DCT service PSA: the "Sucking Jet Pump"

[deansbimmer]

Our shop has always done DCT services which have mostly been procedural fluid and filter jobs over the years. Lately however, we have been seeing an interesting development with increasing regularity. More and more cars come to us with concerns of delayed gear engagement, especially after a cold-start. Over dozens of these jobs we have correlated these symptoms with findings of damaged sucking jet pumps. We believe the two are related.

The DCT sump system has two immediately serviceable parts- the low pressure filter and the sucking jet pump. Much is seen and heard about servicing the sump filter but rarely does anyone mention the sucking jet pump. An odd term for a part- it is a combination anti-return check valve and venturi pump.

It's an important part. Its correct function can help mitigate the hydraulic circuits in the transmission case from leaking down when the car is off. This permits a faster pump-up time with less aeration and cavitation when the car is started and put into gear. The result seems to be quicker gear engagement with less sensation of shudder or slippage.

Now that these cars are aging we see more and more of the check valve balls being heavily worn and damaged to the point they cannot perform their oil-holding function. We have also noted that vehicles with these damaged pumps also have louder than usual oil pumps (gear whine).

Most DCT's by now are leaking heavily, especially at the mechatronics seal on the top of the transmission case. At this point, our shop recommends a full DCT service. This requires transmission removal. We replace every external soft seal and gasket and both filters. While removed, it's also recommended to remove the clutch assembly for inspection and also inspect the oil pump hardware. On several units we have found loose screws holding the oil pump to the case, with some bolt even broken. This causes critical internal oil leaks, low oil pressures, clutch overheating, poor engagement, etc.

The moral of this story is to not overlook your DCT. It's fun to buy fancy aluminum oil pans but don't neglect the functional parts inside the unit. Oil leaks are just the tip of the iceberg. We suggest that by now every DCT should be removed and fully serviced to ensure peak performance and enjoyability.

Here are some pictures of these which we've done in our shop.

[drwankel]

Really great info. Next time I do DCT service I'll probably replace that thing as preventative maintenance.

[DukeofAlexandria]

Great write up Dean as always.

Like you said, with this platform seeing higher mileage you'll see more items like this pop up for repair.

Have you noticed a correlation to a specific mileage interval where these seem to be occurring? 75K, 100K, 125K, etc.?

-Duke

[buldogge]

Thanks for the heads-up deansbimmer...

Are you guys using the Getrag replacement part, or the BMW supplied part (assumedly might be the same)...?

TIA
-Mark in St. Louis

[nick3753]

I'm no where near you, so maybe a moot point to me, but how much does this service run. It looks quite involved.

[deansbimmer]

Originally Posted by DukeofAlexandria

Have you noticed a correlation to a specific mileage interval where these seem to be occurring? 75K, 100K, 125K, etc.?

Not particularly. Unless it's leaking profusely or malfunctioning, we seem to find it difficult to "sell" a client on DCT work until after 100k miles. Preconceived notions of "lifetime oil" are hard to break. It looks like most of our invoices for the full DCT jobs show the work orders have been on cars 105k-170k.

Originally Posted by buldogge

Thanks for the heads-up deansbimmer...

Are you guys using the Getrag replacement part, or the BMW supplied part (assumedly might be the same)...?

If you buy the part from BMW it is a Getrag part and box with a BMW label on it. We just order from Getrag (S-tec).

Originally Posted by nick3753

I'm no where near you, so maybe a moot point to me, but how much does this service run. It looks quite involved.

The Jet pump is only a $75 part and no more intensive to install when doing a fluid and filter service. We usually do DCT's as a comprehensive full service job which tends to all of its serviceable components. Since it requires removal from the car and followup software actions, it runs from $2600-2800 at our shop.

[sergbaja5t]

Originally Posted by deansbimmer

The Jet pump is only a $75 part and no more intensive to install when doing a fluid and filter service. We usually do DCT's as a comprehensive full service job which tends to all of its serviceable components. Since it requires removal from the car and followup software actions, it runs from $2600-2800 at our shop.

What is included with the above mentioned service price. I just performed a service to my DCT with just under 206K and did not se any metal, debris, and the fluid was black, but more of a maple syrup color. The transmission is operating normally, but in the back of my head, I am some what concerned about the clutch pack @ 206k.

[Redd]

Great info as always, deansbimmer!

[DrFerry]

Sub’d. deansbimmer I wish you were closer to Greenville, SC. Oh well. Perhaps there’s a DFW road trip in my future.

[Assimilator1]

Very odd how that check valve ball wore, I know it (they) have done north of 105k miles, but you'd think a stainless steel (presumably!) ball would last better than that in a plastic housing.
Glad I chose a manual version! lol (because there's less to go wrong).

[nick3753]

Anyone have the torque spec for the screw holding the pump on?

