manual transmission shifting, whats normal?
07-10-2015, 02:13 PM
#16
Rennlist Member
Yeah....
Actually, when the vehicle is stopped, the engine is at idle, and the clutch is depressed, the energy required to stop the rotating mass is exactly the same, regardless of which synchro you choose to do that job. Remember, the clutch disc, the torque tube shaft, and all of the gears (on both shafts) are rotating until the clutch is depressed. The only thing not rotating is the pinion shaft, reverse gear, and the hubs with the sliders attached.
In reality, because the lower gears are spinning significantly slower than the higher gears, there would be less wear on the synchro and the slider if the lowest gear possible (1st gear) was selected to stop the transmission, before putting the transmission into reverse. Stopping the transmission with a higher gear and then putting the vehicle into 1st gear is actually wearing two different synchros and sliders to do the same job. This, obviously, would wear both of the synchros and sliders used...a very poor idea.
I'm not saying that it's not a good idea to use one of the higher gear's synchros, to put the transmission into reverse, on a transmission that has significant synchro wear (less used, therefore they have less wear), it's just that your logic to do so is very flawed.
Actually, when the vehicle is stopped, the engine is at idle, and the clutch is depressed, the energy required to stop the rotating mass is exactly the same, regardless of which synchro you choose to do that job. Remember, the clutch disc, the torque tube shaft, and all of the gears (on both shafts) are rotating until the clutch is depressed. The only thing not rotating is the pinion shaft, reverse gear, and the hubs with the sliders attached.
In reality, because the lower gears are spinning significantly slower than the higher gears, there would be less wear on the synchro and the slider if the lowest gear possible (1st gear) was selected to stop the transmission, before putting the transmission into reverse. Stopping the transmission with a higher gear and then putting the vehicle into 1st gear is actually wearing two different synchros and sliders to do the same job. This, obviously, would wear both of the synchros and sliders used...a very poor idea.
I'm not saying that it's not a good idea to use one of the higher gear's synchros, to put the transmission into reverse, on a transmission that has significant synchro wear (less used, therefore they have less wear), it's just that your logic to do so is very flawed.
related experiment: try and stop bicycle tire at the hub using your finger at the inner spokes...... then try and stop the wheel at the outer edge with your finger...... same energy.. different forces.
so, i think your theory is a little flawed.. but i could be wrong.. .thoughts?
Personally, i always use another gear to get the driveline stopped quickly before engaging reverse, especially in the older cars. the amount of wear is insignificant, compared to what the synchros are exposed to on a normal upshift or even downshift.. 800rpm to 0 of the driveline and related components vs mis match of RPM post up shift from 6000rpm might be 4500 to 4000rpm. and post downshift, bringing the driveline up to road speed for a particular gear as you shift, wears the synchros even more, and is why the 80% partial depression of the clutch and blip, reduces wear so much.
All transmissions, pre 1985, have no reverse syncro.
Makes it pretty easy, on these cars, to verify if the clutch is releasing properly.
Simply depress the clutch, count to 1002 and see if reverse can be directly engaged (without stopping mass by engaging another gear first) without grinding.
Try this both hot and cold. (When cold, the gear oil is thicker and will help reduce the energy from the spinning mass.)
If it can be engaged, clutch definitely releases.
It's a very good, quick test, to verify clutch operation.
Makes it pretty easy, on these cars, to verify if the clutch is releasing properly.
Simply depress the clutch, count to 1002 and see if reverse can be directly engaged (without stopping mass by engaging another gear first) without grinding.
Try this both hot and cold. (When cold, the gear oil is thicker and will help reduce the energy from the spinning mass.)
If it can be engaged, clutch definitely releases.
It's a very good, quick test, to verify clutch operation.
07-10-2015, 02:15 PM
#17
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
07-10-2015, 02:39 PM
#18
Shameful Thread Killer
Rennlist Member
Rennlist Member
Just a suggestion but after changing the fluid, it might now be too slick to get the baulk ring to match the gear speed to the counter-shaft? Thus requiring extra time? I know there are friction modifiers in the trans fluid I use in the Ferrari with LSD so that the friction disks can work properly. Maybe a similar system if the OP is using a syn oil in the trans. Don't know if it's syn or not, but something to consider I guess. The synchonizer ring slows or speeds the gear being driven by the shift fork, and if it can't match the right speed quickly, it will present with a resistance.
07-10-2015, 03:33 PM
#19
Rennlist Member
Thread Starter
I have not noticed any issue getting into reverse after having been in a forward gear regardless of the time which I have to admit I was not counting.
I been routinely backing into a parking spot at work and have not hesitated at all to shift from 1st or second into reverse after getting the car stopped. based on what i have read here that is a good thing.
That said I am lost by the engineering discussion around syncros and spinning forces. Who knew shifting was so complex.
I am using the Mobile 1 75/90 synthetic. Should I use something different?
I been routinely backing into a parking spot at work and have not hesitated at all to shift from 1st or second into reverse after getting the car stopped. based on what i have read here that is a good thing.
That said I am lost by the engineering discussion around syncros and spinning forces. Who knew shifting was so complex.
I am using the Mobile 1 75/90 synthetic. Should I use something different?
07-10-2015, 04:06 PM
#20
Shameful Thread Killer
Rennlist Member
Rennlist Member
The trans was designed with a dino oil base back in the last century. The modern oils, particularly the syn oils are so far superior to what we had just 20 years ago it's like a revolution in metal lubrication. Modern engines with syn oils are going 3-400k miles. Viscosities keep going down, in part because friction surfaces keep getting tighter, and it also aids lowering inertia. This seems to me to be counter-productive in a case where you are desiring a bit of 'grip' if you will between the baulk ring and the slider associated with the gear being meshed. As a general statement, I think syn oils are absolutely great -- for systems designed for syn oils like my kids 2014 Prius C. For systems designed for what would today be considered the slippery mud of 75-90 GL-5(GL-4?), I guess that would change the dynamics in there.
I could tell you horror stories about using syn oils in vintage design aircraft engines. Crashes happened, people died, money was lost and Mobil had to pay huge settlements all because they recommended a syn oil for air cooled, 1930s engine technology. It did not work well.
07-10-2015, 06:12 PM
#21
Former Sponsor
Hmmmm , i think your logic is flawed... see if you follow me and find the error in my thinking..... sure, it takes the same "energy " to stop the spinning mass, BUT, since we are talking about wear here, its the force we are really looking at. there is a much greater mechanical advantage in the 4th gear synchro, so it takes less force to slow the mass down, even though rotational speed is the same (error in your logic in that the gears are spinning at different speeds. but , the surface speed at the circumference are different, yes). No error. The input shaft is spinning 5th gear, which turns the layshaft, which in turn spins the fixed portion of each individual gear on that layshaft. Each of the individual gears on the layshaft are turning their sister gear on the pinion shaft...all spinning at different speeds, depending on each individual gear ratio. (little 1st gear on the layshaft turns the big 1st gear on the pinion shaft slower than any of the other gears.) All so, as in all "torque" related discussions... wear is going to be related to force... less force, less wear...
related experiment: try and stop bicycle tire at the hub using your finger at the inner spokes...... then try and stop the wheel at the outer edge with your finger...... same energy.. different forces.
so, i think your theory is a little flawed.. but i could be wrong.. .thoughts? Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
Personally, i always use another gear to get the driveline stopped quickly before engaging reverse, especially in the older cars. the amount of wear is insignificant, compared to what the synchros are exposed to on a normal upshift or even downshift.. 800rpm to 0 of the driveline and related components vs mis match of RPM post up shift from 6000rpm might be 4500 to 4000rpm. and post downshift, bringing the driveline up to road speed for a particular gear as you shift, wears the synchros even more, and is why the 80% partial depression of the clutch and blip, reduces wear so much.
yep, the best acid test!
related experiment: try and stop bicycle tire at the hub using your finger at the inner spokes...... then try and stop the wheel at the outer edge with your finger...... same energy.. different forces.
so, i think your theory is a little flawed.. but i could be wrong.. .thoughts? Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
Personally, i always use another gear to get the driveline stopped quickly before engaging reverse, especially in the older cars. the amount of wear is insignificant, compared to what the synchros are exposed to on a normal upshift or even downshift.. 800rpm to 0 of the driveline and related components vs mis match of RPM post up shift from 6000rpm might be 4500 to 4000rpm. and post downshift, bringing the driveline up to road speed for a particular gear as you shift, wears the synchros even more, and is why the 80% partial depression of the clutch and blip, reduces wear so much.
yep, the best acid test!
07-10-2015, 06:29 PM
#22
Rennlist Member
Join Date: Jul 2002
Location: Deep in the Heart of Texas!
