[Pmari]

I hate learning things like this the hard way. This is along the lines of never try to reset the odometer when the car is moving <img src="/forum/images/smilies/968/excl.png" class="smilie" alt="" />







[quote name='flash' timestamp='1276520206' post='94714']

my bet is the retaining pin on the shoe - those things snap



it is definitely a parking brake and not an emergency brake



rule 1: NEVER move the car with parking brake engaged - not one inch - forgetting about this will lead to the pin snapping



rule 2: do not engage the parking brake when the brakes are hot



rule 3: don't use the parking brake unless you have to (i.e. a slope) - just leave it in first if you can

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[flash]

yup. same goes for putting more than 3 years on timing belts. expensive lesson.

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[ds968]

Since most of the time you use the parking brake would be after you drove the car for a while and consequently the brakes are likely pretty hot, are you guys saying that unless you park on a very steep slope ( and even then leaving it in one of the gears , or in P for tips should be enough for almost any incline ? ) that , essentially , you should never use that hand brake as it serves little or no purpose and all you're doing is risking getting stuck with a broken pin / spring ? Or I am reading too much into these posts and what you meant by brakes being hot is only when tracking the car or after spirited canyon run, etc.. ?

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[flash]

that is correct. we all know about the self-starting gremlin, but the parking brake probably wouldn't prevent the car launching itself anyway. the parking brake is a secondary mechanism, due to its design and tendency to fail. hence, it should not be used unless absolutely necessary.

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[Paul W]

I would not agree with the statement that the parking brake should not be used. Yes, there are sound reasons not to drive with it on (or pull away with it on), but to say it should never be used is a little overboard.

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[Inkedupfatboy]

I try never to use mine - I have had lots of stick shift autos over the years and I have rarely used mine. I just leave it in first.

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[flash]

your brakes are hot when you stop. generally they are about 300 degrees. that is enough to soften the metals in that assembly enough for them to be more pliable.



drum brakes (which is what the parking brake is) when engaged hot and left there to cool, warp drums. reason 1



the springs are very subject to heat, and cycled repeatedly due to engagement when hot, break. reason 2



there is no reason to use the brake on flat or nearly flat ground. just put it in 1st gear. reason 3



when you break one of these springs, it usually results in paralyzing the car. putting yourself in a position of risking that is just silly. reason 4



i don't know anybody who uses the parking break on an automatic. been that way for decades. reason 5



yes, i know that if the starter cables are degraded, that the car may start itself. that a good reason to get in there and fix your starter cables, but not a good reason to deal with the rest of the problems associated with engaging the parking break when hot.

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[ryker]

Great design, rear wheel may lock up at 80 mph and send me careening off the road? Has this happened to anybody besides Langley? Shall I be afraid to get on the freeway?



Let's see...don't use the parking brake, don't use the sun roof or it may fly through the air and smash into the vehicle following behind me, don't use the rear wiper, change belts every 3 years because no manufacturer can design a belt that does not degrade in such a short time, check starter cables or my car may lurch through the back of my garage, check battery cables or my car may burn to the ground, don't use rear hatch very often or it will delaminate (will it fly through the air at speeds as well?). What other calamities am I missing? Are we all a bit masochistic?

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[tamathumper]

Don't reset the odometer while moving, lest the tach needle come flying out of the instrument panel and spear you in the throat. At high speed.

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[Paul W]

Don't drive the car unless every hose has been changed at a minimum interval of at least 10 years or planes could start falling from the sky and kill you. Or something like that.

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[flash]

lol - the parking brake will tell you before you even get out of the driveway. the way it fails is the metal becomes brittle from the heat. it will sork fine, and then one day you release the brake and the spring snaps. this causes the brake shoe to fall loose. you back up and all is fine. then you go forward and the shoe lodges itself. the sound is horrendous. i've never hear of it failing while driving. it's always right after starting to move.



these are 20 year old cars. stuff gets old. they need to have some parts replaced if you don't want them to fail. it's the nature of the beast.

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[MB968]

[quote name='flash' timestamp='1276526674' post='94722']

the rotors don't warp - there is a drum brake inside - that surface can deform - it isn't a lot but it does do it if you repeatedly engage the parking brake when the rotor is more than 250 degrees, which is well below the melting point



the real risk is moving the car with the brake engaged

[/quote]



A little known fact, even by a lot of engineers unless you've worked with materials, and I quote from one source "Ferrous metals reach their maximum strength and resistance levels at about 392 degrees Fahrenheit". You can google this if you don't believe me. So, unless the brakes are getting a lot hotter, and I mean over 400 Centigrade, we need to look for another cause for warped drums.



Sounds like another area on our cars that some preventative maint. is in order. I'll be looking at mine soon. Langley, thanks for highlighting this issue.

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[flash]

it's not like you would ever notice warping on the 968, since you don't engage it while driving, but i know i used to warp the drums on an old dodge van. you could feel it in the pedal. did it twice on two sets of new drums. as soon as i stopped using the parking brake, and of course put on another new set of drums, the problem stopped and never returned.



i'm not finding any empirical data on this. i only know it has happened, and to a number of other people too, though on other cars.



the big issue with the 968 is the dumb spring. that thing fails way too often. there are a few threads here that have stories of people snapping that danged thing.

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[tamathumper]

I never use the e-brake out of fear, but I did have to engage it last week and sure enough I backed up about two feet before realizing it was on. Now I'm just waiting for the dreaded rear-end explosion that's sure to ensue.

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[flash]

lol - yeah - it was one of the first things that broke on my car. at the time, i was using a mechanic that had worked on a bunch of these. he said it happened all the time. since then, i think i've heard of at least a dozen others. pain in the butt, since you have to pull the rotor to replace a $4 part.

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[Langley968]

[quote name='flash' timestamp='1384705602' post='152392']

i've never hear of it failing while driving. it's always right after starting to move.

[/quote]



If you re-read post #1, you will see that my brake locked up "while driving". I was speeding up after just merging into freeway traffic, so my estimate is that I was probably doing around 100 km/hr. A loud metal snapping noise had caught my attention about 5 minutes earlier (also mentioned in post #1) which must have been the spring snapping and making contact with the drum. The rear wheel locking up was not a pleasant feeling. I am just glad it did not warp or bend anything.

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[flash]

lol - yeah - not sure how i missed that. yours is the first time i've heard of that happening, without first hearing it right after moving. that's ugly.



that reminds me, i need to change the ones in the white car.

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[MB968]

Is there a particular spring that is the normal cause of failure. There are three shown in the parts listing. I'd like to get mine replaced soon.

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[flash]

as i remember, it's the compression spring. i have a spare here, because when it broke, i got an extra one. it should still be in the porsche baggie. i'll pull it and get the part number.

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[MB968]

Has anyone ever looked at a failed spring under a microscope to see it "beaches" were evident from a fatigue failure?

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