Manual Shift Difficulty

[ted280sl]

My car has recently become very sensitive when I shift. If I do not fully depress the clutch pedal and very gently shift I will either hear the gears grind or feel the gears shift. In response to this problem I changed the flex hose and bled the clutch. When releasing myy clutch, it engages near the bottom. The clutch was replaced within several thousand miles. Any suggestions would be appreciated.
Ted
1969 280SL w/ shifting dilema

[Mike]

I have some very recent experience with this very issue.  I was advised by a mechanic friend to have the transmission overhauled.  I tried to locate someone through this site that would overhaul it but I never got a single reply to my request.  I located a trusted local transmission specialist who specializes in rebuilding Porsche transaxles but never opened a Mercedes transmission.  He agreed to have a look and I agreed to let him as I have had only good experiences with him on other projects.  He took it apart and found that all bearings and other components were fine except for the "brass blocker rings" which, as I undertsand it, are part of the synchros. These had worn out owing to what he believes is a design flaw that prevents proper lubrication.  I ordered a new set of four from Ray Paul at SL Classics (these rings cost over $250 for the set).  My transmission mechanic plans to file grooves in these rings for better oil passage unless the  replacements already have such grooves.  He claims that, unless he does this, the grinding that I (and apparently you) experienced will return in time.  I have not yet received my parts so I cannot tell you how my situation was resolved.  Further, it could be that you have an entirely different problem.  I simply wanted you to hear my story since my experience shows that there is not a lot of manual transmission knowledge among our group.

Michael L. Hund

[ja17]

Hello Ted,
Sometimes the rear output shaft slotted nut becomes loose. When this happens the gear cluster loosens up causing all kinds of shifting problems as it becomes looser. Typically the speedometer drive gear, which is on this cluster, also becomes loose. This causes the speedometer needle to jump or become erratic, especially when accelerating or de-accelerating.
The tightness of this slotted "spanner" nut can be checked by unhooking the front driveshaft at the transmission and moving it rearward. The slotted nut is nested in the output flange. A lockplate normally keeps the nut from working itself loose.  Mercedes supplies a special four pronged socket to tighten this nut. Some people make there own with a die grinder and a regular socket.
Sometimes just tightening the nut cures the problem. If left alone, eventually a keyed sleeve on the gear cluister will move out of position and transmission disassembly may be required.
Let us know if your speedo is acting strange.

Joe Alexander
Blacklick, Ohio

[ted280sl]

I appreciate the feedback, even if it does not sound good. I was under the dash last night looking at the clutch pedal adjustment because the clutch release so low. I removed the pin that goes into the clutch master cylinder and found it covered in oil. The clutch master cylinder looks like the original so I plan to change it and see if it has an impact.
  I will let you know if this helps.
Thanks,
Ted
1969 280SL w/ clutch problem hoping for inexpensive solutions

[ted280sl]

Mike & Joe,
  I followed my hunch and invested $35 in a clutch master cylinder rebuild kit. Getting the clutch master cylinder out and re-installing it was a real challenge. I got it back in a few minutes ago and I am very happy to report that my clutch now releases much higher and my shifting problems seem to be gone.
  I really do appreciate the advice which you both offered.
Thank you,
Ted
1969 280SL w/ a shiny rebuilt functional clutch master cylinder

[ja17]

Hello Ted,
Glad to see a simple fix worked. Did you have any trouble getting the master to prime-up?  They can be a little testy sometimes.

Joe Alexander
Blacklick, Ohio

[Benz Dr.]

The syncros have grooves in them from what I remember. I rebuild standard trans but must have missed your post. Make sure you use ATF in the gear box - I've seen a few with gear lube which will eventually harden the gears and make them brittle. I use AMS/OIL 100% synthetic ATF and ony this stuff in my 5 speed. They have steel syncros and shift VERY poorly when cold. MB boxes are very smooth shifting at any temp due to the brass syncros.

OK class. How do you know if a syncro is worn out once you have the trans all apart?

Dan Caron
SL Barn

Daniel G Caron

[ted280sl]

Joe,
  Getting the master going took a while. I tried pumping it to get it going and it seemed that nothing was happening. I have a compressor so I shot air in through the resevoir. The air pushed the hydraulic fluid in. The pedal came right up.
Thanks again for the advice.
Ted

[Mike Hughes]

OK class. How do you know if a syncro is worn out once you have the trans all apart?

The high spots of the grooved areas will eventually flatten off.  When the flattened area is wider than the valley between the high spots, the synchro ring is fairly well worn.

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[ja17]

Ted,
You can also use a front brake caliper to bleed the clutch master. Hook a tube to the bleeder on the brake caliper and the other end on the clutch master cyl. bleeder. Open both and gently push the brakes!


Joe Alexander
Blacklick, Ohio

[Benz Dr.]

Nope. You can't see the wear to the point that they look bad. This is a VERY fine tolerance. Either they work or they don't - how can you tell during a rebuild?
 OK. The one that was grinding would be a good answer but sometimes that isn't why it was doing that.
So, there's a way to tell - what is that way?



Daniel G Caron