w123 4 speed autobox thump

woyzeck

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Mercedes W123 200
Hi there,

I recently bought my first classic merc, a 1984 w123 200. It runs beautifully, and I am very happy that I took the plunge. There are, of course, a couple of issues with it, which I was hoping that somebody might be able to steer me on:

1> There seems to be a small, rhythmic thump from the gearbox when engaged in drive or reverse, whic comes and goes, but seems to be prevalent when cold. It isn't loud, but is noticeable. Could this be the central bearing going perhaps, or would flushing the tranny fluid and refilling with a thicker solution be a good starting point?

2> The dash lights aren't illuminating the speedo, which I understand is a common problem. i don't think it is the fuse, as other lights, but I was wondering whether somebody might have a link to a guide (hopefully with photos!) that demonstrates the process of removing the cluster to replace the bulbs/ clean and fiddle with the rheostat.

Many thanks for reading.
 

Ted

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Turn the dimmer from end to end a few times first! It may just be dirty contacts in the rheostat.
Also, the dash lights on a W123 aren't very bright to start off with, and can't be seen in daylight like a lot of modern cars - are they definitely not working?
 

James1976

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+1 on fiddling with the rheostat - they're often dirty and fiddling with them quite a bit will make them work.

My old 200T also had a bit of a lumpy box to be honest and that was low mileage at 42,000.

It used to be worst when cold and always used to wind up in reverse and then launch you at the car behind as I'm sure yours does too. Change the fluid by all means to new (don't think they come in many different viscosities you use the specified one) which might make it a bit better, but I think it's symptomatic of the box. They're not the smoothest you'll have tried!

And lastly enjoy - the W123 is a cracking car.
 

grober

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Change the fluid and filter. Its called a "fluid" for a reason- don't thicken it. Its designed for Dexron 2 type fluid but might benefit from using Dexron 3 which is backwards compatible and has slightly better performance when cold. e.g. FUCHS TITAN ATF 4000

standard fluid would be FUCH TITAN 3000 DEXRON 2 http://www.opieoils.co.uk/t-recommendations-car-or-bike.aspx
 
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jaymanek

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Like above, the W123 box is not that smooth. My 60K mile W123 sometimes produces the odd lurch or harsh change, but thats how they are.
When I first got my car, I took it to a Mercedes transmission expert who told me to save my money as that is how they left the factory.
That said, there is a vacuum solenoid on the side of the box that can be adjusted for smoother changing. Although it doesnt make that much difference.

A fluid change is never a bad idea and dont forget to drain the torque convertor which holds more fluid than the sump itself. IIRC total fluid required is around 7 litres!

With the rheostat there is a very easy fix. Just get a little bit of copper wire and bridge the two copper metallic strips on the back of the rheostat. It will be on max all the time... even on max it is not that bright really!

Jay
 
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woyzeck

woyzeck

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Mercedes W123 200
Thanks for all the help so far.
 

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