Am I killing my transmission?

[nascarnation]

The clutch pack will last longer.
Other parts (splines, drums, etc) get more stress.
Not familiar enough with this design to know where the next weak link is when run to failure.

 

[Mainia]

I run Redline D6 in all my Honda trans and I run 3-4 qts of Redline Racing ATF, (Type F) Low viscosity racing and regular racing to closer match ther D6 viscosity, to reduce the slip agent. Makes for nice clean and low slip shifts. Low slip means low heat. Ran an Odyssey on this for 75,000 miles with no issues. Also a Honda Fit and a Rav4. All running great with cleaner less slip filled shifting. Also the Civic that has Valvoline MaxLife with 50% Redline racing reg/Racing low visc cocktail 60,000 into the change. I had a slipping trans before, when bought used. Still going strong with no slip.

 

[Avery4]

Originally Posted by Pelican
Originally Posted by Avery4



Generally the more overlap (smoothness) in gear changes the more clutch material is used, the more abrupt the less. Factory settings are a compromise between what the transmission needs to last a reasonable amount of time and what is acceptable to the buyer.


That is what I thought. My understanding was that the shifts are so slow from the factory because most people don't like hard shifts, not because that is best for longevity. Would you expect that clutch longevity may be improved by my modifications since it now shifts much quicker? Thanks


I do think that it will improve longevity, but only you can judge if it is too harsh [/quote]
Thank you, I appreciate your help. From what a transmission rebuilder told me, the clutches are the weak link in these transmissions. The clutches fail, the friction material plugs up the internal filter screen, line pressure drops from restricted filter, trans slips even more, and eventually totally destroys the clutches.

Without being a transmission expert, I don't think it is shifting too harshly. The shifts aren't nearly hard enough to break the tires loose or anything like that, just nice and firm without much slip. I like the feel of the shifts, and if it helps keep the clutches happy for longer.

 

[Avery4]

Originally Posted by Mainia
I run Redline D6 in all my Honda trans and I run 3-4 qts of Redline Racing ATF, (Type F) Low viscosity racing and regular racing to closer match ther D6 viscosity, to reduce the slip agent. Makes for nice clean and low slip shifts. Low slip means low heat. Ran an Odyssey on this for 75,000 miles with no issues. Also a Honda Fit and a Rav4. All running great with cleaner less slip filled shifting. Also the Civic that has Valvoline MaxLife with 50% Redline racing reg/Racing low visc cocktail 60,000 into the change. I had a slipping trans before, when bought used. Still going strong with no slip.


That's an interesting idea to use a bit of racing fluid to help firm the shifts up, thanks for sharing. I thought about doing that, but I decided against it because I didn't want to kill the bearings, gears, differential, pump, and other hard parts by using a fluid that doesn't lubricate them as well. Hard shifts beat on all that stuff either way with the exception of the pump, but at least firming up the shifts by increasing line pressure doesn't reduce the lubrication of other parts. Not saying what you did is wrong, just explaining why I chose to go the route I did.

 

[Avery4]

Originally Posted by nascarnation
The clutch pack will last longer.
Other parts (splines, drums, etc) get more stress.
Not familiar enough with this design to know where the next weak link is when run to failure.

That's what I thought, thanks. Obviously shifting with a locked converter will stress other things more, but would it cause the clutches to wear more?

 

[zeng]

Originally Posted by Avery4
Hello everyone, I am wondering if it is bad for my 2005 Honda Civic's transmission to shift with the torque converter locked up. With my solenoid mods to raise line pressure, it shifts somewhat hard when locked up and I am wondering if this is bad on it. I'm a performance guy and I like hard shifts, but I certainly don't want to destroy my new (to me) JDM SLXA transmission by shifting it with a locked torque converter. I don't allow it to shift while the converter is locked up because I am unsure of the long term effects of doing do.

Also, I modified my pressure control solenoids so the trans runs at a higher line pressure so it shifts quicker and so the TCC instantly fully applies whenever I want it to (I control it manually with a switch). What I did is I unplugged the pressure control solenoids and plugged in extra solenoids so it doesn't set a code and go into limp mode. I have been running it for about 10K miles this way and nothing bad has happened yet that I can tell, but I am wondering if shifting with high line pressure is bad for the trans in the long run.

