Terry L

Last week, I pulled off of the track at the end of two days at Summit Point, stopped at pit in, and found that the car wouldn't move. The top caliper bolt on the right rear caliper had pulled out - you can still see the aluminum from the threads in the upright contained in the threads of the bolt - and the caliper had tilted forward, bending the bottom caliper bolt, until it started to contact the wheel. The caliper itself was worn down from friction with the wheel and the pads showed only two surfaces, indicating that the failure was sudden. The bolts had been in place for a year or so, since my last rear pad replacement, and were properly torqued at the time. I'm guessing 15-20 or so track days since then. There were no warning signs of which I was aware.
I count myself extremely lucky - having that brake seize at 145 mph would not have been pretty and I only came in because I was running out of gas. The caliper is toast but the upright has been repaired with a Time-sert and there is no other damage. Car is still under warranty and I plan to ask Dr Porsche to look into this as a warranty claim.
Before someone asks, Loctite blue wouldn't have helped as the aluminum thread pulled out. But check the torque of those bolts and if you feel anything funny, the threads in the caliper may be failing.

mobonic

any pics

Carrera GT

This is a worry. Ever since I got the 997.1 GT3 I was unhappy about having to remove bolts to do pads -- that's just poor engineering from Porsche to go backwards in the design.

I don't have the service instructions handy, but for starters, DON'T go and "check the torque" on the caliper bolts. By all means "nut and bolt" them (that is: put a hand wrench on the bolt and check that it has not failed) but don't get out the torque wrench and throw 100lbs+ at the bolt.

Here's some questions (please take these as constructive, not critical or presumptive ... this could just as easily happened to me or anyone with a 997.x)

Did you do the work yourself?
Did you clean the threads in the wheel carrier?
Did you use new bolts?
Was there any anti-seize or any treatment on the threads at all?
What's the state of the other side? (the other rear wheel caliper)

When you say "showing two faces" I'm not clear what that means about the pads. I think I understand your description of how the caliper had reared up, bent the remaining bolt and contacted the inside of the wheel.

Is the wheel also compromised?

Do you have photos of the situation before, during after?

By the way, rather than time-serts, I think going to a stud is the long term solution (still disgusting to have to pull a caliper to swap a pad, but there it is.) I wonder what time-sert says about their product in an alloy wheel carrier at the given torque with the heat ranges and various forces.

Is there an after-market brake vendor with an alternate rear caliper design that's hot-swap for pads? I presume the spendy stuff from Brembo or Stop Tech is better?

How much more "fail" can we stand from Porsche with the GT cars? It's not just the few things that have cropped up (rear caliper bolts, rear brake cooling, main crank seal leak, insta-fail diff) it's the heaping shovel loads of steaming denial that Porsche expects customers to take.

Bob Rouleau

Caliper bolts are one time use only. You are supposed to replace them every time. Dunno if this was the case in your car.

Terry L

The caliper bolts were replaced with new ones the last time the calipers were removed. I do not believe that I cleaned out the threads nor am I clear that this is either necessary or helpful. I No anti-seize or other treatment to the bolts was used . I did the work myself. The other side seems fine although I have not backed out the bolts. The wheel looks good - very minor scrapes on the inside of the barrel. By two faces on the pad, I mean that there was not a progressive flattening of the pad - just the regular face and then the face caused by the rotor as it contacted the pad in its new position. Sorry but I don't have pix and dropped off the parts at the P-car dealer today. As to the capacities of Time-serts, I don't know - my shop should know and I will ask them. I guess studs would fit the bill as would a new upright.

Terry L

I believe the torque spec is 65 lbs - obviously you shouldn't try for more when these bolts are designed to stretch.

TRAKCAR

I agree, IMHO this is the worst part of the 997 GT3 and they did not even fix it for the MKII!

Yes, the torque spec is 65 for a steel stretch bolt in an aluminium housing. With perfect care maybe they last long enough, but for the average do it yourselfer it is asking for trouble. Most track junkies change their own pads every 3-4 months. I have seen MANY GT3's with the same problem.

The same thing happened to me, one one side the calipers came lose on track and the only thing holding on the caliper was the wheel. I had to buy a new upright. After that I had the Time Serts installed, but with the new car I had the studs installed before I needed to do my first pad change. I know that is how the CUP cars are but the stud size is different.

Once the calipers are a few years old and nice and crispy dark brown, I will look for an alternative caliper.

savyboy

Sure would like to learn what is involved to replace with studs? Anyone care to chime in? Part numbers? Procedure? Thanks!

TRAKCAR

I'll ask about part numbers and procedure when I pick up the car on Tuesday night.

sasportas

We have all had to re-thread the carriers with thread inserts. The TimeCerts that I used have held up for 3 years without any problems. I'd advise that you place the time certs on all 4 rear bolt holes before you encounter a problem. And yes, change the bolts with every pad change. Don't over torque the bolts (53-56 ft lbs.)

scott40

Excuse me if this a dumb question, but can the Time Serts just be replaced for the stock or is a rethread of the carrier needed?

Carrera GT

It's one of those things that looks tough the first time, but then it's easy. You have to drill out the diameter to accept the time-sert. Then countersink the top of the hole for the top of the timesert. Then tap the hole with the provided (oversized) tap. There's an insertion tool to hold the time-sert to turn it down the newly tapped hole. As the time-sert seats into the counter-sink, the insertion tool expands the last three threads of the time-sert into the newly tapped threads. When the insertion tool loses its grip, you just unwind it out of the time-sert and bingo, you've got a very hard thread firmly in place.

This is ideal for damage, but not something I necessarily do in anticipation of damage. The wheel carrier has so much meat to it, that the time-sert will surely work well and it's not like a engine where you're worried about the drilled and tapped material and debris going places (like valves or bearings.)

I'm not clear on how time-sert works with stretch fasteners, but I imagine they provide the right torque response on the thread surface and the time-sert is presumably strong enough to resist deformation.

Asquared

I'm planning on changing my pads this weekend. Does anyone have the part number for the bolts I need?

TIA.

TRAKCAR

999-067-053-09 CYLINDER SCRE FRONT CALIPER BOLTS
999-067-040-01 PAN-HEAD SCRE REAR CALIPER BOLTS

Asquared

Many thanks.