Auto Gearbox Problem

[DavidBrough]

I think I may be seeing the first signs of a gearbox problem and wonder if anyone has any ideas as to fault and remedy.

When pulling out of my drive the other day the gear changed from second to third almost immediately but seemed to slip into a neutral first allowing the engine to rev slightly before engaging third with a thump. It then seemed to work OK even when I stopped and restarted again, although by then the oil was warm. Had no further problems until today when it happened again. What does seem odd is that it only seems to happen when I turn sharp left out of my drive, when I set off and turn right everything seems OK. This may be just chance of course but it does seem odd. I have checked the oil which is at the correct level and clean and I changed the filter last year.

Does anyone have any thoughts or ideas on this.


David Brough
1969 280SL Auto with A/C

[graphic66]

Could it a bad tranny or engine mount causing the linkage to shift to neutral when turning?

[Benz Dr.]

Keep turning right. You'll find your way home eventually.....

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[DavidBrough]

Thanks David, I was sort of hoping it might be something to do with the gear selector so had already checked the engine and gearbox mounts and the selector leaver moved and selected freely.

All mounts were new about a year ago and still seem OK. Although I must admit that I have never been completely happy with the gearbox mount as it has a rubber washer between the bolt and underside of the gearbox mounting plate which hampers tightening it up, does anyone know if this is correct? Anyway, I decided to take it off and was able to properly tighten the bolt but that hasn’t made any difference. It still seems to select a false neutral briefly before re-engaging gear so still staying on the selector theory I will have a look at the selector arm adjustment as I also changed the bushes about a year ago but it does feel OK. I will also wait for the weekend and find a deserted car park for further evaluation as it is difficult to test an intermittent fault on the road.

Any further thoughts and ideas gratefully received.

I did think about taking Dan’s advice but on reflection it would be against Health & Safety guidelines due to the possibility of RRI or repetitive righturn injury.


David Brough
1969 280SL with A/C

[DavidBrough]

Well, I’ve completed some testing and checking but the problem still persists and I’m really stumped. I have checked the selector linkage and the three position solenoid and all is OK. I have driven the car with the gearbox inspection covers removed to check for an electrical problem with the three position solenoid and any untoward movement but nothing, all appears fine. All mountings are new and tight oil is clean and between the marks when hot and there are no visible leaks.

However, second gear still slips when moving off with left hand lock. I know it sounds bizarre but this does not occur when moving straight or right, just left and only happens when the gearbox is cold. Once heated up everything works OK. I drove round and round a deserted car park yesterday and could not replicate the problem as the car was quite hot by the time I got there. But this morning when starting from cold a little left lock in second induced slip but straight ahead or right did not and once warmed up everything worked OK. All gears are available in both manual and auto modes with changes occurring when they should.

All thoughts and suggestions gratefully received.


David Brough
1969 280Sl Auto with A/C

[hands_aus]

David,
JoeA always recommends adjusting the transmission valve body bolts when changing the filter and fluid.

I don't know if that would help in your situation.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[DavidBrough]

Thanks Bob. I did change the fluid and filter about a year ago but didn't know about re torquing the valve body bolts. Something to try if I have to start taking the tranny apart to find a fix.

David Brough
1969 280SL Auto with A/C

[graphic66]

Could it be in the differential?