Re: A place to use the parking brake, and put the car in gear:

This from an old Rennlist member:

"I'd suggest leaving the box out of gear and using the parking brake. The gears aren't designed to be held static face to face, the oil will separate and leave metal-to-metal contact as well as needlessly compressing the syncro's and transmitting movement into the engine, which is also not designed to take bearing load or move pistons without temperature and continuous lubrication. If need be, use reverse."

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"Thanks for the heads-up on leaving the car parked in gear. I had no idea. I always leave it in reverse. I also heard it's not good to set the parking break when the discs are hot, which confuses me a bit on what to do.

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As for parking brakes and hot rotors, the issue is simply that a hot rotor needs to cool uniformly or it can warp over time. The pressure of the parking brake is a pair of "shoes" inside the drum of the rear rotors ... hence the name "drum brake" ... much the same as truck brakes dating back a century ... heavy, ineffective, expensive, prone to failure and expensive to maintain.

The drum brake for parking uses two shoes which expand outwards inside the drum to press against two opposite areas on a machine surface inside the hub of the rotor where it bolts to the car's wheel axle hub -- effectively applying pressure at the same time as changing the rate of contraction and cooling simply because the contact of the brake shoes to the hub creates a larger connected thermal mass than just the metal of the hub itself. Over time, if the rotors are hot from track driving and repeatedly subjected to cooling while in contact with the parking brake shoes, there's the risk of two problems: the rotor can change shape around the drum as it cools faster where the hub is not in contact with the parking brake and not surrounded by the brake caliper and its pads; and, the friction material held on the face of the parking brake shoe can be dissolved by heat and pressure, and "transfer" to the parking brake hub on its machined surface, causing the brake action to be irregular and less reliable because it will have "sticky" points with less gap between shoe and hub in some places with wider points with more gap and less friction between shoe and hub. The same thing happens between a hot rotor and caliper brake pads -- it's vitally important to cool down brakes from track driving or after even one extreme application such as a panic brake from freeway speeds -- the instantaneous heat soak into the rotor can cause pad transfer if the driver holds the brake pedal to keep the pads forced against the rotor while the car is stopped. One lap at a brisk rolling pace with zero brake pedal application is enough to cool the rotors ... rolling too slowly so as to take longer is counterproductive because it's airflow through the rotor veins that cools the rotor, not time ... given time, the rotors will stay hot almost indefinitely, but with airflow at speed, the cooling process is efficient (efficient enough to keep the brakes operating lap after lap.)

For even the most aggressive driving on public roads, it's practically impossible to get the rotors to temperatures where precautions are necessary. The only exception would be hilly driving at freeway speeds where there's intermittent snow or deep standing water that could contact the rotor in sufficient effect to change the rotor temperature abruptly.

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

Parking brake is shoes in the drum part of the rear rotors. Not sure if that's true of the 981.

i've had quite a few pad material transfer issues on my Audi. never on the porsche.

This is generally a sign that the pads have exceeded their operating temp range. E.g.: go down a long downhill, using brakes, stop at bottom, sit with foot on pedal.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I put a couple of bevelled wood pieces behind the rear tires (garage floor has a slight slope for water drainage) and let the car ease into them. Then I leave it in neutral with parking brake off for the least amount of stress on clutch, gears, brake cables etc.

Just refering back to the article - I avoid applying breaks. They're too expensive to fix.

During the driving season, the CURVEN8R only gets short naps between drives. Then it's parking brake on first, then slip it into first gear. That way, should the brakes fail, then the power train will still hold the car. (Not sure if this would apply to San Francisco parking or not.)

I never put the parking brake on when i come off the track, for example.

That said, i have never ever warped a rotor even with them exceeding 500 deg after cool-down laps.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I'm much more intrigued by the first part of the comment:

Quote

I'd suggest leaving the box out of gear and using the parking brake. The gears aren't designed to be held static face to face, the oil will separate and leave metal-to-metal contact as well as needlessly compressing the syncro's and transmitting movement into the engine, which is also not designed to take bearing load or move pistons without temperature and continuous lubrication. If need be, use reverse.

To me, this seems ridiculously paranoid, not to mention outright ignorant of modern metallurgy and lubrication. But, since I'm neither a metallurgist or tribologist, I thought someone more informed might like to comment? FWIW, when my cars are put away for winter storage, I've always left them in first gear, parking brake off (to avoid cable stretching, perhaps another misguided idea) - so far no issues after ~30 years...

- JohnL
Boston

Quote
jlegelis
I'm much more intrigued by the first part of the comment:

Quote

I'd suggest leaving the box out of gear and using the parking brake. The gears aren't designed to be held static face to face, the oil will separate and leave metal-to-metal contact as well as needlessly compressing the syncro's and transmitting movement into the engine, which is also not designed to take bearing load or move pistons without temperature and continuous lubrication. If need be, use reverse.

To me, this seems ridiculously paranoid, not to mention outright ignorant of modern metallurgy and lubrication. But, since I'm neither a metallurgist or tribologist, I thought someone more informed might like to comment? FWIW, when my cars are put away for winter storage, I've always left them in first gear, parking brake off (to avoid cable stretching, perhaps another misguided idea) - so far no issues after ~30 years...

