Am I killing my transmission?

[Avery4]

Originally Posted by 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.

Thank you for the information! Just curious what kind of vehicle/transmission you had that the torque converter splines sheared off?

 

[SoNic67]

It was a Ford, but IMO the higher torque killed it.
That's why I said that "depends of design". I think that mechanical shocks, that are not accounted for during design, might do that.
After all the splines take ALL the engine torque and sends it to the resisting one. TQ is in between, to allow some elasticity.
https://lmr.com/products/mustang-10-spline-26-spline

 

[Avery4]

Originally Posted by SoNic67
It was a Ford, but IMO the higher torque killed it.
That's why I said that "depends of design". I think that mechanical shocks, that are not accounted for during design, might do that.
After all the splines take ALL the engine torque and sends it to the resisting one. TQ is in between, to allow some elasticity.
https://lmr.com/products/mustang-10-spline-26-spline

Cool, thank you! I presume shifting with a locked torque converter has more potential to be harmful the more harsh the shift feels? Shifting from 3rd-4th locked doesn't feel too harsh, so I presume that's less likely to be harmful than a harsher shift like 2nd-3rd locked? Thanks

 

[SoNic67]

Actually it feels smoother because the car inertia resistance momentum (from wheels) is "amplified" by the gearing versus the engine resistance.
Or if you look from engine, the engine torque is de-multiplied by gearing and has a lesser impact on car inertia.

But the resisting torque it's the same in magnitude at the engine side. It makes sense, the engine torque is depending only on actual engine RPM, not wheels RPM.
That's where that input shaft is located - at the engine side.

 

[Avery4]

Originally Posted by SoNic67
Actually it feels smoother because the car inertia resistance momentum (from wheels) is "amplified" by the gearing versus the engine resistance.
Or if you look from engine, the engine torque is de-multiplied by gearing and has a lesser impact on car inertia.

But the resisting torque it's the same in magnitude at the engine side. It makes sense, the engine torque is depending only on actual engine RPM, not wheels RPM.
That's where that input shaft is located - at the engine side.

Thank you for the information, that makes sense! I took a look at my old transmission's input shaft splines and they actually look perfect after probably 5K miles of running with high line pressure and some locked shifts, so that's encouraging. And I gave that old trans [censored], I have done quite a few full throttle 4th to 2nd downshifts with the torque converter locked with a decent amount more power than stock, which I think would pretty much be worst case scenario as far as damaging the input shaft splines. There may be fatigue that I don't see though and there also may be damage inside the trans that I don't see and doing this more may have had more of an effect. But either
way I don't do that anymore, I now always unlock the converter before mashing it to avoid problems.

 

[zeng]

During an upshift, there is always a Shift Loss , never a Shift Gain if any .
A Shift Loss would be demonstrated in the phenomenon of a drop in rotational speed rpm during UP-Shift , whilst
a Shift Gain, if any exists ,would be demonstrated by an immediate increase in rotational speed rpm during UP-Shift .
For typical Shift Loss to occur during Up-Shift, the temporary drop in rpm is as a result of time-delay (in miliseconds or seconds) between prior Disengage activation and subsequent Engage activation. .


Edit/Note: Amount or Quantity of Shift Loss (and, Shift Gain if any exists) during Up-Shift is influenced by the differential pressure between P(SE) and P(Kiss) .
This pressure differential in itself does not determine the phenomenon of either Shift Loss or Shift Gain (if any exists) during Up-Shift .
I repeat, a Shift Loss is reflected in Loss in rotational speed rpm phenomenon during Up-Shift, whilst;
a Shift Gain (if any exists) would be reflected in GAIN in rotational speed rpm during Up-Shift .

 

[Avery4]

Thanks everyone for your help! I have one more question. I ended up with an extra 10AN hose kit, long story but I bought a hose kit for my oil cooler and it had a defective fitting, so the seller just sent me a whole new kit. I would like to use these hoses for transmission cooler lines. However, these lines are significantly larger than the stock 3/8 lines and I have heard that this will reduce pressure and could cause a problem by restricting the fluid flow less. Could using larger than stock cooler lines cause a problem with the transmission, or is that an okay thing to do? If it matters, the fluid is just dumped back into the case of the trans after it goes through the cooler. Thanks

 

[zeng]

It is okay.
The pressure drop across a (enlarged ID) hose is reduced, albeit miniscule .
It doesn't cause reduced (absolute or gauge) pressure vis-a-vis orig hose and it doesn't restrict flow but improve it .

