Auto Gearbox Problem - Not Pulling from Standstill

[paul_GB]

Can anyone help with this problem on my 64 230SL auto..? I recently rebuilt a replacement engine and installed it along with auto box (that I had rebuilt at a shop). I set up everything on the engine and it is running pretty. I took it for a test drive last night and this happened :

1) From standstill with the auto box selector in '4' it simply revved hard with very minimal drive engaging (just like a manual box slipping its clutch very badly). On trying position '2' on the selector there was marginally more 'traction'.. but still free revving.
2) After persistence (and a slight downhill gradient) at about 15-20mph 3rd gear suddenly engaged firmly and then at higher speed 4th dropped in nicely.
3) It dropped through 4th to 3rd when slowing (pretty smoothly), but trying to pull away again at low speed it revved lots again as if 2nd gear not engaging.

It might well be something obvious and Im too close to see it! Things Ive checked :

- Engine linkages (as per 'linkage tour')
- New Auto box oil (Dexron III) and filter.
- Oil level - with car sitting flat the oil level is half way between high/low lines on dipstick when hot (after test drive)
- 3 way solenoid operating fine (checked thro the tunnel access hole - as per excellent instructions on this site)
- Throttle switch operates fine (opens when throttle flap starts to open)
- Wiring to the connector block terminals checked out (fortunately I took photos before removal)

I haven't tried checking vacuum or pressures yet. Could there be a fluid airlock maybe?
Has anyone experienced this before.. any ideas are very welcome?! Thanks.

My plan to take the car to the Classic Lemans 24hr weekend on 8th Jul are just about dashed. But rather have a reliable car at the end!

Paul

[Tyler S]

I dont think there would be an air lock.
The trans takes about 5 quarts when filling the first time. Are you checking the fluid level with the engine running?
Check pressures next. If pump pressure checks out (which is probably ok) then there is most likely a damaged lip seal on the 1/2 clutch pack.

[paul_GB]

Thanks Tyler.. I was actually checking with engine off after getting it up to temperature, is that wrong? Do you know what the level needs to be with the engine running..? I'll check that and see if it's wrong.

Cheers
Paul

[Tyler S]

Absolutely check with the engine running! Set the level to the upper mark when hot.
hopefully no damage was done running it with a low level.

[Paul & Dolly]

Paul,

There is a procedure in the handbook for checking the Auto transmission fluid level, after filling it.

By memory, I think it should be done when it is hot, with the engine running,at idle speed, and after selecting   P- R-N-4-N-R and then P,
each position should be engaged for a few seconds, and then the level checked in P whilst the engine is still running (apply handbrake !)

Good luck

Paul

[paul_GB]

Thanks guys..  This morning I added more oil to bring the level up to upper mark (engine hot and running). I checked and re checked. Went for a short drive and unfortunately no improvement in the gearbox performance 🤔. I dont have the facilities at home to measure the pressures so thinking I probably need to get the car off to the garage that did the gearbox rebuild. Suppose I could try tweeting the pressure marginally (as per guides on this site).. just to see if the problem changes is some way. Although maybe there's internal damage as Tyler suggests.

Paul

[wwheeler]

Has the trans ever successfully run after the rebuild? Or was this the first experience? How much more oil did you add?

Yes, Absolutely check trans fluid with the engine running and hot! Note: the trans oil takes much longer to get hot than does then engine oil. The trans oil level will rise significantly as it gets fully warm. From my recollection, it takes maybe 2 quarts of oil to fill the trans to the correct level with the engine running when compared to checking it with the engine NOT running. So you were driving it down around (2) quarts or so of ATF sounds like. Is the oil now dark and sort of maroon? If so the oil is burnt and hopefully not.

Again, if you never driven this freshly rebuilt trans, the pressure could very well be way tool low and wasn't set correctly to begin with. It is very easy to overfill the trans and just make sure it is piping hot when you do check it. 

   

[merrill]

hi
check this site for ideas.

http://mercedesdismantlers.com/AutomaticTransmissionInformation.html

you can also call Marc (the owner) he is very helpful.

[ctaylor738]

Have you checked the linkage and the position of the lever on the trans to be sure you are firmly in "4" when you move the lever to that position?

[paul_GB]

wwheeler.. yes when I rechecked the oil it was looking a bit of a dull maroon colour. Sounds like I need to drain and refill with fresh oil then?!
This was the first time the rebuilt gearbox had run so pressures could well be out.

Ctaylor.. I did check all the selector positions from under the car (especially 4th), all are fine and click firmly into place when selected.

Merrill.. thanks for the contact

[wwheeler]

That's not good news in my opinion. Does it smell different than new ATF? Dark ATF could mean it got really hot which leads me to believe there may be internal damage. You can send off your oil to have an analysis done. They can check many things such as if it is burnt, if it has metal particles from premature wear, etc. That might be a good first step before going too far. This is getting over my skill level and others more experienced in auto transmissions may want to help. Yes ask Merrill's contact and see what they say. The pressure could have been way too low and caused slippage and therefore too much heat?

I just know that in a normal situation, ATF shouldn't change color from one test drive. I hope for the best!

[paul_GB]

I don't detect any burning smell, but the oil is definitely more opaque when compared to the transparent 'new' oil. As you say the oil was probably overheated by the excessive slippage.. that sounds logical. Agree, the oil shouldn't change colour on one very short drive. I have asked the gearbox rebuilder to take a look and I will let you know the outcome.

Thanks again for sharing your knowledge.. it all helps a lot, even if the news isn't great.

[wwheeler]

Sorry, I hope it turns out for the best. These are pretty tough units, so maybe just an adjustment here and there will get it back to full working order.

[paul_GB]

My hopes are pinned on the pressures being set 'way-out' and no permanent damage from overheating. Will report back when the garage have sorted it one way or another. Thanks again for your help and support on this!