I have a 1983 300CD. Probably somewhere around 320000 miles. It’s acting very strange where the car will only attempt to shift into 4th once on a cold start and it’s rare that she will actually shift. The car will flare into I get back down to 2nd gear and then won’t try again until she sits and cools off. Once in the past month, I got her to 65 with 4100 rpm’s and shifted to S then back to D and she shifted into 4th. If I kept the throttle a little bit past maintaining 65 , she would climb higher in speed but if I gave it too much gas she would slip.

The vacuum modulator holds vacuum and she shifts very nicely , no jerking but you can feel it. She shifts from 2nd to 3rd at 20mph each time. I unplugged the kick down switch to see if that would help and it did not. I’ve been trying to read the transmission fluid level and I keep getting very different results. Yesterday I drove her for 30 minutes , parked on level ground , cleaned off the dipstick put it all the way back in and it read at the max line. Then today I checked it after the engine got to 90c and it read below the minimum line , then I drove for about 10 minutes and now it’s reading way past the max line. I guess you can’t double dip and get good results. I don’t really know. The engine was running in all these tests.

I’m totally confused as to what could cause the engine to only search for fourth once and never again.

Your help is greatly appreciated. Probably going to do a fluid exchange tomorrow and see if that does anything. Only had the car a month , the fluid doesn’t look burnt. No idea how much is actually in there tho.

Suggest starting with a fluid exchange as you mentioned with dropping the pan, changing the filter and draining the torque converter. I've had good success with Valvoline ATF in the red bottle.

Pretty good chance of a sticky valve in the valve body, I've had good luck with Lubegard for that on vehicles.

Please post your results.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

The dipstick is quite hard to read. If you double dip, generally you are getting oil that is left inside the tube and it is difficult to get an accurate reading.

I have read about filing a small indention at the full level mark on the dipstick; it is supposed to fill with oil and give a better reading. Have not tried it.

I believe your first reading of the day is accurate if done with a warm tranny.

OK fluid and filter changed with Lubegard added. I shifted into 4th but can't maintain any faster than 40 mph. as soon as it down shifts from slowing down, it will never try again until she sits. she is also shifting into 4th at 28 mph give or take instead of 40.

I want to rule everything out before I go for a R & R on a transmission. She is only a weekend car, going everywhere around town at 60 mph in 3rd gear isn't the end of the world if its for a few months. might consider Sun Valley Transmission and do it once for life as i would never daily the car.

Before considering a trans R&R, find a known good valve body and governor. They can be changed in the car.

Sun Valley is very good, they would probably answer an email concerning the problem.

If the other shifts are also early or stacked right after one another, confirm good vacuum to the modulator even replace the hose. If that doesn't fix it I'd try a modulator.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Frank, Do governors on these get sticky weights like GM's? Is it worth cleaning one?

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

There are two somewhat conflicting symptoms being presented:
1) Failure to initiate the 3-4 shift.
2) Slipping/flaring if a 3-4 shift is initiated, and slipping in 4th with increased torque.

Both of these symptoms could be caused by overall low hydraulic pressure. Low pressure could result from a worn pump, or from a defective pressure regulator in the valve body (VB). Clutch K2 (4th only) will slip if pressure is low, which could also result from a defective K2 accumulator. Hence the suggestion to change valve bodies, as a test.
The governor is less suspected, and can be changed separately from a VB change.

The car will shift into 4th with high enough RPMs the very first time it is driven and cycles through the gears. Once it is in 4th, you are pretty much stuck at 40mph without redlining the engine. once you hit the brake, it will shift back into third and from then on out will pretend to be a three speed until the transmission cools off. once you down shift out of 4th , it will make zero attempt from them on out to try and shift into 4th. there is also at clunking noise when braking and driving at low speed. I'm not sure if its the transmission or read suspension.

the transmission had no metal shavings or metal bits in the pan but the fluid was almost an engine oil brown and smelt a little burnt. it also had a glitter to it when light was shown on it.

I can get a used transmission from a junkyard that lists it as an A rating and pull the Valve body. is it an easy R and R job?

Glitter in fluid,( metal) Fluid burnt, not shifting into fourth, unless cold, slips, YES sounds
Like jammed valve body, but what other problems because of lack of maintenance?
Hard road some times, guessing, guessing, sometimes you could get lucky.
How much effort, time, money, are you willing to spend on guess work?
That is the only decision that needs to be made. Best of luck to you.

Checking transmission fluid, is to be checked WARM, in park. If car has not been driven
can place shifter in drive wait a few seconds than reverse than park.
pull out dip stick wipe reinstall wait a few seconds remove, check both sides the lowest
level is your true mark, still may need to check several times to be sure. Engine running.

I'll continue to look for a valve body , I reckon it has to come from a transmission that is the exact same model?

I'm leaning towards just having a three speed Mercedes until I have the money saved for a sun valley transmission that will probably outlive me.

Sun Valley would probably offer advice if you emailed them. They are good folks

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Sun valley says its very likely a clogged governor pressure filter in the rear valve body, going to search the forum to see if anyone has done this before. they said it was very easy to do once the rear valve body is out.

I've heard of that filter getting clogged but have zero experience with cleaning that filter. Please let us know what you find.

When R&R'ing the valve body cleanliness is critical as is torque, have an inch pound torque wrench on hand and valve body gaskets. Go slowly and keep track of all check balls and springs.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer