grinding going from 2nd to 3rd gear at high revs
09-24-2002, 04:45 AM
#1
Burning Brakes
Thread Starter
grinding going from 2nd to 3rd gear at high revs
Hi All!
I just completed a DE event, where I had a ton of fun
However, I noticed that when I power shifted from 2nd to 3rd at about 6000rpm, there was a noticeable grind - like the syncros couldn't catch up fast enough.
It didn't happen going into any other gear.
Has anyone experience this before? Is this to be expected when pushing the transmission that much? Is there anything that can be done to correct the problem or minimize the damage? Like replacing transmission fluid?
Thanks.
Erick
I just completed a DE event, where I had a ton of fun
However, I noticed that when I power shifted from 2nd to 3rd at about 6000rpm, there was a noticeable grind - like the syncros couldn't catch up fast enough.
It didn't happen going into any other gear.Has anyone experience this before? Is this to be expected when pushing the transmission that much? Is there anything that can be done to correct the problem or minimize the damage? Like replacing transmission fluid?
Thanks.
Erick
09-24-2002, 11:18 AM
#2
Driver Carries No Cash
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I've noticed the exact same behavior in my '90 C4 Cabriolet. I wish I knew why it happened. I'd agree with you - it "feels" like the transmission can't keep up with a very quick gear change. (completely unscientific opinion - backed up by the butt dyno!) I've just drilled it into my thick head to hold the clutch in a tick longer before releasing into 3rd. I'd rather be a bit slower than rebuild my gearbox!
09-24-2002, 02:39 PM
#3
Rennlist Member
I also have the same issue, only on one particular turn at one track - NHIS. I'd be interested if someone has some insight...
Thanks!
Thanks!
09-24-2002, 04:01 PM
#4
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[quote]Originally posted by RSAErick:
<strong>I noticed that when I power shifted from 2nd to 3rd at about 6000rpm, there was a noticeable grind - like the syncros couldn't catch up fast enough.</strong><hr></blockquote>
Are you talking about shifting without the clutch? Just looking for clarification. I don't normally do this but would love to hear other's thoughts on the subject.
<strong>I noticed that when I power shifted from 2nd to 3rd at about 6000rpm, there was a noticeable grind - like the syncros couldn't catch up fast enough.</strong><hr></blockquote>
Are you talking about shifting without the clutch? Just looking for clarification. I don't normally do this but would love to hear other's thoughts on the subject.
09-24-2002, 04:09 PM
#5
Burning Brakes
Thread Starter
Apparently I'm not alone with this problem!
Joey, I NEVER shift without the clutch... can you?
Like C4_guy, I started slowing down my 2-3 shift - holding the clutch in for a second longer before shifting:
clutch in - 2nd to neutral - pause - neutral to 3rd - clutch out
Infuriating when trying to go fast!
Anyway, I've heard that transmission fluids can make a large difference, but didn't know which direction to go....
Thanks.
Erick
Joey, I NEVER shift without the clutch... can you?
Like C4_guy, I started slowing down my 2-3 shift - holding the clutch in for a second longer before shifting:
clutch in - 2nd to neutral - pause - neutral to 3rd - clutch out
Infuriating when trying to go fast!
Anyway, I've heard that transmission fluids can make a large difference, but didn't know which direction to go....
Thanks.
Erick
09-24-2002, 05:08 PM
#6
Technical Specialist
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[quote]<strong>Anyway, I've heard that transmission fluids can make a large difference, but didn't know which direction to go</strong><hr></blockquote>
Erick,
Generally accepted G50 gear lube is Mobil 1. There are also other manufacturer's gear lubes that meet the Porsche specs, and would work for you. You don't want to use Swepco, which is the lube of choice for 915 transmissions.
Here's a how-to article for changing the lube: <a href="http://p-car.com/diy/transmissionfluid/" target="_blank">http://p-car.com/diy/transmissionfluid/</a>
Erick,
Generally accepted G50 gear lube is Mobil 1. There are also other manufacturer's gear lubes that meet the Porsche specs, and would work for you. You don't want to use Swepco, which is the lube of choice for 915 transmissions.
Here's a how-to article for changing the lube: <a href="http://p-car.com/diy/transmissionfluid/" target="_blank">http://p-car.com/diy/transmissionfluid/</a>
09-25-2002, 01:34 AM
#7
Race Car
Guys! ...don't fret, it happens with my transmission as well, only once it's good and hot.
Yes, I have pretty much attributed it to the synchros getting nice and warm and basically "not being able to catch up" just about sums it up.
I'm sure Erick is NOT "speed shifting" as it's next to impossible with a 911, correct me if I'm wrong.
I've tried all sorts of tricks, changing fluid to Mobil 1, changing shifter bushings and checking everything in the world out! <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
I've even bled the clutch master/slave cylinder several times...still have the sticking clutch pedal, and still bump the engagement teeth when upshifting to third gear.
Just wait until you're going into a left hand turn where you need to downshift into second gear and you pull the shifter too far to the left and try to engage second!! ...there's NOTHING there!! It took me awhile to figure out what I was doing, thought I had a problem, then second would work everywhere else??
