downshifting problem
01-26-2004, 11:09 AM
#46
Race Director
'Engine braking' with a lift vs. engine braking with a downshift are two different animals.
Again I must say, Slowing the car by downshifting is an improper technique. Many people do this, and these people wonder why their clutch & tranny only lasts half as long as expected. Brake pads and rotors are much cheaper to replace.
Brake with your brake pedal. Use your engine to accelerate.
Slowing down or accelerating in the pits is a different story than slowing down for a corner on the track, btw. (But let's not confuse the issue here with that!)
Kevin, I believe you are translating what you hear on the race track into what you believe. Have you ever driven on the track yourself? Based on your own comments, it seems you haven't. How can you consider yourself to be an expert at proper downshifting techniques without any track experience? I suggest you talk with your track buddies to clarify their braking technique. You mention Mike Canney, Sam Asinugo: I believe Canney ran in NASA's American Iron Series, and Asinugo runs in SCCA ITS in VA. Basically local racers. BTW: the guys I mentioned, Vic Elford, Bob Bondurant, Skip Barber, Ross Bentley are or were world class pros, not local amateurs. Still, I suggest you ask your track buddies for more details and clarification on their braking technique: I think you don't quite understand what they are actually doing.
I am not trying to be harsh here: we are a bunch of car enthusiasts that like to share our experiences here. But too often inaccurate inforamation is given here, and people believe it to be truth. Using your engine to slow down by downshifting is not a good technique. The pros don't do it, the driver schools don't teach it, so why promote such a technique?
Ok, maybe I've had too much coffee this morning....
Sorry for the rant,
-Z-man.
Again I must say, Slowing the car by downshifting is an improper technique. Many people do this, and these people wonder why their clutch & tranny only lasts half as long as expected. Brake pads and rotors are much cheaper to replace.
Brake with your brake pedal. Use your engine to accelerate.
Slowing down or accelerating in the pits is a different story than slowing down for a corner on the track, btw. (But let's not confuse the issue here with that!)
Kevin, I believe you are translating what you hear on the race track into what you believe. Have you ever driven on the track yourself? Based on your own comments, it seems you haven't. How can you consider yourself to be an expert at proper downshifting techniques without any track experience? I suggest you talk with your track buddies to clarify their braking technique. You mention Mike Canney, Sam Asinugo: I believe Canney ran in NASA's American Iron Series, and Asinugo runs in SCCA ITS in VA. Basically local racers. BTW: the guys I mentioned, Vic Elford, Bob Bondurant, Skip Barber, Ross Bentley are or were world class pros, not local amateurs. Still, I suggest you ask your track buddies for more details and clarification on their braking technique: I think you don't quite understand what they are actually doing.
I am not trying to be harsh here: we are a bunch of car enthusiasts that like to share our experiences here. But too often inaccurate inforamation is given here, and people believe it to be truth. Using your engine to slow down by downshifting is not a good technique. The pros don't do it, the driver schools don't teach it, so why promote such a technique?
Ok, maybe I've had too much coffee this morning....
Sorry for the rant,
-Z-man.
01-26-2004, 02:39 PM
#47
Rennlist Member
Originally posted by Dsalillas
I'll have to go back and check the reciepts but I believe the clutch has less than 5k on it.
I'll have to go back and check the reciepts but I believe the clutch has less than 5k on it.
01-26-2004, 08:41 PM
#48
TRB0 GUY
Rennlist Member
Rennlist Member
Join Date: Nov 2003
Location: Daphne, AL
Posts: 3,769
Likes: 0
Received 0 Likes
on
0 Posts
Ouch Z... but keep the hits coming man, it's making for a good debate. Yep those are a few of my shop's customers, locals really. I wasn't referring to slowing down IN the pits, I was refering to turn 10 (right before the long straight) you can hear the cars coming to turn 10 early-downshifting to engine brake. I have yet to race on the point myself, I've only been on there sitting shotty for a joy ride. I've only had the chance to race Florida Tech's FSAE car on a small auto-x track. Please don't insuly my intelligence by saying that I don't "quite understand what they're doing" though. Ever heard of Frank Sanchez?? He raced GT1 and did pretty well for a while (not sure what he's up to these days)... hearing his blue vette come down to turn 10, he'd always early downshift and if you were on the watch tower, you could see the flames spit out of the exhaust each time he'd let off the gas. Z, I hate to "brake" it to you, but a lot of racers downshift early... and though it might not be healthy for everyday driving, nothing in racing really is!
