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Depressing Clutch to Start Car

 
Old 02-09-2019, 02:26 PM
  #16  
993pbug
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Originally Posted by Ivan J View Post
Those of you who depress the clutch pedal when starting the engine should read post #4 in this thread....

https://rennlist.com/forums/993-turb...g-failure.html

I was taught to always disengage the clutch as well; but, I stopped doing that once I understood the above.
I whole-heartedly respect Steve’s wisdom without question or concern as he was exceptionally supportive not only during my search, but also after I made a purchase.

Being a mechanical engineer in the nuclear / aerospace / defense industries, there is one key phrase is his post (#4 referenced above) that caught my eye: “ ... when lubrication is at a minimum.” Even those with basic mechanical knowledge knows that operating bearings with minimal lubrication is a bad idea. However, since there is no way to easily check how well lubricated the thrust bearing is, prudence suggests assuming it is always low. Combining that premise with the additional knowledge that the less you use a mechanical system the longer it will typically last, it is now easy to see why the practice of not having to depress the clutch on start-up has its definitive benefits on thrust bearing life-expectancy.

Now, in an effort to help myself better understand the loads applied to the thrust bearing during start-up, how do these loads differ from those induced during regular shifting or holding the pedal down for a few seconds while waiting for traffic to roll after a green light? The only variable between those scenarios is the fact that the engine is running. Does the centripetal force of the driveline rotating reduce the clamping force of the PP thereby making the loading of the thrust bearing lower during shifting when compared to those at start-up?

Regardless of loads, I would think that since the frequency of using the clutch during normal driving far exceeds the use during start-up, it would have far greater impact on life-expectancy.

I am obviously not versed well enough in this scenario to render an official opinion and absolutely defer to Steve’s infinite wisdom. With that, apologies for getting into the weeds, and I’ll again blame it on the day job! Personally, I can’t get past the safety aspect of the interlock, but that’s just me.
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Old 02-09-2019, 02:27 PM
  #17  
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Originally Posted by goofballdeluxe View Post
Yeah, I remember reading Steve Weiner's posts about NOT depressing the clutch as one starts the car. As a result, I never depress the clutch on my '96 when I crank it over.
Same here... I just add it to the list of things that make the 993 awesome.
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Old 02-09-2019, 03:05 PM
  #18  
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Originally Posted by Ivan J View Post
Those of you who depress the clutch pedal when starting the engine should read post #4 in this thread....

https://rennlist.com/forums/993-turb...g-failure.html

I was taught to always disengage the clutch as well; but, I stopped doing that once I understood the above.
Interesting counterpoint but I think I’ll keep starting with the clutch depressed. With decades of manual transmission driving as well as multiple manuals in the fleet, I am not going to try to change my approach for some cars. But interesting point to consider nonetheless.

In fairness, part of my die hard, “don’t turn the key unless the left foot is fully extended” rule dates back to starting my grandfathers car in the garage when I was 11 or 12 and having it lurch forward from the starter and nearly hit the wall. It was in gear and I had not fully depressed the clutch (it was a long reach for my legs at the time). Obviously that may raise the question of whether it is wise to let a child start and back out your car but this was a different time and place and it passed the smell test at the time. Thankfully no one saw me do it or my underage ‘driving’ privileges surely would have been revoked but it made an impression.
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Old 02-09-2019, 03:22 PM
  #19  
HenryPcar
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Originally Posted by RudyP View Post
Genuinely curious - why would you care or even try to start without clutch depressed? I have never tried to start any manual car without first depressing the clutch. It’s safer and most cars require it anyway, I wouldn’t save any time by skipping this 0.05 second step if I had to think on it for s bit first to remember if this car requires it or not. But maybe there’s a reason I’m missing.

Yes makes you wonder the rationale of needing to disable this function.
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Old 02-09-2019, 03:49 PM
  #20  
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Originally Posted by HenryPcar View Post
Yes makes you wonder the rationale of needing to disable this function.
According to Steve Weiner, here's why: "Holding the clutch depressed when starting. The entire thrust load (the clamp load of the PP) rests against the bearing shoulders when lubrication is at minimum."
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Old 02-09-2019, 04:36 PM
  #21  
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Originally Posted by HenryPcar View Post
Yes makes you wonder the rationale of needing to disable this function.
When that clutch microswitch fails or gets out of adjustment and you can't start your car, you'll wish you'd by-passed it.

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Old 02-09-2019, 06:14 PM
  #22  
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Originally Posted by goofballdeluxe View Post
According to Steve Weiner, here's why: "Holding the clutch depressed when starting. The entire thrust load (the clamp load of the PP) rests against the bearing shoulders when lubrication is at minimum."
I never start with the clutch depressed. Many sources also suggest you should not hold the clutch in at lights etc. in any car. Stresses slave and if you've had to replace one on a turbo, you'll sit at lights in neutral.
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Old 02-09-2019, 06:22 PM
  #23  
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Originally Posted by ronnie993tt View Post
I never start with the clutch depressed. Many sources also suggest you should not hold the clutch in at lights etc. in any car. Stresses slave and if you've had to replace one on a turbo, you'll sit at lights in neutral.
Two very different things though. I start with the clutch depressed 100% of the time and I hold the clutch at lights 0% of the time. I also don’t cover/ride the clutch while driving around (eg in between shifts) like some people seem to do. I spend very little time with the clutch not 100% released but I do for a second or two while starting.

I'm probably at 400,000 miles or so of manual driving and have yet to replace a clutch - including over 100,000 miles on a single car.
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Old 02-09-2019, 06:25 PM
  #24  
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Originally Posted by ronnie993tt View Post
Many sources also suggest you should not hold the clutch in at lights etc. in any car.
Absolutely agree with this. I don’t hold the clutch in for any longer than perhaps 3 to 5 seconds in any situation as I always felt it put undue loads on the system ... glad to know I was in-line with others on this.
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Old 02-09-2019, 06:47 PM
  #25  
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Wow, never heard of this issue. Seems strange it's not talked about more often. Is the 993 clutch design different than any other 911 model? I don't think so, especially since I have a GT3 pressure plate in mine.

I think we should ask the guy with the cab from PA (forget his name) with over 300K, what he does.
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Old 02-09-2019, 10:37 PM
  #26  
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Originally Posted by swmic View Post
.

I think we should ask the guy with the cab from PA (forget his name) with over 300K, what he does.
That was Rich (Richardew) who unfortunately died in a traffic accident in his Boxster in October of 2017.


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Old 02-11-2019, 07:13 AM
  #27  
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The lawyers added the clutch interlock switch to our cars. One too many people trying to start their car (not necessarily Porsches) in gear with the resultant lurch forward. It was never required otherwise and never existed on cars prior to the 1990s.
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Old 02-11-2019, 04:39 PM
  #28  
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I have 98 and I don't think I am able to start the car without step on the clutch first...

Andy
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Old 02-11-2019, 10:11 PM
  #29  
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I’ve owned numerous manuals, Porsche over the years and always depress the clutch before starting but always in N clutch out at lights with zero issues ever.
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