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Another person's. Looks like they got it dried out a bit...
Is that a little by-pass valve in the photo? I think I've seen this idea before - but you have to wonder if they could have put a pressure sensor or two in there that could detect that the filter is "full". My John Deere 455 diesel has a sensor to detect when the air cleaner needs to be changed. As it gets full, there is spring loaded disc that starts to move in clear plastic cylinder, with tic marks that are probably proportional to vacuum "pressure". If a bypass valve can pop open at a certain differential pressure, seems like a couple of pressure sensors could also see that.
This seems to be a good thread to bring up another thing I have been thinking about. The manual says to change the fluid and filter every 24 hours of track use. So, how would that affect the normal mileage interval? If one has just changed the filter, and then accumulates 12 hours of track use, can you still go for the full mileage for the next change interval. How about 22 hours of track use? Seem pretty clear to me that the answer is no - any track use should also require the filter and fluid to be changed sooner than the normal mileage interval. And, pulling that thread further, it seems like heavy street use - might also require the filter and fluid to be changed sooner. I think that's the point being made by some others.
Yes it's a bypass valve. Pretty sturdy one. I haven't measured the bypass weight (not pressure).
I like your idea of knowing when it bypasses.
You probably know this but for those that don't yes the DCT filters the opposite of most oil filters. It flows from inside filter to outside of filter.
Good point about driving conditions impacting fluid life.
It's not the DCT filter discussed in the track prep guide but the fluid itself which I can't help but think they are concerned about fluid degradation due to heat rather than filter loading or increased contaminants.
I'm conservative anyways and generally half the recommendations but it's a good question about how much of a sliding scale is there.
Yes it's a bypass valve. Pretty sturdy one. I haven't measured the bypass weight (not pressure).
I like your idea of knowing when it bypasses.
You probably know this but for those that don't yes the DCT filters the opposite of most oil filters. It flows from inside filter to outside of filter.
Good point about driving conditions impacting fluid life.
It's not just the DCT filter discussed in the track prep guide but the fluid itself which I can't help but think they are concerned about fluid degradation due to heat rather than only filter loading or increased contaminants.
I'm conservative anyways and generally half the recommendations but it's a good question about how much of a sliding scale is there.
Yes it's a bypass valve. Pretty sturdy one. I haven't measured the bypass weight (not pressure).
I like your idea of knowing when it bypasses.
You probably know this but for those that don't yes the DCT filters the opposite of most oil filters. It flows from inside filter to outside of filter.
Good point about driving conditions impacting fluid life.
It's not just the DCT filter discussed in the track prep guide but the fluid itself which I can't help but think they are concerned about fluid degradation due to heat rather than only filter loading or increased contaminants.
I'm conservative anyways and generally half the recommendations but it's a good question about how much of a sliding scale is there.
As you mentioned… reverse flow thru the filter. So it needs to be cut apart and opened up to see the debris like the first sets of photos.
I mention the reverse flow to ask another question. The small tube coming out of the top of the filter housing… is that the in for oil to the filter or the out for oil going back to the trans?
I am thinking it’s the return/ out going back to the trans.
I do find it odd they did reverse flow. They way normal oil filters work with the outside of the filter gives a larger area for debris to get trapped. Bad design on this filter?
It almost looks like an after thought design added after orig testing by GM?
Why not a spin on filter?
Last edited by 2024VETT; Jul 27, 2023 at 10:39 AM.
Are the transmission shafts riding in pressure lubricated bearings as they are for an engine cranskhsaft or camshaft? I have been assuming that the clutches including the eDiff clutches and gears are just riding in an oil bath but the shafts could be on pressure lubricated bearings. Do we know if there is also spray lubrication? I've been assuming that the return path is normally just running back to the pan after the fluid has been distributed by the pump to the valves, hydraulic actuators, and spray (if it does any of that). And I've been assuming - hoping - that all of the fluid goes through the canister filter before it goes to any pressure lubricated components, valves, and actuators.
Is that a little by-pass valve in the photo? I think I've seen this idea before - but you have to wonder if they could have put a pressure sensor or two in there that could detect that the filter is "full". My John Deere 455 diesel has a sensor to detect when the air cleaner needs to be changed. As it gets full, there is spring loaded disc that starts to move in clear plastic cylinder, with tic marks that are probably proportional to vacuum "pressure". If a bypass valve can pop open at a certain differential pressure, seems like a couple of pressure sensors could also see that.
