GEARBOX CHANGE ON W126 500SEL

GNJ

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I have managed to fry the gearbox on my 1982 500SEL. I have managed to source a 1989 box from a 560SEL, but having got the old box out, I see that there are a couple of differences on the connections and I want to make sure that I can proceed to make the change without any problem.
The attached photos show the differences.
Photos A-C are of the old box and D-F are of the replacement.
Difference 1: In picture E a vacuum link can be seen that is not on the old box (picture B). This appears to relate to a transmission 'mode selector' which I am assuming is something like 'normal', 'sport' etc., which I do not have on the car itself. So can I just nip this off so it is non-functional?
Difference 2: In picture D there is an electrical connection that is absent on the old box (picture A). I have no idea what this is for, so I don't know what effect it will have on the functioning of the box if I just ignore it. There is nothing on the old box, so I am hoping it is for a newly fitted function that will not interfere with the operation of the gearbox itself if I just leave it unconnected. Can I just ignore it without any problems?
I have included photos of the part numbers of the old box (picture C) and of the new one (picture F) in case that will help to answer my question of whether I can just bolt in the new box.
I will be very grateful for any help on this!
Thank you
Gavin
 

Attachments

  • 560 Gbox Part number DSC05953s F.jpg
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  • 560 Gbox DSC05947s+arrow E.jpg
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  • 560 Gbox DSC05944s+arrow D.jpg
    560 Gbox DSC05944s+arrow D.jpg
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  • 500 Gbox Part number DSC05951s C.jpg
    500 Gbox Part number DSC05951s C.jpg
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  • 500 Gbox DSC05940s+arrow A.jpg
    500 Gbox DSC05940s+arrow A.jpg
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  • 500 Gbox DSC05942s+arrow B.jpg
    500 Gbox DSC05942s+arrow B.jpg
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brianbrian

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The vaccumm on the box replacement, would be fitted to a car that has a vaccumm pump, or vaccumm pipe coming of the inlet manifold. This is for adjusting when the car changes gear. So if not fitted, the gear change could be very rough.
 
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GNJ

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Thanks for that. And do you have any idea what the electrical connection on the other side of the gearbox is for?
 

star

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The vacuum/cable should be able to swop over, the electrical connection is the load protection switch fitted to 560's. The modulating vacuum should work as normal
 
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Great, thank you. So, if I understand your answer correctly, I can put the gearbox in without any issues?
 

star

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I can’t be 100. % sure.
 
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GNJ

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Sure, I understand that - you haven't seen the actual car and gearboxes!
It sounds from your messages that not connecting the electrical connection will not have any effect. I don't fully understand your statement that the 'vacuum/cable should be able to swop over'. On the old box there is a connection for the Bowden cable only, but on the new box there is also a vacuum connection. I am assuming that if I just nip it off and make it non-operational then it should be ok (although BrianBrian notes that it could change the characteristics of the gear change, making them rough).
If you would explain your statement in a bit more detail I will be very grateful.
Thanks and regards
 

star

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The electrical connection can be left disconnected as it’s a load protection switch to reduce the torque generated by the engine on full load gear changes.
The vacuum (modulating) on the opposite side of Bowden cable affects the gear change.
I can remember if the Bowden cable vacuum is just for switchable modes. I’m pretty sure you can put your old cable in.
 
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GNJ

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Perfect! Thanks for your help and support. I will see how it goes and let you know.
 
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GNJ

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An update on the gearbox change. Attached are four photos:
'G' and 'H' show a connection at the back of the old gearbox. On the replacement gearbox the mechanic said he had to put on a 'jumper'. I am not clear what this actually involved - a jumper to me is an electrical connection!
'I' shows the same view as 'A' and 'D' in the original set of photos. As there was nothing to connect to the electrical connector on the replacement box we just ignored it (see advice from Star above).
'J' shows the Bowden cable on the old box. The Bowden cable on the replacement box was a straightforward connection (also see advice from Star above).
I have now driven the car for about 500 miles, including a 300+ mile round trip, without any problems. The upchange is a little slow and the downchange is a bit eager, but the gearchange is working fine in both directions.
The next step is to fine tune the pressures to see if I can make the changes a little sweeter.
So all in all a successful change.
Thanks to Star and Brianbrian for their input and support!
 

Attachments

  • 500 Gbox DSC05961cr+arrow J.pdf
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  • 500 Gbox DSC05960cr+arrow I.pdf
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  • 500 Gbox DSC05959cr+arrow H.pdf
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  • 500 Gbox DSC05958cr+arrow G.pdf
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