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Hard shift transmission

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HMS09's picture
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I recently purchased a 1984 300D Turbo. The transmission shifts hard and lurches in to gear from 1st to second. The harder I accelerate, the smoother the shift. Is this normal for these cars? Can I add an additive to smooth it out? Any help would be appreciated. Car has 246K Miles.

 

Thanks,

Harry

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BoiseBenzes's picture
Boise, ID
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1987 300SDL
1983 300DT
Welcome Harry! Just say no to

Welcome Harry!

Just say no to additives!!!!!!!!!!!!!!!!!!!!!!! x 1e57  And don't adjust ANYTHING--yet.

Along with the "bowden cable," our diesels use a "complicated" system to provide a vacuum signal, not normally found on a diesel engine, to allow the "gasser" transmission to determine when and how to up- and downshift. The system allows for smooth/comfortable shifts at light acceleration, and firmer/clutch-prolonging shifts at heavier acceleration.

A vacuum leak, typical with old rubber connectors, makes the transmission valve body always "think" you are flooring it, and commands the firm shifts. Under light acceleration they can then be quite jarring. Check on the left side of the transmission where the rigid line (plastic, usually black, about 3/16" 4 mm diameter), which heads down/aft from near the valve cover at #5, transitions to the modulator with about a 2" piece of rubber vacuum line. Also check the collection of small lines near the vacuum brake booster, but be "careful" (?) not to break anything with a too-vigorous--whatever that means--inspection. Some, me included, put tiny tie wraps (zip ties, whatever) on each rubber connector piece (whether straight, tee, or four-way) to snug it up. Additional sources of vacuum aggravation can include the lock system and climate control. If your locks, climate, and shutdown (does the engine stall quickly when keyed to "off"?) all work, it's probably just that line to the transmission. Too many other leaks will prevent sufficient vacuum from making it to the modulator, even if all the transmission vacuum stuff is otherwise perfect. 

A normal shift on one of these cars will be quite "firm" to someone used to, say, my Suburban.

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James Marriott 1987 300SDL (155k, mein Auto, 100% homebio 3 years) 1983 300D (221k, frau Auto, 100% homebio 3 years) 1997 Suburban (149k, gas/4WD towmaster 6000) www.engineeringworks.biz 1982 300SD junker, 265k

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Thanks Boise. I will stay

Thanks Boise. I will stay away from additives. In the meantime, until I can get it looked at by my mechanic, is there any danger in driving it under these hard shift conditions?

 

Thanks again,

Harry

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hard shift transmission.

I didnt know it was adjustable. Does it require tools or do I just adjust it by hand?? wHICH WAY WOULD i TURN IT TO SOFTEN THE SHIFT??

Thanks,

HARRY

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BoiseBenzes's picture
Boise, ID
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1983 300DT
If there's a vacuum leak,

If there's a vacuum leak, adjustments won't help. The first thing to do is restore the proper function, then go about making any NECESSARY adjustments. All of the below-listed items must work in concert, with a good vacuum systems, to effect a proper (read, "damn, that's firm!") MB shift.

If you are bound and determined to adjust something, you can mess with:

*** the bowden cable on the fuel linkage. Tightening the cable will make for a later/higher-RPM shift.

***the Vacuum Control Valve (VCV) on the side of the fuel linkage

***the modulator "tee" on the left side of the transmission. Out adjustment makes for stiffer shifts.

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James Marriott 1987 300SDL (155k, mein Auto, 100% homebio 3 years) 1983 300D (221k, frau Auto, 100% homebio 3 years) 1997 Suburban (149k, gas/4WD towmaster 6000) www.engineeringworks.biz 1982 300SD junker, 265k

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Robert Goodwin's picture
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1987 300SDL
1999 E300 Turbo Diesel
Hard shift transmission

You may be able to shorten this process a little bit. Pull the vacuum hose off the modulator. If transmission fluid is present, replace the modulator. If not, start at the modulator looking for your lost vacuum. Should be 10 inches or more. Many times, this condition is caused by a vacuum line that has been dislodged or one of the rubber connector hoses has rotted away due to age.

A national transmission shop would likely charge $2,000 to fix the problem. The $1 hose connector and the modulator would probably cost extra.

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hard shift transmission

$2,000 seems extremely high to switch out a modulator. One response I received said it was a DIY for an average mechanic. Another said 1 hour labor plus parts. The part is around $45 from what I have seen. I cant do the work myself because of age and other infirmities. However, 30 years ago, I would have jumped right on it..

 

One last question.....will this hard shift damage the trans or do I need to get it in the shop ASAP?

 

Thanks again,

Harry

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Robert Goodwin's picture
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1999 E300 Turbo Diesel
Hard shift transmission

A national transmission chain does not want to fix your vacuum issue for a hundred bucks or so. They want to get $2,000 out of you. Ever notice that a chiropractor is never done with you until you have forked over a total of $750?

 

I would not drive the car in this condition any more than absolutely neccessary. A long trip with few gear changes would be preferable to a short commute in heavy traffic. The harshness you are feeling is mechanical parts being stressed. Stress them enough and they will break.

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Thanks Robert, I will get it

Thanks Robert, I will get it to the shop asap.

 

Thanks,

Harry

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hard shift transmission

I wanted to get back to the group to give final results on my hard shift transmission. (84 300d Turbo). The exact diagnosis was "vacuum leak from vacuum source to transmission" Total cost was one half hour labor and no parts=$40.00. Transmission now shifts smooth as silk!!And as smooth as Boises surburban. Apparently, a vacuum hose had dislodged since there was no charge for parts as Robert and others suggested.

 

Thanks to all that responded.

 

Harry

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