Is there a way to tell quantitatively how much the filter is loaded? When I see the photos of dissected filters, they often look pretty much the same - it leaves me wondering how accurate a visible inspection actually is. Except cases where there is metallic debris or chunks - but that something different and maybe worse than loading.

 

Without input from GM you'd need to do some flow testing. Flow a new filter with fluid as a baseline and introduce known amounts of contamination in the size of interest until the filter starts bypassing.
Just a gut feeling but the amount of contamination I've seen in pictures that have been posted aren't close to bypassing. In general filters can take a fair amount of loading before significant pressure drops start happening.

 

I think the answer is a "No!". #1 the way you actually handle the DCT filter on removal has a big impact (based on my observations). When you remove the filter canister the entrapped DCT fluid leaks down through the filter element and tends to "wash" the debris on the filter downwards, especially the really small sintered-sized bits, an so some of the debris moves from the top and accumulates at the bottom area of the filter. What I have then found to work best is to keep the filter as vertical as possible as you remove it and place it in a secure plastic bag, then keep it as vertical as possible until you get it to a work area and study it closer. Regardless, as soon as you tip the filter some debris does tend to wash out with any remaining fluid but, at least with the bag, you can see the debris flowing with any DCT fluid.

On the first one I did I was careful to capture the filter in a clean pan but did not keep it vertical. The small particles could easily be seen reflecting in the light as any remaining fluid drained out and so from then on, I have tried to keep the filter vertical in the removal process.

#2 also by my observation, the mere act of handling the filter media causes the debris to move around on the face of the filter, and I think that explains why some areas seem lighter than others. The act of cutting the filter causes some shift and when handling the media plies you can make the dark areas move around quite easily.

So, how accurate? I'd say better than not looking! I've not regretted pulling them early since I think it is a way to gain confidence on how long your filter may perform on your vehicle and the way you drive it. I pulled the first DCT filter at 2,500 miles and was glad I did. Looking at it I think it would have performed just fine to the 7,500 mile mark but I felt that it gave me a good data point. A new trans went in at 3,500 miles (porous case) and I changed that filter at 2,500 miles also; then it was changed at the 7,500 mile GM-service and again at 11,000 miles (equalled 7,500 miles on the new trans so just maintaining the recommended GM service interval). Filters looked good to my eye and so I am happy to let the current filter go to the 22,500 service mark.

Just based on how i use the C8 the next couple of filter changes will happen with 10,000 miles on each filter and I feel confident that they will be just fine for me. After the 3-year fluid change it is likely that that filter will be in for just 15,000 miles before the next milestone is reached and that will likely be the longest any DCT filter will be in there; I don't see a scenario for me where I will be changing filters at the 22,500 mile range based on the current annual mileages that I do.

 

Doesn't the DCT have a variety of sensors monitoring the internal pressure and flows inside the body of the trans that would also "alarm" if they started experiencing pressure drops and/or flow issues?

 

With all the sensors the DCT has you'd think it would know if the pressure drop across the filter is getting out of range. But I haven't seen anything that states it monitors filter pressure drop.

 

Yes, it has lots of fluid pressure sensors and lots of fluid pressure control valves. They dont show the routing of fluid. But from the descriptions of those sensors, it does not sound like there is a sensor before and after the filter that could determine a differential pressure across the filter. There could be, but its not evident. But yes, I think it will sense a low pressure condition and there are DTCs associated with out of range pressures. Attached is a procedure to follow for one of the low pressure events. It does include steps that involve replacing the filter, replacing the fluid, and replacing internal so-called lifetime filter in the pan. So, apparently a clogged filter might be detected by this condition. But does not necessarily mean it will detect the pressure drop that leads to a bypass event. That is, there may be a pressure drop across the filter that can lead to a by pass event without dropping the pressure downstream enough to trigger the low pressure DTCs.

Transmission Oil Filler or Drain Plug Replacement is actually a drain and fill procedure.
Automatic Transmission Fluid Filter and Seal Replacement is replacing the external canister filter.
Automatic Transmission Fluid, Fluid Pan and/or Filter Replacement includes the steps to replace the internal filter.

 

I had a failure that is not common. I have only read of one other similar to mine. Mine was a groaning sound that was RPM dependent. You could be in park and rev the engine and the sound would change with RPM. I thought it must be a bearing or a pump. Does anyone know if that high-volume pump is electrical or mechanical? If mechanical, that may have been what failed. I will never know, but am curious. Car was 11 months old with 4,300 miles. Never tracked and only performed one launch. Driven in automatic mode nearly 100% of the time.

