tranny problem

Got a problem with a 4 speed auto in an 1982 300D. Taking it easy, all gears shift normally except from 3rd to 4th. I get a flair where the rpm's increase quite a bit before it will "catch" and hold in 4th gear.
Normally, I've been letting off the gas when it changes into 4th so it doesn't flair.
Here's the kicker. If I'm going 60 mph in 4th gear and I floor it, the tranny will kick down into third gear. It will shift flawlessly into 4th with no flair at all when I hit 70-75mph.
What could cause this? Makes no sense to me.....
Roger
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You need to install a repair kit in the valve body. I am home right now, info is at work.

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Go to http://boostnbenz.1baddsm.com/DIY / and they go into great detail on adjustments,repair, and flair on W123 diesel !
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Another poster gave you a great link to go to. K1 is the 2/3 shift http://transmission.articles.mbz.org/k1 / If I remember right, K2 on the other end is 3/4.

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Flaring is usually cured by either a fluid and filter change or a rebuilt transmission.
Suggest your box needs the former, especially since it does shift briskly at full throttle!
The fluid and filter ought to be changed after 30K miles, you may also want to drain the torque converter so all the old fluid is drained and replaced.
That ought to fix it for now.
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Your car is a diesel which is controlled by vacuum. Find the vacuum pump on the front of the engine and the vacuum hose coming off the top. If it goes into an "H" shaped rubber fitting, remove the two left tiny tubes from the fitting, and plug the left openings. This will greatly increase the vacuum going to the tranny and improve things.

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