1973 450 SE Transmission Question - Mercedes-Benz Forum
 
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post #1 of 6 Old 04-04-2014, 06:50 PM Thread Starter
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1973 450 SE Transmission Question

Hello,

I have just purchased a 1973 450 SE. Aside from a few issues (a few areas of surface rust and a few cracks on the dash) the car is in amazing condition..... with one exception. The car had not been driven for quite some time and the transmission seems to have trouble-- it delays in shifting from 2nd to 3rd and seems to hang in and almost 'neutral' position before shifting at times (the reason i say 'almost neutral' is that the car still appears to have forward momentum).

At first, I was thinking I would need to replace the transmission. However, my mechanic changed the fluid and filter and stated that "it's okay-- it just need to be driven for a while before it shifts smoothly."

I have known him for years and he has always been honest-- and I hear no 'grinding' and the fluid is (and was) free of any metal of debris.... I am hoping he is right (as usual) but am a bit worried about driving it this way.

Have any of you had (or heard of) a situation like this? Any opinions/tips???

Many thanks,

John
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post #2 of 6 Old 04-06-2014, 04:37 AM
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I think you need to adapt to the car, it is an old style tranny and is nothing like the modern transmissions we have today, give it some time and see.

ERIC
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post #3 of 6 Old 04-29-2014, 05:56 PM Thread Starter
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Hi Eric,

Thanks so much for your reply. I have tried your advice and have seen some improvement. Unfortunately, there are still significant intervals where the car will not shift (it's almost like I have the clutch in, but i'm still moving forward to a degree). and I slow up the traffic behind me(!).

My mechanic now thinks my transmission needs to be rebuilt or replaced. I have found one (used for $450 USD). I have also found someone who wants to trade for his 1975 280, which is in good working order. Any thoughts???

By the way, I see you're posting from the PRC! I used to live and work in Dalian... Small world.

Many thanks (xie xie),

John
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post #4 of 6 Old 04-30-2014, 01:22 AM
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I would stay with your present car and put another transmission in it. I have been in China for 20 years and watching the pollution getting worse especially north from Nanjing.

ERIC
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post #5 of 6 Old 05-01-2014, 06:58 PM Thread Starter
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Thanks Eric,

I have heard a couple of hopeful avenues of exploration before putting in a new transmission. One individual suggested that I look at the 'vacuum modulator' on the transmission (he determined that my shifting problems only occur in 'D'-- the transmission seems to function normally in the 2 lower gear settings.

The other individual told me of an intriguing possibility. He stated that there is a 'little switch' that can be found under the accelerator pedal and that this switch can become stuck. He suggested checking the fuses and then moving this little switch up-and-down several times. Have you ever heard of something like this? I'll give it a try- though I can't imagine what the function of the little switch would be.

I can only imagine the pollution situation-- I was in the PRC between '84-'87. It was a whole different world then. I remember coming in from my Beijing bike commute black from coal soot but I can't imagine the pollution there must be currently....
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post #6 of 6 Old 05-02-2014, 03:27 AM
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I have not worked on this model for very many years so my knowledge is somewhat faded.

The switch under the throttle is probably the kick down switch and if stuck in the on position then the car will shift late.

The modulator box is controlled by vacuum and it has a small diaphram inside which can become damaged. This modulator controls line pressure and could be your problem.

If you remove the little cover on the end of the modulator there is a key inside it, remove the key and turn it over then re insert it, then you can turn the modulator clockwise to increase line pressure and vicky verky to decrease line pressure.

Be careful not to turn it too much as you do not have a line pressure guage to take readings.

ERIC
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