 

[Avery4]

Originally Posted by zeng
It is okay.
The pressure drop across a (enlarged ID) hose is reduced, albeit miniscule .
It doesn't cause reduced (absolute or gauge) pressure vis-a-vis orig hose and it doesn't restrict flow but improve it .

That's what I thought, thanks. I was worried because I have read that reducing the restriction in the cooler and lines such as by installing larger lines will allow more fluid to flow through and reduce line pressure or cause other issues. If that's not the case though I'm good. Just out of curiosity, where does the cooler get its fluid from? My understanding was that all the fluid that exits the torque converter goes through the cooler, but some people have said that only some of the flow goes through the cooler and some bypasses it? Also, is the cooler flow regulated in any way, or does it just increase with RPM as the pump spins faster? Thanks again, you have been very helpful and I really appreciate it!

 

[SoNic67]

The transmission pump has a pressure/flow regulator that will dump back the fluid into the pan at higher RPM's. Example:

Then there is another pressure regulator, in the valve body, more precise and that can be commanded by ECU to change (boost) the pressure as needed:

 

[Avery4]

Originally Posted by SoNic67
The transmission pump has a pressure regulator that will dump back the fluid into the pan at higher RPM's.

Thank you! So basically it has a relief valve like the engine oil pump? If I am understanding correctly, if I reduce the restriction in the cooler lines the pressure regulator won't dump as much fluid back into the sump at higher RPM and that fluid will go through the cooler instead? If so, that sounds like a win to reduce the restriction in the cooler circuit as long as doing so won't affect line pressure, and I don't see why it would from my (relatively limited) understanding of how the cooler circuit works.

 

[zeng]

Originally Posted by Avery4
Originally Posted by zeng
It is okay.
The pressure drop across a (enlarged ID) hose is reduced, albeit miniscule .
It doesn't cause reduced (absolute or gauge) pressure vis-a-vis orig hose and it doesn't restrict flow but improve it .

That's what I thought, thanks. I was worried because I have read that reducing the restriction in the cooler and lines such as by installing larger lines will allow more fluid to flow through and reduce line pressure or cause other issues. If that's not the case though I'm good. Just out of curiosity, where does the cooler get its fluid from? My understanding was that all the fluid that exits the torque converter goes through the cooler,

You're right .


Originally Posted by Avery4
, but some people have said that only some of the flow goes through the cooler and some bypasses it?

Bypasss, if any, occurs only under ALL the following conditions :
a ) Presence of thermostatically-controled valve in the circuit , located after torque converter outlet and before the oil cooler inlet . Not all auto trans has this feature though . AND,
b ) Oil supply temperature is cold during say, morning start and oil is operating below 'set temperature' , some or all oil is bypassed direct into sump, so as to prevent over-cooling of transmission oil hurting fuel economy in 'modern' and 'CAFE' driven systems .

At oil operating temperatures above the 'set temperature' , no bypass occurs .


Originally Posted by Avery4
Also, is the cooler flow regulated in any way, or does it just increase with RPM as the pump spins faster?

Increasing RPM of mechanical pump will increase cooler flow, though not proportional .

Typically there is a pressure-controlled relief valve in between pump outlet and supply lines to torque converter and bearings .

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4
Originally Posted by zeng
It is okay.
The pressure drop across a (enlarged ID) hose is reduced, albeit miniscule .
It doesn't cause reduced (absolute or gauge) pressure vis-a-vis orig hose and it doesn't restrict flow but improve it .

That's what I thought, thanks. I was worried because I have read that reducing the restriction in the cooler and lines such as by installing larger lines will allow more fluid to flow through and reduce line pressure or cause other issues. If that's not the case though I'm good. Just out of curiosity, where does the cooler get its fluid from? My understanding was that all the fluid that exits the torque converter goes through the cooler,

You're right .


Originally Posted by Avery4
, but some people have said that only some of the flow goes through the cooler and some bypasses it?

Bypasss, if any, occurs only under ALL the following conditions :
a ) Presence of thermostatically-controled valve in the circuit , located after torque converter outlet and before the oil cooler inlet . Not all auto trans has this feature though . AND,
b ) Oil supply temperature is cold during say, morning start and oil is operating below 'set temperature' , some or all oil is bypassed direct into sump, so as to prevent over-cooling of transmission oil hurting fuel economy in 'modern' and 'CAFE' driven systems .

