Hi, I am new to the forum! I have owned an 85 300d for a couple of ears now and it just hit 132k miles. Pretty low for these things. So ever since I have had the car first gear is touchy. Basically, when I start from a stop I have to give it very little throttle because if I floor it or even give it more than half throttle it will jump out of gear into neutral and rev up. As soon as it gets out of first gear the rest of the gears are fine. I can floor it in 2nd 3rd and 4th. It wasn't that bad when I first bought it but now it's getting worse. If I am stopped on a really steep hill I am pretty screwed. Anything I can adjust? maybe a vacuum problem? or I have heard maybe could be a B2 piston problem or seal. The transmission fuild smells slightly burnt im going to change it but I do not think the fluid could be making only first gear a problem.

What you described can be your B2 piston on the way out. Mine did that and changing the filter and fluid fixed it but less then a year later my B2 Piston broke. When it breaks you cannot go forward.

There is the piston itself a lip seal and if it is the original there is an aluminum bushing. So you have a 30+ year old lip seal and a aluminum bushing that kind of grabs onto the B2 piston. The replacement bushing is made of nylon.

On a W123 the B2 piston area is up in the tunnel so it is slightly more complicated then on some of models from the same year.
The new piston has also been updated. I don't know if the 1985 has the updated piston already or not. I would ask member Deliveryvalve about that and also about your actual transmission issue.

In the attached picture of my broken piston the red arrow points to where the Piston was binding on that aluminum bushing.

And oddly the lip on the lip seal faces outwards.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

The B2 band and its piston are applied in 1st, 2nd, & 3rd. Hence, any failure of the B2 components will affect 2nd & 3rd as well as 1st. The component that is unique to 1st is the freewheel clutch, also called a one-way clutch or sprag. When it fails completely there will be no 1st or reverse.

I have reverse it's actually very solid, one thing that might be worth mentioning is that when I put it into drive I have to wait a second for is to actually engage. Maybe its something to do with the vacuum? I disconnected the line that goes to the tranny to see if it makes it worse but it didn't make a difference maybe I have a leak there.

I was thinking it might be B2 but its only first gear that is it all of my other gears work perfectly fine.

I am just saying mine started off flaring in first. I had to rev up to finally engage. The other forward gears worked. I changed the fluid and filter and got most of another year before the B2 Broke.

So there is symptoms of a B2 piston issues which are different from symptoms of what happens when the B2 piston breaks. But that is just my opinion.

Anther thing I have noticed is that the American Cars I have had with like 200 thousand miles on it still have strong transmissions. I think that the ZF Transmissions in the Mercedes must not be as well made as it does not seem that they hold up as well.

The attached pic is text from the ASTG transmission manual.
"Complaint: Transmission slips when starting in first or second gear or forward start impossible but reverse speed in order."
Notice that there is 2 separate sets of symptoms.

If you cannot move forward in any gear the B2 Piston has broken or the B2 band has broken.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Yeah, when my B2 went out, it would start slipping off the line at lights. I guess this was 1st. I stupidly ignored it because it would hook up if I shifted the car to neutral and revved it or if I put it in park, killed and restarted the engine.

Then one night at a red light in a bad part of Oakland...pop. No more first. Sometimes it would go in and I could drive along in 2nd. Crazily I backed the car up in R back to my friends place over several blocks.

So I suggest stop driving and get the car up on stands. Pull the B2 access cover and see what falls out. Mine was cracked.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles

Yeah I am going to take it to a shop cause I really have no place to wrench I live in Moraga people here freak out when you work on your car where they can see you.

I am taking it to a shop to see if they can diagnose a couple of things so hopefully they do not just tell me the whole transmission needs a rebuild, which is most likely not the case. Ill let you all know how it goes.

If the shop does not do transmission work they will likely say you need the rebuild. Part of the reason they would not want to work on it is that they have to warrant the work and they rally cant do that in this case.

The ZF transmissions are used in other euro cars. I don't know if they have the same issues or not but my bet would be yes. That means place that specializes in foreign Cars is more likely to know about it.

Maybe someone here knows what other Cars use the same Transmission.

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84 300D, 82 Volvo 244Gl Diesel

b2 band valve easy to change, search around there might be a how to

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85 300d in progress

https://www.google.com/search?newwindow=1&client=safari&rls=en&sxsrf=ACYBGNQvsMSXYBxOq1VigNT_Tb1cVTr2Ig%3A1572187754796&ei=aq61Xc-nMLKK5wKEjpWgDw&q=b2+band+piston+replacement&oq=b2+band+piston+replacement&gs_l=psy-ab.12...23479.25794..28347...0.0..0.77.453.6......0....1..gws-wiz.rd639SYn3NI&ved=0ahUKEwjPhJTl17zlAhUyxVkKHQRHBfQQ4dUDCAo

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85 300d in progress

Transmission:

and on this site

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85 300d in progress

Hi Axelreed,
sorry to hear you have a transmission problem.
Before you take the car to a shop let me ask a good friend who lives near you in Orinda where he takes his car. He has an Indy that would I believe be a good place to go.
Like others said, most mechanics who do not understand Mercedes transmissions will just say it needs a rebuild.

OTOH the '85 series 300D used a tranny that is smaller than ones used in previous years. It has been said it was not as reliable as the earlier ones but I can't say that was my experience. I owned an '85 300TD and never had a problem with the transmission but unfortunately it was wrecked before it got to 250K. It was the best running W123 I owned, and I've owned three, an '83 and the present 300TD I drive with 375K on it (I confess it has a rebuilt transmission
And if you do find you need a rebuild I know an Indy on the peninsula that still does them or you could drive to MZF in Burlingame and pay a bunch of $$ and get it fixed or whatever it takes by the experts.
I will send you a PM or otherwise let you know the Indy thats local to you.
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

My blue 85 Cali 300d has that little trans. I learned the hard way when I tried to change the pan gasket from my collection of 82 300sd parts. Sorry to hear they may be weak. My car is a low mile car and it has already had a rebuilt trans at about 160k miles. I chalked it up to abuse but maybe you’re on to something.

Too bad the op cannot open the access panel on the side of the trans and check for a broken B2. It was easy on my SD because the 126 tunnel had a lot of space on the side. I have read here that the w123 needs more loosening of the mounts and wedging to get to the panel. Heck, I should go downstairs and check my blue 300d to see just how much space there is.

If I still lived in Los Altos I’d have offered to help. And my millionaire neighbor did freak out when she saw me replace my B2 piston myself. She got a nice view of my feet as I laid under the car all day. I later saw her at Peets and she asked me what I was doing. When I told her transmission problems she said “hope you fix it, that gets expensive.” I told her, “already did” and pointed to the SD parked nearby. I’m sure Moraga is the same. I almost moved to Lamorinda because it felt like Los Altos.

You’re going to have to find a very good mechanic who will just fix a B2 piston for you. Most will just sell you a rebuild.

I was tempted to try that guy you mention in Burlingame because they looked like they knew their stuff. Fortunately my 722 made it to LA before it blew and I got a rebuilt from Marc at Sun Valley. By far the best upgrade for that car. Way better than the rebuild in my 300d done by an unknown import shop.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles