Something is seriously wrong with 240D: clutch or manual transmission? - PeachParts Mercedes-Benz Forum

gastropodus · #1 11-19-2017, 02:25 PM

So, coming home last night after an hour and half of freeway driving (at 55mph, this is a 240D after all), I was pulling out from the freeway off-ramp in first gear. I got up to about 5mph and was in the middle of the intersection when I heard and felt a big CLUNK, seemingly from the rear. i thought at first someone had rear-ended me, but then I realized that I had NO power at all going to the wheels. With the clutch engaged and the car in any gear I got a kind of growling from underneath the car, again seemingly from the rear. Some kind folks helped me push the car off to the side of the road, and I called AAA for a tow truck. Brought the car home and had them dump it in front of house until I could look at it in daylight.

This morning I blocked the front wheels, and jacked up the rear driver side to look underneath. The half shafts are dry and the boots look intact. No leaks are evident anywhere: up near the transmission it looks dry, nothing from the differential, nothing from the boots. I put the car in gear with the engine off, and I'm able to turn the jacked up wheel with some resistance, almost like a spline is slipping: nub-nub-nub-nub. The other rear wheel is in contact with the ground, so turning the jacked wheel makes the half shaft turn, which goes through the differential and makes the main drive shaft turn. The universal joint in the center turns and the flex disc up at the transmission turns and looks intact. The nub-nub-nub noise is happening up at the transmission end of the driveshaft, but I can't tell if it is in the transmission or if it is in the clutch. With the car out of gear the wheel spins more easily and nothing makes noise, all the shafts turn as before.

Some other facts about what I've observed about the clutch and transmission. The clutch was replaced six years ago and about 25k miles ago when I put in the new engine. It wasn't a genuine Mercedes part, which I now regret. After about a year I would hear a little ringing / scraping noise from what I thought was the clutch, but everything else was OK so I ignored it. I drained and filled the transmission with red ATF during that same time period. Transmission has never popped out of any gears; about the worst thing that ever has happened is it will grind going into second if I don't wait for engine RPM to drop far enough to match the wheel speed.

So, any ideas on how to further diagnose this? Thanks,

Kurt

Diseasel300 · #2 11-19-2017, 02:36 PM

Flex disk?

sixto · #3 11-19-2017, 02:59 PM

Hopefully just the flex disc. Not unheard of for an AT yoke to come loose from the output shaft or the splines to shear.

Sixto
98 E320s sedan and wagon

gastropodus · #4 11-19-2017, 03:21 PM

Quote:

Originally Posted by sixto

Hopefully just the flex disc. Not unheard of for an AT yoke to come loose from the output shaft or the splines to shear.

Sixto
98 E320s sedan and wagon

It's a manual transmission. I'll get under there again and look closely at the back side of the flex disc, may take some pictures.

Frank Reiner · #5 11-19-2017, 03:31 PM

gp:

Based on your observations and descriptions, the most likely point of failure is the internal splines of the output yoke of the gearbox. The splines of the output shaft are harder than those of the yoke, and usually are little damaged.

As a further test, place both rear trailing arms on stands or blocks, and with engine running, place the transmission in 1st & engage clutch. The rear wheels should turn, perhaps accompanied by the popping sound. While the wheels are being driven, step on the brakes. Do the wheels stop and the engine continue to run? If so, with the aid of an assistant to step on the brakes, you can better ascertain from under the car the point of origin of the noise.

gastropodus · #6 11-19-2017, 05:02 PM

Quote:

Originally Posted by Frank Reiner

gp:

Based on your observations and descriptions, the most likely point of failure is the internal splines of the output yoke of the gearbox. The splines of the output shaft are harder than those of the yoke, and usually are little damaged.

As a further test, place both rear trailing arms on stands or blocks, and with engine running, place the transmission in 1st & engage clutch. The rear wheels should turn, perhaps accompanied by the popping sound. While the wheels are being driven, step on the brakes. Do the wheels stop and the engine continue to run? If so, with the aid of an assistant to step on the brakes, you can better ascertain from under the car the point of origin of the noise.

