240D potential transmission failure - PeachParts Mercedes-Benz Forum

steeleygreg · #1 01-20-2014, 12:17 AM

I suspect that what I have is a auto trans failure and I'm looking for wisdom from this collective group of guru's. The car is an 83 240D. So here is the story.
About 4 months ago this trans problem first appeared. I went to the store, put the car in park and left the engine running. After returning I put the shifter into drive and the car would not move at all. I cycled through the all gears which didn't produce any movement in the car. I turned the engine off and let the car sit for about 5 minutes. Once I re-started the engine, I was able to drive home without a problem. Checking out the VCV it was discovered to be bad, so I replaced it. I installed both a vacuum and pressure gauge to assist in both knowlege of what the trans was doing but also hopefully if this problem re-occured I could trap something. This was back in september of 2013.
Fast forward to 1/18/2014. I was headed home and sitting at a stoplight. When the light turned green, I pressed the GO pedal and as the rpm's increased, the car stay motionless. Looking over at the pressure gauge, the reading was 0. It should normally be around 20 psi at idle. I tried the same trick which had worked 4 months ago and turned the engine off and let it sit for about 2 minutes this time. After re-starting the car, I got pressure and quickly tried get the car moving. It did move but soon started slipping with a fluctuating needle on the pressure gauge and then went to 0. Stepping on the pedal resulted in just the engines rpm's going up. This happened a few other times going home which was about 1/4 mile away, but I got home.
Once in the driveway, the pressure again went to 0. I was hopping that the fluid levels where low, but the opposite occured. The fluid was about 1 to 2 inches higher on the stick than it should have been. The fluid looked pink and didn't smell. I didn't give the fluid level another thought until today. More about that in a little bit.
Today upon starting the car, the pressure went up to 20 psi and was steady as it has been since installing the guages a few months ago. I was able to shift through all gears and moved the car forward and backward in the driveway. All of a sudden the pressure dropped to 0 resulting in no power to the rear wheel. Before the pressure dropped to 0 and was holding steady at 20 psi I checked the fluid level at idle and in drive. It was right on the mark between full and add.
I have my suspicions and I have one more pressure check to do and that is the working pressure. I'll get a connector and a gauge to do this today, but as I've mentioned I'm looking for the collective wisdom of the forum.
Here are pic's of what I've found so far:
Pic3G1 shows vacuum to the VCV and pressure at idle
Pic5G2 shows vacuum going down and pressure starting to rise as rpm's are increased to around 1k.
Pic6G3 shows vacuum on acceleration but pressure needle started fluctuating and dropping towards 0. After the pic was taken the needle moved back to 20 psi.

Thanks you in advance

whunter · #2 01-20-2014, 06:46 AM

Isolate the modulator
Use your hand pump to verify the modulator holds vacuum.

I don't recall if you replaced the filter, could it have fallen off?

The symptom sounds suspiciously like several recent units that had a broken spring in the valve body.

Serious varnish on the valves in the body can mimic this issue.

Failing gaskets between the valve body and transmission case can mimic this issue.

Loose bolts holding the valve body to transmission case can mimic this issue.

.

steeleygreg · #3 01-20-2014, 09:06 AM

Very interesting. Can the valve body be rebuilt or should a new one be used ?

As for the modulator, I installed a new one back in October after the first episode of the car not moving when shifted into drive. The original was bad. I have changed the tranny fluid but not the filter.

Once I get the car in the garage, I'll drop the pan and let you know what I find.

charmalu · #4 01-20-2014, 10:36 AM

You mentioned the fluid was 1- 2 inches higher on the stick, and was pink.
Should be red.

Maybe the Transmission Cooler in the bottom of the Radiator is leaking Coolant into the Transmission.
What does the Coolant look like in the Radiator?

Charlie

steeleygreg · #5 01-20-2014, 12:54 PM

Radiator fluid is still green. I suspected fluid leaking from the radiator in to the trans also. Didn't see any traces of red dots floating around in the fluid.
As for the color of the tranny fluid, charmalu your correct in it is red, just depends on how the sun light hits the dip-stick.

whunter · #6 01-20-2014, 06:50 PM

Quote:

Originally Posted by charmalu

You mentioned the fluid was 1- 2 inches higher on the stick, and was pink.
Should be red.

Maybe the Transmission Cooler in the bottom of the Radiator is leaking Coolant into the Transmission.
What does the Coolant look like in the Radiator?

Charlie

I suspect an internal leak sucking AIR = making FOAM.
The fluid level is random high, then comes back down to normal level = common symptom of internal AIR on the suction side = making FOAM.