The trans does not shift excessively hard (by my standards) from the solenoid modifications, so I would expect that this modification could actually extend the life of my trans because it shifts quicker, meaning the clutches engage faster and slip for a shorter amount of time, but I don't know a lot about automatic transmissions, so I may be missing something.

I just did a drain and fill on the trans yesterday and I didn't see anything disturbing in the old fluid after 10K miles of use, but I have an engine oil filter on my trans to catch particles, so I may not see anything. I could upload a pic of the old fluid if that would be helpful, I use Valvoline Import Full Synthetic ATF.

Thank you very much in advance, I really appreciate your help.

With my limited understanding on how your Civic lockup clutch and wet clutches works , IMHO, you should be fine to the extent of how 'harsh' was the Civic driven .

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4
Hello everyone, I am wondering if it is bad for my 2005 Honda Civic's transmission to shift with the torque converter locked up. With my solenoid mods to raise line pressure, it shifts somewhat hard when locked up and I am wondering if this is bad on it. I'm a performance guy and I like hard shifts, but I certainly don't want to destroy my new (to me) JDM SLXA transmission by shifting it with a locked torque converter. I don't allow it to shift while the converter is locked up because I am unsure of the long term effects of doing do.

Also, I modified my pressure control solenoids so the trans runs at a higher line pressure so it shifts quicker and so the TCC instantly fully applies whenever I want it to (I control it manually with a switch). What I did is I unplugged the pressure control solenoids and plugged in extra solenoids so it doesn't set a code and go into limp mode. I have been running it for about 10K miles this way and nothing bad has happened yet that I can tell, but I am wondering if shifting with high line pressure is bad for the trans in the long run.

The trans does not shift excessively hard (by my standards) from the solenoid modifications, so I would expect that this modification could actually extend the life of my trans because it shifts quicker, meaning the clutches engage faster and slip for a shorter amount of time, but I don't know a lot about automatic transmissions, so I may be missing something.

I just did a drain and fill on the trans yesterday and I didn't see anything disturbing in the old fluid after 10K miles of use, but I have an engine oil filter on my trans to catch particles, so I may not see anything. I could upload a pic of the old fluid if that would be helpful, I use Valvoline Import Full Synthetic ATF.

Thank you very much in advance, I really appreciate your help.

With my limited understanding on how your Civic lockup clutch and wet clutches works , IMHO, you should be fine to the extent of how 'harsh' was the Civic driven .

Thank you. Do you mean I should be fine with higher line pressure, or I should be fine with shifting with a locked converter too?

 

[zeng]

Originally Posted by Avery4
Originally Posted by zeng

With my limited understanding on how your Civic lockup clutch and wet clutches works , IMHO, you should be fine to the extent of how 'harsh' was the Civic driven .

Thank you. Do you mean I should be fine with higher line pressure, or I should be fine with shifting with a locked converter too?

Both, IMO.
At a particular clutch system (of First Gear, or Second Gear and so on within a transmission system), individual line pressures (psi) AND clutch friction material areas(square inches) are selected to meet a typical design criteria of 3 times peak torque (lbs-in) value .
Acknowledging this torque transfer capacity would deteriorate with use, in particular in relation to oil aging(?) phenomenon, the increased line pressue allows a larger margin of deterioration of torque transfer capacity , hence increased 'abuse' of oil aging one could tolerate .
Now, would this increased line pressure leads to oil seal leaks ?
I would speculate no as typical auto transmission line pressure is typically 25 - 35 psi say, whereas as a typical oil seal system could withstand thousands , if not hundreds of psi .(Note: What is your increased pressure value?)
A locked converter shift would result in marginally higher 'shock' during torque transfer phenomenon, in relation to unlocked converter shift .
However, this increased 'shock' (from locked converter) would be milder in relation to a typical manual transmission torque transfer shock with dry clutch system .
Hence, its longevity cannot be worse off than a typical manual transmission as found in similar Honda Civic .
Just my

 

[nascarnation]

Originally Posted by Avery4
Originally Posted by nascarnation
The clutch pack will last longer.
Other parts (splines, drums, etc) get more stress.
Not familiar enough with this design to know where the next weak link is when run to failure.

That's what I thought, thanks. Obviously shifting with a locked converter will stress other things more, but would it cause the clutches to wear more?


A correctly designed (and performing!) clutch pack in an automatic will last pretty much forever, the heat load being transmitted into the lube oil. It's not like a dry clutch in a manual which is designed to wear over time like brake pads. I'm not familiar with the specifics of the Honda design, but most modern automatics are going into lockup early and most of the range shifts are done with lockup applied. So don't worry.

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4
Originally Posted by zeng

With my limited understanding on how your Civic lockup clutch and wet clutches works , IMHO, you should be fine to the extent of how 'harsh' was the Civic driven .

Thank you. Do you mean I should be fine with higher line pressure, or I should be fine with shifting with a locked converter too?

Both, IMO.
At a particular clutch system (of First Gear, or Second Gear and so on within a transmission system), individual line pressures (psi) AND clutch friction material areas(square inches) are selected to meet a typical design criteria of 3 times peak torque (lbs-in) value .
Acknowledging this torque transfer capacity would deteriorate with use, in particular in relation to oil aging(?) phenomenon, the increased line pressue allows a larger margin of deterioration of torque transfer capacity , hence increased 'abuse' of oil aging one could tolerate .
Now, would this increased line pressure leads to oil seal leaks ?
I would speculate no as typical auto transmission line pressure is typically 25 - 35 psi say, whereas as a typical oil seal system could withstand thousands , if not hundreds of psi .(Note: What is your increased pressure value?)
A locked converter shift would result in marginally higher 'shock' during torque transfer phenomenon, in relation to unlocked converter shift .
However, this increased 'shock' (from locked converter) would be milder in relation to a typical manual transmission torque transfer shock with dry clutch system .
Hence, its longevity cannot be worse off than a typical manual transmission as found in similar Honda Civic .
Just my

That makes sense, thanks for all the great information! So is the person who told me that I am causing excessive clutch wear by causing gear overlap wrong? The way he explained it, the PCM normally momentarily reduces pressure during shifts to create an "in between gears" moment so one clutch disengages before the next engages so there aren't two clutches engaged at the same time, but now that the PCM can't reduce pressure, one set of clutches is engaging before the previous set is completely released, basically causing the transmission to be in 2 gears at the same time fighting itself internally for a split second every time it shifts.


Does what he said make any sense to you? I would think that I would be reducing overlap if anything since the shifts are now quicker. Thanks

 

[Avery4]

Originally Posted by nascarnation
Originally Posted by Avery4
Originally Posted by nascarnation
The clutch pack will last longer.
Other parts (splines, drums, etc) get more stress.
Not familiar enough with this design to know where the next weak link is when run to failure.

That's what I thought, thanks. Obviously shifting with a locked converter will stress other things more, but would it cause the clutches to wear more?


A correctly designed (and performing!) clutch pack in an automatic will last pretty much forever, the heat load being transmitted into the lube oil. It's not like a dry clutch in a manual which is designed to wear over time like brake pads. I'm not familiar with the specifics of the Honda design, but most modern automatics are going into lockup early and most of the range shifts are done with lockup applied. So don't worry.

Thanks, I always thought of the clutch packs as the main wear item in the transmission. Is that not accurate?

 

[meep]

I for one applaud the OP's initiative to tinker. Many of us here have been there and done that, learning good advice along the way like letting the DD be stock so there's always a backup, or vice versa, but at least in my case, I had the initiative to tinker before I had the judgment to be more wise. To the OP - I applaud your experimentation. It's an ironic question to put a machine out of it's oem design and then ask if it's going to harm it... as so many other unknown factors get stirred up. But it's the pushing of the envelope that gains unique experience, so that's good... as long as we aren't blinded by the bling and ignore greater responsibilities (family, job, personal and public safety).

A slam shift at 5k rpm will hit harder and fatigue parts much faster than a slam shift at 2k rpm. Clutch wear is only one factor. Metal fatigue is another. Shock loading plays a role, and the material (give) of the engine/trans/suspension mounts will come into play with slam shifting. Cushion gives some protection, but soft mounts then yield sloppier vehicle dynamics. So we can optimize one area of a vehicle, and by optimizing this one thing, de-optimize the whole. It can become a joyful hobby, or a disease.

I think the above posts on going manual are a better path, if you are seeking a driver-vehicle-control-reliability optimized outcome. Nothing beats a manual for unleashing a nearly-forgotten art of balancing with the other side of the gas pedal (lift-off). If you are enjoying the learning more, just have a backup plan so you can be stone-cold-reliable for those who count on you and watch out for the safety of yourself and others.

 

[zeng]

Originally Posted by Avery4
Originally Posted by zeng
Both, IMO.
At a particular clutch system (of First Gear, or Second Gear and so on within a transmission system), individual line pressures (psi) AND clutch friction material areas(square inches) are selected to meet a typical design criteria of 3 times peak torque (lbs-in) value .
Acknowledging this torque transfer capacity would deteriorate with use, in particular in relation to oil aging(?) phenomenon, the increased line pressue allows a larger margin of deterioration of torque transfer capacity , hence increased 'abuse' of oil aging one could tolerate .
Now, would this increased line pressure leads to oil seal leaks ?
I would speculate no as typical auto transmission line pressure is typically 25 - 35 psi say, whereas as a typical oil seal system could withstand thousands , if not hundreds of psi .(Note: What is your increased pressure value?)
A locked converter shift would result in marginally higher 'shock' during torque transfer phenomenon, in relation to unlocked converter shift .
However, this increased 'shock' (from locked converter) would be milder in relation to a typical manual transmission torque transfer shock with dry clutch system .
Hence, its longevity cannot be worse off than a typical manual transmission as found in similar Honda Civic .
Just my

That makes sense, thanks for all the great information! So is the person who told me that I am causing excessive clutch wear by causing gear overlap wrong?
There cannot be a phenomenon of gear overlap, if by overlap means gearing sets for two different output speeds are engaged and function simultaneously within a transmission system .
Instead in up-shifting, there is a time delay in prior release of lower speed gear engagement to be followed by subsequent engagement of higher speed gear , never overlap in simultaneous gear engagement of two differing speeds .


Quote
The way he explained it, the PCM normally momentarily reduces pressure during shifts to create an "in between gears" moment so one clutch disengages before the next engages so there aren't two clutches engaged at the same time, but now that the PCM can't reduce pressure, one set of clutches is engaging before the previous set is completely released, basically causing the transmission to be in 2 gears at the same time fighting itself internally for a split second every time it shifts.

In up-shifting, once the lower speed gear/clutch disengages (as determined and instructed by PCM with time as a function) the fluid pressure (of say 30 psi) is released to transmission oil sump at near zero 'atmospheric' pressure in a normally function system . During pressure drop phenomenon ,it's pressure cannot be maintained at reduced value of say, 25 or 20 psi (for so many seconds or miliseconds) AND continue to 'perform' a function within the said gear/clutch system .

Time delay (in miliseconds or seconds) is the primary parameter in the initial release of lower speed gear/clutch system to be followed by subsequent engagement of higher speed gear/clutch system .

An engaged gear/clutch system comprises piston pressure of say, 30 psi (as per design and construction) .
A disengaged gear/clutch system has a piston pressure of 0, in a normally functioned system


Quote
I would think that I would be reducing overlap if anything since the shifts are now quicker. Thanks

Putting it in another way, I would say a quicker shift comes with a reduced or lower time delay in between engagement/disengagement .

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4
Originally Posted by zeng
Both, IMO.
At a particular clutch system (of First Gear, or Second Gear and so on within a transmission system), individual line pressures (psi) AND clutch friction material areas(square inches) are selected to meet a typical design criteria of 3 times peak torque (lbs-in) value .
Acknowledging this torque transfer capacity would deteriorate with use, in particular in relation to oil aging(?) phenomenon, the increased line pressue allows a larger margin of deterioration of torque transfer capacity , hence increased 'abuse' of oil aging one could tolerate .
Now, would this increased line pressure leads to oil seal leaks ?
I would speculate no as typical auto transmission line pressure is typically 25 - 35 psi say, whereas as a typical oil seal system could withstand thousands , if not hundreds of psi .(Note: What is your increased pressure value?)
A locked converter shift would result in marginally higher 'shock' during torque transfer phenomenon, in relation to unlocked converter shift .
However, this increased 'shock' (from locked converter) would be milder in relation to a typical manual transmission torque transfer shock with dry clutch system .
Hence, its longevity cannot be worse off than a typical manual transmission as found in similar Honda Civic .
Just my

