300D Transmission problems

84 300D 280k miles on it. The transmission has been acting up, and now it will only shift at redline. I changed the fluid and filter a couple of weeks ago (per
Tiger's advice to everyone with transmission troubles), and while it does seem to be better, and shift smoother, it still only shifts at redline. I can, however, make it shift if I go to neutral, then back to "D" and it will go to the correct gear. I feel like this could be ruining the transmission though, so I don't want this to be a long term solution. I originally thought it was the vacuum modulator, that I saw had come disconnected from a loose vacuum connection at the modulator. I fixed that and it still doesn't work. I think that I have tracked down the problem, but I would like some advice on how to go about fixing it, and whether this is most likely the cause. I had an injector (or two) get clogged just before this happened and was flooring the pedal to help clean everything out one night. Unfortunately, my kickdown solenoid has a short or some kind in it and will blow a fuse whenever it is depressed. I thought this was the cause, but I disconnected the switch and it did not fix the problem. (I did a diesel purge later and this helped tremendously, I'm doing another next week to see if I can get some vibration out of the engine). The car does shake while driving, but I attribute this to the engine being out of tune rather than the transmission, could the shaking be linked to the transmission issues? The motor mounts appear to be good, but the engine shock on the driver side looks to be at its end of life. I believe the problem is in the control pressure cable. I checked it after reading many repair articles that mentioned it, and it is definitely not correct. It has slack in it all the time, and appears to be stuck in the "full throttle" position. I am wondering if I broke the cable (when flooring the accelerator), or if I caused the mechanism that it is attached to to be stuck? So, what do I do to fix the control pressure cable, and what are the implications of the kickdown switch being bad, or disconnected?
Thanks, DougS
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I think you just answered your own question when you checked the pressure cable... and seems to be loose all the time and seems fully engaged as in full throttle. This will cause the transmission to stay full on until it senses change in throttle position.
Drop the pan, trace where that cable comes into the tranny... and you can see that mechanism... that cables comes into the transmission and pulls on a cam which pushes the 'green' piston in. See what is going on in this section.
If the piston is stuck , you should be able to pull it out and I believe it has a clip and bolt to hold that piston from coming all the way out. You can remove that plate and pull the piston out more.. and there is a spring underneath that piston... make sure the spring is good.
Any chance that 280,000 miles transmission is rebuilt?
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hanks for the response guys. I haven't checked the cable at the transmission yet, but I will when I jack it up to change out the brakes this week. Like I said, I narrowed it down pretty close doing all the standard (easy) stuff first. If at all possible, I'm gonna try and fix this without dropping the transmission pan, but I think that will be the final route. I don't know about the transmission being rebuilt or not, I've only had the car for a little over a year, and there were no service records. The transmission does shift very confidently though, and seems to be very strong. Overall, the car is in excellent condition, even the dash is still in good shape. I plan on trying to get rid of the shake first hopefully with a good thorough injector cleaning, and I will adjust the valves as soon as I get some wrenches to do that job. (Any chance someone wants to loan me a set?) Concerning the fuel rack damper, I don't think thats the cause, I've read about that pretty often, but I could be wrong.
Thanks again, DougS
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At 280,000 miles, you really do need to change the timing chain and tensioner... and guides. Your timing gotta bo so far off by now.
Same for the timing chain on the fuel distributor... best left to qualified mechanic.
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After you fix or free the pressure cable, its correct adjustment is done:
Pry the cable's end socket off of its peg on the throttle linkage on the engine's top rear. Gently pull the cable and allow it to return to its natural, default position.
The cable is correctly adjusted IF it's socket can be reattached to its peg - WITHOUT pulling or pushing the cable. If not, adjust the cable's mounting nut to lengthen or shorten the cable so it's socket can be attached to its peg without pulling or pushing the cable. That's it.
A motor and transmission that's done 280K miles is no candidate to drive to red line - unless you're out to destroy it. Adjust the valves and add some injector cleaner to the fuel to smooth it out. And, if it shakes at idle after some higher speed driving, you should tighten (1/4 turn) the fuel rack's damper pin / bolt on the aft end of the injection pump. Its function is to dampen the fuel rack's vibration oscillations.
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