Lee Marks, a Porsche tuner in Cali, wrote a book about racing called "Race Driving Fundamentals"... let's take a look at a clip from chapter seven, "Braking":
-----Phil Hill was a master at “setting” a car. I remember watching him at Monterey in a Chapperal racecar. It was as though he was doing a ballet with the car. There were no abrupt movements or jerky reactions to his inputs of steering, shifting, braking, clutching or applying the gas pedal.
In “setting”, let us say that you are accelerating down a short straight away and you are in third gear. You have a breaking point picked out, an immovable object or at some tracks a marker. You apply the brakes hard at this point you have picked and then as soon as your speed is down where you can downshift without overriding the engine you must “heel and toe” in order to change into second gear. This helps your braking even more.-----
Now, I'm not trying to say what's right and what's wrong here Z... nor am I trying to prove anyone wrong. All I'm saying here is that there are plenty of people who practice both ways... and both are the "right way" if done correctly. Downshifting early is a track-biased driving technique really, so I'm not advocating doing this whenever one brakes in his volvo on the way to get milk... though I do find it fun to do every once in a while (probably not in a volvo though, lol)
Just my $0.02
-Kevin
Lee Marks, a Porsche tuner in Cali, wrote a book about racing called "Race Driving Fundamentals"... let's take a look at a clip from chapter seven, "Braking":
-----Phil Hill was a master at “setting” a car. I remember watching him at Monterey in a Chapperal racecar. It was as though he was doing a ballet with the car. There were no abrupt movements or jerky reactions to his inputs of steering, shifting, braking, clutching or applying the gas pedal.
In “setting”, let us say that you are accelerating down a short straight away and you are in third gear. You have a breaking point picked out, an immovable object or at some tracks a marker. You apply the brakes hard at this point you have picked and then as soon as your speed is down where you can downshift without overriding the engine you must “heel and toe” in order to change into second gear. This helps your braking even more.-----
Now, I'm not trying to say what's right and what's wrong here Z... nor am I trying to prove anyone wrong. All I'm saying here is that there are plenty of people who practice both ways... and both are the "right way" if done correctly. Downshifting early is a track-biased driving technique really, so I'm not advocating doing this whenever one brakes in his volvo on the way to get milk... though I do find it fun to do every once in a while (probably not in a volvo though, lol)
Just my $0.02
-Kevin
01-26-2004, 10:53 PM
#49
Race Director
Kevin:
Ok, I found Lee Mark's stuff online (Ref: http://www.motormeister.com/suz/ptw_book/ch_1.htm) Motormiester is a performance shop. Lee Mark is their head technitian, and he's been racing with SCCA, PCA And POC since 1964. I'll try to email him and ask him to clarify his statements, so I can better understand what he's saying.
Kevin, I'm not trying to insult your intelligence: I apologyze if you feel I have done so. I know that you have an autocross background, as I do myself. However, the whole downshifting technique is typically not called for in the autox environment: at least here, it's shift from first to second and leave it there till the finish line.
The quote you have is regarding Phil Hill driving a Chapperal race car. Do you know how old that car is? Mid 1960's. Back then, race cars had very ineffective brakes: sub-standard when compared to even today's higher end street brakes. IE: Like I said before, back then, they had to use the engine to slow the car down, 'cause their brakes would fail them quite quickly into a race.
Also: your comments about hearing the engine revving higher (ex: the Vette in turn 10) doesn't necessarily mean that driver is using the engine to slow the car: he most likely completed his heel-toe-downshift, and since he's in a lower gear, the engine is revving higher.
