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Transmission warning signs?

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mrotondi's picture
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At the very end of a 200 mile trip with my 1987 300TDT I stopped at a friends house for a second left the car running then jusmped back in an put it in gear. The transmission shifted hard between gears and stayed in gear too long. It also seemed like it did not shift into over drive or reved up higher than normal on the highway. I used it the next day and same thing for a short trip. When I used it again a while later the transmission seemed to be back to normal with smooth shiffting around town and on the highway. Is this an indication of something? Bad Modulator valve? Should I have a part on hand to change out? I am going on a very long trip in a couple of weeks 22 hour drive. Any suggestions? Thanks

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1987 300TD

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stricht8's picture
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Re: Transmission warning signs?

My transmission knowledge is severely lacking however, from my experience, the early sign of a worn MB tranny is hesitation going into reverse.

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Re: Transmission warning signs?

mrotondi;194985 wrote:
At the very end of a 200 mile trip with my 1987 300TDT I stopped at a friends house for a second left the car running then jusmped back in an put it in gear. The transmission shifted hard between gears and stayed in gear too long. It also seemed like it did not shift into over drive or reved up higher than normal on the highway. I used it the next day and same thing for a short trip. When I used it again a while later the transmission seemed to be back to normal with smooth shiffting around town and on the highway. Is this an indication of something? Bad Modulator valve? Should I have a part on hand to change out? I am going on a very long trip in a couple of weeks 22 hour drive. Any suggestions? Thanks

Hard to say but needless to say it's not good. At the very least I'd drop the pan and have a look at the fluid and filter. Make sure it's full and the filter is clean. The condition of the fluid should also give you more information about the condition of the internals.

Finally, what is the mileage on the transmission? Despite what people like to think -- no one wants to deal with cost of overhauling an automatic -- automatic transmissions have a lifespan of about 150k miles. A bit more on the diesels because they are generally less powerful and thus impose less force on the transmissions than would a large gasoline motor -- say closer to 200k. But if the car is at these mileages, you should start to budget for overhaul.

But first things first. Check the pan and fluid, then go from there. But I wouldn't take the car on a thousand mile roadtrip without finding out what is going on.

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Re: Transmission warning signs?

Could be the modulator, but it's cheaper and easier to check for, and solve, an intermittent vacuum leak. The hard plastic black line running down to the tranny from near the rear of the valve cover has a 2"/50 mm soft line at the modulator; check/change that. While changing that, use your mityvac to see that the modulator is holding vacuum.

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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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Re: Transmission warning signs?

I would be checking and rechecking vacuum all the way back to the source before I would spend a dime.................unless it's for someone else to check the vacuum. May or may not be the problem, but it is a good candidate and checking it is cheap as it requires no disassembly or parts.

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Re: Transmission warning signs?

Does any one have a pic of this area, the modulator and line? or diagram? so I know what I am looking for? 220k on the car. Fluid looks good. Not sure about fluid or filter change history I've owned it since 207k

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Re: Transmission warning signs?

You transmission has but one plastic vacuum line going to it. It is attached to the modulator which is on the driver's side of the transmission. Round thing, plastic hose, 90 degree rubber hose elbow.

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Virginia Beach VA

87 300SDL
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