gears grind over 2000rpm

[tbarrie]

I just joined the forum and did a brief search but didnt come across exactly my issue, I just inherited my grandfathers '66 230sl, 4 speed and when driving I cannot shift into 2nd or 3rd over 2000rpm without the gears grinding.  4th is no problem but i seem to have the same problem on th way down the gear box also.  I read through a few posts and am thinking that it might be the bushings or syncros, anyone have a similar problem or thoughts?  I am a "starving student" and cannot afford a lot right now, but at the same time it is my only car at the moment and I will do whatever I can to remedy it.  If anyone can point me in the right direction or offer some advise I would be eternally greatful.  Could also use the name of a good MB mechanic in North Carolina, just moved here from San Diego and I already miss my local expert.  Thanks

[jeffc280sl]

Welcome.  Have you checked the fluid level in the transmission?  Do you know anything about the condition of the clutch, clutch master and slave cylinders? Is the clutch fluid tank leaking?  Read up about the clutch operation and check for clutch fluid leaks from the slave and master.

I think the syncros and transmission in general are very robust.  When I tore mine down I did so because a bearing failed.  Everything else inside the housing was in very good shape.

[ja17]

Hello and welcome,

Quite often the issue is that the slotted nut on the back of the transmission flange has come loose, allowing the gear cluster to loosen.  This condition can cause these issues with shifting.  The speedometer needle may become irratic and will bounce up when you let off the gas pedal if the cause.

I have information and photos which I can post if this is the case.

[tbarrie]

    Jeff- I'm not sure about the condition of the clutch, but there does not seem to be any "obvious" leaks, though there has been about 25 years worth of a slow oil leak coating under the car ( I am in the works to both clean and find the issue)  next paycheck I will look into flushing and replacing the tranny fluid though- anyone know of a good shop in North Carolina in the Charlotte area?-  It does seem that the clutch has to be pushed all the way to the floor to shift though, but as I said it is only a problem in 1-2 or 2-3 shift, and then again on the way down. I have no problem shifting from 3-4 even at high revs.. that why I was thinking of an internal problem with the gear box.  Not too sure about the master or slave cylinders, I just recently inherited the car and unfortunately I there were not any recent record, I have list of things that my grandfather did 30 years ago but thats not much help.

Jay- thanks for the info, can you either post or send me a pic of the location of the nut you were speaking of, it might be the case and would be nice if it was such an easy fix,though I have not seen any fluctuations in the tach during driving.  Would there be any other symptoms to look for if this was the issue?

Thanks to you both for such quick responses, I have wanted this car for my whole life, but I don't have any experience with old MBZ and am scared to death of hurting it.  I am glad that I found a comunity of like-minded people who have some knowledge and experience to draw from. 

[Miloslav Maun]

I have the same issue. My transmission was rebuilt recently but it did not help (we changed all the synchros and bearings). Then we have changed the three finger pressure plate (one of the fingeres was a bit weaker which might have caused the clutch disk to be released unevenly). This helped a bit (the grind-revs went from 2000 to 3500).

Now I have obtained a used transmission which should be ok according to the seller. I do not know yet if this helps...

[jharkin]

call Junior at Gunter Mercedes in Rock Hill, about 25 mi south of Charlotte.
his number and address are
803 327 7039 or 327 1448
336 saluda st
rock hill 29730

[ja17]

If your speedometer has become irratic, and your transmission is not shifting smoothy, the slotted spanner nut on the output flange of the tranmission may have come loose.  This slotted nut holds the entire third fourth gear cluster tight. In addition the drive gear for the speedometer is NOT keyed to the shaft but depends on the tightness of the cluster and slotted nut before it can operate correctly. 

To check for this condition, test drive the car and confirm the speedometer needle pops upward  when letting of the gas pedal or may also change when the clutch is depressed.  These actions load and momentarily tighten the gear cluster and cause the speedometer to function briefly.

Consider inspecting and replacing  the rear tranmission mount, the drive shaft rubber flex disc, and  the rear transmission seal if needed during the transmission work.

Start by removing the multi-bolt tunnel plate and transmission mounting plate. Remove the rear transmission mount and bracket. Remove the 19mm driveshaft bolts.  Pay close attention to the configuration. There are three long bolts and three shorter bolts.  Refer to the information and diagrams for re-assembly.  This must be installed exactly or the rubber disc will not last or will come apart.
 
The drive shaft has a slip joint half way back.  Loosen the 44mm and 46mm slip joint and slide the drive shaft rearward. This will allow you to split the drive shaft at the drive shaft flange/centering bushing connection and enable you to remove the flex disc, and move the drive shaft out of the way.

Check the slotted spanner nut for tightness. If it is loose it must be re-tightened. A special four prong socket is still available from Mercedes for these nuts. Some mechanics make their own with a die grinder  and a 1/2" drive 1 1/8"   deep well socket.  In a pinch the nut can be driven tight using a drift and hammer (not recomended).  The sheet metal lock ring must be "staked" outward and inward to prevent the slotted nut from comming loose again.

Before re-instlling the flex disc, check it for conditon also note that the three tabs on the flex disc MUST be postitioned on the three flanges of the transmission out-put shaft (see diagram).  Notice locations of the long and short diveshaft bolts and the washers. Review the diagrams, this is critical. Notice that three of the washers are positioned under the bolt heads and the other three under the nuts of the other three bolts. In every case the washers are positioned next to the rubber flex disc. The nylock nuts can be reused if the condition is ok and everything is re-assembled correctly. The driveshaft bolts should be quite tight and you may feel the nuts bottom out against the bolt shoulder as you tighten them down.

Pump a bit of grease into the driveshaft end at the Zerk to lubricate the centering bushing assembly.

Install the transmission mount paying attention to the spacer washer between the mount and the mounting plate. Tighten the drive shaft slip joint last after the tranmission is secured.

Good luck! Keep us up to date.