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Old 08-27-2007, 08:43 PM
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Location: Niceville, FL
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Tranny Flare and Vacuum Correlation Question

It has been a while since I had a question related to a diesel, but I picked up an '83 300D Turbo last week. As expected, it has a couple problems: (1) Under say a 1/3 depressed pedal the transmission shifts first to second just fine, second to third it flares a bit, third to fourth it sometimes takes forever to get there. Suspect at least part of the problem might be the modulator valve on the transmission. I know there are a lot of threads on this topic and I have read several of them. However, haven't been able to discern if the flaring is an overpressure or an underpressure problem.

Under a slower start, the shift from first to second is good, from second to third sometimes good and sometimes a little flare, from third to fourth when it doesn't flare it sort of just "drops" into fourth without the normal shift. Don't really understand what is going on here.

One thing that might be influencing the shifting is that the vacuum element for the front and rear passenger side door locks appear to be bad. Sometimes the doors will lock when using the key and sometimes they won't. I've got a couple on order and will replace them this weekend. Don't really want to start messing with the modulator valve until I have got what I believe are all the vacuum issues resolved. Sometimes they will all unlock using the key and sometimes the right side doesn't unlock. Weird.

Interestingly, when slowing and downshifting from second into first there is a clunking in the rear end. However, when I lock the doors using the lock on the driver's door and then slow it downshifts normally. Can someone enlighten me on the correlation between having the doors locked and it downshifting normally and leaving the doors unlocked and getting the clunking noise?

My son is the genius mechanic in the family and we'll meet in Baton Rouge this weekend for some quality family time while pulling the dash to replace the two center vacuum pods, adjust valves, replace door vacuum elements and whatever else we find that needs taking care of. However, would appreciate anyone who can enlighten on the vacuum and transmission issues above. As always, appreciate the help that's provided on this site!

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'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000
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Old 08-27-2007, 08:53 PM
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Both the transmission modulator AND the door locks work off of vacuum. Try disconnecting the YELLOW with RED stripe vacuum line and plugging the rubber connector that you pull the line from. This disables the vacuum locks and hopefully the vacuum leak. Test drive the car and see if the shifting improves. 2-3 flair is common. There is a shift kit modification that Mercedes sells that eliminated the flair.
The part # for the kit. 126-270-44-77
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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

Last edited by Motorhead; 08-27-2007 at 10:42 PM.
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Old 08-27-2007, 09:03 PM
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Motorhead,

I saw where the vacuum line comes into the modulator on the transmission, but find it strange that the clunk sounds like it's coming from the rear-end and not the transmission.

Will check out the kit, but the link you posted didn't work. Thanks again.
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'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000
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Old 08-27-2007, 10:44 PM
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I tried to re list the link and It doesn't work. Try searching "K-1 Install"

Can someone out there tell me why I CAN open up a link in my messages but when I copy and post it, It says "NOT FOUND"

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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