 06 and an 07, can be "jiggly" under the best of circumstances. Porsche certainly leaned on the side of good driver feedback, at the expense of damping out minor vibrations.
There might be an issue with the brake discs. Based on track events, there is a scenario where we get a sudden red flag and have to pull over and stop with hot brakes. The disc is locally shielded from heat disipation in the area under the brake discs. Rumor has it that this can have bad effects such as warping of the disc, although I think cracking is a more likely result. There is also a phenomena where the brake pad material is built up unevenly on the disc. This is a second order effect but the point is small imbalances can become noticable as the speed of the wheel rotation increases. I find the Cayman steering on my 2 cars, an 06 and an 07, can be "jiggly" under the best of circumstances. Porsche certainly leaned on the side of good driver feedback, at the expense of damping out minor vibrations.
06-09-2022, 03:49 PM
#9
Racer
Thread Starter
I agree to an extent, but if the calipers were to be "upgraded" if that indeed is what going from 987 to 981 rotors is doing, then I would suggest they all be swapped out. Someone on the marketplace has a full set available with low mileage from a 981 for a good price relative to just two new 987 fronts.
Last edited by Live Steam; 06-09-2022 at 03:50 PM.
06-09-2022, 07:26 PM
#10
it would be helpful if it were known if the shimmy is occurring while braking at the 80 mph specified.
if not, then the chances of both brake calipers being the problem is remote. practically zero in fact. if so, then a warped rotor on one side or the other, and NOT the calipers (!), would very much be a possible cause of the shimmy. a very easy and relatively simple and inexpensive fix. the front tires could also need balancing. believe it or not, i recently bought new set of front tires to remedy a significant steering wheel vibration at speeds above 60mph, and after a years worth of time and expense a road-force balancer determined that they were not round enough to balance properly. another new set of front tires fixed the problem, finally!
although if it does turn out to be a warped rotor, it's probably not a bad idea to replace both of them. using the logic that they are possibly sub-standard and that the other one will suffer a similar fate in the not too distant future. i would be suspicious of the current diagnosis and remedy given to the owner.
if not, then the chances of both brake calipers being the problem is remote. practically zero in fact. if so, then a warped rotor on one side or the other, and NOT the calipers (!), would very much be a possible cause of the shimmy. a very easy and relatively simple and inexpensive fix. the front tires could also need balancing. believe it or not, i recently bought new set of front tires to remedy a significant steering wheel vibration at speeds above 60mph, and after a years worth of time and expense a road-force balancer determined that they were not round enough to balance properly. another new set of front tires fixed the problem, finally!
although if it does turn out to be a warped rotor, it's probably not a bad idea to replace both of them. using the logic that they are possibly sub-standard and that the other one will suffer a similar fate in the not too distant future. i would be suspicious of the current diagnosis and remedy given to the owner.
Last edited by hueyhoolihan; 06-09-2022 at 07:44 PM.
06-09-2022, 08:31 PM
#11
Rennlist Member
Road Force balancing does indeed check for out of round. Some shops don't like it as they wind up getting a lot of rejectable tires. I had a 50% failure rate years ago when I was stuck with a single brand (based on availability for my 928). Fortunately Tire Rack was good about sending out new tires until we got it right. A new set of Michelin 4S tires on my wife's car came through with no issues.
06-10-2022, 11:02 AM
#13
Rennlist Member
A couple of things to think about...
If a caliper is bad and a pad is dragging on the rotor, you will usually get a "pull" toward the side of the car that has the problem; you will also get a lot more brake dust on the "bad" wheel because the pad is constantly rubbing; you may "smell" heat from the bad pad after a drive and sometimes the wheel will be warm due to heat transference from the hotter-than-usual rotor.
If a seal is bad on a caliper, you will get leakage of brake fluid via the bad seal and usually will see it on the wheel.
If over 80 MPH is the only time the vibration/shimmy appears, it's probably a balance issue, a tire or a warped/bent wheel, but check tie rod ends and wheel bearings just in case.
Finally, I don't think 981 calipers will bolt up to a 987 upright. The design of the 981 caliper is completely different when compared to the 987 caliper. Plus, if you did that, I'd think you'd want go to 981 calipers and rotors on all four wheels, not just the front. Also, the ABS concern stated above by jsscott82 is not insignificant.
Hope this helps.
If a caliper is bad and a pad is dragging on the rotor, you will usually get a "pull" toward the side of the car that has the problem; you will also get a lot more brake dust on the "bad" wheel because the pad is constantly rubbing; you may "smell" heat from the bad pad after a drive and sometimes the wheel will be warm due to heat transference from the hotter-than-usual rotor.
If a seal is bad on a caliper, you will get leakage of brake fluid via the bad seal and usually will see it on the wheel.
If over 80 MPH is the only time the vibration/shimmy appears, it's probably a balance issue, a tire or a warped/bent wheel, but check tie rod ends and wheel bearings just in case.
Finally, I don't think 981 calipers will bolt up to a 987 upright. The design of the 981 caliper is completely different when compared to the 987 caliper. Plus, if you did that, I'd think you'd want go to 981 calipers and rotors on all four wheels, not just the front. Also, the ABS concern stated above by jsscott82 is not insignificant.
Hope this helps.
Last edited by TMc993; 06-10-2022 at 05:09 PM. Reason: Clarity
06-10-2022, 11:30 AM
#14
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Terry is spot on. I've experience this recently with changing out rotors and pads. One of the pistons was not retracting properly and pushing the pad on the rotor unevenly. This caused extremely vibration of the car and the tell-tale pull in the steering. It drove like it was out of alignment. In fact, the brakes started to smoke. Had to completely take the brake system apart and compress the pistons evenly. After that, everything was fine. Thankfully it was fixed. I thought I was going to have to replace the caliper.