Anyone ever miss a shift?

Summer of 1994, and I was the sales manager of the Porsche dealership here in Calgary.

I got to work one Monday morning and the car of a "very good" customer was in the service area, obviously having been towed in earlier judging from the way it had been parked.

Funny thing was, there were white shoe polish numbers on the rear 1/4 glass.

Hmmmm.........

Apparently there had been a track day of the local exotic car club that Sunday at "Race City Speedway" and my client had taken his new 911 C4 out to the event.

As there was no "drop off envelope" with an explanation of what service was needed, I made an initial phone call to see what we could do for him.

Me: Hi Mr. ******, I saw your car was towed in yesterday, what can we do for you ?

Client: I don't know really....I was at the track yesterday and the car suddenly stopped running for some reason. Call me when you figure it out.

Turns out our mechanic didn't have to do much "exploratory" work after all. Out of curiosity, I called some of the other members of the club, who told me that at the end of the straight where you can hit 200-220 KMH before turn 1, he had downshifted from 5th to 2nd......instead of 4th........and, well, you know the rest. There's no rev-limiter on downshifts.

Now, here's where it got interesting, this guy was a "very good" customer as he bought on average 2 new 911's a year from me and had been a Porsche customer for about 10 years. And.....he was a really decent guy too.....and that's worth something in my books.

The exotic car club was full of mainly Lambo and Ferrari guys, who, while rightfully proud owners of beautiful cars, often were roundly joked with by the Porsche guys who drove all day long, stopping only to pee, while they came in after 3-4 laps, worried about braking their cars or overheating something.

After a phone call to Randy Koster, the Porsche National Sales Manger, I had convinced him to "warranty" my clients $30,000 "non-warranty" motor rebuild as a goodwill gesture due to the nature of the incident, those 50 or so Lambo and Ferrari owners present, and the potential for some GREAT public relations therein.

My explanation to the client (who fell out of his chair BTW) was that Porsche had deemed his car as being used in the manner in which it was intended, therefore his loyalty as a client was being rewarded accordingly.

 

When I first started driving my car I missed a couple. 5th to 2nd downshifts instead of going to 4th. My car did not like that Luckily I caught it by feeling the clutch before I completely disengaged it and screwed up the engine.

 

I've pulled away from a stop light in reverse a couple of times in my 348 - does that count? Didn't hit anything, but it wakes you up real quick!

 

What I'd like to know is this...when you do it badly enough, what's going to break and why?

 

I'm not technical, But I think your engine will try to keep up with the speeds of your wheels, and because the gear is way to low, that will be way too fast. So I think your engine will try to reach the same rpm-level as a F1 engine, and then something breaks, don't ask me what

 

All I know is in M3 Land it's called "the money shift". My wife used to date a guy with an M3 who did this on the 405 and had to replace the transmission, $$$. Stock M3's have (what seem to me to be) long throws that are sloppy. I installed a UUC short shift kit and UUC tranny mount enforcers as protection against a mistake.

The worst I've done was a quick upshift to 2nd during some spirited driving - I remember thinking, wow that was really a fast shift, when it suddenly kicked back out of gear with a slight crunch once I applied more throttle. Argh, bad driving! After that, I'm always careful to make sure I shift properly and smoothly.

 

The wheels force the engine to spin faster than it was designed...
usually that results in the valves being opened and closed faster than they were designed... in particular, with more force than the valve springs holding them in were designed... resulting in the valve stem being literally thrown into the cylinder... such that its still in there when the piston reaches top... resulting in contact... chaos ensues from there (bent valves, bent rods, cracked pistons, projectile ... ).

 

What are the chances of doing this causing a rod to go through the block? There is a reason I ask this.

 

My apologies if this sounds stupid but was rasied saying there is no such thing as a stupid question.

Does the Euro 1985 308GTS QV have a rev limiter???

Enjoy the Drive,

Steven R. Rochlin

 

No it doesn't Steven.

