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Old 10-15-2006, 01:23 PM
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Join Date: Oct 2006
Posts: 5
300DT transmission problems

I've also posted this issue under another thread regarding another persons 300D trans problems, feel free to reply to whatever thread....

I'm currently having transmission problems with my 83 300DT. It has 280K miles and here are the problems.

The biggest issue is every now and then when going up a very steep hill the transmission will completely slip ( this could happen when the car has been warmed up or cold, but usually more likely when cold). The shift lever is really loose and usually I have to take is it out of gear and reshift back into Drive.

It feels like even the power output (when it initially slips and I put it back into gear) is not as great as it should be. it doesn't really grab the road, and its like the torque coming up the hill has been downgraded. it almost sounds like its slipping but my RPMS don't go through the roof or anything, I can only describe it as not as much torque. sometimes to shift the car into its last gear I have to bring the shift lever obove drive almost in between N and D. shift lever linkage is deff in need of some help.

usually I have problems, (the car not pulling up a hill good) when I have to start out from a stop. its interesting because the car is sluggest at slow speeds (Pickup isn't what it should be) but the turbo is deff working while I'm on the highway and seems to kick in later at around 70 MPH or so. I've owned other 300DT. my previous deff didn't feel as sluggish off the gate. I don't think its the turbo boost sensor. I cleaned the banjo and replaced the line, and the turbo is deff working on highways and higher speeds, where shifting isn't needed. The other issue with the vehicle is a low vacuum condition. when I drive the vehicle when its cold (engine, after it sits overnight ) I don't have any brakes. usually once vacuum picks up, usually in about 15 seconds, breaks are fine. (I recently preplace my brake booster and before that didn't have any vacuum assisted brakes). So I guess my question here would be could low vacuum suction to the vacuum modultor cause poor torque conditions to the transmission? I'm going flush the transfluid and replace the filter and all that stuff. shifting and power deff improves/increases once the vehicle is warmed up.
The only other piece of the puzzle I would like to add is this. When usually cold and when I try and hammer the car, you know really hit the gas the vehicle surges, almost feels like the engine is reving to 3000 rpms then backing off. at first I thought this was an engine issue, but now I'm thinking its the trans slipping real quick then ingaging again. it does this especially when going up a hill (thats when its not completing slipping and I have to reset the shift lever) doesn't usually do these high quick bursts of hi revs when warmed up.

Vehicle shifts good when warmed up , and transmission problems aren't very noticable at operating temp conditions. I guess the transfluid is thinner/hotter.

In my head I'm thinking the possible issues are:

1 ) torque converters, do these go out on these cars? are there any similarities between my car and a bad converter?

2) vacuum modulator/ low vacuum condition. thow doesn't this just control shift points? hard shift does occur at times, sometimes it shifts nice and smooth.

3) shift linkage just being out of wack and inbetween gears, if this is possible. my cars shift lever is deff the loosest I've felt in one of these cars

Thanks for any advice you may add.
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Old 10-15-2006, 11:35 PM
Mustang_man298's Avatar
Man of the fire
Join Date: May 2006
Location: Shingletown,Ca
Posts: 941
Shift lever shouldn't be loose, either the lever assy has worn bushings, or in the case of my '80 240, I found one of the urethane bushings gone from the bottom of the lever where the linkage connects to it (and noticed MANY with same problem in wrecking yard while trying to find another one). If your linkage is the same as mine it is a 2 piece linkage with a threaded section and a jamnut to adjust the linkage, Make sure all your bushings are there, then if you have to move the shifter around still to get it into the right gears, You might try (car turned off, chock your wheels-in case you should bump it out of park) put shifter in park, get under and unhook linkage from shifter, wiggle linkage to make sure it is seated comfortably in the park detent on the trans, then as you try to hook the linkage back to the shifter, it should line right up to the hole without pulling or pushing on it, if not, loosen the jam nut and adjust as needed, then tighten the nut and reassemble the linkage. Go from there and see what happens.
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Old 10-16-2006, 12:40 AM
Join Date: Dec 2005
Location: CA... No. of S.F.
Posts: 890
Start by completing your Signature so we will have a reference...

Ben - Welcome to your own THREAD... where I'm all but certain others here will give you a hand with your car's problems.
Originally Posted by Britten View Post
In my head I'm thinking the possible issues are:
1 ) torque converters, do these go out on these cars? are there any similarities between my car and a bad converter?
2) vacuum modulator/ low vacuum condition. thow doesn't this just control shift points? hard shift does occur at times, sometimes it shifts nice and smooth.
3) shift linkage just being out of wack and inbetween gears, if this is possible. my cars shift lever is deff the loosest I've felt in one of these cars
Completing your Signature will help us get the right mind-set when we are reading your future POSTS in this and other THREADs... use my Signature at the bottom as a model for what I'm talking about.

Q1 - Do you have a combo vacuum pump/gauge?... IF NOT you will need one OR I and others on this FORUM are going to be of far less help! We have to be able to have you make checks under the hood!

It appears that you have either/both engine and tranny issues with your MBZ.

Q2 - How many miles on the car [chassis], the engine, and the transmission?... and I suggest you include this in your Signature as you see in mine below.