Imagine that you pretty much have to brace yourself for a good left turn, carousel or hook - so you might possibly pull a bit too much to the left on the shifter, there ya go.
Once I figured out what I was doing, I got a good laugh out of it...and was relieved that there were no troubles with the trans. <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
...so watch out for that one, it's a dooooozy!
Yes, I have pretty much attributed it to the synchros getting nice and warm and basically "not being able to catch up" just about sums it up.
I'm sure Erick is NOT "speed shifting" as it's next to impossible with a 911, correct me if I'm wrong.
I've tried all sorts of tricks, changing fluid to Mobil 1, changing shifter bushings and checking everything in the world out! <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
I've even bled the clutch master/slave cylinder several times...still have the sticking clutch pedal, and still bump the engagement teeth when upshifting to third gear.
Just wait until you're going into a left hand turn where you need to downshift into second gear and you pull the shifter too far to the left and try to engage second!! ...there's NOTHING there!! It took me awhile to figure out what I was doing, thought I had a problem, then second would work everywhere else??
Imagine that you pretty much have to brace yourself for a good left turn, carousel or hook - so you might possibly pull a bit too much to the left on the shifter, there ya go.
Once I figured out what I was doing, I got a good laugh out of it...and was relieved that there were no troubles with the trans. <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
...so watch out for that one, it's a dooooozy!
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09-25-2002, 08:02 AM
#8
Racer
Hi,
I experience the same problem shifting very fast from 2nd to 3rd at high revs - but I have a 993 6-speeder installed (G50-20) in my 964 C2. So the problem seems to affect other variants of the G50 box, too. The gearbox only has some 5000 careful km on it, so the synchros should not be worn at all.
However, it may sound cynical but I am happy others report the same situation because I was about to lynch the guy selling me the gearbox!
Anatol
I experience the same problem shifting very fast from 2nd to 3rd at high revs - but I have a 993 6-speeder installed (G50-20) in my 964 C2. So the problem seems to affect other variants of the G50 box, too. The gearbox only has some 5000 careful km on it, so the synchros should not be worn at all.
However, it may sound cynical but I am happy others report the same situation because I was about to lynch the guy selling me the gearbox!
Anatol
09-25-2002, 03:25 PM
#9
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[quote]Originally posted by RSAErick:
<strong>Joey, I NEVER shift without the clutch... can you?</strong><hr></blockquote>
Sure, all the fast track guys do it!
Actually, it is possible. A couple hours ago I grinded my way from 2nd to 3rd at high revs which reminded me of your question. So, for the 3rd to 4th shift, I lifted off the throttle and eased the **** back. It was notchy but there was no grind.
I believe racers opt to skip the clutch and I know you can get by with moderate clutch travel after 1st gear. But definitely, get off the throttle before attempting these moves.
<strong>Joey, I NEVER shift without the clutch... can you?</strong><hr></blockquote>
Sure, all the fast track guys do it!
Actually, it is possible. A couple hours ago I grinded my way from 2nd to 3rd at high revs which reminded me of your question. So, for the 3rd to 4th shift, I lifted off the throttle and eased the **** back. It was notchy but there was no grind.
I believe racers opt to skip the clutch and I know you can get by with moderate clutch travel after 1st gear. But definitely, get off the throttle before attempting these moves.
09-26-2002, 07:12 AM
#11
Race Car
<img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
...now that's funny! I don't know ANYBODY that shifts "clutchless" with a 915 -or- G-50 gearbox.
If there is someone that does it...and gets away with it, I'm listening.
Guys, PLEASE don't try this, I can't tell you how many times I've had a 915 apart because someone either missed a shift or engaged the clutch and stomped on the gas BEFORE the gear they selected was fully engaged...the gearbox is just not designed for it.
As for a G-50, I haven't had mine all the way apart, so I haven't studied the much-improved design of the shafts and gear related components.
Either way, I'm about positive the G-50 would have a complete and total aversion to being "speed shifted" or going "clutchless".
The act of speed shifting in my book is keeping the gas to the floor and shifting so fast that the engine just revs up a bit towards redline, most motorcycles can do this effortlessly, some muscle cars too...but a transaxle - NO.
...now that's funny! I don't know ANYBODY that shifts "clutchless" with a 915 -or- G-50 gearbox.
If there is someone that does it...and gets away with it, I'm listening.
Guys, PLEASE don't try this, I can't tell you how many times I've had a 915 apart because someone either missed a shift or engaged the clutch and stomped on the gas BEFORE the gear they selected was fully engaged...the gearbox is just not designed for it.
As for a G-50, I haven't had mine all the way apart, so I haven't studied the much-improved design of the shafts and gear related components.
Either way, I'm about positive the G-50 would have a complete and total aversion to being "speed shifted" or going "clutchless".
The act of speed shifting in my book is keeping the gas to the floor and shifting so fast that the engine just revs up a bit towards redline, most motorcycles can do this effortlessly, some muscle cars too...but a transaxle - NO.