Posts: 3,267
Likes: 0
Received 5 Likes
on
4 Posts
The more things change, the more they're the same ... discussion reminds me very much of my 968's shifting behavior.
It was very balky when cold, smooth and light in all the higher gears but often needed coaxing to go into first, and it loved fresh trans oil. I wound up changing it every year or so just because it felt so much nicer right afterwards.
I bought it with 43K miles and sold it at 95K and can honestly say it was pretty much the same the whole time. It's almost like there's a Porsche 'shifting personality' ... will never be like a Honda or other mass-produced cars, just has a specific Porsche feel ...
It was very balky when cold, smooth and light in all the higher gears but often needed coaxing to go into first, and it loved fresh trans oil. I wound up changing it every year or so just because it felt so much nicer right afterwards.
I bought it with 43K miles and sold it at 95K and can honestly say it was pretty much the same the whole time. It's almost like there's a Porsche 'shifting personality' ... will never be like a Honda or other mass-produced cars, just has a specific Porsche feel ...
07-10-2015, 07:34 PM
#23
Rennlist Member
Yes it is... that's how we learn... So, yes, i guess i see your point of the speeds of the gears moving at different speeds. I was thinking they are all on the same shaft and move at the same speed but are different diameters. (teeth count). thats only the layshaft... the output shafts have all the gears spinning at different speeds. this doesnt change my main point, in fact it adds fuel to it. when you engage 4th 1:1, there is a much lower force to slow the input shaft (torque tube, clutch discs)than when engaging 1st which requires more force due to the gear ratio and leverage to slow the spinning mass down.
BUT, as far as same energy, NO, i dont think that is correct that the force will be the same... it cant be, that's why we have a mechanical advantages and the forces is lower to do the same work. again, look at my analogy of stopping a bicycle wheel at the hub vs the tire. same work, different forces.
tell me how a 5th gear synchro will have the same force to slow the inertia of the driveline vs the 1st gear synchro. Its ok to be wrong Greg! and, if i am, Ill learn something here too!
You said: Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
So, "synchros work by friction"... pure energy absorbers? "dont care about force".... Serously greg????? ahem..........Friction IS A FORCE! again, like you said, its ok to be wrong!
the force will be much lower... 4th is spinning faster, and needs less force (friction ) and 1st will need more force, (more friction) to slow the driveline.
BUT, as far as same energy, NO, i dont think that is correct that the force will be the same... it cant be, that's why we have a mechanical advantages and the forces is lower to do the same work. again, look at my analogy of stopping a bicycle wheel at the hub vs the tire. same work, different forces.
tell me how a 5th gear synchro will have the same force to slow the inertia of the driveline vs the 1st gear synchro. Its ok to be wrong Greg!
and, if i am, Ill learn something here too!You said: Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
So, "synchros work by friction"... pure energy absorbers? "dont care about force".... Serously greg????? ahem..........Friction IS A FORCE!
again, like you said, its ok to be wrong!the force will be much lower... 4th is spinning faster, and needs less force (friction
) and 1st will need more force, (more friction) to slow the driveline.
Last edited by mark kibort; 07-10-2015 at 08:39 PM.
07-10-2015, 07:38 PM
#24
Rennlist Member
I have not noticed any issue getting into reverse after having been in a forward gear regardless of the time which I have to admit I was not counting.
I been routinely backing into a parking spot at work and have not hesitated at all to shift from 1st or second into reverse after getting the car stopped. based on what i have read here that is a good thing.
That said I am lost by the engineering discussion around syncros and spinning forces. Who knew shifting was so complex.
I am using the Mobile 1 75/90 synthetic. Should I use something different?
I been routinely backing into a parking spot at work and have not hesitated at all to shift from 1st or second into reverse after getting the car stopped. based on what i have read here that is a good thing.
That said I am lost by the engineering discussion around syncros and spinning forces. Who knew shifting was so complex.
I am using the Mobile 1 75/90 synthetic. Should I use something different?
i would highly recommend Sweptco for the transmission of older ages. it was kind of a miricle worker for my 84 transmission... not needed for the borg warner transmission of US '85 and newer.
07-10-2015, 09:04 PM
#25
Rennlist Member
Thread Starter
is there a Swepco version specific for gearboxes?
07-10-2015, 09:11 PM
#26
Former Sponsor
The more things change, the more they're the same ... discussion reminds me very much of my 968's shifting behavior.