That makes sense, thanks for all the great information! So is the person who told me that I am causing excessive clutch wear by causing gear overlap wrong?
There cannot be a phenomenon of gear overlap, if by overlap means gearing sets for two different output speeds are engaged and function simultaneously within a transmission system .
Instead in up-shifting, there is a time delay in prior release of lower speed gear engagement to be followed by subsequent engagement of higher speed gear , never overlap in simultaneous gear engagement of two differing speeds .


Quote
The way he explained it, the PCM normally momentarily reduces pressure during shifts to create an "in between gears" moment so one clutch disengages before the next engages so there aren't two clutches engaged at the same time, but now that the PCM can't reduce pressure, one set of clutches is engaging before the previous set is completely released, basically causing the transmission to be in 2 gears at the same time fighting itself internally for a split second every time it shifts.

In up-shifting, once the lower speed gear/clutch disengages (as determined and instructed by PCM with time as a function) the fluid pressure (of say 30 psi) is released to transmission oil sump at near zero 'atmospheric' pressure in a normally function system . During pressure drop phenomenon ,it's pressure cannot be maintained at reduced value of say, 25 or 20 psi (for so many seconds or miliseconds) AND continue to 'perform' a function within the said gear/clutch system .

Time delay (in miliseconds or seconds) is the primary parameter in the initial release of lower speed gear/clutch system to be followed by subsequent engagement of higher speed gear/clutch system .

An engaged gear/clutch system comprises piston pressure of say, 30 psi (as per design and construction) .
A disengaged gear/clutch system has a piston pressure of 0, in a normally functioned system


Quote
I would think that I would be reducing overlap if anything since the shifts are now quicker. Thanks

Putting it in another way, I would say a quicker shift comes with a reduced or lower time delay in between engagement/disengagement .

Great explanation, thank you so much! I was wondering if I was possibly increasing the engine's load by maintaining a higher line pressure, so I tested that. To put it simply, what I did is I plugged the solenoids back in, lifted the front end of the car, started the engine, shifted to drive, and noted the speed that the speedo read idling in 4th gear, about 35 MPH. Then while it was running I unplugged the solenoids to raise the pressure to maximum. I noticed no change in the engine's sound and the speedo didn't drop.

From this quick test, I came to the conclusion that I am not increasing the load on the engine by maintaining a higher line pressure. This test is sensitive enough that I can drop the speedo reading by several MPH simply by turning the headlights on, so if there is any additional load on the engine, it is way less than the load of the headlights. Thought you or someone else may find that interesting since I sure did

Also, I'm wondering what you think of having the old fluid analyzed to see what the wear metals are. Would this provide any useful information? I am thinking since that wouldn't tall me anything about metal fatigue it would be a waste of my money, but what are your thoughts on this?

 

[zeng]

Originally Posted by Avery4

Great explanation, thank you so much! I was wondering if I was possibly increasing the engine's load by maintaining a higher line pressure, so I tested that.
Yes, but miniscule and academic probably with no real world implications .
Work done by transmission pump is proportional to product of Pump Flow Rate X Fluid Pressure .
Increasing line pressure by 20 % would increase Pump Power Draw by 20 % , assuming friction loss is negligible .
As your test (Thank you) demonstrates , the increased power draw is miniscule , imperceptible and academic .


Quote
To put it simply, what I did is I plugged the solenoids back in, lifted the front end of the car, started the engine, shifted to drive, and noted the speed that the speedo read idling in 4th gear, about 35 MPH. Then while it was running I unplugged the solenoids to raise the pressure to maximum. I noticed no change in the engine's sound and the speedo didn't drop.

The miniscule difference in power (loss) ,as a result of increased line pressure ,is miniscule, imperceptible and probably immeasurable if you care to measure it .

Quote
From this quick test, I came to the conclusion that I am not increasing the load on the engine by maintaining a higher line pressure.

