Transmission / driveline clunks, 3-4 shift flare, delay+clunk into R and D - PeachParts Mercedes-Benz Forum

pwalsh53 · #1 10-14-2006, 09:46 PM

Hi everyone. First let me thank this forum for being so helpful this far. I've had my '84 300D turbo (first time W123 owner) for less than a week and have learned so much from this great resource.

I have searched the forums and websites long and hard but I can't seem to find a concrete solution (or solutions) to my tranny problem.

First of all, when I shift from Park to Reverse or Drive, there is a substantial delay and then a hard CLUNK when it does shift. And when I let off the gas while driving, I can hear something clunk in the drivetrain. Fairly loud. There is no vibration when accelerating though, so I don't think it's a flex disc or support bearing (I don't think.) Diff mount maybe?

It also clunks when it downshifts coming to a stop, and the shift from 3-4 at any throttle input is much softer than it should be, and flares occasionally. I know that the 2-3 flare is common and fixable with the K1 spring kit, but my question is, would that kit fix this problem as well? I haven't yet pulled vacuum on all vital components of the system but I am getting there. The vacuum line from the little green check valve to that plastic valve on the injection pump is shot. That green valve may very well be shot too. I looked at the vac. valve levers on top of the engine and they don't look too bad. I think they still have a little life left.

I am going to change the trans fluid and filter tomorrow but I might hold off if anyone thinks I should try the K1 upgrade. 1-2 and 2-3 are bang on, and very crisp at WOT, but 3-4 is the problem area.

I'm pretty sure there is a vacuum issue somewhere about the car. The door locks can be finicky and very very slow at times. Sometimes the RR door doesn't even lock when I lock them. I'm starting to think that little yellow check valve may be leaking too, it looks like its the original one haha.

Any help is much appreciated,
By the way these cars ROCK!

Patrick

pwalsh53 · #2 10-15-2006, 01:49 AM

^^^

Samuel M. Ross · #3 10-15-2006, 02:14 AM

a little more thoroughly... somewhat like mine below, and this will tell us the important mileage numbers your car, tranny etc. have on them.

pwalsh53 · #4 10-15-2006, 02:49 AM

Done. Thanks for the advice.

I've done a little more looking at it seems this could be a B2 piston problem. Or is that just totally inaccurate.

The thing I am most worried about is the severe clunking when I let off the gas.

Patrick

DubMutant · #5 10-15-2006, 05:04 AM

Ours just had the drive shaft bearing and rear tranny mount done.
Before it was fixed, when it kicked down, the drive shaft popped into the floor boards. It wasnt so good. It was really loud and violent. It wasnt too bad under acceleration compared to how obvious in was dunring deceleration.

It drives ALOT more smoothly now. It is a little lumpy but I cant really tell- I haven't driven enough Mercedes 300D's to know if it was right, or or needed tweaking.

arcticathlon · #6 10-15-2006, 10:22 AM

i had a clunk when i would put my car in reverse and drive backwards. that was a bad rear axle. after replacing that, i had no more issues. just food for thought.

Samuel M. Ross · #7 10-15-2006, 10:53 AM

Quote:

Originally Posted by arcticathlon

i had a clunk when i would put my car in reverse and drive backwards. that was a bad rear axle. after replacing that, i had no more issues. just food for thought.

When we took possession of our 1980 300D, I found the rear-End gear oil only ~half full... so be sure to check this... and consider trying a heavier oil as a diagnostic test as to this being worn differential gears!
Regards,

JamesStein · #8 10-15-2006, 11:30 AM

Check your flex disc's, transmission mount and differential mount as well.

running-snail · #9 10-15-2006, 12:16 PM

You indicated a need to check vacuum. I believe this is your biggest contributor to off-throttle downshift 'clunking'

Get a vacuum guage and see if you can pull vacuum on the line going down to your transmission.

Mine was not connected, when I did connect with new tubing it would pull vacuum but not hold vacuum for very long. Shifts are smoother now under throttle but can still clunk off-throttle.