It was very balky when cold, smooth and light in all the higher gears but often needed coaxing to go into first, and it loved fresh trans oil. I wound up changing it every year or so just because it felt so much nicer right afterwards.
I bought it with 43K miles and sold it at 95K and can honestly say it was pretty much the same the whole time. It's almost like there's a Porsche 'shifting personality' ... will never be like a Honda or other mass-produced cars, just has a specific Porsche feel ...
It was very balky when cold, smooth and light in all the higher gears but often needed coaxing to go into first, and it loved fresh trans oil. I wound up changing it every year or so just because it felt so much nicer right afterwards.
I bought it with 43K miles and sold it at 95K and can honestly say it was pretty much the same the whole time. It's almost like there's a Porsche 'shifting personality' ... will never be like a Honda or other mass-produced cars, just has a specific Porsche feel ...
They love thin gear oil.
Because the friction surfaces are internal, they have a tougher time getting cool, fresh gear oil to them. The 968 transmission does have some internal oil passages to feed oil to the synchros, whereas the late 928 does not. This should help them get more cool fresh oil.
The 968 transmissions came with a brass synchro that had machined grooves in them to do the actual "friction" work. These were superceeded to a brass synchro that had a sprayed moly surface on it (like the later 928 synchro) for the friction surface. Perhaps the supercession was to help with the original issue you experienced....they changed it for some reason.
07-10-2015, 09:36 PM
#27
Former Sponsor
Yes it is... that's how we learn... So, yes, i guess i see your point of the speeds of the gears moving at different speeds. I was thinking they are all on the same shaft and move at the same speed but are different diameters. (teeth count). thats only the layshaft... the output shafts have all the gears spinning at different speeds. this doesnt change my main point, in fact it adds fuel to it. when you engage 4th 1:1, there is a much lower force to slow the input shaft (torque tube, clutch discs)than when engaging 1st which requires more force due to the gear ratio and leverage to slow the spinning mass down.
BUT, as far as same energy, NO, i dont think that is correct that the force will be the same... it cant be, that's why we have a mechanical advantages and the forces is lower to do the same work. again, look at my analogy of stopping a bicycle wheel at the hub vs the tire. same work, different forces.
tell me how a 5th gear synchro will have the same force to slow the inertia of the driveline vs the 1st gear synchro. Its ok to be wrong Greg! and, if i am, Ill learn something here too!
You said: Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
So, "synchros work by friction"... pure energy absorbers? "dont care about force".... Serously greg????? ahem..........Friction IS A FORCE! again, like you said, its ok to be wrong!
the force will be much lower... 4th is spinning faster, and needs less force (friction ) and 1st will need more force, (more friction) to slow the driveline.
BUT, as far as same energy, NO, i dont think that is correct that the force will be the same... it cant be, that's why we have a mechanical advantages and the forces is lower to do the same work. again, look at my analogy of stopping a bicycle wheel at the hub vs the tire. same work, different forces.
tell me how a 5th gear synchro will have the same force to slow the inertia of the driveline vs the 1st gear synchro. Its ok to be wrong Greg!
and, if i am, Ill learn something here too!You said: Energy required is exactly the same....because the mass to be stopped is exactly the same. The syncros work only by friction....pure energy absorbers. They don't care about force.
So, "synchros work by friction"... pure energy absorbers? "dont care about force".... Serously greg????? ahem..........Friction IS A FORCE!
again, like you said, its ok to be wrong!the force will be much lower... 4th is spinning faster, and needs less force (friction
) and 1st will need more force, (more friction) to slow the driveline.Your last sentence.....you're still missing the entire point.....you're just not getting it.
Same mass to stop requires the same amount of energy.....doesn't matter what gear you choose to do that job...the required friction is exactly the same, therefore the amount of wear is exactly the same.
You claimed there would be less wear. That is incorrect.
The only reason to use a higher gear to stop the transmission from turning to engage reverse is to "spread" the wear onto synchros that are not used as much as 1st and 2nd gear's synchros.
That's my point. And that is correct.
It's not a huge deal, just an error from a lack of understanding, on your part, of what is happening inside the transmission.
07-11-2015, 12:02 AM
#28
Rennlist Member
I'm aware that friction is a force. And I'm pretty sure you understand the context of my use of the word.
Your last sentence.....you're still missing the entire point.....you're just not getting it.