 

That poster says the pump is "gear driven". Sound mechanical. And it says it is for the hydraulic controls, lubrication and cooling, and park actuation.

 

Here is something for you to think about: pulling both paddles 'declutches' the transmission. The owners manual describes this as 'temporarily disconnecting the engine from the wheels, similar to N (Neutral)'.

What really happens when you pull both paddles? The engine still has to be driving an input shaft, otherwise, the trans pump would stop turning and the oil pressure would drop to zero . So, at least one of the main clutches has to still be engaged. Is there a neutral position for the shift forks or are the differential clutches released?

 

There is, documented in the Service Manual a specific position for all the forks when N is selected. But I do not believe that the double paddle declutch puts them there. I think this because when I shift between N and D or N and R or R and D, I can hear a sound from the back, which I believe is the sound of the forks moving. And a definite feel of the car being "bumped" which I interpret as taking up drive line slack. I hear nothing and feel nothing at all when I double paddle declutch with the foot brake also applied. You have a good point about how the trans gets it hydraulic power when declutched. The must be a shaft turning the drive side of the clutches that also turns the pump, regardless of whether the driven side of the clutches is engaged or not. The driven side of the clutches simply connects it to the gear shafts.

 

So, there has to be an input shaft always turning which means there must be no gearset locked to this shaft when not moving. I don't see where there would be any clutch slippage when at rest if this is true.This must be similar to having a manual transmission in neutral with your foot off the clutch pedal. The input shaft turns, but none of the gearsets are locked to this shaft.

 

Where to buy the filter? Best price?

 

When you pull both paddles it is similar to a manual transmission with the clutch pedal depressed. If it was in gear when the paddles were pulled it is still in gear.

The hydraulic pump is driven whether or not the clutch packs are engaged. In the example below it is driven by an innermost shaft and two additional shafts drive the clutches. I don't know if Tremec does it this way.

https://www.transmissiondigest.com/h...-clutch-units/

 

Maybe but not how I had it pictured. I envisioned it this way (hypothetical):

The input shaft that is spinning the drive side of the clutch, at the RPM of the engine is also somehow connected to the hydraulic pump - but not via the driven side of the clutch. With the clutch not engaged, the driven side of the clutch is stationary, and the shaft connected to it is not turning because the clutch is not engaged. The gearset for first gear ( if in 1) is fully locked on that drive side shaft and ready to go as soon as the clutch engaged.

Just to add to this - the clutches themselves are hydraulically actuated. They are normally open - not engaged. Hydraulic pressure is required to engage the clutches. Therefore whatever shaft/gear is turning the pump shaft (its gear drive) has to be spinning before the clutch has engaged.

There is poster that says the pump is gear driven. Attached is a diagram from the service manual that show what I think is the pump. There is no key I can find that identifies the parts though. And, it really does not show exactly how that gear is driven. But it can't be on the driven side of the clutch because hydraulic pressure is required to engage the clutch. It has to be on the side that is spinning with the engine crankshaft.

I'm sorry I don't necessarily have the right nomenclature for this - but by drive side of the clutch I mean the part that is always spinning when the engine runs. The driven side of the clutch, I mean to be the side that spins once the clutch is engaged - also the side (or sides, its concentric) that turn the odd and even gear shafts.

 

Just got back from a trip. Thanks for posting this. It's sort of what I was thinking - some sort of concentric arrangement of shafts, that allowed one of them to turn the hydraulic pump regardless of clutch position or shift fork position. Apparently the C8 must be similar because the pump is gear driven and not electric - and it can't be shifted without the engine running. There's been discussion that it is or may be electric in the eRay - I have not followed closely. It would seem cheaper to me to make it electric rather than have an extra shaft to drive a gear driven pump.

 

@RKCRLR , After looking more closely at this, (and I know its not the C8 transmission), notice that there is some fluid that flows through a "valve body" that goes only through the suction filter in the sump (equivalent to the pan filter in the C8), but not through the "pressure filter" which I think is equivalent to the external canister filter in the C8. This is related to my question (in this or another thread I did not check) - but maybe there are other lines in C8 transmission that do not normally pass through the canister filter but do potentially collect debris that is released into the sump (or to the external canister filter) during the hydrualic system flush (HSF). If true, it would explain the need for the periodic HSF at every DCT filter change (at the prescribed intervals).

 

The way I saw it described the E-Ray has an auxiliary electric pump in addition to the main mechanical pump.

 

Is the external DCT filter the very first thing in the path of fluid after the internal screen and pump?

i.e. Internal -> Pump -> External