At oil operating temperatures above the 'set temperature' , no bypass occurs .


Originally Posted by Avery4
Also, is the cooler flow regulated in any way, or does it just increase with RPM as the pump spins faster?

Increasing RPM of mechanical pump will increase cooler flow, though not proportional .

Typically there is a pressure-controlled relief valve in between pump outlet and supply lines to torque converter and bearings .

Thank you so much for explaining this! Could increasing the size of the cooler lines reduce line pressure by allowing the fluid to flow too freely? I have heard someone say that their transmission shifts soft after installing larger cooler lines from reduced line pressure and I certainly don't want that. Thanks

 

[Avery4]

Actually I think the real restriction is the transmission itself, not the stock lines. I tried blowing through the cooler supply port on the old transmission and it is actually surprisingly hard to blow through! Not sure if the transmission's internal cooler passages are just really restrictive or if there is some other type of restriction like a valve or something.

After seeing how restrictive the transmission itself is I don't think upgrading the cooler lines to larger ones would change internal pressures or cooler flow significantly if at all since all the fluid still needs to go through the transmission itself before it could get to the cooler lines and the fluid can only flow as well as the most restrictive part of the system allows, and the most restrictive part appears to be the transmission itself rather than the external lines. Put another way, if the transmission's internal passages are only 1/8 of an inch in diameter, changing the external lines from 3/8 to 5/8 of an inch would still not really reduce the restriction since the real restriction seems to be in the trans.

 

[zeng]

Originally Posted by Avery4
Could increasing the size of the cooler lines reduce line pressure by allowing the fluid to flow too freely?

Yes, but miniscule and academic .
The flow rate at similar pump rpm rotation is the same , but the smaller pressure drop by slight increased line size (of very short lengths in inches) may results in pump supply pressure drops to say 59.9 psi from 60.0 psi . Hence a miniscule drop in pump power too .
Originally Posted by Avery4
I have heard someone say that their transmission shifts soft after installing larger cooler lines from reduced line pressure and I certainly don't want that. Thanks

The main line pressure in clutch control system is say, about 50 psi .
The 'line' presssures into the respective clutches may be say, 28 psi for Clutch A, 32 psi for Clutch B , 35 psi for Clutch C and so on .
These pressure readings are independent of another parallel oil circuit from Pump > Torque Converter > Cooler Inlet line > Cooler assembly > Cooler Outlet line > transmission oil sump .
Any changes in pressure drops (and hence changes in respective gauge pressure ) in ANY components within the TC/Cooler circuit has no bearings whatsoever to the pressure readings of 50 , 28 , 32 and 35 psi , which is in ANOTHER parallel oil flow circuit that's independent of the Former circuit .

 

[Avery4]

Originally Posted by zeng
Originally Posted by Avery4
Could increasing the size of the cooler lines reduce line pressure by allowing the fluid to flow too freely?

Yes, but miniscule and academic .
The flow rate at similar pump rpm rotation is the same , but the smaller pressure drop by slight increased line size (of very short lengths in inches) may results in pump supply pressure drops to say 59.9 psi from 60.0 psi . Hence a miniscule drop in pump power too .
Originally Posted by Avery4
I have heard someone say that their transmission shifts soft after installing larger cooler lines from reduced line pressure and I certainly don't want that. Thanks

The main line pressure in clutch control system is say, about 50 psi .
The 'line' presssures into the respective clutches may be say, 28 psi for Clutch A, 32 psi for Clutch B , 35 psi for Clutch C and so on .
These pressure readings are independent of another parallel oil circuit from Pump > Torque Converter > Cooler Inlet line > Cooler assembly > Cooler Outlet line > transmission oil sump .
Any changes in pressure drops (and hence changes in respective gauge pressure ) in ANY components within the TC/Cooler circuit has no bearings whatsoever to the pressure readings of 50 , 28 , 32 and 35 psi , which is in ANOTHER parallel oil flow circuit that's independent of the Former circuit .

Thanks, so it sounds like I have nothing to worry about if I upgrade to larger cooler lines. Presuming upgrading to larger lines does actually reduce the restriction in the cooler circuit to a lower than stock level, what would the benefit be, if any? I would assume more flow through the torque converter and cooler and therefore lower temps? Also, as you said, if the pump doesn't have to work as hard to push the fluid, it would use a little less power. I suppose I might also extend the life of my engine's thrust washers a little bit if I reduce pressure in the torque converter since it won't be pushing against the crankshaft with as much force.

