6.9 Transmission woes

[daantjie]

Hi guys

Been scouring the forums for some advice, hoping the W116 team will chime in here!?

Recently had my radiator recored, and after fitting, the trans is acting up.  Not sure if this is related, but I have to think so.  Did not seem to loose a lot of ATF when I disconnected the lines to the trans cooler, so I topped it off a little bit, but now I am getting bad flaring from 2 - 3 shift.  Also attempted kickdown results in revs climbing rapidly but no kick down, so I have to let off the pedal.

Also, sometimes it will not downshift smoothly to 1st when I roll to a stop, and it will rev up and do so with a thud as I come to a stop.

Goes into drive and reverse nice and smooth with minimal delay.  Also fluid does not appear to be burnt.

Checked the fluid multiple times and reading full hot on the stick.

Any ideas?  Haven't checked the vacuum modulator yet

Cheers

[oversize]

Lets hope the cooler was cleaned prior to re-installation....  I've seen plenty that had water in the cooler after the recore/repairs and that obviously makes its way into the transmission.  I'd change the fluid and filter and see how it goes then.  PS don't forget to drain the convertor and the cooler/pipes.

[daantjie]

Thanks oversize.  Yup I was thinking about that as well.  Fluid off the dipstick appears bright red and not milky pink colour, which would indicate no water, or maybe very little.  Will even a little water mean it is terminal for the trans?

Either way I will have to drop the pan and see what I can see.

[daantjie]

Well, dropped the pan, fluid looked OK, did not smell burnt.

There was a fair bit of dark silt- like material at the bottom of the pan, and the filter was quite dirty.

No big metal parts though, only minute flecks for the most part.

Any thoughts?

[motec6.9]

Hopefully with new filter and fluid . Stay away from syn with old trans. It will return to normal function . I doubt it is modulator as it will draw trans fluid through motor and smoke screen can be seen from space. I believe bands can be adjusted by trans shops on these trans just not sure how to tighten shift. Good luck. 

[daantjie]

Thanks Motec
Yup I am hopeful. I am using Febi Dex III fluid with Mann filter.
If it is still having fits, might chuck in a bottle of Lucas Trans fix and pray 

[daantjie]

Update:

So I filled her up and took her for a spin.

Shifts under light/idle throttle is silky smooth, no drama.  Also engages into drive and reverse with no issues.

But under hard/part throttle it is flaring like crazy now both between 1/2 and 2/3 if I push it harder than light throttle  Could this be vacuum modulator that is toast, or perhaps vac leak in the rubber line to the modulator?

Of course I have since found out that the vacuum modulator is NLA, grrrr

Any help appreciated.

Cheers

[motec6.9]

like I said shift can be adjusted on these gearbox but its not something I have ever looked at . You may need to find a gearbox specialist. Someone who works on older hydraulic boxes would be better stay away from new car style business as they will just want to replace everything.

[daantjie]

Thanks again Motec.

Trying to avoid a big bill, and do not really want to take it to a "specialist" who will charge me for troubleshooting I can hopefully do myself.  Unfortunately most of the shops here will not touch a 6.9 with a barge pole

I've heard of a test, taking the vacuum line off the modulator and seeing if it will shift real firm.  Apparently if it does not shift hard with no vacuum, the trans is toast..?

[motec6.9]

Hi Daniel Kent Bergsman is boring as hell to watch but his videos are very useful . Hopefully this will help. https://mercedessource.com/problems/search?chassis=24&location=169

[daantjie]

Thanks, I am already a Kent Bergsma "disciple"

[daantjie]

OK planning on taking off the vac supply line to the modulator and seeing how she rolls.

Anybody done this?  Any risk of really buggering up the trans?

[daantjie]

OK, so taking the vacuum line off had absolutely no effect on the shift.  Still soft and slurry under idle throttle and flaring like hell under half - full throttle.  Guess this means my trans is saying "sayonara"

Chucked a bottle of Lucas Trans fix in there as a last resort, but I am thinking it is terminal

[TJ 450]

I'm thinking the pin may have fallen out of your modulator vacuum unit if there was no change when moving the vacuum line. Don't give up just yet.

Something like this, but usually without the spring. It should be glued in place with Loctitite 620 "Shaft fit" or similar product.



Tim

[TJ 450]

Then I would check that the modulator is adjusted properly... this means the car needs to be taken to a specialist who knows how to work on these transmissions.

Failing that, yes the transmission will probably need a rebuild.

Tim