09-26-2002, 05:37 PM
#12
Burning Brakes
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I noticed on my recent trackday that I was crunching the change from 2nd to 3rd. I had thought that this was due to my new clutch/LWF, since it didn`t happen with the old clutch/DMF but since eveyones at it I guess I need not worry.
09-27-2002, 10:19 PM
#13
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I had the same problem several years ago...and ended up getting my transmission rebuilt.
My advice: don't force the 2nd to 3rd shift. Let the synchros do their job, even if it seems like that particular shift is agonizingly slow.
Needless to say, I don't even attempt to speed shift anymore. I've played around enough to get a good feel for the speed of shift I can get away with.
My advice: don't force the 2nd to 3rd shift. Let the synchros do their job, even if it seems like that particular shift is agonizingly slow.
Needless to say, I don't even attempt to speed shift anymore. I've played around enough to get a good feel for the speed of shift I can get away with.
09-30-2002, 03:54 AM
#14
Race Car
Interesting Rich, as I thought the introduction of this problem in my car was after I installed the "Cup" lightweight clutch/flywheel...but then I hadn't tracked the car prior to changing it.
You've had your car for years when we changed your clutch to a "Cup" setup - thought maybe you would encounter the issue discussed once we changed it??
...guess not?
I kinda figured that's why my transmission did that, because the reduction in rotational mass allows the RPM of the engine and anything attached to "slow" very quickly, including the shafts in the transmission. So then you go to shift, the speed of all the components drops and you go for another gear - AH, I have it all confused, apparently.
Anyway, just got back from a weekend at VIR and noticed that the issue of shifting from 2nd to 3rd only showed up once the car was good and HOT...I could run for awhile without issue, then it would show up.
As before, and to add "amplifying information" to this post...I tried a few different things - just so you know, the only thing that worked was to incorporate a slight pause into my routine when shifting up to 3rd...it worked like a champ...every time.
Another thing I'm starting to notice is when finishing off a straightaway, in 5th - I have always downshifted to 3rd vice 4th, then 3rd.
I understand I'm not the only one who does this.
Again, the engine slowing issue, you know, rotational mass decreased, so rotational inertia goes out the window, so on and so forth.
I get a pretty healthy grind when downshifting if I don't try and match the downshift with high revs to the engine.
Mind you, I use what I call "fat foot" vice heel/toe, basically using the width of my foot and have it rolled over onto the gas pedal when I first get on the brakes so my engine is revved and I can downshift into third without incident.
BUT, when I slip up and forget to match the revs...GRIIIIIIND! ...it's a horrible sound.
But it'll get over it. <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
You've had your car for years when we changed your clutch to a "Cup" setup - thought maybe you would encounter the issue discussed once we changed it??
...guess not?
I kinda figured that's why my transmission did that, because the reduction in rotational mass allows the RPM of the engine and anything attached to "slow" very quickly, including the shafts in the transmission. So then you go to shift, the speed of all the components drops and you go for another gear - AH, I have it all confused, apparently.
Anyway, just got back from a weekend at VIR and noticed that the issue of shifting from 2nd to 3rd only showed up once the car was good and HOT...I could run for awhile without issue, then it would show up.
As before, and to add "amplifying information" to this post...I tried a few different things - just so you know, the only thing that worked was to incorporate a slight pause into my routine when shifting up to 3rd...it worked like a champ...every time.
Another thing I'm starting to notice is when finishing off a straightaway, in 5th - I have always downshifted to 3rd vice 4th, then 3rd.
I understand I'm not the only one who does this.
Again, the engine slowing issue, you know, rotational mass decreased, so rotational inertia goes out the window, so on and so forth.
I get a pretty healthy grind when downshifting if I don't try and match the downshift with high revs to the engine.
Mind you, I use what I call "fat foot" vice heel/toe, basically using the width of my foot and have it rolled over onto the gas pedal when I first get on the brakes so my engine is revved and I can downshift into third without incident.
BUT, when I slip up and forget to match the revs...GRIIIIIIND! ...it's a horrible sound.
But it'll get over it. <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
09-30-2002, 04:20 AM
#15
Burning Brakes
Thread Starter
Jeff,
I also noticed the same grinding when downshifting if I didn't match the revs enough. It sometimes happened when executing that 5th to 3rd shift because it was harder to get the revs up accurately when you're threshold braking from 140mph to 40 for a corner. Getting those revs just right while stomping on the brakes HARD is tough to do!
I may have experience more grinding when HOT also... I wonder if tranny fluid losing some viscosity at very high temps might have something to do with it. Maybe a little thicker fluid at high temps might be a little better?
Erick
I also noticed the same grinding when downshifting if I didn't match the revs enough. It sometimes happened when executing that 5th to 3rd shift because it was harder to get the revs up accurately when you're threshold braking from 140mph to 40 for a corner. Getting those revs just right while stomping on the brakes HARD is tough to do!
I may have experience more grinding when HOT also... I wonder if tranny fluid losing some viscosity at very high temps might have something to do with it. Maybe a little thicker fluid at high temps might be a little better?
Erick