Ok, here are some of my resources:
And
Two very successful racers who now teach people about performance driving. BOTH of these guys state that downshifting to slow down a car is not the proper technique.
Am I beating a dead horse? Probably, by now. but like I said before, the method you describe is improper. Why promote it as a good technique?
Regards,
-Z-man.
Ok, I found Lee Mark's stuff online (Ref: http://www.motormeister.com/suz/ptw_book/ch_1.htm) Motormiester is a performance shop. Lee Mark is their head technitian, and he's been racing with SCCA, PCA And POC since 1964. I'll try to email him and ask him to clarify his statements, so I can better understand what he's saying.
Kevin, I'm not trying to insult your intelligence: I apologyze if you feel I have done so. I know that you have an autocross background, as I do myself. However, the whole downshifting technique is typically not called for in the autox environment: at least here, it's shift from first to second and leave it there till the finish line.
The quote you have is regarding Phil Hill driving a Chapperal race car. Do you know how old that car is? Mid 1960's. Back then, race cars had very ineffective brakes: sub-standard when compared to even today's higher end street brakes. IE: Like I said before, back then, they had to use the engine to slow the car down, 'cause their brakes would fail them quite quickly into a race.
Also: your comments about hearing the engine revving higher (ex: the Vette in turn 10) doesn't necessarily mean that driver is using the engine to slow the car: he most likely completed his heel-toe-downshift, and since he's in a lower gear, the engine is revving higher.
Ok, here are some of my resources:
From Speed Secrets by Ross Bently, pg. 20
Downshifting is one of the most misunderstood and misued techniques in driving. What is the real reason for downshifting? Many drivers think it's to use the eninge to help slow the car down. Wrong again! The engine is meant to increase your speed, not to decrease it. In fact, by using the engine to slow the car you can actually hinder accurate brake modulation and balance. Race drivers, and good street drivers, downshift during the approach to a corner, simply to be in the proper gear, at the optimum engine rpm, to allow maximum acceleration out of the corner.
Again, the reason for downshifting is not to slow the car. I can't emphasize this enough. That's what brakes are for. Too many drivers try to use the engine compression braking effect to slow the car. All they really achieve is upsetting the balance of the car and hindering the braking effectiveness (if the brakes are right at the limit before locking up and then you add engine braking to the rear wheels, you will probably lock up the rear brakes), and more wear and tear on the engine. Brake first, then downshift.
Downshifting is one of the most misunderstood and misued techniques in driving. What is the real reason for downshifting? Many drivers think it's to use the eninge to help slow the car down. Wrong again! The engine is meant to increase your speed, not to decrease it. In fact, by using the engine to slow the car you can actually hinder accurate brake modulation and balance. Race drivers, and good street drivers, downshift during the approach to a corner, simply to be in the proper gear, at the optimum engine rpm, to allow maximum acceleration out of the corner.
Again, the reason for downshifting is not to slow the car. I can't emphasize this enough. That's what brakes are for. Too many drivers try to use the engine compression braking effect to slow the car. All they really achieve is upsetting the balance of the car and hindering the braking effectiveness (if the brakes are right at the limit before locking up and then you add engine braking to the rear wheels, you will probably lock up the rear brakes), and more wear and tear on the engine. Brake first, then downshift.
From Bob Bondurant on High Performance Driving by Bob Bondurant and John Blakemore, pg. 54 - 55
I find that the first problem that my students have with heel-and-toe down-shifting is a misconception. Many think that an important reason for downshifting is to take advantage of the engine's braking effect. That though has somehow survived from the days of skinny tires, fat drivers, and rapidly fading drum brakes. Modern ventilated disc brakes have really changed that. With the great stopping power of modern brakes, it is unneccessary, and with high-stressed modern engines, it si a good way to break them.
I find that the first problem that my students have with heel-and-toe down-shifting is a misconception. Many think that an important reason for downshifting is to take advantage of the engine's braking effect. That though has somehow survived from the days of skinny tires, fat drivers, and rapidly fading drum brakes. Modern ventilated disc brakes have really changed that. With the great stopping power of modern brakes, it is unneccessary, and with high-stressed modern engines, it si a good way to break them.