Hi Frank, thanks for responding. How hard would it be, do you think, to undo the cross member and the flex plate to try and drop the drive shaft and get a look at that yoke? Do-able without pulling the engine off its mounts to create clearance? Thanks,

Kurt

Diseasel300 · #7 11-19-2017, 05:33 PM

The yoke on the output flange is just that - the output flange of the transmission (that connects to the driveshaft via flex-disk). You should be able to gain access very easily. The crossmember comes out once you've supported the transmission with a jack or something to take the load off the crossmember.

Frank Reiner · #8 11-19-2017, 06:53 PM

Quote:

Originally Posted by gastropodus

Hi Frank, thanks for responding. How hard would it be, do you think, to undo the cross member and the flex disc plate to try and drop the drive shaft and get a look at that yoke? Do-able without pulling the engine off its mounts to create clearance? Thanks,

Kurt

Straight-forward. As noted above, a bit of support on the trans, and the crossmember & mount are readily removed. With the flex disc bolts removed the front section of the drive-line can be collapsed enough for inspection of the yoke (three-legged flange). If you feel it necessary, the center bearing support, and the rear flex disc can be undone, and the whole drive-line can be slid rearward.

whunter · #9 11-19-2017, 07:02 PM

Quote:

Originally Posted by gastropodus

So, coming home last night after an hour and half of freeway driving (at 55mph, this is a 240D after all), I was pulling out from the freeway off-ramp in first gear. I got up to about 5mph and was in the middle of the intersection when I heard and felt a big CLUNK, seemingly from the rear. i thought at first someone had rear-ended me, but then I realized that I had NO power at all going to the wheels. With the clutch engaged and the car in any gear I got a kind of growling from underneath the car, again seemingly from the rear. Some kind folks helped me push the car off to the side of the road, and I called AAA for a tow truck. Brought the car home and had them dump it in front of house until I could look at it in daylight.

This morning I blocked the front wheels, and jacked up the rear driver side to look underneath. The half shafts are dry and the boots look intact. No leaks are evident anywhere: up near the transmission it looks dry, nothing from the differential, nothing from the boots. I put the car in gear with the engine off, and I'm able to turn the jacked up wheel with some resistance, almost like a spline is slipping: nub-nub-nub-nub. The other rear wheel is in contact with the ground, so turning the jacked wheel makes the half shaft turn, which goes through the differential and makes the main drive shaft turn. The universal joint in the center turns and the flex disc up at the transmission turns and looks intact. The nub-nub-nub noise is happening up at the transmission end of the driveshaft, but I can't tell if it is in the transmission or if it is in the clutch. With the car out of gear the wheel spins more easily and nothing makes noise, all the shafts turn as before.

Some other facts about what I've observed about the clutch and transmission. The clutch was replaced six years ago and about 25k miles ago when I put in the new engine. It wasn't a genuine Mercedes part, which I now regret. After about a year I would hear a little ringing / scraping noise from what I thought was the clutch, but everything else was OK so I ignored it. I drained and filled the transmission with red ATF during that same time period. Transmission has never popped out of any gears; about the worst thing that ever has happened is it will grind going into second if I don't wait for engine RPM to drop far enough to match the wheel speed.

So, any ideas on how to further diagnose this? Thanks,

Kurt

Your power loss description fits this:

This issue is becoming more common.
Bad 722.xxx-transmission output flange spinning on shaft

Transmission Problem & Fix

Output flange, 722.xxx transmission

The second gear rpm grind you describe is 99% odds

The pilot bearing inner diameter is overly tight on the pilot shaft = when installing the transmission the pilot shaft fails to smoothly slide into the bearing = excess rear pressure along the shaft through the internal bearings, and pinched synchromesh.
All of this causes you to shift up/down through second gear = step fully on clutch awaiting rpm reduction longer than is expected/desirable, often getting a poor/bad rpm match = grind gears only in second.

Solution:
#1. Remove the transmission.
#2. Measure the pilot bearing inner diameter.
#3. Clean the pilot shaft outer diameter with Crocus Cloth 220 Grit.
#4. Measure the pilot shaft outer diameter.
#5. Here is a link to help you determine if the dimensions are compatible.
[quote]It should have between 0.002" and 0.003" clearance on the transmission shaft when installed.[quote/]
http://www.crankshaftcoalition.com/wiki/Pilot_bearing_and_bushings
#6. The pilot shaft outer diameter can usually be worked down 0.002" with Crocus Cloth 220 Grit.
#7. If The pilot bearing inner diameter exceeds your working dimension = it must be replaced = always test fit new pilot bearings to the shaft before installing.
#8. Use a light coat of bearing grease on the pilot shaft, and install the transmission.