Same mass to stop requires the same amount of energy.....doesn't matter what gear you choose to do that job...the required friction is exactly the same, therefore the amount of wear is exactly the same.
You claimed there would be less wear. That is incorrect.
The only reason to use a higher gear to stop the transmission from turning to engage reverse is to "spread" the wear onto synchros that are not used as much as 1st and 2nd gear's synchros.
That's my point. And that is correct.
It's not a huge deal, just an error from a lack of understanding, on your part, of what is happening inside the transmission.
Your last sentence.....you're still missing the entire point.....you're just not getting it.
Same mass to stop requires the same amount of energy.....doesn't matter what gear you choose to do that job...the required friction is exactly the same, therefore the amount of wear is exactly the same.
You claimed there would be less wear. That is incorrect.
The only reason to use a higher gear to stop the transmission from turning to engage reverse is to "spread" the wear onto synchros that are not used as much as 1st and 2nd gear's synchros.
That's my point. And that is correct.
It's not a huge deal, just an error from a lack of understanding, on your part, of what is happening inside the transmission.
you said: The syncros work only by friction....pure energy absorbers. They don't care about force. but then you say, you are aware that friction IS a force...... Hmmmmm
energy is not force..... right?
I get that the energy , or power , or best said, rate of change of KE, to slow and stop the driveline is the same, in the same period of time, but at the point of sychro ring contact , there are two different speeds . 5th gear for example is 1:1.... so the force is the force to slow and stop the driveline. However, in 1st, the force is NOT the same, because the mechanical advantage is different. you LOSE the mechanical advantage in 1st, slowing the driveline. just as you GAIN the mechanical advantage by driving the gear box from the input gear to the output shaft.
that said, the friction force is proportionally higher for 1st gear sychros vs the 5th gear synchros. think about this before you respond because I don't think you are correct. I could be wrong but I could be right!
Now, think about two things. the force required to stop the driveline connected to the INPUT shaft of the transmission by putting transmission in 5th (1:1) gear OR putting it in 1st gear. 4:1 reduction (actually its the opposite)
Its ok to be wrong here Greg... really! If Im wrong, ill buy you lunch!
let me summarize...... if it takes 5lbs of force at the synchro to slow the driveline down in 5th gear (1:1) then, in 1st gear it will take 20lbs of force to create the same friction at the synchros due to the actually, 1:4 gear ration facing the input shaft. this increased force is what wears the synchro!
you know I like analogies..... two same mass vehicles powered by an F1 car engine and a Semi engine, need 1000hp to accelerate... they both use 1000hp to accelerate over some speed range.........the F1 has only 200ftlbs of torque, the semi might have 1000ftlbs acting on the driveline. if they both use a driveline rated for 300ft-lbs, which one is going to break, even though the same mass is being accelerated at the same rate. (same as the synchros slowing the drive line) .
Last edited by mark kibort; 07-11-2015 at 12:19 AM.
07-11-2015, 12:21 AM
#29
Rennlist Member
07-12-2015, 06:47 PM
#30
Nordschleife Master
All transmissions, pre 1985, have no reverse syncro.
Makes it pretty easy, on these cars, to verify if the clutch is releasing properly.
Simply depress the clutch, count to 1002 and see if reverse can be directly engaged (without stopping mass by engaging another gear first) without grinding.
Try this both hot and cold. (When cold, the gear oil is thicker and will help reduce the energy from the spinning mass.)
If it can be engaged, clutch definitely releases.
It's a very good, quick test, to verify clutch operation.
Makes it pretty easy, on these cars, to verify if the clutch is releasing properly.
Simply depress the clutch, count to 1002 and see if reverse can be directly engaged (without stopping mass by engaging another gear first) without grinding.
Try this both hot and cold. (When cold, the gear oil is thicker and will help reduce the energy from the spinning mass.)
If it can be engaged, clutch definitely releases.
It's a very good, quick test, to verify clutch operation.
How much noise should a "normal" torque tube make?
I know my clutch works well, because if I'm in neutral and depress the clutch pedal, I can hear the TT stop. If I release (engage) it, I can hear the TT spin again.
There's no "grinding" to it, nothing abnormal sounding, it's not even loud. I need to be either inside the garage or right next to my house to hear it (the sound reflects off the wall). Out in the open, I can only hear it if I listen closely (and I know what to listen for).
I've considered it normal because it sounds to me like a normal "stuff spinning" noise.