No, you're increasing the engine load , though academic .
But power available to drivelines/tires doesn't drop perceptibly .

Quote
This test is sensitive enough that I can drop the speedo reading by several MPH simply by turning the headlights on, so if there is any additional load on the engine, it is way less than the load of the headlights. Thought you or someone else may find that interesting since I sure did

Yes, you're right .
During your test, let's assume this test engine power output was some 10,000 Watts (some 10-20 % of engine peak power at said test engine rotation) , your headlights was some 70-150 Watts .
Hence the increase in transmission pump power draw from increased line pressure may be some 5- 20 Watts .
Now, what is 20 Watts increase in a power system of say, 10000 Watts .
0.2 % .
Bearing in mind , there is an engine power reserve of some 80 - 90 % of Engine Peak Power always available on Demand , should the need arises .

Quote
Also, I'm wondering what you think of having the old fluid analyzed to see what the wear metals are. Would this provide any useful information? I am thinking since that wouldn't tall me anything about metal fatigue it would be a waste of my money, but what are your thoughts on this?

IMO, having gone through numerous UOA's (mostly engine oil) it is a waste of money . It doesn't matter if you have prior series of similar UOA's on hand .
But someone among us might find it interesting .

 

[clinebarger]

Shift Overlap is a very real phenomenon in many automatic transmissions! Without the use of "Mechanical Diodes".....A slight overlap is about the best you can do.

I'm not going to say elevated line pressure would affect whatever overlap is engineered into this particular unit!

A Chrysler A727 vs a GM TH400 is a perfect example of a slight overlap vs a Mechanical Diode!......

The A727 has a Band that stalls/holds the Direct Drum in 2nd gear, During a 2-3 shift....The band has to be released & the Direct Clutches have to engage & rotate the Direct Drum. The synchronized event is impossible to get timed exactly, So a slight overlap is engineered into it to prevent a Flare between 2nd & 3rd gear.

The TH400 uses the same principle....The Direct Drum has to be held stationary for 2nd gear & Rotate for 3rd gear. But it uses a Intermediate Clutch pack that can stall the direct drum via a Mechanical Diode.....Then the Direct Clutch engages during the 2-3 shift & the Direct drum rotates.....But the Intermediate clutch never disengages.....The Mechanical Diode is now Overrunning.

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4

Great explanation, thank you so much! I was wondering if I was possibly increasing the engine's load by maintaining a higher line pressure, so I tested that.
Yes, but miniscule and academic probably with no real world implications .
Work done by transmission pump is proportional to product of Pump Flow Rate X Fluid Pressure .
Increasing line pressure by 20 % would increase Pump Power Draw by 20 % , assuming friction loss is negligible .
As your test (Thank you) demonstrates , the increased power draw is miniscule , imperceptible and academic .


Quote
To put it simply, what I did is I plugged the solenoids back in, lifted the front end of the car, started the engine, shifted to drive, and noted the speed that the speedo read idling in 4th gear, about 35 MPH. Then while it was running I unplugged the solenoids to raise the pressure to maximum. I noticed no change in the engine's sound and the speedo didn't drop.

The miniscule difference in power (loss) ,as a result of increased line pressure ,is miniscule, imperceptible and probably immeasurable if you care to measure it .

Quote
From this quick test, I came to the conclusion that I am not increasing the load on the engine by maintaining a higher line pressure.

No, you're increasing the engine load , though academic .
But power available to drivelines/tires doesn't drop perceptibly .

Quote
This test is sensitive enough that I can drop the speedo reading by several MPH simply by turning the headlights on, so if there is any additional load on the engine, it is way less than the load of the headlights. Thought you or someone else may find that interesting since I sure did

Yes, you're right .
During your test, let's assume this test engine power output was some 10,000 Watts (some 10-20 % of engine peak power at said test engine rotation) , your headlights was some 70-150 Watts .
Hence the increase in transmission pump power draw from increased line pressure may be some 5- 20 Watts .
Now, what is 20 Watts increase in a power system of say, 10000 Watts .
0.2 % .
Bearing in mind , there is an engine power reserve of some 80 - 90 % of Engine Peak Power always available on Demand , should the need arises .

