Rough shifting manual transmission overnight - PeachParts Mercedes-Benz Forum

sjefke · #1 12-19-2007, 11:03 AM

I need some first, second or third opinions. My coupe's transmission (manual 4 speed) is suddenly shifting much rougher than a couple of days ago. Problem started yesterday morning when it was freezing in Atlanta. Symptoms now: hard to shift in 1st, tough to get in 2nd, 3d a bit easier, and I haven't been in fourth yet. At first I thought it was just an issue of the cold, but it has been persisting even after driving for a while.

I will check transmission fluids soon, but the funny thing is that it happened almost overnight. Clutch disengages the transmission fine, so getting out of gear is no problem, but getting in gear it seems like the gears are still rotating and/or not meshing right. Sometimes it feels like it is a bit easier than other times.

Here are my theories:

1 - Cold is affecting transmission fluid making it tough to shift (meaning: problem should go away with temperature, but I know the problem still persists after 5 mile drives)
2 - Air in the system (that's what I would suspect, but it would not happen overnight, correct? And where would it come from? I checked reservoir level and it is fine)
3 - Either slave or master cylinder seal got brittle in cold and cracked a bit and is leaking (to me, this could explain it, but I would expect to have more pressure loss. I can stand in gear idling with clutch pedal pressed with no problem).
4 - Synchromesh ring(s) busted (a bit hard to believe given that 1, 2, and 3 suffer from similar symptoms)

Anybody had something like this before? Again, this happened overnight from Monday to Tuesday in cold weather. Usually when I have had hydraulic clutch seal failure before (like in my MGs), it would not pressurize the clutch at all, but here I can keep the clutch disengaged (without problems or car movement) while idling in gear at traffic light. So, I am a bit baffled by this problem.

Any advice is appreciated.

Thanks,

Bert

Arthur Dalton · #2 12-19-2007, 11:15 AM

Your manual trans needs ATF , not trans gear oil.
Check that they have not used gear oil ..Benz uses ATF in their manual trannies.............

Mark DiSilvestro · #3 12-19-2007, 12:02 PM

Sounds like the clutch is dragging. Check the clutch fluid - may have seeped just enough to prevent the clutch disengaging completely. Maybe not enough to creep or affect shifts out of gear but will certainly hamper shifts INTO gear. Otherwise could have malfunction of the clutch itself - disc or pressure-plate, pilot bearing?

Happy Motoring, Mark

sjefke · #4 12-19-2007, 01:18 PM

Quote:

Originally Posted by Mark DiSilvestro

Sounds like the clutch is dragging. Check the clutch fluid - may have seeped just enough to prevent the clutch disengaging completely. Maybe not enough to creep or affect shifts out of gear but will certainly hamper shifts INTO gear. Otherwise could have malfunction of the clutch itself - disc or pressure-plate, pilot bearing?

Happy Motoring, Mark

Mark, that's what it feels like - a dragging clutch, but I am baffled as to how.

I replaced the release bearing last summer after a catastrophic failure and had the transmission out. Pressure plate and friction plate were fine (had been replaced in 1995/6) and I suspect the slave cylinder was renewed too (even transmission had a partial rebuilt according to records). Friction plates wear down so you only get more play (and slippage) rather than stickage. Sticky pilot bearing is a thought, but I wonder how that can reduce suddenly reduce in tolerance play rather than get more through wear. Usually things get looser over time rather than tighter.

I think I will start with bleeding the system first using the official MB brake caliper to slave cylinder approach (worked great last summer) and see what that does. Maybe air just seeped in there through one of the metal hydraulic lines or connections due to it shrinking a bit in the cold. It's a long shot, but who knows. I'll check/tighten all connections too.

Arthur, yes, I do know it needs (and has) ATF, but I will check that level too (any recommendations on brand and type?). I learned a long time ago never to assume anything on transmission "oils" because my MGB must have 20W50 engine oil, my MG V8 hypoid oil and the MB ATF.

Again, if anybody has other opinions/thoughts, please let me know.