[spammysammich]

I think it’s 4NM. I can’t find the document I referenced but I did this service a couple months ago and I’m pretty sure this is the spec. There are a couple different low torque value screws in that area and I recall the jet pump screw being in the middle of the range. Sorry I can’t be more helpful. I’ll try to find the TIS reference later.

Edit: I found it reference on YouTube as 6NM as per ISTA on an M4 but it’s the same pump.

[nick3753]

Originally Posted by spammysammich

I think it’s 4NM. I can’t find the document I referenced but I did this service a couple months ago and I’m pretty sure this is the spec. There are a couple different low torque value screws in that area and I recall the jet pump screw being in the middle of the range. Sorry I can’t be more helpful. I’ll try to find the TIS reference later.

Edit: I found it reference on YouTube as 6NM as per ISTA on an M4 but it’s the same pump.

Thank you.

[cdr5150]

Sub'd.

[SN1P3]

Useful, thank you!

[chocstraw]

part number 28107842838 btw

https://www.autohausaz.com/pn/OE-28107842838


cheapest I'm seeing.

[chocstraw]

Now Deansbimmer is one of the most reliable sources on this forum, but I do believe that he understated the importance of this. Yes the car will drive for a while, but for $70, this should be a top priority.

I have 126k on my '11 M3, and I drive the balls off of it. I started getting locked out of the odd gears, and noticed a much louder whine when driving in odd gears. I usually change the DCT fluid every ~40k miles (it even came out more of an amber color than black), but I suppose years of sediment moving past this check ball renders it unable to do its job.

If you are changing your fluid + filters, be sure to add this to the list. It's so simple that it's just one additional hex key holding it in place, and you don't have to move anything besides the pan to get to it. Pan, filters, even the cylindrical filter isn't that hard. My personal strategy is the jack up the side with the fill hole, put an extra liter or so of fluid in, then let it down while the car is still running (~2k rpm for 30-60 seconds) and cap off the fill hole then shut it down. Helps to elevate the car or wear gloves.

No more lurching when coming from a stop. Great looking out Deans

first photo is a fresh check ball.

[Shredicus]

Deansbimmer has always been a treasure to this forum. Thanks for the PSA, I grabbed one of these to toss in when I put my new pan on.

[ronniem3]

Replacing mine today

[chocstraw]

Jumping back on this thread to report that the transmission did actually fail. Says insufficient pressure to clutch one and locks out odd gears (and reverse as a consequence). Mechatronics.

I've sourced a really nice low mileage unit for $1000 and will be transferring the new check ball over, and using FCP's replacement policy for the first time to get 2 new filters and a new pan. I have a new gasket from Getrag / S-Tech for the side mechatronics cover.

Couple questions
- With the Pentosin fluid being super expensive now, has anyone tried liquimoly 8100 ? I have 7 liters and will be trying it.
- Does a transmission swap require any electrical / flashing ? Will I have to get winKFP working again to flash it with the VIN?
- anyone know offhand if there's a good DIY guide to removing the DCT or a general list of things to look for?
- Should I replace the top mechatronic sleeve as a whole or will a new O-ring suffice? Those can leak but less often and less severely.

I've dealt with enough transmissions to know that it's better to swap a used unit in rather than chase down issues. Issues and costs add up really fast when trying to fix a trans.

[spammysammich]

I’ve used LiquiMoly before. Even topped it off with Pentosin. As long as it’s all FFL-4 fluid you should be fine. Sorry to hear your DCT is shot.

[deansbimmer]

Originally Posted by chocstraw

I've sourced a really nice low mileage unit for $1000 and will be transferring the new check ball over, and using FCP's replacement policy for the first time to get 2 new filters and a new pan. I have a new gasket from Getrag / S-Tech for the side mechatronics cover.

Couple questions
- With the Pentosin fluid being super expensive now, has anyone tried liquimoly 8100 ? I have 7 liters and will be trying it.
- Does a transmission swap require any electrical / flashing ? Will I have to get winKFP working again to flash it with the VIN?
- anyone know offhand if there's a good DIY guide to removing the DCT or a general list of things to look for?
- Should I replace the top mechatronic sleeve as a whole or will a new O-ring suffice? Those can leak but less often and less severely.

Gutsy...I wouldn't be inclined to trust a $1000 unit...

Absolutely replace all external seals including mechatronics seal. You'll kick yourself if you don't and have to pull the trans to later replace it.

LM 8100 is fine- it carries the BMW certification. Same as Motul DCTF, Pentosin, Redline, Shell...

There are differences in early DCT and late DCT units with electrical and grounding schematics etc. Best to find one from a similar year, or at a minimum match Pre/post LCI.

DCT swap absolutely requires specialized software actions and is not a simple WinKFP session for someone loading it up for the first time. Recommend contracting a specialist for this operation.