Something is seriously wrong with 240D: clutch or manual transmission?
 

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

Flex disk?

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.

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

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.

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.

Answer
 

Your power loss description fits this:

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

http://www.peachparts.com/shopforum/diesel-discussion/301813-transmission-problem-fix.html

http://www.peachparts.com/shopforum/mercedes-parts-reference-library/301849-output-flange-722-xxx-transmission.html

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

.

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

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

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.

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.

Answer
 

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
.

Answer
 

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

.

Can i ask, how long have mercedes used ATF for manual gearboxes ? .I know a few makers used it in the past .

Sorry you do need atf you learn more every day

See post #5 above.

There is, or should be, a nut hidden in the dirt and grease inside the yoke. That nut screws onto the mainshaft/output shaft to retain the yoke.
As noted in post #5, the shaft splines are harder than the yoke, and may have survived.

There's a big staked nut holding it on. It's like the end of a contemporary CV joint.

Should it have been visible in the photograph I took, on the rearward side of the yoke? Because all I removed was the flex disc, nothing else, and that’s how it looked. It’s a ‘79 car; perhaps later models have the nut? Thanks to all for responses!

I’d really like to get the yoke off, which would uncover the splines and reveal whether the shaft splines are ok.

In early cars, the nut isn’t a 6-point hex but an annulus with 4 recesses. In ATs the annulus can be replaced with a more conventional nut.

http://www.peachparts.com/shopforum/...ecial-tool.jpg

I found a deep socket that matched the outer diameter of the nut, ground the open end into prongs that fit the recesses, then blasted off the nut with an impact wrench.

Sixto
98 E320s sedan and wagon

Dang, I think I have the annulus style.

An older Mercedes mechanic may loan you the tool. Of course offer to leave a reasonable deposit. It does sound in general that the splines will be usable again. Or at least the odds they are might be in your favor.

Hunters description of the second gear grinding that is really not that uncommon on the 240ds. Plus his information in an attempt to rectify it should be helpful to many. Neither of ours grinds into second gear though.

They are 1979 and a 1983 versions. Rust unfortunately has gotten the upper hand on the relatively low milage 1983 24Od. I will still retain it as a parts car for the 1979.

Fortunately these old transmission are still not that hard or expensive to find if the need is there either. I even have one in a 1972 gas coupe.

Good luck with the repair .

Thanks, optimusprime. Sixto has generously agreed to send me his tool, so once that arrives I'll have a go at getting the fastener off. In the meantime, I need to grind off the staked portion of the fastener. I noticed from Sixto's photo that it appears that he was able to block the yoke from rotating while loosening the fastener - since my yoke is stripped I think I will have to put the car in 4th gear and put a breaker bar on the front of the crankshaft , similar to what I do when turning the engine while adjusting the valves. Does anyone see any problem with that?

I know that with these diesels the engine should only ever turn clockwise, never counter-clockwise. I verified yesterday that when the car is in a forward gear, the sense of rotation is preserved as the motion is transmitted through the transmission - that is, when the rear wheels turn as though the car is moving forward, the transmission output shaft turns counter-clockwise when viewed from the rear. CCW from the rear is the same as CW from the front, hence preserved. All of this is a long-winded way of saying that when loosening that fastener (CCW) I'll be trying to turn the engine in the natural clockwise (viewed from front) direction, so low risk. When tightening the nut I can block the yoke and leave the car out of gear, so no risk there, either.

Chime in if you see any flaws in my reasoning... thanks, guys.

Kurt

That’s not my picture, just one I found on the site. It might be our good friend stretch. I used an impact wrench which doesn’t need much resistance. The safest bet is to use a ring gear lock. There’s one that holds the ring gear at the very bottom and one that fits in place of the starter. I suppose you can hold the crank pulley bolt but lash down the stop lever since CCW at the yoke is CW at the crank; i.e., the engine might start. Also, mind that you don’t loosen the crank pulley bolt in the process.

Don’t 615/6/7 engines have a keyway so you can lock the crank damper against the front cover?

http://www.samstagsales.com/mercedes/bu601-0240.jpg

Sixto
98 E320s sedan and wagon

Nice bit of kit that one .

BMW still uses ATF in manual gearboxes. The only reason to use heavier gear oil is when its combined with the diff as an integrated transaxle.