I agree that with all the other sensors in the DCT one would think that the system monitors the pressure drop across the filter and would throw a code if a limit is exceeded but we don't know. I believe that the air filter monitor in the newer C8s works off monitoring differential pressure.
My 2000 Chevy pickup has a tell-tale indicator that works off of differential pressure to let you know when the filter needs to be changed.
As you mentioned… reverse flow thru the filter. So it needs to be cut apart and opened up to see the debris like the first sets of photos.
I mention the reverse flow to ask another question. The small tube coming out of the top of the filter housing… is that the in for oil to the filter or the out for oil going back to the trans?
I am thinking it’s the return/ out going back to the trans.
I do find it odd they did reverse flow. They way normal oil filters work with the outside of the filter gives a larger area for debris to get trapped. Bad design on this filter?
It almost looks like an after thought design added after orig testing by GM?
Why not a spin on filter?
There isn't a significant reduction in surface area when flowing from the inside to the outside in a pleated filter design. While flowing from the outside to the inside is more common it isn't unheard of to flow in the other direction. The support structure just needs to be on the downstream side.
I agree a spin-on would have been nice. Perhaps they had packaging constraints or didn't want to develop one that would meet the requirements. The operating pressure may be pretty high.
What's the filter change process like? Could you do it without a fluid change if you want to change filters frequently? If so, how much fluid is lost in the process? Is it just *early* in the life of the trans that it makes so much debris? The photos make me think that's a lot of wear. Did anyone cut open a filter after always babying it?
Yes it's a bypass valve. Pretty sturdy one. I haven't measured the bypass weight (not pressure).
I like your idea of knowing when it bypasses.
You probably know this but for those that don't yes the DCT filters the opposite of most oil filters. It flows from inside filter to outside of filter.
Good point about driving conditions impacting fluid life.
It's not just the DCT filter discussed in the track prep guide but the fluid itself which I can't help but think they are concerned about fluid degradation due to heat rather than only filter loading or increased contaminants.
I'm conservative anyways and generally half the recommendations but it's a good question about how much of a sliding scale is there.
This is purely by my personal observation having changed out 4 filters so far:
The finer sized debris on the filter media is easily washed out in the process of removing the filter element. Once is when you remove the cover and the DCT fluid (little that it is) drains down through the filter; and secondly when you actually remove the filter element and some additional fluid washes over the media.
If you just take the filter off and lay it in a pan you can observe the finer sized debris washing out with the DCT fluid running off the filter from the inside. What I do now is try and keep the filter in the vertical orientation and stand it upright (bypass valve "down") in a clean pan and leave it as long as I can to drain from the inside out. This maximizes the amount of debris retained in the filter media, BUT it still washes down. I'm inclined to believe that this is part of the reason the filter media looks stratified when cut apart. I think it is important to understand how that filter works and not be misled into thinking your filter is not too clogged when in fact half the debris was washed out into a catch pan before you observed what was really in there.
The bypass valve seems to be more of a poppet-type rather than a progressive one (ie open or closed).
My opinion is that if the bypass does open at all, then it is not good! I would rather have a high DP warning than a "Hey, your in bypass mode". Why? The bypass valve is at the bottom of the filter and so when it opens the DCT fluid washes across the full length of the filter and, based on my #1 and #2 observations, would/could strip off a lot of the collected debris from the filter media and carry it straight into the main transmission which would (I assume) be very bad. To avoid this the bypass would need to be separated from the filter element and be located ahead of the filter, say at the 90-degree inlet pipe.
On my first transmission I changed the filter at 2,500 miles. Based on what I saw, it would have probably been fine to the 7,500 mile mark but I was still glad that I did look at it early and start collecting data. Unfortunately a porous trans case popped up and trans #1 was out by 3,000 miles!
On the second transmission I changed the filter at a trans life of 2,000 miles. Again, that filter looked relatively good. The filter was next changed at a trans life of 4,500 miles which was done as part of the 7,500 mile GM service (car was at the 7,500 mark even though the trans was behind in actual mileage. Filter was by observation a bit worse than I expected but still relatively clean.
To avoid any issued with GM and the "service at 7,500 miles regardless", the DCT filter was again changed at the trans life of 7,500 miles, or 3,000 miles of filter service, and it looked fairly debris free and sufficiently adequate to consider not doing another filter until the 22,500 mile maintenance cycle.
You do realize that your pictures are showing the clean side of the filter, right?
Yes as I posted they were not my pictures and already posted the flow diagram on the filter. The media does saturate all the way through though... At least all the one I've cut open.