Am I beating a dead horse? Probably, by now. but like I said before, the method you describe is improper. Why promote it as a good technique?
Regards,
-Z-man.
01-26-2004, 11:40 PM
#50
TRB0 GUY
Rennlist Member
Rennlist Member
Join Date: Nov 2003
Location: Daphne, AL
Posts: 3,769
Likes: 0
Received 0 Likes
on
0 Posts
Because it's used by many drivers, very well... Hearing 2 downshifts in ~2 sec intervals before the turn doesn't quite sound like heel-and-toe'ing after slowing down does it?
I understand absolutely no part of this has any relevance with auto-x.... I was just stating my backround really. For the FSAE cars, it's second and third gears mostly
(thats a longer story all together)
I understand that it's all but outdated... but many people still do it! And many of them are winning drivers... granted with Super 600 fluid, agressive compound pads, and a decent set of rotors (cooling ducts are wonderful too, but not usually needed for most weekender's)... you will never need to use engine braking. Does that mean some people still won't prefer to use it? Nope...
Different strokes for different folks, lol... and here's another cliche, to each his own. If some drivers still prefer to engine brake... who's to say it's bad? It seems to keep some winning still!
-Kevin
I understand absolutely no part of this has any relevance with auto-x.... I was just stating my backround really. For the FSAE cars, it's second and third gears mostly
(thats a longer story all together)I understand that it's all but outdated... but many people still do it! And many of them are winning drivers... granted with Super 600 fluid, agressive compound pads, and a decent set of rotors (cooling ducts are wonderful too, but not usually needed for most weekender's)... you will never need to use engine braking. Does that mean some people still won't prefer to use it? Nope...
Different strokes for different folks, lol... and here's another cliche, to each his own. If some drivers still prefer to engine brake... who's to say it's bad? It seems to keep some winning still!
-Kevin
01-27-2004, 12:16 AM
#51
Intermediate
Join Date: Jun 2003
Location: Big Stone Gap, Virginia
Posts: 29
Likes: 0
Received 0 Likes
on
0 Posts
Last year I bought a 944 s2 cab. The clutch went out shortly after I bought it. I was told the metal sping clutch was better. I ordered the Sach clutch and my mechanic installed replacing rubber hub clutch.
He put the clutch in and there was this AWFUL shudder on downshifting to 2nd gear. He has done many clutches with none coming back on him so he was pretty upset. We ordered another clutch and installed it-- same shudder. My supplier talked to Sachs and found that a certain series of clutches had a flaw -something was not long enough to connect to the torque tube or something like that. We ordered the third clutch -OEM rubber hub clutch- the supplier paid to have it installed- the car runs nicely and smoothly on down shift.
Several weeks after we completed the 3rd clutch job with rubber hub there was a post on Rennlist that listed a corrected part number for the sping hinge clutch that was redesigned to eliminate the problem. I had researched this problem for several months on rennlist with no suscess. I'm sorry that I do not have the exact post to help. The Sach rep had made no effort to advise us of the redesign or the new part number.
I suppose I'll wait another hundred thousand miles to have a spring hinge clutch.
So I don't think it has anything to do with your technique of shifting but everything to do with a bad clutch. Let me know if this helps.
He put the clutch in and there was this AWFUL shudder on downshifting to 2nd gear. He has done many clutches with none coming back on him so he was pretty upset. We ordered another clutch and installed it-- same shudder. My supplier talked to Sachs and found that a certain series of clutches had a flaw -something was not long enough to connect to the torque tube or something like that. We ordered the third clutch -OEM rubber hub clutch- the supplier paid to have it installed- the car runs nicely and smoothly on down shift.
Several weeks after we completed the 3rd clutch job with rubber hub there was a post on Rennlist that listed a corrected part number for the sping hinge clutch that was redesigned to eliminate the problem. I had researched this problem for several months on rennlist with no suscess. I'm sorry that I do not have the exact post to help. The Sach rep had made no effort to advise us of the redesign or the new part number.
I suppose I'll wait another hundred thousand miles to have a spring hinge clutch.