 

308GTS,

Many thanks my friend. Had a feeling there was no rev limiter and did not want to "experiment" to find out. Missed upshifting to fourth once (am careful so no harm no foul) after the recent 60k service. They tightened things and it had new gaskets and whatnot. Took me that one time to realize fourth needed a more solid push than previously (glad i have LONG arms!). Shifting to fourth seems like it is W-A-Y O-V-E-R T-H-E-R-E at times.

Enjoy the Drive,

Steven R. Rochlin

 

It is the valves that drop usually, then the piston is damaged and then it's possible for an individual piston to grab and throw a rod. That's worst case scenario. On the older cars sodium fillled valves make it even more nasty!

My quick story and then I'll leave you with a quote from Mario.

As I pulled onto a busy freeway from a stoplight, I rev'd out first gear and went for second, lifting only slightly. Well, I missed second with my foot still FIRMLY in the throttle. OOPS! Even backing ouut as quickly as I could, the tach needle travelled well past 7800 redline and went to, oh, about 10,500. Holy ****! I was still rolling so re-engaged second. Then went to third. The engine stumbled for a few seconds as some carbon flakes blew out that had no doubt been camping out on the top of my valve train for many years. Once the plugs came back on line, I motored off with no ill effects, long term.

In Mario's auto bio, he makes an observation about this. During his racing career, he observed that if you ever over rev'ed a Cosworth, you might as well pull over and park it, because it wasn't going to last even two more laps. He said when he blew a redline in a Ferrari, he would pit and advise the crew to check things out, the mechanics would look at each other, shrug their shoulders, and send him back out!

CAUTION: ACTUAL RESULTS MAY VARY!!!!!! LOL

 

Not possible because modern Ferrari engines do NOT use pushrods. Enless you meant a connection rod, that has a chance of going through your oil pan, or just self combusting in your block.

 

A few years ago, I was at a track event and a "pro racer" (not Ferraris) was giving instructions on how to drive your car. I let him behind the wheel and he went from 4th to 3rd instead of 5th with the revs already pegged above 7k. Tach went well over 9k and I felt like murdering him. All he could say was "I'm really sorry!".

No damage done, but that incident gave me an epiphany about letting just anyone drive my car in the future...

 

Speedy308,

>>>... the mechanics would look at each other, shrug their shoulders, and send him back out<<<

Worked back then and still works now. So pretty much what they do today

It is a car dammit, now get out there and DRIVE it

Gotta LOVE the Italians

Enjoy the Drive,

Steven R. Rochlin

 

Damn right!

You'll have to drop down to Houston some time. We got some hot blues and alt. country guys kickin' down here.

I got stopped downtown going fast and loud the other night.
No worries, 'cause I was going in to START partying!

They caught my "throw down" 2 year expired safety sticker! LOL

Thanked 'em for doing such a fine job.

 

This is an all-too common occurence with 911s because of the imprecise feel of the shift linkage. As a Porsche Club instructor for many years, I have seen even the best drivers do it occasionally. The usual result is a bent valve.

I have noticed in Ferraris that it could be very easy to attempt an upshift from 3d and hit 2nd instead of 4th. I did it once in a 308, but caught myself before dropping the clutch. When you push the shift lever forward from 3d, it centers in the gate, rather than moving rightward below the 4th gear slot. I have trained myself to bang the lever over against the metal on the far right before pushing it forward.

I'm surprised that Ferrari didn't spring load the lever to move sequentially to the right as it advances through the gears.

 

Wow,

No offense but some of you guys need to pass on that next Rolex purchase and enroll thyself in a basic automotive principals course or something. There are two totally seperate things being discussed here and the original poster doesn't make it clear which he is asking about.