[quote]The pilot bushing is only functional when the clutch is disengaged but it is a factor in input gear alignment at ALL times.[quote/]
http://www.crankshaftcoalition.com/wiki/Pilot_bearing_and_bushings

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Frank Reiner · #10 11-19-2017, 08:32 PM

Quote:

Originally Posted by whunter

Bad 722.xxx-transmission output flange spinning on shaft

722.xxx denotes auto box; the OP's trans is manual.
However, as described above, the output yoke may be the culprit.

Quote:

The pilot bearing inner diameter is overly tight on the pilot shaft

1) The pilot bearing is a ball bearing. The input shaft axial location/thrust in MB boxes is determined entirely by the input shaft bearing, and is not passed thru to the mainshaft. Hence, there are no thrust loads from the pilot bearing passed to the synchros.
2) After 35+ years probably not too tight

sixto · #11 11-19-2017, 09:14 PM

In my second ‘83 SD the yoke splines were about stripped clean and the output shaft splines were too far gone for me feel comfortable returning to service. Again, AT rather than MT but have an experienced set of eyes have a look before you decide a yoke is all you need.

Sixto
98 E320s sedan and wagon

gastropodus · #12 11-21-2017, 02:29 AM

OK, so the weather was dry tonight, and I was able to get under the car and undo the flex disc from the driveshaft. I loosened the 46mm nut on the driveshaft back by the center bearing, and that allowed me to push the shaft toward the rear and remove the rubber disc. I took a movie of what is going on, but the file limit is so small for posting WMV files that I couldn't upload it. So, I'll just have to settle for posting a picture and a verbal description.

The three-eared yoke does indeed turn independently and easily from the shaft that is protruding with the piece of blue tape on it. As I turn it I can hear splines rubbing, nub-nub-nub, but not catching. Clearly, when I'm turning that yoke with very little finger pressure I'm not turning anything that makes anything in the transmission itself move. You can see what looks like a larger shaft diameter at the base of the shaft marked with tape; it appears that the splines are on the outside of that part of the transmission shaft, and there are (were?) corresponding splines on the inside of the yoke diameter. There is about an 1/8th inch of axial play in the yoke; when I press the yoke toward the transmission the splines appear to catch and there is resistance then.

I don't know what holds the yoke in place axially. Based on a conversation I had with a forum member I was expecting an axial bolt that was going to hold the yoke in place, but I'm guessing that somewhere under the grease there is a circlip.

I'm kind of guessing that the transmission is toast as a result of this.

gastropodus · #13 11-21-2017, 03:20 AM

I managed to extract a snippet of audio from the movie that would meet the file size restriction. This is the sound it made as I twisted the yoke back and forth.

whunter · #14 11-21-2017, 03:53 AM

Quote:

Originally Posted by Frank Reiner

722.xxx denotes auto box; the OP's trans is manual.
However, as described above, the output yoke may be the culprit.

1) The pilot bearing is a ball bearing. The input shaft axial location/thrust in MB boxes is determined entirely by the input shaft bearing, and is not passed thru to the mainshaft. Hence, there are no thrust loads from the pilot bearing passed to the synchros.
2) After 35+ years probably not too tight

The output yoke issue applies to manual and automatic transmissions, I have replaced more than I care to recall.

I don't know where your data comes from regarding the input/main shaft?
My statement is correct.
My fleet includes a 1980 240D four speed manual, which had this issue = replaced the pilot bearing instant issue = pulled the transmission checked dimension, sanded the pilot shaft 0.002 = second gear grind gone.
I have demonstrated the issue as described, at local technical sessions using a couple of spare 240D transmissions.

Sadly I have little time these days to do technical sessions, attend car club meetings, or do more than maintenance on my fleet.
I am stealing sleep time for this response.
Have a great day.
Roy
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whunter · #15 11-21-2017, 04:30 AM

Quote:

Originally Posted by gastropodus

I managed to extract a snippet of audio from the movie that would meet the file size restriction. This is the sound it made as I twisted the yoke back and forth.

Assuming the transmission was in gear when you rotated the yoke:
Sounds like the yoke splines are damaged and slipping.

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