So I don't think it has anything to do with your technique of shifting but everything to do with a bad clutch. Let me know if this helps.
01-27-2004, 12:27 AM
#52
Rennlist Member
From Tom Pultz's excellent site (http://www.944s2.com - look under "ENGINE") I actually bit the bullet and bought the $700 dealer clutch for my S2. No vibration whatsoever.
FLYWHEEL AND CLUTCH UPGRADE
Tom Pultz
After more than 82,000 miles it became apparent that the stock clutch in my 944 S2 was on it's last legs... or should I say (diaphragm) fingers? The S2 and other NA models are infamous for their rubber center clutch disc and the resultant "shuddering" that comes with age and heat. With track season looming I decided to replace the OEM clutch package with the Sachs Sport Disc and normal S2 Sachs Pressure Plate. I also considered the Centerforce clutch kit, available at a really great price from Performance Intl. However, after careful evaluation I concluded the Sachs clutch kit was a "safer" choice based on the unknown (to me) reliability record of the Centerforce unit. Little did I know this Sport disc may not have been the wisest choice.
The Sport Disc shown above is a spring center disc with three pairs of different size springs. It is significantly lighter than the OEM rubber center disc and has a different type of friction surface with higher power handling capability and greater longevity. Like most things in life, you lose a little here... you gain a little there. In the case of the spring center disc, you lose the big, fat rubber donut damper and get very smooth engagement and shifting... but you also gain some transmission noise in the process... or in my case, a LOT of transmission noise... and a vibration in the gear shift lever between 3200-3400 rpm that gives your fingertips a vigorous massage. Hmmm, something fishy is going on here... better investigate.
Here's the latest on my clutch disc investigation. Shown above is a comparison of the Sachs standard spring center disc and the Sport version. As you can see, the standard version has a longer hub design, with a corresponding longer length for splines engagement, and maybe more important, the splines contact area has been shifted rearward slightly to more closely mimic the engagement position of the rubber center disc. Compared to the Sport disc it has different color-coded damping springs and a slightly different type of friction facing. This standard spring center disc should be similar or identical to the genuine Porsche spring center disc, part number 944-116-011-02. This new disc supersedes the old rubber center disc, part number 944-116-012-11. At a list price of over $700, I doubt they'll be many takers for this new Porsche disc... but if you really want one you can buy it for approximately $205.00 plus 15% markup from Sunset Porsche in Beaverton, OR (cost + 15% prices not applicable to Oregon and Washington residents).
Anytime the clutch components are replaced the flywheel should be resurfaced. In my case I chose to install a lightened and resurfaced stock flywheel from Huntley Racing. HR claims it weighs 4 lbs less than the stock weight of 16 lbs. I guess I'll never know for sure because time constraints prevented me from weighing the lightened unit before installation. Personally, I have my doubts.
Except for the severe shifter vibration and noise problems I'm having, I really like the way the new clutch functions. It is very smooth and shifting is much easier than with my old setup. The lighter disc weight combined with the lightened flywheel does seem to improve the engine's throttle response and desire to rev. The more I drive it the better I like it... but I hate the vibration!
The cause of my noise and vibration problems were finally traced to the flywheel, which apparently was either not balanced, or was improperly balanced by Huntley Racing. I ended up pulling out the flywheel and having it checked for balance, which was found to be severely out. Once that was corrected, 95% of my shifter vibration was gone.
FLYWHEEL AND CLUTCH UPGRADE
Tom Pultz
After more than 82,000 miles it became apparent that the stock clutch in my 944 S2 was on it's last legs... or should I say (diaphragm) fingers? The S2 and other NA models are infamous for their rubber center clutch disc and the resultant "shuddering" that comes with age and heat. With track season looming I decided to replace the OEM clutch package with the Sachs Sport Disc and normal S2 Sachs Pressure Plate. I also considered the Centerforce clutch kit, available at a really great price from Performance Intl. However, after careful evaluation I concluded the Sachs clutch kit was a "safer" choice based on the unknown (to me) reliability record of the Centerforce unit. Little did I know this Sport disc may not have been the wisest choice.
