Transmission issues summary

[SlickGT1]

RRPhil. I wanted to ask you something for a while.

Can the whine I am getting at 2000rpm be the torque converter?

When driving, at 2k rpm, every gear I get a steady whine. If I go below 2k rpm, or above 2k rpm, it goes away.

I took a long drive on Sunday, the whine went away about 30 min into the drive. It came back after the car stood for 6 hours. And again went away 30 min into the drive home.

It will whine at 2k rpm in neutral and park as well, much less noticeable, I am guessing due to no load.

Had this since day one of owning the car.

Please advise if you can. Thanks.

[RRPhil]

If it’s not the engine itself then engine speed dependent noises tend to be torque converter or oil pump based if heard in Park & Neutral. Why it should make a noise specifically at 2000rpm and no other speed is much more difficult to fathom.

I believe you have a 4.8is with the 6HP26 transmission? I need to check because I don’t know if the pump flow control uses the same system as the 5-speed but one of the big challenges with the design of a fixed-displacement pump like the ones used in the 5HP24 (below) and 6HP26



is, once you’ve provided adequate flow at the minimum engine speed (say 600rpm), how do you then deal with the surplus flow when the pump is producing 10 times that amount of flow at 6000rpm – way in excess of what’s needed. In the 5HP24 there’s a flow control valve in the pump housing that deals with the excess flow by feeding it back into the suction side of the pump (thereby also saving power & reducing cavitation)



The flow control kicks in at 2000rpm (see graph) – you can see where I’m going here…



As I mentioned before, I need to check if the 6HP26 system is the same, but I was wondering if your noise might stem from the pump/flow-control area of the transmission?

On the 5HP24 the flow control valve can be removed and checked (spring free length should be 82mm)



by undoing the retaining plug on the LH side of the intermediate housing





I guess this isn't a particularly likely cause of your noise, but I will check to see if the 6-speed uses the same system.

Phil

[SlickGT1]

Wow thank you Phil, I'm very happy you are taking the time to help me diagnose this.

I like your train of thought. Yes you are correct, I have a 4.8is with the 6HP26 trans. Yes the noise "feels", like its right under my feet. And it happens right around the 2k rpm range (maybe 1900 rpm) and hangs on for a couple of hundred rpm. Then it seems to subside.

I am going to try to do my fuel filter tonight, and I will check if I have that plug in that location.

Am I to expect fluid to come out if I remove that bolt? If so how much, do I need to prepare for another fluid top off?

If no fluid comes out, I can take out (presuming I have it) that plug, valve, spring and measure. I just need to know what the speck would be, and where I can pick up those components.

Thank you in advance.

[RRPhil]

Having looked into this a bit further I now get the impression that the 6HP26 doesn’t have a pump flow control system like its dad, the 5HP24. It still uses a fixed-displacement internal crescent moon pump but it’s a smaller capacity (at 19.1 cc/rev) than the 5-speed because of reduced leakages and a lower cooling flow requirement in the 6-speed. The hydraulic circuit doesn’t show any flow control valve for the pump.




Sorry to have given you false hope!

Phil

[SlickGT1]

Thanks Phil. I was under the car yesterday, and could not find the bolt for the flow control valve.

So this brings me back to the same question. What can be causing the 2k rpm whine, that can be felt under my feet? And can a failing Torque Converter be doing this?

Thanks in advance.

[TiAgX5]

WOW, RRPhil know BMW transmission! Were you involved in the design?

[SlickGT1]

I think he is an Uber trans re builder, fixer, guru, the man.

[TiAgX5]

No doubt! He says it, it's gospel. He backs it up with pic, graphs, schematics to boot!

[Helmuth]

RRPhil, Sir,

may I ask you what my "RRRRRRRRRRRRRR" at exact the same rpm on a 3.0d 2002 may be. It is only in "D" not in "S". BMW was not able to find it, they wanted to change the tranny. Seems I have the same symptoms as SlickGT1 but a rattling noise and vibrations instead of a whining sound.
BMW specialists (if they exist when it comes to transmission probs) told me that the transmission will fail and I will not be able to move with the car in some time. They also told me that this is happening several times per year around their garage .........

Thank you in advance

Helmuth

[RRPhil]

Yes, unfortunately the GM 5L40-E (BMW call it the A5S390R) transmission fitted to your 3.0 d suffers badly from issues relating to reduced hydraulic pressures caused by increased leakage in the valve block due to wear.
One significant consequence is that the lock-up clutch in the torque converter wears through its lining and deposits huge quantities of metallic debris into the fluid



The noise you’re hearing may therefore be the lock-up clutch giving up the ghost (and not absorbing the engine’s torsional vibrations). You can sometimes see the engine revs on the rev. counter bouncing up and down by a couple of hundred rpm during the vibration.

The lock-up clutch operates on a different shift map in the ‘D’ and ‘S’ modes.

Another possibility is that the screens on the PWM solenoid that activates the lock-up clutch have become blocked or damaged





I think as a starting point you need to have the fluid drained and checked to see if there’s metallic debris in there (or stuck to the sump magnet). If the LUC has worn through its lining then, as the BMW specialist has said, it’s just a matter of time before the hydraulic circuitry becomes affected and the transmission starts to drop into failsafe mode.

Sorry, that didn’t sound very optimistic did it?

Phil