Quote
Also, I'm wondering what you think of having the old fluid analyzed to see what the wear metals are. Would this provide any useful information? I am thinking since that wouldn't tall me anything about metal fatigue it would be a waste of my money, but what are your thoughts on this?

IMO, having gone through numerous UOA's (mostly engine oil) it is a waste of money . It doesn't matter if you have prior series of similar UOA's on hand .
But someone among us might find it interesting .

Thank you for all the great info! I am surprised that the difference is as tiny as it is since the difference in the power steering is very noticeable. Back when I had hydraulic power steering on this car, I could drop the idle quite significantly by holding the steering wheel at full lock because of the load on the pump, so I would expect the same thing with the transmission. Actually the idle will still drop when holding the wheel on the steering lock with my electric rack because of the alternator load.

That's pretty much what I thought that there wouldn't be much benefit to have the used fluid analyzed because it wouldn't tell me anything about if the metal parts are being fatigued. Actually, when my original transmission failed at 243K miles, the old fluid still looked and smelled fine, no visible particles or burned smell. Not what I would expect. Also, I removed my transmission cooler and flushed it with acetone and compressed air in case there were any particles in it from the old trans, and it was spotlessly clean. Go figure.

 

[zeng]

Originally Posted by clinebarger
Shift Overlap is a very real phenomenon in many automatic transmissions! Without the use of "Mechanical Diodes".....A slight overlap is about the best you can do.

I'm not going to say elevated line pressure would affect whatever overlap is engineered into this particular unit!

A Chrysler A727 vs a GM TH400 is a perfect example of a slight overlap vs a Mechanical Diode!......

The A727 has a Band that stalls/holds the Direct Drum in 2nd gear, During a 2-3 shift....The band has to be released & the Direct Clutches have to engage & rotate the Direct Drum. The synchronized event is impossible to get timed exactly, So a slight overlap is engineered into it to prevent a Flare between 2nd & 3rd gear.

The TH400 uses the same principle....The Direct Drum has to be held stationary for 2nd gear & Rotate for 3rd gear. But it uses a Intermediate Clutch pack that can stall the direct drum via a Mechanical Diode.....Then the Direct Clutch engages during the 2-3 shift & the Direct drum rotates.....But the Intermediate clutch never disengages.....The Mechanical Diode is now Overrunning.


Thank you for your detailed descriptions of shift overlap above .
In the above cases, I can understand sometimes the limitations faced by OEMs in reducing 'moment of inertia' of Disengaging 2nd Gear system and/or further increasing the 'moment of inertia' of Engaging 3rd Gear systems so as to improve/promote the 'absence of shift overlap' as described .
I too can understand limiting values of time delay available to OEM to avoid the flare phenomenon , and hence a compromise in selection .
IMO, allowing and accepting the presence of 'shift overlap' phenomenon without an in-built 'Mechanical Diodes' ( or any other forms of engineering improvements) mechanisms is a Design Flaw , that should be eliminated by whatever means possible in order to ultimately improve user experiences and components longevity .
This sort of 'half-cooked' menus are generally absent in Japanese/Asian products , IME .

 

[Avery4]

Thank you to everyone who replied, I really appreciate your help. Correct me if I am wrong, but here are the conclusions I came to from the responses I got:

1. Clutch wear will not be adversely affected by increasing line pressure or shifting with a locked torque converter and may be decreased

2. Other parts of the transmission could possibly suffer fatigue failures over time from harder shifts

3. The increased shock load from shifting with a locked torque converter could increase the chance of a fatigue failure by causing the trans to shift even harder

4. There is no way to really know what effect I am having on the transmission until it fails

 

[SoNic67]

Automatic transmissions, with traditional hydraulic systems and torque converter, always overlap gears via the clutches. That's why they shift so smoothly compared to the manual gear shifts, where one can feel the slight "gap" in engine thrust (acceleration) between two gears. The slippage is controlled by the hydraulic pressure, so shorter slipping times will do well for the clutches.

Side note - The Automatic Dual Clutch transmissions are basically electrically controlled manual transmissions. They use those two clutches to simulate a smooth shifting by holding two gears at transition time (with added extra wear of course).

But... I had one torque converter shaft splines shear off, so, depending on the design and the actual torque reserve, yours might shear too. In my case it was sudden.