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  #1  
Old 04-05-2001, 02:38 AM
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Location: Houston, TX
Posts: 27
Original problem was what I guess they call that "3-4 flare". While accelerating normal, the transmission will practically skip 3rd gear and go to fourth. Read in several places that maybe the modulator valve is going bad.
Replaced modulator valve,(new one looked kind of different - old one had this rod with a spring around it sticking out the end that goes into the transmission, new one didn't have this at all; made sure it was correct part, mb said it was, but couldn't or wouldn't explain why there was a difference) Now I'll try and accelerate normal, and before I even reach about 20 mph, I'm already in fourth gear.
Checked vacuum, 20Hg, good from what I hear. Checked the three way valve on top of the valve cover, good. Checked the vacuum valve on the ignition pump, and it's good. Made sure vacuum was getting down there to the valve, and it is. I know there's an adjustment on the modulator valve, but how to set it? I tried several positions on it and test drove each time, but with no avail. Noticed from Haynes manual that I didn't have a "throttle linkage control pressure rod". Could this have anything to do with this? And nothing is hooked up to that 'bell' on top of the injection pump. Never was able to downshift from flooring the accelerator, even after intentionally hitting that switch behind the pedal. I'm pretty sure the tranny oil is at correct level.
Can anyone help? 123k miles on car. Have this nasty feeling tranny is going to have to be replaced.
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'80 240D (sold) wish I didn't.
'85 300D (240K miles)
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  #2  
Old 04-06-2001, 01:54 AM
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Give this a try

Greetings Koon Koon,

So that we are on the same page, is this car somewhat new to you, or has this problem just occurred out of nowhere?
The reason I am asking is that it seems I had a similar problem on my 300TD wagon, and am slowly correcting it while adjusting and fixing other non tranny related items. I know it sounds dumb or somewhat far fetched, but to start with, MB diesels start out in second gear unless you drop the shifter to it's lowest setting manually. Trust me, you only get about 10 mph out of first gear, then shifting to "s" you get second and third gear, and by 40 mph it's asking you to shift to fourth. After doing a linkage adjustment, it didn't change things at all so I lived with it until I started finding other things out of adjustment that would cause the engine to lag and not build up for the next shift. I replaced a leaking vacuum diaphragm on the vac pump, I reset the valve timing back to specs, and now I am in the process of getting my IP properly back into injection timing specs, and that has helped the most by suppling more power to the tranny to make it do the job correctly. Check the above items before assuming the tranny is gone, it's probably not. The part you describe as your replacement vac modulator from Benz, was it given to you from the chassis number of the vehicle or from the engine number found on the block? Just a thought that the engine had been changed out at one time, and a different year engine and tranny were reinstalled, thus the part would also be wrong for that year tranny.


Charles
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  #3  
Old 04-07-2001, 10:20 PM
engatwork's Avatar
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my 300D "project" car

does the same thing. I will be trying to figure it out over the next few weeks. If you shift manually it does great and it does not leak fluid.
Jim
'85 300D 218k miles
'95 E320 104k miles
'97 CRV 82k miles
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  #4  
Old 04-07-2001, 10:46 PM
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Check out this site

Greetings,

Please check out the following site to troubleshoot your tranny and modulator valve.

http://www.mbz.org/articles/trans/


Charles

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  #5  
Old 04-07-2001, 11:16 PM
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Your problem goes back to your modulator replacement. They have made some changes to the modulators but the diaphram has to have its whole linkage to work the actual piston inside. The pin and spring must be moved from one modulator to the other.
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  #6  
Old 04-07-2001, 11:58 PM
Larry R
 
Join Date: Feb 2001
Location: Oklahoma
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Transmission problem

I hate to be the bearer of bad news but my 1984 190E was doing the same thing. Unless I got taken it had to have a rebuild. It does work good after the rebuild.

Larry
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  #7  
Old 04-08-2001, 02:32 AM
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linkage or no linkage, that is the question

Thanks everyone for the replies. I feel like a baby elephant, and the whole herd is taking turns to take care of me. TXBill, do you still have your '79 240D? If so, does it have a throttle linkage control pressure rod? Or anyone with experience with an '80 240D know if that model year came with one of those? I just don't understand how the previous owner can just throw out a whole linkage. I'm going to go to a junk yard tomorrow and see if I can find a linkage in another W123. The thing is that I don't see any extra places for any kind of linkage to hook up to or mount to. No extra ball joints, mounting holes, brackets, or anything. But I still haven't checked out the left side of the transmission to see if there's a control pressure lever. Can-do Charles, I've already read the site that you suggested, but thanks anyways. Everyone seems to have problems with there tranny not being able to shift. I feel like I'm the only person with the "too many shifts" problem. Anyways, let's see how tomorrow turns out.
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  #8  
Old 04-08-2001, 11:59 AM
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There is NO throttle valve linkage on 80-83 240D. The 80-81 300D was the same. These units use only VACUUM controls.

My previous post most have been misinterpreted. The vacuum modulator is a vacuum diaphram working against a spring (internal to the chamber). The device then moves a piston in the tailhousing. The rod and spring that was part of the original modulator must be removed and installed into the new modulator so that it can move the internal piston.

It sounds to me that this didn't take place and the modulator pressure is stuck in the undepresed condition(similar to high vacuum state).

Your problem started with the modulator replacement, you need to return there to solve the problem IMHO.

BTW there is no aluminum seal ring used on the modulator. Adding a ring can do a similar gross adjustment of the modulator.

BTW again, this transmission is totally different from 82 on transmissions used in any other MB.
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  #9  
Old 04-08-2001, 10:38 PM
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Praise Master Brotherton!

My 240D is scoot'n like it's supposed to now, thanks to Steve. That rod and spring did the trick. I was wondering how the modulator works, and now I do. MB should include that rod and spring with every modulator. The info about the throttle valve linkage, I haven't seen that anywhere else; so I think that's a first. But one thing I noticed was when I turn the key clockwise, I get a harsher shift; and when I turn it counter-clockwise, I get a smoother shift. This is different from what I've read elsewhere. But, again, thanks Steve for sharing your great knowledge.
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'80 240D (sold) wish I didn't.
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  #10  
Old 04-08-2001, 11:29 PM
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Sorry You Felt Confused, Glad You're Running Again

Greetings Koon Koon,


Sorry if I confused you on the issue, but like Steve said, and I guess I assume too much sometimes. You either have a mechanical linkage shift or a vacuum controlled shift. After you mentioned the modulator, I knew you only had a vacuum operated shift, but I think you understood us all to think you should have both for it to work properly.

Sorry,

Charles

Glad to hear the beast is up and shifting to snuff again, takes more than that to kill a MB tranny. A lot of parts that are supplied either as original or aftermarket just contain the wear, so to speak part and not the attaching parts that generally don't wear out at the same rate.
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  #11  
Old 04-09-2001, 01:04 AM
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The elephant herd

No reason to be sorry charles. We're all trying to help each other out here. And that's the only thing that matters. Thanks to everyone.
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'80 240D (sold) wish I didn't.
'85 300D (240K miles)
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  #12  
Old 04-09-2001, 07:50 AM
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what causes this problem

on the '85 300D with the throttle valve linkage? When I had the linkage disconnected and the car off I pulled on it and the resistance was slightly different at the end of the pull versus say the first 75%.

The only things I have done so far was insure that the Bowden cable is correctly set and I have changed the fluid and filter. When I dropped the pan to change the filter visually everything looked great - clean, no burnt smell, etc.

thanks,
Jim
'85 300D
'95 E320
'97 CRV
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