The Sport Disc shown above is a spring center disc with three pairs of different size springs. It is significantly lighter than the OEM rubber center disc and has a different type of friction surface with higher power handling capability and greater longevity. Like most things in life, you lose a little here... you gain a little there. In the case of the spring center disc, you lose the big, fat rubber donut damper and get very smooth engagement and shifting... but you also gain some transmission noise in the process... or in my case, a LOT of transmission noise... and a vibration in the gear shift lever between 3200-3400 rpm that gives your fingertips a vigorous massage. Hmmm, something fishy is going on here... better investigate.
Here's the latest on my clutch disc investigation. Shown above is a comparison of the Sachs standard spring center disc and the Sport version. As you can see, the standard version has a longer hub design, with a corresponding longer length for splines engagement, and maybe more important, the splines contact area has been shifted rearward slightly to more closely mimic the engagement position of the rubber center disc. Compared to the Sport disc it has different color-coded damping springs and a slightly different type of friction facing. This standard spring center disc should be similar or identical to the genuine Porsche spring center disc, part number 944-116-011-02. This new disc supersedes the old rubber center disc, part number 944-116-012-11. At a list price of over $700, I doubt they'll be many takers for this new Porsche disc... but if you really want one you can buy it for approximately $205.00 plus 15% markup from Sunset Porsche in Beaverton, OR (cost + 15% prices not applicable to Oregon and Washington residents).
Anytime the clutch components are replaced the flywheel should be resurfaced. In my case I chose to install a lightened and resurfaced stock flywheel from Huntley Racing. HR claims it weighs 4 lbs less than the stock weight of 16 lbs. I guess I'll never know for sure because time constraints prevented me from weighing the lightened unit before installation. Personally, I have my doubts.
Except for the severe shifter vibration and noise problems I'm having, I really like the way the new clutch functions. It is very smooth and shifting is much easier than with my old setup. The lighter disc weight combined with the lightened flywheel does seem to improve the engine's throttle response and desire to rev. The more I drive it the better I like it... but I hate the vibration!
The cause of my noise and vibration problems were finally traced to the flywheel, which apparently was either not balanced, or was improperly balanced by Huntley Racing. I ended up pulling out the flywheel and having it checked for balance, which was found to be severely out. Once that was corrected, 95% of my shifter vibration was gone.
01-27-2004, 12:45 AM
#53
Racer
Thread Starter
Join Date: Apr 2002
Location: B'ham, Alabama
Posts: 410
Likes: 0
Received 0 Likes
on
0 Posts
Thanks guys,
At least I know now, it's not only my car that has this problem in second. I haven't checked the receipts yet. I'm in no hurry since I'm garaging the car while I work on my S.
I'm leaning towards the clutch being the wrong one since that's what most of the threads on this problem concluded. I can live with it until it needs replacing again.
At least I know now, it's not only my car that has this problem in second. I haven't checked the receipts yet. I'm in no hurry since I'm garaging the car while I work on my S.
I'm leaning towards the clutch being the wrong one since that's what most of the threads on this problem concluded. I can live with it until it needs replacing again.
01-27-2004, 04:49 AM
#54
Drifting
Join Date: Nov 2003
Location: Vancouver, BC, Canada
Posts: 2,310
Likes: 0
Received 6 Likes
on
3 Posts
Question: might I have problems in a 944 with the heel-toe technique with my size 14 feet? I have not practiced this before, my car's in storage right now, I can't test it...
I find depending on what shoes I'm wearing my instep of my right foot can catch on the brake pedal if I'm not really paying attention...
On another note, my father had to drive his old Citroen several hilly kilometers home one winter when the clutch gave out on him, ****fing precisely at the proper times...oh man what a story that was!
I find depending on what shoes I'm wearing my instep of my right foot can catch on the brake pedal if I'm not really paying attention...
On another note, my father had to drive his old Citroen several hilly kilometers home one winter when the clutch gave out on him, ****fing precisely at the proper times...oh man what a story that was!