- JohnL
Boston

While over time considerable transmission fluid will drain away from all surfaces enough residual fluid remains that real metal to metal contact is not a concern. Remember that when the engine is started the gears turn without really having to transmit any torque/force. Also, the gear teeth are involute which means the gear teeth faces actually roll against each other so there's no real concern about wear.

Next I might point out these transmissions are constant mesh which means even in neutral the all gears on the input shaft are in mesh with their counterparts on the output shaft. IIRC, only a gear in the reverse gear set is completely not engaged with any other gear.

Anyhow, even though just residual oil remains, as the engine cranks and begins to run the input shaft and the gears upon it turn and these in turn spin the gears on the output shaft. Almost immediately the gears and all other critical components will receive more than sufficient oiling.

Now there is a good argument to be made to leave the transmission out of gear. This leaves the shift forks in their least loaded position and as the gears spin up they will carry tranny fluid along and lube the shifter fork working faces before they have any real load applied to them. But even in gear if the shifter fork face in real contact with the gear there is an adjustment problem of a shifter fork is bent (which can happen if a shift is forced).

Anyhow synchros are not under pressure when the gears are engaged. The gear dogs which are used to enage/lock gears together are under minimal pressure unless you store the car parked on a steep hill with the parking brake not set and with the wheels not blocked and the transmission in gear and thus relying solely upon engine compression to keep the car from moving.

Even on the steepest slope that provided sufficient traction for a car to remain motionless the engine will not turn over from as the car is tugged down slope by gravity.

For putting your car away for some time in the off season my advice is to not set the parking brake -- even though "dry" the parking brake shoes and the drums against which they grip might develop a layer of rust (which can have the the shoes breaking loose creating a gosh awful snap/bang) or the exposed drum surface develops rust but where the shoes press does not (but what this might result in I'm not sure) -- and leave the tranny in neutral and just be sure to adequately block the wheels. In a Tip/PDK car leave the transmission in Park or neutral (the owners manual may have a preferred position so you should always consult your owners manual (I have no real Tip/PDK experience)) and block the wheels.

Then relax. And try not to think of mice...

Keeping it on during the wash might help to keep water from getting onto the drum/shoe interface. Disengaging afterwards allows whatever water that might've gotten between to evaporate, and to not cause the drum to rust/fuse to the shoe. That snap/bang is likely harmless, but it sounds awful. (Or for you neologistiphilic hipsters: it sounds awesome!)



Edited 1 time(s). Last edit at 11/27/2012 06:22PM by Laz. (view changes)

I do not. It depends where I wash the car. In a DIY car wash the car sits in a bay in on a concrete pad that is dished so the car tends to remain stationary. Regardless, I always leave the transmission in gear.

After the washing once on the road I use the brakes hard enough after to dry them out thoroughly.

The parking brake drums probably get a bit of water in them and develop a bit of rust but I seldom think about it.

When I do think about it I lightly apply the parking brake while the car is moving slowly just to scrub away any rust that may have built up.

[www.wildnatureimages.com]

Don't forget to turn the wheels so the front of the tire points toward the curb if you are facing down hill.....or the rear of the tire if you are facing up hill.

Bill

I'd certainly use the parking brake, leave the manual transmission in gear, and turn the wheels just in case both the parking brake and tranny/engine failed to hold the car.

Well, even those driveways require lots of precautions!
If I correctly recall (reaching back to '74) Lombard continues down the other side of the hill, and it's a long, straight steep downhill with on street parking. Wheel turn-in might be an official parking regulation, too.

Exactly.. I mean, if gears and lube couldn't hold up under static conditions, how on earth would they be expected to endure high temp 6k rpm double-clutch down shifts?

My wife found this after an extended time under the car cover. There were huge nests in both trunks made from carpet padding and insulation. I will have to wait till I get home to get rid of the urine smell! BTW, my wife read somewhere that dryer sheets repel mice. Yeah, they used them for their nest. So much for that one.

Every Porsche I've come across with rodent damage has had engine harness wiring chewed up, hoses, the interiors of seats, the lines that run down the center of the car in that little tunnel which is covered over by the under body panels, and even radiator duct rubber sheeting.

In all cases the amount of damage had the owner falling back on his home owners insurance.

They ward off rodents.

but that concern isn't it!

A significant bang (might, unlikely) put some strain on the gears; its harder to roll; uhhhh.

In fact the whole post was mostly concern over nothing, although pad deposits can be an issue, as i said above, it only comes into play when you exceed the MOT of the pad, really. In fact, material transfer is a central part of how brakes work today, and "bedding" is achieved by heating the pads to near their MOT (max operating temp), and leaving a uniform layer - that's why we get to a hgih speed, hit the brakles hard, DO NOT STOP, rinse and repeat.

The time not to set the brake is coming off a track, after a long, long down-grade, or, well, that's about it.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

about something in the parking brake hardware snapping and causing a hub to be damaged.