Rev Limiters: An electronic programming, typically in the ECU, that modifies fuel and/or spark to stop the engine from rotating any faster. The word "soft" used to describe a rev limiter usually refers to one that modifies timing advance to rob power from the engine, just enough that it stop accelerating. The opposite, a "hard" limiter typically refers to a system where fuel is simply cut for a period of time. In "hard" cutoffs, since fuel is completely cut, the engine begins to drop towards idle, then, fuel cuts on again ... it makes for very jerky on/off motions. The "soft" limiters don't fully cut fuel, so typically you don't stop/go/stop/go/stop/go ... you just stop accelerating. Soft systems are easier on driveline components and on the stomach, but make for horrible combustion effeciency which spark plugs and O2 sensors don't like. What's key here, is that a rev limiter isn't a "brake" of any kind. Imagine you are in 1st gear at redline. A car comes up on your rear bumper and pushes your car faster while you are still in gear. There is nothing your car/motor will do to "slow down" and prevent the engine from over-reving.

The story about the Porsche is the "really bad" interpretation of a missed shift. Going from 5th to 2nd is where this most often happens. Basically, as you let the clutch out in second, your drive wheels and the weight/momentum of your moving vehicle accelerate the crank to match engine speed accordingly. The engine over revs and you typically break-off and chuck a rod/piston combo through something more expensive than you care for it to be at that very moment.

There is another way that this scenario can unfold however. Physics tells us nothing moves "instantly", even light takes time to get from point A to point B. If a clutch is engaged overly quickly, "popped" for instance ... something will have to "give" while the engine speeds up. Typically, what gives is grip. Depending on how much grip your drive wheels have, you may slow them enough that they slide a bit (I'm sure everyone here has at some point slipped a foot off the clutch pedal accidenately in any manual transmission vehicle and heard the tires chirp). Other things that can give are the clutch, it might slip a little (though this is uncommon), or in extreme cases, where there is tons of grip (think AWD and slicks) and the motor has a lot of rotational mass, you might overstress the drivetrain and pop the transmission out of gear or even snap a driveshaft.

There's a video that went around the net maybe 8 months ago of a first time track goer in his RT/10 Viper kick his rear around while on the brakes coming into a slow left-hand corner. This student had no idea what heel/toe'ing was and didn't match revs at all, when he let out the clutch too fast in 2nd gear, the heavy rotational mass of that V10 overcame traction for a split second and kicked his car sideways ... ultimately into the infield wall.

The other type of "missed shift" is the one where you fail to push the shift level fully into the next gate before engaging the clutch. Yes, it's possible to shear a tooth or two off the cog, but 99% of the time the tranny will just spit the selector back into neutral. Might damage the synchros though, but they're relatively cheap/easy to replace.

Bill in Brooklyn

 

Wrong. A missed shift can cause ANY engine to mechanically over rev and hand granade completely destroying the engine and endangering the driver as well as bystanders. I've seen a Lambo Muria where the entire engine was ripped out of the car by a 5th to R shift which is possible in that car. My P4 has a seq. shifter that prevents these shifts as do GT40 Race ZF boxes. A French journalist recently destroyed a Carrera GT engine with a missed shift. It's simply physics.

 

when i first bought my 308, i had it delivered and went for a drive right off the truck. well, i did not use enough force to put the car in first gear and i did not realize the tranny was somewhere in limbo - most likely fifth gear. so it was a struggle launching from a dead start in fifth gear - all the while thinking this car lost a lot of power going from sea level to 6000 feet here in colorado. i was quite thrilled when i 'found' first gear a few shifts later.

 

When I first got my Europa the unusual design of the shift linkage made for some fishing trips to find 4th. I remember going on to a highway, redline in 3rd and then getting stuck in no mans land (neutral trying to find 4th). I must have slowed to about 50 (from 80) when I finally found 3rd again. 10 seconds of sheer panic! I have since tightened it up.

 

Absolutely possible. When the engine is "mechanically overrevved" by a 5 to 2 downshift, internal chaos is certain if the clutch is not disengaged pronto, and that chaos could certainly include a con rod out the side of the block.

Gary

 

FWIW.........the case and crank of this 911 engine were OK as were the rods. Porsche basically ended up rebalancing and blueprinting (now there's an old term) the engine to a zero gram tolerance after replacing numerous internal parts. The case was not cracked, nor was there any torsional shifting either. Quit remarkable considering the rotational forces that must have been in place at the time of the downshift.

That was one sweet engine when it was finished too. A little trick machine work, and a part here and there can make quite a difference.