Thanks,

Bert

t walgamuth · #5 12-19-2007, 01:27 PM

You might have one broken finger on your pressure plate. This will allow it to drag a bit.

Tom W

Arthur Dalton · #6 12-19-2007, 01:36 PM

Mercron 2 or 3 is what I use .
These trans also have a common shift/syncro problem if the tailshaft nut loosens. You can tell that b/c your speedo will jump around , specially when excelerating and then letting off. That is first indication of loose tailshaft nut....common complaint...
Your first check should be pedall travel for clutch engagement. If too close to floor, adjust the rod at slave after you bleed.....

Jim Anderson · #7 12-19-2007, 10:33 PM

Mine recently started doing "funny" things, not like your though. I started looking around underneath and noticed the bushings were way too old. I replaced them and things I thought wouldn't be caused by bad bushings stopped happening. They are cheep and could be considered maintance.

I also put Redline synthetic MTL in, per recomondation from this site. I couldn't really tell the difference but it's got better all temperature rating.

truckinik · #8 12-19-2007, 10:41 PM

Just drop that '70, 111/c 3.5 litre, 4 speed. car over here @ my hizouse. It seems to be a rather troublesome little bugger...Allow me to take it off your hands for you....Free of charge.

Trucky

300SDog · #9 12-20-2007, 02:25 PM

Porous fabric coated rubber hydraulic lines is the only thing not mentioned, so I'll add that too.

sjefke · #10 12-20-2007, 03:44 PM

Well, so I started bleeding the system using the MB prescribed way with a clear hose from right front brake caliper to clutch slave. After several attemps, I got even worse shifting. Then I started chasing leaks and noticed a drop under the clutch master cylinder. Basically, whenever I press the clutch pedal, a bit of hydraulic fluid comes out along the master cylinder pedal stem. Don't know what you think, but that sure did not look good to me.

I thought I was prepared and had a new one already. Whenever I buy a car, I always expect to have to replace the main hydraulics, so I had ordered a slave and master cylinder way back in 2001 when I got the car. Annoyingly, it turned out to be a MC for a 280sl/8 and as the service manual states "they cannot be differentiated by their looks". Bummer. So now I have to wait for the new one to arrive from Germany. MC was still available ($200).

I am wondering though how it is that I have even less pressure now. Maybe the seal started to really give way with the backpressure from bleeding the system.

I'll try one more bleeding operation tomorrow morning with a helper in the car.

Bert

sjefke · #11 01-13-2008, 05:40 PM

Thought you all might want to know how this has ended so far.

So I finally got my new master cylinder this week. I took the old one out yesterday, which was not too bad of a job - just the usual under dash diving. It took me a bit too figure out how to disassemble the old one from its holder, but a vice worked magic to press the old one from the rubber mountings. I was suprised to see that the hose from the reservoir goes into a plastic tube that is simply pressed in a rubber grommet rather than a screw on connector. I took some pictures, because the workshop manual has no section on how to remove the master cylinder.

Anyway, after cleaning the parts, I put everything back in the car (no problems). So I start bleeding again. After having pumped what feels to be the whole reservoir around, I close everything and try the clutch. STILL LOUSY. Then I find that the hydraulic connector is leaking. I post to the forum, but decide to loosen the whole line so it can move a bit, loosen things again, but now get a big plier and wrench out to give it another extra turn. That did the trick. No leaking. Again, back to bleeding. Now it should work, right? NOT! Still bad clutch.

Desperate I get my wife out to press pedals and help bleeding. Still problems.

Then I look to see whether I can hear any movement from the clutch (I am now suspecting leaky slave cylinder). To my surprise I see the slave cylinder MOVE when my wife pressed the clutch pedal. Turns out, one of the bolts is loos and causes movement. So I tighten all that, go through some more bleeding, and voila as the french would say, the clutch works again!

I tested it on the road. Definitely better than what I had a couple of weeks ago. Still feels a bit soft, but that maybe my imagination after having driven the MGB for a while now (that things shifts in no time - very short throw tranny and tight clutch)...

Moral of the story: Check those slave cylinder bolts too!
(not sure anybody mentioned that)

Bert