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Johann
Veteran
Date registered: May 2006
Location: Centurion, South Africa
Vehicle(s): 1999 LWB 290GDT 1981 SWB 240GD+ Cabrio 2015 G63
Posts: 259
| Auto Gearbox Blues
Hi all,
My '99 G has a 4 speed autobox. When driving in slow traffic and you take your foot of the accelerator pedal for it to free wheel it changes gear with a heavy THUMP. It drives me crazy. When accelerating normally through all the gears it is fine but when you take your foot off the pedal to free wheel it goes THUMP. This happens at low speeds and low revs.
A friend of mine's 2001 290 is doing the same. Even after spending $800 in overhauling it is still doing this.
What could be wrong or is this as designed?
Thank you
Johann
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Johann
Veteran
Date registered: May 2006
Location: Centurion, South Africa
Vehicle(s): 1999 LWB 290GDT 1981 SWB 240GD+ Cabrio 2015 G63
Posts: 259
| RE: Auto Gearbox Blues
The problem ended up to be the vacuum unit on the gearbox that was leaking air!
Part number : A126 270 9379 |
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göran
Date registered: Dec 1899
Location:
Vehicle(s):
| RE: Auto Gearbox Blues
Hi,
After a search over problem with automatic gearbox in the forum I wonder if this could be something. The subject is "auto gearbox blues".
I have a noise like a whistle somewhere under my G290TD. It comes around 60-70Km/h and is gone around 15-20Km/h. It is like a air sound in high frequency but is the same level on the sound if I drive fast or slow. The gearbox works fine (also oil level checked) and it is not a sound from turbo charger or from a bearing somewhere. The problem are only in driving on road and not when run up engine in park or neutral and not when take the back wheel up in air and run the engine in drive position.
It is realy difficult to found the problem and my last chance is if someone here have expereince from it or have any idea.
Göran.
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DesertStar
Expert
Date registered: Apr 2006
Location: San Diego, CA USA
Vehicle(s): 85-280GE/95-G320/08-G500
Posts: 2156
| RE: Auto Gearbox Blues
goran, I am curious if this noise is coming from your transfercase. Have you tried to see if it makes the noise when in or out of 4WD ? I have a real faint "whine", as I call it, and believe it to be all the gears in the transfercase singing in harmony. I used to hear similar noise in an old Jeep and Bronco....its not really noticable but there.
I am also curious if it is the insulation of the center console letting some noises in...ie: W460/W461 versus W463. A W463 would tend to "hide" any noises due to its "more" insulation.
Just some thoughts.
Mike |
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Dr. Rob
Veteran
Date registered: Nov 2006
Location: Stockholm, Sweden
Vehicle(s): 280GE LWB, 280E Ambulance
Posts: 216
| Re: Auto Gearbox Blues
Noticed the same, Johann. Maybe not such a big thump, but more like downshifting from 3-2 on a manual transmission. Was wondering about that. Stays in low gear when rolling down hills too.
Gotta ask Göran about that whine... Have two whines myself, found a new one yesterday.
One is an intermittent duuut that makes you look around for emergency vehicles, because it sounds like a siren. It comes and goes as it pleases.
The other is a high-pitched wheeiiee, like wind around the corners of your house on a stormy night. Source unknown.
Sound familiar, Göran? |
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nadd
Expert
Date registered: Apr 2006
Location: UAE, Dubai
Vehicle(s): G500 2016 LHD, numerous Chevys
Posts: 1285
| Re: Auto Gearbox Blues
I am not sure if you have the same transmission as the early 300GEs (1990-1994), but if you do (it is also a 4-speed auto), with that engine a vacuum tube goes from near the inlet manifold to the side of the transmission, very hard to see, but easier traced by hand.
When I changed the head gasket I had to take the manifold off, and this hose was accidentally pulled. The resulting symptom was very rough (thud) up-shifts on low or part-throttle, but perfect upshifting at full or near-full throttle, until I put the tube back in the side of the tranny, now all is fine.
And that noise, the one that comes and goes randomly and sounds a bit wind-like, check if it is related to the throttle position (under the same load conditions, it changes with load and vehicle angle). In mine there is a charcoal fuel vapour canister in the right rear wheel well (on 463s as far as I know) that seemed to be well past its sell-by date, and would whine at will. After changing it the whining went. See if you have anything similar in the fuel system (access to an EPC would be helpful here).
Other questions, msg/email me, as I do not browse as often these days as I used to. |
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Johann
Veteran
Date registered: May 2006
Location: Centurion, South Africa
Vehicle(s): 1999 LWB 290GDT 1981 SWB 240GD+ Cabrio 2015 G63
Posts: 259
| RE: Auto Gearbox Blues
Nadd: The place that tude plugs into the tranny is the vacuum unit I need to replace(got the part still have to get it done). If anybody has similar problems do a pressure test on tude and vacuum unit to check if there is a leak somewhere.
(I already know of 4 290GTD's in South Affrica who's 4 speed auto's is doing this. Seems like some design flaw?)
Göran: Not sure if this will help. I had a blowing noice similar to a small exhaust hole which drove me crazy. This was only at highway speeds.
It ended up to be my no. 1 injector blowing air. I assume this could make various noices depended on the size of the leak.
Some dumbnut previously putted in a steel washer and it should be copper that can expand to seal properly.
Johann
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Johann
Veteran
Date registered: May 2006
Location: Centurion, South Africa
Vehicle(s): 1999 LWB 290GDT 1981 SWB 240GD+ Cabrio 2015 G63
Posts: 259
| RE: Auto Gearbox Blues
For everybody's benefit.
I replaced the filter in the auto box and it is now as smooth as a baby bum!
Johann
Edited by Johann 6/16/2007 6:52 AM
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