Q3 - How long you had this MBZ and/or other MBZ?
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Old 10-16-2006, 07:01 PM
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Join Date: Oct 2006
Posts: 5
1983 280k tranny problems

thanks for the shift linkage feedback Mustang_man298.
appreciate it. my linkage does still need to be checked out.

now in regards to Samuel M. Ross's questions

well I do have a vacuum gage with a handle to pull vacuum too. This is my 2nd Mercedes 300DT I've owned. the one I am having problems with is the 83 280k 300DT. I've only owned this one for about 5 months and the 1st 82 300d for about 3 years. I've yet to take either to a repair shop, and am slowly starting to figure out this trans vacuum system. after downloading more information on checking the vacuum system heres were I'm at.

Currently the transmission shifts too quick rather prematurely. i've adjusted the modulator at the injection pump to pull 12hg. initially when I downloaded the vacuum schematics for my MBZ I did notice the trans wasn't getting any vacuum at all. so I figured out were it was disconnected and took it for a drive. tranny operated worse. not staying in 4th gear but kicking back and forth between 3 and 4. so thats when I figured out how to adjust modulator vacuum initially putting it at 15 throttling down to zero at full throttle. and this fixed the kick down problem between 3 and 4. then I lowered it more to see if this would fix my premature shift problem and ajusted it to 12hg which is currently what its at.. and still the vehicle shifts
1 to 2, and then immedialy to 3 like a second after it shifts to 2, not letting the turbo really spool up to take advantage of the turbo power at higher rpms. also it flairs, sometmes from 1 to 2 and most of the time from 2 to 3, flairing is not too bad. Shifting into 4 is pretty good. I wish I could tell you what the rpm shift points were but my tach is super flaky and never really works. so It seems like adjusting modulator didn't do anything to help premature shifting. essentially I thought I had low torqe but its shifting too quick which up hills doesn't do me any good when I should be in 2nd and it quickly shifts to 3.

Also turbo maybe leaking pressure. you can really hear the turbo whinning and is loud. Sounds like my first MBZ when I put a straight intake air filter kit on it... but with my first vehicle i noticed I didn't really hear the turbo too much with the stock air filter assembly, unlike this 83'.

I have cleaned the banjo and put a new line from the manifold to the boost pressure sensor thingy. what is it a aernator or something. cleaning this really didn't do to much. also at higher RPMs mostly higway use 70mph or so the turbo is deff woorking. I want to put a turbo pressure gauge like the article by Steve Brotherton

to make sure I'm pulling the right amount of turbo. and I need a pressure gauge for that not the vacuum gauge I currently own ehh?

points of confusion about Steve's article are: at the point you have the right vacuum curve what then do you adjust to do the finessing. I understand the screw adjustment on the shift cable one of the later points of adjustment in the article, but am confused specifically here:

The proportioning valve adjustment allows the range of vacuum to be expanded. For example, a range of 10 in. to 0 in. could be expanded to 12 in. to 0 in. or 15 in. to 0 in. and, in some instances, raised above zero (such as 12 to 2). Generally speaking, a wider range is better, but older trannies with a lot of clutch wear often benefit from a reduced range. Worn clutches are more susceptible to shifts at low pressure. By adjusting to a smaller range and reducing the basic modulator pressure, a slow shift can be modified. Moving the vacuum range also has been of use to cover up valve body problems concerning shift spacing (for example an early shift into 2nd or 3rd).

All vacuum adjustments should be done after the proper modulator pressure is achieved through adjustments at the modulator. The proper method would be to install a gauge at the case pressure port. (?) Remove the vacuum line and run the engine at 2,000 rpm. The pressure is adjusted up or down to meet the figures in the data manual by turning the tee handle (see Fig. 5). We do this with rebuilt units but, in used units, I always do it by feel as the necessary vacuum adjustment may never reach zero. I drive the car full throttle (monitoring the vacuum) and set the modulator such that these shifts are appropriately firm. All the other shifts are modified from this point using the above adjustments. The range of vacuum and its relationship to throttle movement can be varied to achieve relief from the internal problems described above.

anyway any help would be ausume. I think specific help on taking care of premature shifting would be best and what to modify after a good vacuum is reached. I currently have a vacuum gauge in my car Teed up to the line which goes to the tranny so if you need a reading just let me know..

thank you so much.
Ben Britten
82' 300DT [W123] ~155K... Engine/Tranny~155K
83' 300DT [W123] ~280K... Engine /~280K... Tranny
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Old 10-17-2006, 12:00 AM
Mustang_man298's Avatar
Man of the fire
Join Date: May 2006
Location: Shingletown,Ca
Posts: 941
Hopefully someone gets you on the right track with it,lol. Seems I am developing some trans issues of my own now, what I thought was flaring between 2nd-3rd or 3rd-4th, shifts are too soft to really tell, It went away after the first day I put it back on the road, wrote it off as the tranny needed to work in & reseal itself internally. Well it came back yesterday and seems to be staying now, 1st and 2nd are ok, hits 3rd with anything over very light acceleration and the engine slowly spools up until it basically freewheels, and stays that way unless I force it back to 2nd and back with the stick or let back on the throttle, I'm thinking this isnt flaring if it isnt dropping in until I do something to force it in. Wondering if the trans seals are shot, seems to shift somewhat early, might be shifting in too soon and putting too heavy a torque load on the internal clutchpack with too little speed? I just drive it like an autostick for the time being until I get a chance to dig into it (and figure out what the heck I'm doing).

1980 240D w/617 motor

Last edited by Mustang_man298; 10-17-2006 at 12:02 AM. Reason: forgot signature
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