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  #1  
Old 11-01-2007, 10:36 PM
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Location: Oklahoma
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Transmission slipping (???) upon acceleration

I have previoulsy posted on this problem with my 250 - or a similar problem, but I have recently narrowed it down some. I was having problems with the transmission slipping a little and rpm's increasing as the transmission approached shift points.

Symptoms: Seems to shift fine if I accelerate slowly, but if I give it some gas the rpm's increase and shift is delayed. And, even after the car gets in gear -say 4th gear - if I hit the gas pedal around 40 mph and try to speed up quickly it feels then like the tranny is slipping and rpm's increase. If I accelerate more slowly and smoothly, I don't notice any problems. I have checked and adjusted the accelerator linkage - and the linkage between the carbs - but I wouldn't swear I have it right.

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 11-02-2007, 12:15 AM
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Location: brisbane,Qld.Australia
Posts: 1,994
You need to get a trans shop to measure the modulating pressure.The trans is getting old and the bands etc are worn so a little more pressure is needed to enable them to grip better. Have you changed the oil and filter lately? It's surprising what fresh trans fluid will do.
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  #3  
Old 11-04-2007, 10:42 PM
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Join Date: Aug 2004
Location: Western Washington
Posts: 504
Adustment of tranny pump pressure

I have a similar problem and I have adjusted the pump pressure linkage for both less amd more, by adjusting the length of the rod (which is connected to the throttle linkage). Here are my results:

1. Lengthen rod (less pressure) resulted in no flaring between 2 & 3 & 4th,
but slipping in 4th upon acceleration. All shifts occur sooner.

2. Shorten rod (more pressure) resulted in a flare between 2 & 3rd, however
no slipping in 4th when accelerating. All shifts occur later.

I am not sure there is a "happy medium"; I suspect my tranny is just worn.


Modulator pressure- a 1/4 turn at a time???:

"Try turning the modulator valve on the driver's side of the transmission clockwise. A search will tell you more about the modulator valve than you ever wanted to know If you're having trouble finding it, it's next to the neutral safety switch and has a vacuum line (should be black) going to it."
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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old

Last edited by MunichTaxi; 11-04-2007 at 10:46 PM. Reason: addition
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  #4  
Old 11-04-2007, 11:16 PM
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Location: Oklahoma
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I'm not exactly sure which "rod" you're talking about - I am assuming you are talking about the one from the carb linkage that connects to the transmission - which I have adjusted... Don't know if it is right though...

Also, I recently pulled the modulator to check it and it looked fine, but I can not figure out ow to adjust the thing. Shop manual says to use a 4mm hex, which I tried, but I couldn't get it to turn???

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #5  
Old 11-05-2007, 09:09 PM
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Location: Western Washington
Posts: 504
Modulator

It could be adjusted to maximum already; did you try to turn counter-clockwise?

These ar easy to remove, and inspect under a bright light. Might have some leakage of tranny fluid; use a rubber plug (or lint-free rag) to stop the flow.
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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old
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  #6  
Old 11-08-2007, 11:30 AM
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Join Date: Feb 2003
Location: roslyn, LI,NY
Posts: 445
slipping transmission and vacum

I had the same problem in delayed and rough shifts.On my 450sl 1977. Found that fouled spark plugs caused vacum loss. How long since tuneup or plug change? When I changed to new plugs, everything improved and now shifting normally. Good luck, Abe G
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  #7  
Old 11-10-2007, 08:11 PM
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Join Date: Feb 2003
Location: Oklahoma
Posts: 995
Had the car in a transmission shop all week and they figured out NOTHING! Waste of time - it is really hard to find someone local to work on this car w/o paying an arm or a leg!

They did check all the linkage and ruled that out as a problem and they did only measure 11 inches of vacuum at the modulator valve. I am thinking that it is a vacuum problem with the delayed shift but a local mechanic told me that the symptoms don't fit. He indicated that with lowered vacuum the transmission was under greater hydraulic pressure and I shouldn't have the type of problems that I'm having. He said it sounded like an internal problem - not what I wanted to hear, but I'm still not convinced this is not vacuum related. Just not sure now to check....?