 

[zeng]

Originally Posted by Avery4

The main line pressure in clutch control system is say, about 50 psi .
The 'line' presssures into the respective clutches may be say, 28 psi for Clutch A, 32 psi for Clutch B , 35 psi for Clutch C and so on .
These pressure readings are independent of another parallel oil circuit from Pump > Torque Converter > Cooler Inlet line > Cooler assembly > Cooler Outlet line > transmission oil sump .
Any changes in pressure drops (and hence changes in respective gauge pressure ) in ANY components within the TC/Cooler circuit has no bearings whatsoever to the pressure readings of 50 , 28 , 32 and 35 psi , which is in ANOTHER parallel oil flow circuit that's independent of the Former circuit .


Originally Posted by Avery4
Thanks, so it sounds like I have nothing to worry about if I upgrade to larger cooler lines.

Yes .

Quote
Presuming upgrading to larger lines does actually reduce the restriction in the cooler circuit to a lower than stock level, what would the benefit be, if any?

2 benefits, if it matters :
a ) lower system pressure of 59.9 psi (instead of 60.0 psi) . Does it increases components life ? IMHO, it is academic .
b ) lower pump horsepower output at certain operating flow rate/pressures/temperatures, from say 2.00 hp to 1.9999 horsepower when system pump power is designed at 5 to 6 horsepower with an maximum engine horsepower up to say, 120 hp .

Quote
I would assume more flow through the torque converter and cooler and therefore lower temps?

More flow rate ? No .
Easier to flow ? Yes, as lower power is required to push this similar pump to say, 3000 rpm rotation up to an operating pressure of 59.9 psi, and not 60.0 psi .

Quote
Also, as you said, if the pump doesn't have to work as hard to push the fluid, it would use a little less power.

Yes, drop in hp would be = (K constant) X (Flow rate at specific rpm say, 3000 rpm) X (60.0 - 59.9 ) psi in units of say, hp or watt .

Quote
I suppose I might also extend the life of my engine's thrust washers a little bit if I reduce pressure in the torque converter since it won't be pushing against the crankshaft with as much force.

Not really and quite academic .
As I said, if thrust washers are designed base on loadings from engine power delivery of say, 120 hp .
Now,instead of operating transmission oil pump power of 2.00 hp but has now dropped to 1.99 hp , any extension of thrust washer components life is miniscule if any, but surely academic .

 

[Avery4]

I have another question. Would locking the torque converter to reduce heat under a sustained heavy load such as towing something up a long steep mountain be a good idea? For example, when I moved, I pulled a 2500 pound trailer full of my stuff through some pretty long and steep mountains. I did not have a trans temp gauge or manual lockup switch at that time, but I had a large cooler. Would locking the torque converter while, say, climbing 3 miles of 6% grade in 2nd gear towing 2500 lbs be a good idea? I would think it would since it would practically eliminate the heat generation in the torque converter and therefore significantly reduce oil temp, but I have heard arguments against doing so such as reduced oil flow through the cooler, etc. What are your thoughts on this? Thanks

 

[supton]

I'm not sure.

Locking the TC will bring down temps, but, if the engine is being wound out, then slippage should be low. Not zero but lower than if closer to stall. And since you're on a hill, with a small engine, it won't be turning low rpm, locked or not. Whatever small drop in rpm won't impact fluid flow through the cooler all that much--locking up would.

Here's the thing: why didn't the engineers do this? might there be some good reason behind not using lockup at moderate to high rpm, when under load? I can't think of a good reason why, but it seems like all the imports I've had seat time in (admitted few) they sure seem to dislike TC lockup. If it's to smooth out the experience, at the cost of longevity--well, outside of glass Honda V6 transmissions it seems imports tend to have robust automatics--thus it might just not be all that much of a hit on longevity.

If you have a temp sensor hooked up now, you can always just try both ways, locked and not, and see what happens. My guess, at 3-4k rpm, it's not going to be a huge difference--just a SWAG.

 

[CT8]

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.


The torque convertor generates most of the heat , that is why the trans cooler is torque convertor returning to the sump. The harder the shift the more shockload on all the parts..Usually the electric controlled transmissions cut power for a micro second during the shift,