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Old 16-08-2020, 02:25   #1
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Gearbox oil black...problem?

I just did the initial (50-hour) service on my new Volvo D2-75. The gearbox oil in the MS-25 (mechanical) gearbox was BLACK...looked like old engine oil. In my previous diesels, gearbox oil (previously ATF, now 15w40) was always clear at change intervals. Looked like fresh.

Research tells me that the oil shouldnít be darkened like this, especially after just 60 hours. What are your thoughts on possible causes?

Iíve saved some of the oil, and plan to get an oil analysis. The engine, of course, is still under warranty, but I want as much info as possible before taking this up with Volvo. Thanks for any info.
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Old 16-08-2020, 02:54   #2
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Re: Gearbox oil black...problem?

If the gearbox oil is black - almost certainly the oil seal (s) between the engine and the gearbox has failed. Possibly incorrectly fitted in the first place. I 100% agree that g/b oil should never, EVER, get black (indeed - I only change the gearbox oil once every 5 years/250 hours). The sump oil goes black because of combustion products, - therefore, during time, it becomes acidic, that's the reason it is recommended to change engine oil annually regardless of hours run, so that the engine is full of nice clean non-acidic oil during the layup period.
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Old 16-08-2020, 02:56   #3
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Re: Gearbox oil black...problem?

In fact, it's lucky you checked the gearbox oil after only 50 or so hours!
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Old 16-08-2020, 03:10   #4
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Gearbox oil black...problem?

Possibly clutch slip. Check the actuator angle is correctly set in relation to throttle/gear control.

This has been flagged as an issue with the TMC manual gearboxes.
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Old 16-08-2020, 03:38   #5
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Re: Gearbox oil black...problem?

Quote:
Originally Posted by parkstone bay View Post
If the gearbox oil is black - almost certainly the oil seal (s) between the engine and the gearbox has failed. Possibly incorrectly fitted in the first place. I 100% agree that g/b oil should never, EVER, get black (indeed - I only change the gearbox oil once every 5 years/250 hours). The sump oil goes black because of combustion products, - therefore, during time, it becomes acidic, that's the reason it is recommended to change engine oil annually regardless of hours run, so that the engine is full of nice clean non-acidic oil during the layup period.
Hi, I am a little curious, given that the gearbox mounts to the rear of the engine on a spacer that encloses the drive plate, just how would the engine oil possibly enter the gearbox?
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Old 16-08-2020, 04:47   #6
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Re: Gearbox oil black...problem?

Is the oil black, or is it a dark bass boat sparkly type of color?

If itís got sparkles itís the sintered bronze from the clutch packs.

There is no way engine oil has made it out of the engine, around the flywheel, down the spline shaft and back into the transmission front seal. Itís not engine oil.
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Old 16-08-2020, 04:57   #7
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Re: Gearbox oil black...problem?

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Originally Posted by GILow View Post
Possibly clutch slip. Check the actuator angle is correctly set in relation to throttle/gear control.

This has been flagged as an issue with the TMC manual gearboxes.
Pretty much has to be clutch slip. It’s not engine oil, how could it get there?
Does it stink, have a burnt smell?
Enough slip to turn oil black is not a good omen.
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Old 16-08-2020, 05:18   #8
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Re: Gearbox oil black...problem?

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There is no way engine oil has made it out of the engine, around the flywheel, down the spline shaft and back into the transmission front seal. It’s not engine oil.
Sneaky-stealth-engine-oil! You can't trust it!
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Old 16-08-2020, 05:33   #9
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Re: Gearbox oil black...problem?

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Pretty much has to be clutch slip. Itís not engine oil, how could it get there?
Does it stink, have a burnt smell?
Enough slip to turn oil black is not a good omen.

+1 to smell it. It is most likely going to smell burnt, so have clutch plates checked.


Some did have issues in those drives when they switched from ATF to the 15-40W oil
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Old 16-08-2020, 08:24   #10
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Re: Gearbox oil black...problem?

My engine has the gearbox bolted direct to the output shaft at back of the engine: (flywheel is on front, no clutch or drive plates). I'd forgotten that some engines have a different arrangement.
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Old 16-08-2020, 15:25   #11
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Re: Gearbox oil black...problem?

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My engine has the gearbox bolted direct to the output shaft at back of the engine: (flywheel is on front, no clutch or drive plates). I'd forgotten that some engines have a different arrangement.


Seriously? What is the make? I cannot imagine how that could work.
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Old 16-08-2020, 18:11   #12
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Re: Gearbox oil black...problem?

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Seriously? What is the make? I cannot imagine how that could work.


I had an atomic4 that had the gearbox share the line oil sump. But itís also an antique.
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Old 16-08-2020, 19:13   #13
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Re: Gearbox oil black...problem?

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+1 to smell it. It is most likely going to smell burnt, so have clutch plates checked.


Some did have issues in those drives when they switched from ATF to the 15-40W oil
Gearbox oil is not exactly pleasant smelling when new.
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Old 16-08-2020, 19:22   #14
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Re: Gearbox oil black...problem?

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I had an atomic4 that had the gearbox share the line oil sump. But itís also an antique.
Fascinating, I did not know about those. It sounds like my Mini K. One of those systems that are fine, until they are not. I have to use a special engine oil or I can hardly change gears.
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Old 16-08-2020, 23:15   #15
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Re: Gearbox oil black...problem?

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Seriously? What is the make? I cannot imagine how that could work.
Bukh DV24 see pic. I really like it. You'll note that the flywheel is at the forward engine of the the engine, gearbox aft. GB is is directly bolted onto aft of engine interfacing with the output shaft. There's no clutch or drive plate. I like simple.
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