Like you mentioned I actually put a bag under the filter housing as I remove it and then let the filter and all fluid drop right down perfectly into the clear plastic bag to capture it all for inspection
What's the filter change process like? Could you do it without a fluid change if you want to change filters frequently? If so, how much fluid is lost in the process? Is it just *early* in the life of the trans that it makes so much debris? The photos make me think that's a lot of wear. Did anyone cut open a filter after always babying it?
Are the transmission shafts riding in pressure lubricated bearings as they are for an engine cranskhsaft or camshaft? I have been assuming that the clutches including the eDiff clutches and gears are just riding in an oil bath but the shafts could be on pressure lubricated bearings. Do we know if there is also spray lubrication? I've been assuming that the return path is normally just running back to the pan after the fluid has been distributed by the pump to the valves, hydraulic actuators, and spray (if it does any of that). And I've been assuming - hoping - that all of the fluid goes through the canister filter before it goes to any pressure lubricated components, valves, and actuators.
I dont have a shop manual, but because this is an auto/ manual trans I will assume the trans also has an internal filter on the suction of the oil pump. Does the shop manual mention a service time/ milage for that?
If the outside filter is in bypass, that internal filter would get dirty a lot sooner and need a change.
There is an internal filter but some sources say it is a lifetime filter, nothing official from GM. The service manual has a couple of ways to replace the DCT fluid, one with replacing the internal filter and one without but it doesn't say which procedure to use during a normal service. Most 3 year DCT fluid services I've seen reported haven't said the internal filter was replaced but I've seen at least one post that said their dealer included the internal DCT filter replacement along with the fluid replacement.
So, let’s say you take the milage to the full 7500. Pushing the filter to the milage limit.
The shop process has the tech “ flush” the system. I will assume it cycles all the solenoid’s to clear debris. What if the filter is already into a bypass mode due to filter being full of debris. Will the “ flush” really help at all or just move the debris thru the filter?
I would like to get a better understanding of the internal psi of the DCT oil pump. I mean you would think the psi needs to be constant so the trans can shift fast at any speed or rpm. Or does the psi increase as the rpm’s increase to handle the loads of shifting?
If so, higher rpm would mean more bypass once the filter gets dirtier. I understand the flush takes place with the C8 attached to a computer. Does it vary rpm during the test or keep it at idle?
If I decide to change the filter at 3000 miles without a flush, well before the 7500 mile flush, I would think replacing it would keep the system from bypassing debris. Will the fine debris cause the failures we have seen or is it solenoids or internal parts? I know some were casting failures.
So, let’s say you take the milage to the full 7500. Pushing the filter to the milage limit.
The shop process has the tech “ flush” the system. I will assume it cycles all the solenoid’s to clear debris. What if the filter is already into a bypass mode due to filter being full of debris. Will the “ flush” really help at all or just move the debris thru the filter?
I would like to get a better understanding of the internal psi of the DCT oil pump. I mean you would think the psi needs to be constant so the trans can shift fast at any speed or rpm. Or does the psi increase as the rpm’s increase to handle the loads of shifting?
If so, higher rpm would mean more bypass once the filter gets dirtier. I understand the flush takes place with the C8 attached to a computer. Does it vary rpm during the test or keep it at idle?
If I decide to change the filter at 3000 miles without a flush, well before the 7500 mile flush, I would think replacing it would keep the system from bypassing debris. Will the fine debris cause the failures we have seen or is it solenoids or internal parts? I know some were casting failures.
Thoughts??
The notes in the latest version of the filter replacement procedure state that GM is concerned about overloading the filter if the first mileage interval has been exceeded:
The notes in the latest version of the filter replacement procedure state that GM is concerned about overloading the filter if the first mileage interval has been exceeded:
Seeing this GM service info confirms my suspicion that replacing the filter without a flush would help prevent bypass when the flush is done at 7500 miles.
Thanks for the info👍👍
Seeing this GM service info confirms my suspicion that replacing the filter without a flush would help prevent bypass when the flush is done at 7500 miles.
Thanks for the info👍👍
That's assuming that the filter is on the verge of bypassing. So far the pictures I've of filters I've seen don't look like they are verge of bypassing but I'll admit it is hard to tell from pictures (or even direct visual examination) unless it is obviously overloaded.
GM had a lot of filters returned to them for evaluation. One would think that if they determined the filters were on the verge of bypassing at 7500 miles they would have modified the service interval or procedure since they would be on the hook for warranty repairs.
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