Transmission: first gear revs without power - PeachParts Mercedes-Benz Forum

ubertino · #1 11-08-2014, 04:52 PM

I've got a 1982 with an actual 196k on the clock. Almost perfect body, great engine. Ran just fine until this morning.

When things are operating normally, when I put the transmission into Drive there is a small but observable lurch on the car as the gear engages, and when I release the brake it idles forward. All as it should be. First gear is not only responsive, but the car is almost peppy.

This morning, when I put the transmission into Drive, there is no little lurch, and the engine revs with little load until the transmission shifts into 2nd gear, and then power and drivability is as normal. Until it goes down into second. The transmission is shifting fine up and down between gears, it's just in first that it doesn't seem to have any effect.

FYI, the vacuum system is good- the central locks, HVAC is all working like it should and holding pressure.

Since I've never had a transmission fail on me before, is this the fabled slipping that I hear about that leads to transmission death? Or perhaps this could one of the B or K pistons going bad?

I have a very good indy who has a '81 300D as his daily driver, I'm looking for a heads on what I should be preparing for before I bring the car to him on Monday.

Any thoughts would be most appreciated.

Diesel911 · #2 11-08-2014, 05:13 PM

I had a similar issue in what passes for Cold Weather many years ago. I changed the Transmission Fluid and Filter and that cured it till not quite 1 Year later the B2 Piston Broke.

I am speculating that the B2 Piston was sticking during the Cold Weather. Perhaps changing the Filter and Fluid allowed a little more pressure to get it to work.

If it goes out completely a few People have found that it was actually the B2 Band that cracked in two and not a broken B2 Piston. It will be up to you to decied if you want to verify that the Piston is the issue or not.

I had other vehicles to drive so I pulled the B2 (parts) out and did what I could to verify the Band was intact before ordering the B2 Piston and related parts.

leathermang · #3 11-08-2014, 05:23 PM

I noticed that you did not mention the mileage at which you last changed the trans fluid and filter.....?????

Diesel911 · #4 11-08-2014, 05:26 PM

I had a similar issue in what passes for Cold Weather many years ago. I changed the Transmission Fluid and Filter and that cured it till not quite 1 Year later the B2 Piston Broke.

I am speculating that the B2 Piston was sticking during the Cold Weather. Perhaps changing the Filter and Fluid allowed a little more pressure to get it to work.

If it goes out completely a few People have found that it was actually the B2 Band that cracked in two and not a broken B2 Piston. It will be up to you to decied if you want to verify that the Piston is the issue or not.

I had other vehicles to drive so I pulled the B2 (parts) out and did what I could to verify the Band was intact before ordering the B2 Piston and related parts.
At the bottom of the Pic you can see where the Piston was binding on the Aluninum Bushing that came with the Transmission.
The Binding and an old Seal not holding pressure can keep the Piston for working properly.
The replacement Bushing is made of a non-binding Nylon.

ubertino · #5 11-08-2014, 06:01 PM

Fluid and filter were both replaced in April, about 5,000 miles ago.

It is colder (high 30's) than it has been in some time.

leathermang · #6 11-08-2014, 06:12 PM

And you checked for proper fluid level today ?
we have to ask these things... you would be surprised....

ubertino · #7 11-08-2014, 06:16 PM

I did, and it was a tad low. I checked it and topped it up with the engine running, etc.

@Leathermang, I understand, and often need to be reminded of those little things.

leathermang · #8 11-08-2014, 06:23 PM

I sent you a PM..
my battery low..
back later,

ubertino · #9 11-17-2014, 12:58 PM

Just an update, my mechanic, who drives a 83 300D as his daily driver, looked at the transmission, and drove it to a transmission shop that he's worked with, and the consensus is that, while they could fix the piston, and it should fix the slipping in first, it doesn't matter because either the pump or a bearing in the transmission is going.

Fortunately I have a spare transmission in the garage from my last 300TD that I parted (and kept the parts). It's a pretty worn transmission, but it works and will tide me over until I either do a manual swap or get a lower mileage transmission.