I have recently rebuilt the engine and plugs etc. should be fine. Car is running great, other than this shift problem.
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #8  
Old 11-10-2007, 10:48 PM
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Location: Western Washington
Posts: 504
11 inches of vacuum.

If you have 11" of vacuum in the intake manifold, on a carb enginge, at idle, then your engine is 'sick'. Have you tried spraying solvent around the carb gaskets, to see if the rpm's increase?

My understanding of vacuum, at idle, is a minimum of 16",
and the closer to 19" the better. You can disconnect the 'retard' vacuum line on the dizzy, as a source.
__________________
1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old

Last edited by MunichTaxi; 11-10-2007 at 10:58 PM. Reason: spelling
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  #9  
Old 11-14-2007, 05:50 AM
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Join Date: Oct 2000
Posts: 55
Transmission slipping

I too have now started to experience the slippage at 20 mph and at 40. I installed a vacuum modulator which I think did the the trick. Except now the shifts are slipping at lower speeds. I totally destroyed the gasket that seals the vacuum line to modulator. and I probably need another. But where do you get one?
Someone stated that the mod valve is adjustable, I noticed also that half of the valve turned when installing. How does that affect shifting?
I also have a "miss" that makes me to believe that the vacuum line is not making a good connection. Since this line is metal all the way up to the intake. I think that the metal washers that I destroyed has something to do with this.
So, can you direct me to the washers, and help me with the adjustment.
Hope you can make sense of this.
Thank-you
Pococke
73 280
84000
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  #10  
Old 11-14-2007, 09:04 AM
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Location: Oklahoma
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I'm pretty sure my vacuum issues had to do with idle speed and timing - I increased the idle speed a little, setting it a little closer to 850-900 rpm with the transmission in drive. Vacuum increased to 16-17 inches at idle, measured at the rear carb.

As far as the modulator, I am also having trouble adjusting it. I can't get anything to 'turn'. Any crush washer should do the trick for sealing the vacuum connection.

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #11  
Old 11-15-2007, 09:51 PM
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Location: Western Washington
Posts: 504
Suggestion from cth350

The original linkage on the side of the motor is rigged up so that there is about 5mm of travel before the pedal movement impacts the carb. That's there to allow the transmission linkage to do its job.

I don't currently have the 5mm, so I am going to try an adjustment.
Right now there is 1-2 mm, so I will give this a try.
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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old
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  #12  
Old 11-16-2007, 09:01 AM
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Join Date: Feb 2003
Location: Oklahoma
Posts: 995
Questions:

Are you referring to the linkage on the passenger side of the motor that runs under the intake/exhaust manifolds?

Exactly where am I looking for/measuring 5mm of travel? Not sure how to make this measurement???

ryan
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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE
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  #13  
Old 11-16-2007, 10:00 AM
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Join Date: Oct 2006
Posts: 228
Is there any kind of adjustment provision for the bands themselves?
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  #14  
Old 11-16-2007, 08:34 PM
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Join Date: Aug 2004
Location: Western Washington
Posts: 504
Linkage adjust

My interpretation is:

Move the throttle linkage by hand, front to back.
The rod to the transmission should move 5mm.
At that point, the carb linkage will begin to open the butterflies, and rpm's will increase (from idle)

The rod is in the top right portion of this picture:
Attached Thumbnails
Transmission slipping (???) upon acceleration-b27001000055_0001ttt.png  
__________________
1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old

Last edited by MunichTaxi; 11-19-2007 at 01:19 AM.
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  #15  
Old 11-16-2007, 08:38 PM
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Join Date: Aug 2004
Location: Western Washington
Posts: 504
About the bands

Probably what is more important are the 8 friction discs inside. I, personally, have never heard of a band adjustment

If they are worn, it's rebuild time. Remember, these transmissions are very vacuum dependent. (= modulator)
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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old
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Old 11-16-2007, 08:38 PM
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