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  #1  
Old 04-07-2004, 11:01 PM
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Unhappy Auto tranny failure on the way?

I first started noticing last Friday that under lighter acceleration the auto transmission in my '85 300D started shifting strangely. It would shift normally from 1st to 2nd, but my 2nd to 3rd would occur and then it would almost instantly shift to 4th. It would not spend more than maybe a split second in 3rd. Under heavier acceleration it shifts normally through all gears. It never did this before but it's been doing it every day I've been driving it since Friday. Am I looking at needing another rebuild soon? It's got about 115K since the last rebuild. Has anyone in the forum ever tried rebuilding one on their own?

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84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012
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  #2  
Old 04-08-2004, 12:19 AM
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Check the bowden cable? 85 had a lot of updated parts, but funky shift sequencing has been a problem with these things since day one as far as I can tell reading and talking to people, especialy at light throttle. I'd check the bowden cable and change the fluid and filter. Even if it IS wear, if it's not sliping, tighten up on the cable a little, you just cannot set these transmissions up to OE specs when they have a lot of miles on them. Perhaps this is why there so adjustable..

Mine is original at 253K, is that some kind of record yet?
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  #3  
Old 04-08-2004, 09:17 PM
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It doesn't appear to be slipping. I didn't really check the bowden cable adjustment but I the last time I had the valve cover off, which was a few weeks ago, it seemed to be tight enough with no apparent slack. It's wierd that it started doing this all of the sudden. I haven't changed my driving habits. It seems to shift fine when I acclerate with the pedal mid way down anything less and I get the almost instant 2nd to 4th shift. The fluid seemed fine, it still has a nice bright red color with no odd odors just as if the fluid was new. I think it was changed not long before I bought it from the PO over a year ago.
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84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012
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Old 04-08-2004, 09:56 PM
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Quote:
Originally posted by lietuviai
It doesn't appear to be slipping. I didn't really check the bowden cable adjustment but I the last time I had the valve cover off, which was a few weeks ago, it seemed to be tight enough with no apparent slack. It's wierd that it started doing this all of the sudden. I haven't changed my driving habits. It seems to shift fine when I acclerate with the pedal mid way down anything less and I get the almost instant 2nd to 4th shift. The fluid seemed fine, it still has a nice bright red color with no odd odors just as if the fluid was new. I think it was changed not long before I bought it from the PO over a year ago.
hmmmmmmm... valve cover off? How soon after pulling/replacing the valve cover did the tranny issue start? Look to see if there is anyway this could be connected?
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  #5  
Old 04-09-2004, 10:38 AM
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I think that there have been about 4 or 5 weeks between the valve cover removal and the tranny problem so I don't think that the two are related. I'm hoping that all it needs is an adjustment. I don't notice the problem until the car has had a chance to fully warm up though.
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  #6  
Old 04-09-2004, 07:09 PM
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Quote:
Originally posted by lietuviai
I think that there have been about 4 or 5 weeks between the valve cover removal and the tranny problem so I don't think that the two are related. I'm hoping that all it needs is an adjustment. I don't notice the problem until the car has had a chance to fully warm up though.
85 does have a temp switch to alter shifting relative to engine temp. The specifics I'm not sure of, but it has one. Might be worth a look.

Actually I know the 86 SDL has one, but I'd bet the w123 got it in 85 with that blue vacuum amp as well.
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  #7  
Old 04-09-2004, 10:41 PM
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I would try adjusting the Bowden cable first.... sounds like it might be too loose. How does it shift (soft, hard, somewhere in between)? I don't think there is any kind of temp switch that is relative to the shifting, never seen anything like that anyway. I've had good luck adjusting my shifting by adjusting the cable.
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1985 300D Turbo ~225k
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  #8  
Old 04-09-2004, 11:25 PM
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Quote:
Originally posted by Wasuchi
I would try adjusting the Bowden cable first.... sounds like it might be too loose. How does it shift (soft, hard, somewhere in between)? I don't think there is any kind of temp switch that is relative to the shifting, never seen anything like that anyway. I've had good luck adjusting my shifting by adjusting the cable.