Reverse and drive clunking when shifting into gear - I defer to previous posters - rear axle/diff???

Britten · #10 10-15-2006, 12:29 PM

I'm also 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.
Ben.

Samuel M. Ross · #11 10-15-2006, 01:56 PM

Quote:

Originally Posted by Britten

...
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
Ben.

Ben,
Believe me when I say it's easy to spend a bunch of money on a fix-it transmission project by just throwing parts at your MBZ ! I wholeheartedly agree with " Running-Snail " above and also recommend you invest in a basic hand vacuum punp/gauge [ IF you haven't already ] and start what will most likely turn into IMPORTANT lessons learned about your MBZ's engine/tranny vacuum control system(s).

Next [ IF you haven't already ], read and gain a greater understanding of these engine/transmission vacuum control systems by reading Steve Brotherton's article at:
http://www.continentalimports.com/ser_ic20242.html and this should help you to sort through this mystery.
Next take a read of my THREAD at:
It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
I don't think tranny " fix " is a " quickie " unfortunately so settle in and LEARN now for it will stead you well in the long run. No matter how much we on this forum might try to help you, IF I'm correct that this is not a simple " fix ", then YOU need to gain much more first-hand knowledge of this "CRITICAL" vacuum control/actuator system. A systematic step-by-step approach based upon a reasonably good knowledge of how these various vacuum components work... this will help you more in the long-run!
Regards,

pwalsh53 · #12 10-15-2006, 02:40 PM

Thanks again everyone. I have read quite a bit of information about these systems, including Brotherton's extensive article. I guess the next step is a hand vacuum pump. The line going down to the trans vacuum actuator is the one just past the green dashpot right?

Patrick

Britten · #13 10-15-2006, 03:18 PM

[quote=Samuel M. Ross;1303988]Ben,
Believe me when I say it's easy to spend a bunch of money on a fix-it transmission project by just throwing parts at your MBZ ! I wholeheartedly agree with " Running-Snail " above and also recommend you invest in a basic hand vacuum punp/gauge [ IF you haven't already ] and start what will most likely turn into IMPORTANT lessons learned about your MBZ's engine/tranny vacuum control system(s).

great this sounds like a good idea. I'm deffinately not up to full speed on the scope of the vacuum control system and how it effects these transmissions. but I coud imagine if vacuum pump isn't pulling enouph vacuum in the beginning to assist in breaking what would it be doing to the tranny. I do have a gauge and I'm going to start testing vacuum at different points in the system.

Thanks.

Samuel M. Ross · #14 10-15-2006, 03:48 PM

OK guys, I'm not an official of this FORUM or anything but I sincerely suggest:

That you Ben [ aka = " Britten " ] start a new THREAD using much of what you included in your POST: Transmission / driveline clunks, 3-4 shift flare, delay+clunk into R and D
It's not fair to you Patrick [ aka = " pwalsh53 " ] for I think it is detrimental to both of your IF we try to help both of you on the same THREAD… for I feel it dilutes participation by those of us who want to give new users of the FORUM a hand.

Ben – I suggest you give us a final POST regarding your MBZ on this THREAD by giving us the title of your forthcoming new THREAD… I suggest something like: “Auto Transmission Problems – Please HELP! [1983 300D TurboDiesel ] ” this way those of us reading this [ Patrick’s THREAD] can easily recognize and add and monitor your [Ben’s] new THREAD to our automatic e-mail list... AND your THREAD title will be more informative in the future sitting there in the archives.

Otherwise I’m afraid both of you will NOT receive the attention/HELP you need.
Regards

pwalsh53 · #15 10-15-2006, 05:37 PM

Thanks Sam.

As for my car, does anyone think I need the K1 spring kit? My transmission cross section is:

1-2 crisp and fine
2-3 just fine
3-4 always too soft (flares sometimes)
long delay and hard clunk into reverse
clunk when i let off the throttle
softer clunk when gears downshift

Anyone think I might need the K1 spring kit or B2 piston?

Patrick