.

steeleygreg · #7 01-20-2014, 06:58 PM

If there is air on the suction side, wouldn't that indicate a clogged filter ?

whunter · #8 01-20-2014, 07:11 PM

Quote:

Originally Posted by steeleygreg

If there is air on the suction side, wouldn't that indicate a clogged filter ?

Possible, but I can't verify from here.
Change it, while you are in there. Minimal cost fix.

.

steeleygreg · #9 01-28-2014, 01:38 AM

Quote:

Originally Posted by whunter

Isolate the modulator
Use your hand pump to verify the modulator holds vacuum.

I don't recall if you replaced the filter, could it have fallen off?

The symptom sounds suspiciously like several recent units that had a broken spring in the valve body.

Serious varnish on the valves in the body can mimic this issue.

Failing gaskets between the valve body and transmission case can mimic this issue.

Loose bolts holding the valve body to transmission case can mimic this issue.

.

Roy, can the broken springs you mention be replaced ? Can a solvent be used to clean varnish on and within the valve body, or is this a bad idea because it might introduce other problems ?

whunter · #10 01-28-2014, 07:40 AM

Quote:

Originally Posted by steeleygreg

Roy, can the broken springs you mention be replaced ? Can a solvent be used to clean varnish on and within the valve body, or is this a bad idea because it might introduce other problems ?

Trans-x
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I hope this is not the cause
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I seriously doubt the following could be your issue, but it is worth checking.
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.

steeleygreg · #11 01-29-2014, 05:40 PM

Ok, I've got a gauge mounted to the working pressure port. The car was run for about 5 minutes. The ambient temperature was 10 degrees so I guess that constitutes as cold. Also checked vacuum at the VCV and it was holding Hg, as per WHunters request.
The following are initial findings:
Pic1 - shows the vacuum test on the VCV
Pic2 - shows the working pressure port in the upper right corner of the frame.
pic3 - shows the vacuum, modulating and working pressure at idle.
pic5 - shows the vacuum, modulating and working pressure as the GO Pedal is being depressed.

I could not get this to fail, meaning getting the modulator pressure to drop to 0. I moved the car out of the garage and up & down the driveway a few times and still it did not fail.
I'll do some more testing tomorrow before I drop the pan.

97 SL320 · #12 01-29-2014, 07:48 PM

Finally, someone using logic and pressure gauges to diagnose a trans problem.

Just so we are using the same terminology, Working Pressure = Line Pressure? ( the highest pressure in the trans, it comes directly from the front pump. )

Random high fluid levels that don't have obvious foaming are caused by the torque converter not being charged. ( filled with fluid under pressure ) This one of the reasons for no drive and can cause poor acceleration until it fills.

Given you have a drop in modulating pressure and seemingly loss of torque converter charging, I'd lean towards a line pressure regulator issue. Loss of line pressure will result in loss of pressure to apply clutches / bands, it takes a while for the converter to empty so the fluid rise might not be immediately apparent. Shutting the engine off allows the pressure regulator to move towards full pressure.

Does this trans still have a rear pump installed? There are a few check valves in the system to prevent front pump pressure from spinning the rear pump
when it is disengaged. However I'm not sure there would be a large enough internal leak to cause the symptoms you are having.

As for fluid color, if you can see through it you don't have much or any water mix. Water will cause the fluid to become opaque and more towards white. Sometimes in early stages of water mix, you will have bubbles that won't pop. ( water droplets floating in the oil)

Stretch · #13 01-30-2014, 03:56 AM

Quote:

Originally Posted by 97 SL320

Finally, someone using logic and pressure gauges to diagnose a trans problem.

...

He's a good chap who has responded well to behind the scenes emails!

Quote:

Originally Posted by 97 SL320

...

Just so we are using the same terminology, Working Pressure = Line Pressure? ( the highest pressure in the trans, it comes directly from the front pump. )

...

Yes that's correct

Stretch · #14 01-30-2014, 03:58 AM

Picture three - engine at idle

Where was the gear selector?

The data for the test is =>

If it was in "D" the working pressure is possibly good - I need to check the exclusions on the original document though

The modulating pressure is too low.

Stretch · #15 01-30-2014, 04:22 AM

Sorry I forgot to say.

The data needed is for the .117 listed above the highlighted .118 data in the borrowed from someone else picture

You need to drive the car for quite a bit to get the transmission oil warmed up before you start making these measurements - needs to be at the operating temperature (I'll look that up as well)

You need to tell us more about the gear selected - pictures show the position when pressing the "GO" pedal are nice but not relevant to the data in the FSM. If you do the stationary tests in "D" and in reverse as described above and the data is good it is then worthwhile doing the tests at 65 kph.

(The main point of making measurements is to compare with FSM data - if however you loose all pressure at some point then you know what that is!)