Tranny shifting waay too soon
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Tranny shifting waay too soon - 7/21/2006 3:03:23 PM
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danpayton
Posts: 32
Joined: 7/18/2006
Status: offline
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Ok so my 81 300sd shifts way too soon.. by the time i get ti 25 miles an hour its already in overdrive. I adjusted the tranny shift cable - its all the way out.. but it still shifts way soon unless i have my foot in it hard
I have the cable adjusted so its at the end of its travel at wide open throttle
Any thoughts?
thanks!
-Dan
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RE: Tranny shifting waay too soon - 8/8/2006 10:39:05 AM
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PerkHouse
Posts: 5
Joined: 8/7/2006
From: High Point, NC
Status: offline
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Have you tried driving another 300sd from the same year to see if it's normal response for that year/model? If not, I'd suggest doing that first before assuming there is a problem.
If this is your first diesel, you might be babying it too much and if it has a turbo, you can actually damage the turbo by trying to drive for fuel economy.
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Brian
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RE: Tranny shifting waay too soon - 8/8/2006 2:27:08 PM
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danpayton
Posts: 32
Joined: 7/18/2006
Status: offline
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LOL well im pretty sure im not babying it...... BUT when im into the pedal it does seem to shift with more seperation between 3rd and 4th... Thats a good idea to try drving another one. I'll give it a shot! Thanks!
Another question - my tach isnt working as of yet.. so whats a good cruising speed on the highway? is 80 too fast? I drive it about 250 miles the other day and if i went even like 85 for very long it seemed to heat up more then just keeping it bvetween 75 and 80
thanks!
-Dan
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RE: Tranny shifting waay too soon - 10/14/2006 1:09:12 AM
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Mcgyver01
Posts: 7
Joined: 9/29/2006
Status: offline
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Hey did you ever figure this problem out? I have an 80 300SD that does the same thing. Shifts from 1st to 2nd and then like 3 seconds later shifts to third. I don't think I have an overdrive. There's a long pause between gears as well. I'm assuming I need to adjust the bands in the transmission. Has anyone done this? The shifting point though has me baffled
I repaired most of my dash issues but my tach isn't working either. I ran from OH to NC and it seemed to be screaming at 80MPH. It didn't heat up and used 26 gallons on a 500+ mile trip which I don't consider to be too bad.
Mcgyver01
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RE: Tranny shifting waay too soon - 10/14/2006 10:57:21 AM
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timberfield
Posts: 72
Joined: 8/9/2005
Status: offline
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As for the shifting issue. I'm not 100% sure, and you should check a manual, or another member may be able to clairify. I think the cable from the throttle linkage to the trans works backwards. In otherwords, turn the adjustment in (make the inner cable long) to increase the shifting duration. One problem I have come across a few times is the throttle kickdown switch going bad. I is located under the gas peddle.
Cruise speed of 80 MPH is okay. Actually, that is where the 300SD is most efficient. I have run from NY to Miami a couple times, and 80 gets the best gas mileage. You should be in the neighborhood of 3000 RPM's @ 80 MPH. I have had mine up to 100 a few times for short spurts, but would not recommend over 85 for an extended period. Watch your temp guage, that will indicate if the engine is working too hard.
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83 240D 130K
85 300SD 310K
84 300SD 131K
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RE: Tranny shifting waay too soon - 10/14/2006 8:44:52 PM
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carnut
Posts: 157
Joined: 3/31/2006
Status: offline
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Log onto www.dieselgiant.com and read about vacuum issues and how its regulated on a diesel. Great site.
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RE: Tranny shifting waay too soon - 10/23/2006 10:05:48 PM
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Drrty240D
Posts: 160
Joined: 7/30/2006
Status: offline
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Have you tried adjusting the Automatic Transmission Modulator Valve?
On the right (passenger) side of the transmission toward the rear you should see a round device with a vacuum line attached to the top cap. It almost looks like a very large oil pressure sending unit that is screwed into the transmission. Use a needle nose pliers to grip the squeeze clamp and disconnect the vacuum cap, usually made of white plastic. Inside the modulator valve you'll see a metal key.
Make a note of the current position of the key and then pull it out slightly. In order to make the transmission wait longer between shifts you need to turn the key, in one position increments, to the right until the desired shifting is achieved. If you are brave you can try advancing two positions at a time, but make sure you road test after every adjustment.
If this doesn't help, or you are not noticing definite changes in the way the transmission shifts as you make valve adjustments check for a vacuum leak between the valve and the engine, or you can try replacing the AT mod valve altogether. Cost is about $43 from www.thepartsbin.com.
< Message edited by Drrty240D -- 10/23/2006 10:10:03 PM >
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RE: Tranny shifting waay too soon - 10/25/2006 1:34:13 PM
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carnut
Posts: 157
Joined: 3/31/2006
Status: offline
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Its been my experience that the modulator doesn't go out of adjustment but the rod linkage can, as well as vacuum leaks developing causing shifting problems. My point is the modulator should be the last thing adjusted. Verify vacuum control circuit is working as designed first, then throttle rods adjusted to spec then lastly adjust the modulator to fine tune to your preference.
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1981 300CD. had a 72 280SEL 4.5, had a 66 250S
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