http://www.mercedesdismantlers.com/diesel_vacuum_system#Diesel%20Vacuum%20System%20Troubleshooting

If you look at the last vac diagram for the 603 you'll see the temp switch. I *think* it cuts out boost from the vac amplifier till a certain temp. I know the SDL had this, and the photos of an 85 617 I have show what looks to be the same kind of vacuum switch in a similier arangement. Just semi-educated guessing though, I can't find any tech docs on the 85 models systems, my FSM seems to pre-date them. Who knows what was changed on them.
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  #9  
Old 04-10-2004, 04:20 PM
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Hmmmm..... I don't think I've ever run across that on mine. I'll have to go look at it. I'm not saying it isn't there (never looked specifically for it before) or it may have been removed before I owned the car... or it may be different in the same model year even. Looks like it's just a wire running from the temp sensor to some sort of vac thingy?
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1985 300D Turbo ~225k
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1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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  #10  
Old 04-10-2004, 06:46 PM
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Quote:
Originally posted by Wasuchi
Hmmmm..... I don't think I've ever run across that on mine. I'll have to go look at it. I'm not saying it isn't there (never looked specifically for it before) or it may have been removed before I owned the car... or it may be different in the same model year even. Looks like it's just a wire running from the temp sensor to some sort of vac thingy?
My info is sketchy at best, I know the SDL got it, and the w124 diesels. And the 85 SD and D had the vacuum amplifier, and I believe that temp switch was part of that whole system. Who knows what's been done to a given car during it's lifetime though.
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  #11  
Old 04-10-2004, 07:02 PM
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wolf_walker,

The only temp probe on the thermostat housing on my car runs the wire over to the right side of the car and the wire goes into one of the covered bundles beside the expansion tank and appears to run into the cabin behind the glove box. I don't think anything has ever been modified that has anything to do with that probe..... wire is intact. I would bet that there was either a change sometime in the model year or the W123's never had that gizmo. Would be interesting to know what changes were made mid-year on these cars, I bet there are a lot of minor ones.

lietuviai,

Any progress in getting it to shift better? I'll post some transmission troubleshooting links if you want, should be able to do a search and get most of them though.
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1985 300D Turbo ~225k
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1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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  #12  
Old 04-10-2004, 07:14 PM
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Quote:
Originally posted by Wasuchi
wolf_walker,

The only temp probe on the thermostat housing on my car runs the wire over to the right side of the car and the wire goes into one of the covered bundles beside the expansion tank and appears to run into the cabin behind the glove box. I don't think anything has ever been modified that has anything to do with that probe..... wire is intact. I would bet that there was either a change sometime in the model year or the W123's never had that gizmo. Would be interesting to know what changes were made mid-year on these cars, I bet there are a lot of minor ones.

Does yours have this? To the left is a vacuum relay, much like the overboost relay. I'm ASSuming the 85 has the overboost relay in the normal spot on the firewall, and this is something else. It looks like what the diagram I posted a link too shows on the OM603.

Really would love to have some 85ish sercvice docs.
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  #13  
Old 04-20-2004, 07:36 PM
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Follow up after adjustment of bowden cable.

I adjusted the Bowden cable last Saturday and it didn't seem to help my shifting problem. I still wants to skip 3rd and go into 4th gear from 2nd. It still only momentarily stays in 3rd for a split second and goes into 4th on lighter acceleration. It doesn't do it all the time but its got my attention and I'm worried about it. It shifts fine if I accelerate a little harder but I'm trying to keep my fuel consumption down with the price of diesel the way it is now. The Bowden cable adjustment has only helped my down-shifting a little.
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84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012
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  #14  
Old 04-20-2004, 08:26 PM
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Forgot about this thread!

wolf_walker,

I have something that looks like that and is in the same place but the vac lines from it run to the wastegate on the turbo..... so I'm assuming it's the overboost relay. Sounds like stuff on 85's are in different places than other cars!
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1985 300D Turbo ~225k
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1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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  #15  
Old 04-20-2004, 08:32 PM
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I would still change the fluid and filter even if it looks good at this point..... sounds like there might be some crud or something plugging something causing the funny shifting. I would especially do it since you don't know it was changed for sure, just taking the PO word for it.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k
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