'78 300CD Automatic Transmission Question

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markcharles@webtv.net - 04 Mar 2006 21:29 GMT

I'm thinking of buying a 300CD (4 cylinder) that won't shift out of
first. Is this just a matter of tightening the belts and changing the
fluid? If not am I better off getting the original tranny rebuilt? I
know that buying a used one is risky but if I could get one for a few
hundred from a reputable salvage yard it might be worth the risk. How
common is this tranny?
Please post your responses to this group.
Thanks for any info.
Mark

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Karl - 05 Mar 2006 01:03 GMT

A 300CD is a 5 cylinder naturally aspirated diesel coupe.

NOT a 4 cylinder! If it has a 4 in it, run away, run far away.

On that engine/trans combo, the upshift is vacuum controlled. Any vacuum leak in the pump circuit
all the way to the modulator on the trans will screw up the shifts.

> I'm thinking of buying a 300CD (4 cylinder) that won't shift out of
> first. Is this just a matter of tightening the belts and changing the
[quoted text clipped - 5 lines]
> Thanks for any info.
> Mark

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markcharles@webtv.net - 05 Mar 2006 02:17 GMT

It was advertised as a 4 cyl so thanks for clearing that up. Maybe they
meant only 4 cylinders are all that work! Thanks for the info.

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Richard Sexton - 05 Mar 2006 16:20 GMT

>A 300CD is a 5 cylinder naturally aspirated diesel coupe.

turbo in some (one?) year)

>NOT a 4 cylinder! If it has a 4 in it, run away, run far away.
>
>On that engine/trans combo, the upshift is vacuum controlled. Any vacuum leak in the pump circuit
>all the way to the modulator on the trans will screw up the shifts.

vacuum modulates harshness of shifts, but does not control it. if you
pull the vacuum off the tranny it'll still shift. too little vacuum
and it's very harsh. too much and it slips like hell when it shifts,
but it will shift without it

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T.G. Lambach - 05 Mar 2006 01:07 GMT

Why do you want a 28 year old car with a busted transmission???

OK, if it's FREE there are a few things you should know.

This diesel is a five cylinder non-turbo engine that made 77 HP when it
was new. So in TOP condition this car will have lame acceleration.
Remember, it's now 28 years old so getting it back to reasonable
condition will take some $$ and effort on your part.
The climate control is very complicated and can be expensive to repair
so be sure it works and that nobody has "fixed" it for you'll never get
it back to its original operation.

There are lots of these 4 speed transmissions about; they were standard
issue for many model years of the 123 series (this one).

Really, if you want a M-B shop for a '82 or later Turbodiesel. These can
be bought for a few thousand and they have 120 HP - adequate to keep up
in most traffic conditions.

Buying a cheap luxury will be the most expensive way to own one. Old
cars don't get a senior discount.

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markcharles@webtv.net - 05 Mar 2006 02:10 GMT

Thanks for your advice & info. As far as this '78 300CD goes, I'm just
looking for something cheap to get around town in that I can use with
bio-diesel. I'm not looking for luxury but I've always appreciated the
good quality of a MB. As far as old goes I prefer pre-70's cars. I've
never bought a new car and never will because I'd much rather have an
old classic.

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wolfpuppy - 05 Mar 2006 16:26 GMT

> Thanks for your advice & info. As far as this '78 300CD goes, I'm just
> looking for something cheap to get around town in that I can use with
> bio-diesel. I'm not looking for luxury but I've always appreciated the
> good quality of a MB. As far as old goes I prefer pre-70's cars. I've
> never bought a new car and never will because I'd much rather have an
> old classic.

I almost bought the SL body style (late 60's to, I think, '72) because I
love the look. However, I love the body style of the SL that came out in
'91 slightly better, so I got one of those. My mech told me not to touch
one earlier than a '95, though, so I got a '97 SL500. Beautiful car. It's
my toy car. But I love the earliest ones--they have some of the greatest
looking front ends I've ever seen.

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Richard Sexton - 05 Mar 2006 16:36 GMT

>I almost bought the SL body style (late 60's to, I think, '72) because I

113 chassis. some parts are getting stupid expensive now. pistons sets
for early 230's are now mid four-figures and rare. body parts for these
cars became stratospheric ages ago. lovely beasts though.

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Richard Sexton - 05 Mar 2006 16:18 GMT

>I'm thinking of buying a 300CD (4 cylinder) that won't shift out of
>first. Is this just a matter of tightening the belts and changing the
[quoted text clipped - 5 lines]
> Thanks for any info.
>Mark

If this 300CD has four cylniders the somebody stole one. It should
bea diesel, too, hence the "D".

The tranny is pretty good. I have 400K miles on my original one. Fairly
common, it'll never shift as well as say a Chevy one, but it pretty
durable.

I'd do the fluids, filter an fiddle with it first, then swap
in another one if it still doesn't work and labour was chea
or free and the "new" one ws guarenteed to be ok.

While not exacly a classic the diesel coupes have a small cult
following and are very cool cars inasmuch as the mid size 123
series can be. I menan it aint no luxo 111 handbuilt coupe,
but it's not exactly a taxi either. I like'em.

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