Some BMW enthusiasts do a 50/50 mix of ATF and 75w90 gear oil, just for added wear protection when doing autocross or track events, but the viscosity can make the first few cold shifts in the winter kind of difficult.

Update: nut and yoke removed
 

OK, so with Sixto's tool I was able to remove the annular nut holding the yoke on. As I expected, the softer yoke is completely stripped - see photo. The transmission shaft doesn't look too good either, to be frank. I'll post a couple of photos here, for comment by anyone with experience.

By the way, I didn't go to the trouble of blocking the flywheel. I just put it in first gear, figuring that the torque I put on the nut was going to get divided down going through the transmission. The engine didn't even budge when I broke the nut loose carefully.

Anybody got a good yoke they want to sell? Or even one to loan just to put on the shaft and see how much play there would be in the current state? Opinions on brands of rubber for a new flex disk?

Thanks, as always.

Kurt

Sorry to say, the shaft splines are toast.

Kurt;

Used yoke for cheap cheap, pack with JB weld during assembly? Might be worth a try to avoid R&R the transmission.

Get a quote for transmission repair for comparison.

Agreed, that spline is toast. No JB weld would give you any reliability. You'll soon be in the same situation getting a tow.

Time for rebuilding and getting a new shaft. Or just swapping out the trans.


.

Yes, my initial feeling on the shaft splines was that they are toast. Maxbumpo’s comment got me thinking, though: what if I were to install a hardened dowel pin through the shaft and yoke, transverse? The pin would stick out through either side of the shaft, and those two points of contact would drive the yoke through corresponding holes in the yoke body where it encloses the transmission shaft. The difficulty being that the spline contact area is mostly within the protrusion of the housing, and the dowel pin would need to be located outside the housing.

Here are some back of the envelope calculations on this. Read somewhere on the internet that the OM616 puts out 67 hp and 97 ft-lbs of torque at 2400 rpm. A typical gear ratio on a four speed transmission’s first gear is around 3.2:1, so maximum torque at the output shaft of transmission is 310 ft-lbs. 1 foot is 305mm; my eyeballed estimate of the shaft diameter is 20mm. The radius is thus 10mm, and thus the multiplier on the force is (305/10), or 30.5x. 310 lbs times 30.5x is 9467 pounds. This assumes all force is exerted on one side, which would likely be the case until the soft steel of the yoke deforms enough for both sides to carry the load.

McMaster-Carr carries alloy steel dowel pins in various sizes. They rate them for breaking strength in the scenario where a dowel pin goes through a shaft to drive an enclosing part with two points of contact 180 degrees apart, similar to what I’m sketching out here. A 0.250” dowel pin breaks into three pieces with 10,000 lbs force; 5/16” rating is 16,000 pounds; 3/8” rating is 23,000 pounds. The question would then become at what diameter do you equalize the likelihood that the shaft would break or deform relative to the pin?

I would probably shoot for a scenario where the shaft has 50% more cross-sectional area relative to the pin. The cross section of the unmodified shaft is pi() * r^2; using 10mm (0.394”) for radius, I get 0.487 sq inches for shaft cross section. Pin cross section is just length times diameter; for the 5/16” shaft we get 0.246 square inches. I can already see that when we subtract off the pin area from the shaft area we are going to get areas that are approximately equal. So, the 3/8” pin is definitely out. 5/16” pin puts the shaft at risk for breakage, probably. 1/4” pin is definitely at risk for pin breakage. I might refine these numbers a bit with real measurements, but right now the 5/16” pin looks like the best bet.

This is probably a short-term fix at best. But it is cheap and seems do-able. In one sense, what have I got to lose - the transmission is toast at this point regardless. Long-term I would worry about deformation of the mild steel yoke. JB Weld would probably have a place in this type of repair, as a filler/stabilizer between the yoke and shaft. If nothing else it would probably allow me to drive the car to the shop that is going to R & R the transmission.

And that concludes today’s thought exercise in hillbilly engineering!

Clearly you have anticipated a pin-location/assembly-sequence conflict.
To place the pin aft of the tail housing, it would pass through the threaded portion of the shaft. And then, where would the nut go?

A solution, though not the only one, is to place the pin, with a press fit, in the splined area of the shaft. To assemble the yoke, the yoke would be slotted axially to allow it to be slid over the pin and splines.