Late 3-4 shift, Auto transmission, Valve Body Assembly documentation

[Coops]

My 1968 US 280SL has allways late shifted between 3rd and 4th gear (I have had the car for about 20 years!) . All the other shift points as are specified in the BBB.
The transmission has recently been rebuilt but the rebuild seems to have concentrated on the power transfer part of the box and disappointingly has not cured the problem.
Basically on light throttle openings 1to2 2to3 shifts happen at between 1500 and 2000 rpm. The 3to4 shift takes place at 3500 rpm by which time the car is doing 45 MPH/ 65 KPH.
Full throttle shifts are fine all at 4000RPM, kick down shifts are fine all at 5500RPM

I am convinced that the problem is in the valve body assembly.

A cry for help, does anyone have any documentation about which valves are used for what?

I am seriously considering stripping the valve body down! Yes I know I am crazy!

[north clark]

Hi Coops;
I just noticed your problem with the late shifting and you haven't gotten any reply, I think  the problem is with the governor and its kinda common problem the K4A 025 and K4a 050 Trans had, trans with the solenoid on top of the housing, the governor can be taken out by just removing the rear cover and the repair is kinda tricky but done without parts other than new gasket and poss seals.
Good luck, richard k. 

[Coops]

I think that the problem must be specific to the valve body as a common component like the governer would cause late shifts on all gears. My box only late shifts from 3 to 4 all other shifts are normal.

Below is a diagrom of the suspect. I am sure that someone somewhere must have some MB document about which valve does what ??

regards, Martin

[ja17]

Hello,

Make sure your ignition timing is correct, since the modulator pressure is directly influenced by engine vacuum and shifting is directly influenced by modulator pressure.

[nikopu]

I have the MB AT workshop manual, I'll check the details tonight/tomorrow.

In the meantime, here's some nice reading (for a very similar trans.):
http://www.m-100.cc/forum/topic.asp?TOPIC_ID=4432&whichpage=1

Cheers,Niko

[Coops]

Nico,

Thanks, Interesting link. 0n my car whole of the drive train between the fluid flywheel to the output coupling has been renovated with new cluch disks, brake bands, pump, converter (governer), The transmission shifts smoothly with variation depending on the amount throttle used. 1 to 2 and 2 to 3 work pefectly as does 3 to 4 apart from the fact that it shifts at the wrong point with light acceleration!

This means that in town the car screams along in third gear even on a light throttle (accelerator).

See table below

[Coops]

Nico,

I would gladly pay for copying and posting and, if you were to trust me, I would do the copying myself and send you the book back. How many pages are we talking about, and is it in English?

Regards Martin

[wbain]

Make sure the wiring for the solenoid on top of the transmission is connected and the pressure switches are also connected. There is also a switch on the throttle body that controls the solenoid. Check the fuse too.

[Coops]

Solenoid wiring is correct, the two way solenoid is moved in opposite directions both by the switch on the throttle body and the kickdown switch. Kickdown works fine, downshifts on trailing throttle are fine (nice and smooth) apart from 4th to 3rd which happens at too high revs. as above.

Not quite sure what you meen by the pressure switches?

Rgds Martin

[ptooner]

"Not quite sure what you meen by the pressure switches?"  I just went through a somewhat related problem.   There are supposed to be two pressure switches on the transmission, one on each side.  They provide a ground to the idle kickup solenoid when the transmission is in forward or reverse gear.  (Hence the two of them).  My recently replaced transmission does NOT have the pressure switches.  I finally just wired the kickup solenoid directly to ground so that it is always active although I may just disconnect it eventually.  Anyway, I found that the wire that was supposed to go to the pressure switches was wired to the three position solenoid's terminal strip on the left side of the transmission.  That caused odd ball and erratic shifts.  In particular, if the kickdown switch was engaged the transmission stayed in kickdown mode until the engine was switched off.

Gerry

[Coops]

So, tomorrow I start the daunting task of taking out the automatic gearbox hydraulic valve body controller! Logically my late 3 to 4th shifts should come from there. If nothing is obvious with the 4th gear slider control I will just have to put it all back together and live with for another 20 years! Wish me luck.

[Larry & Norma]

Very interested to hear the outcome of this. Good luck

[Coops]

So I remove the auto transmision valve body, Identified the valve that is responsible for the 3 to 4th shift. I did not find any problem with the spring or slider. but there was a misterious pin hole in the cylinder! I am not sure if it is supposed to be there or not so I rebuilt everything and I am living with the problem still. Help!!! Does any one have a photo of a valve body,

[ja17]

Hello Coops,

Possibly the pin hole is for an assembly pin and  removed afterwards? I will take a look at some of the valve bodies I have hear and see if the hole is in them also.

Back to you soon.

[Coops]

Thanks Joe, I would be really grateful. I will keep my fingers crossed. If it is a faulty casting it means that the problem has been there since the car came out of the factory!

Regards, Martin

[nikopu]

Hmmm.. this could be a photo issue, but sure looks different compared to my valvebody.

Hope ja17 will verify!

[Coops]

nikopu, you have given me hope! And thanks once again for the documentation. I too am keeping my fingers crossed for JA17 reply. If this turns out to be true I will spend a day putting the english translation that I made of the valve-body on the technical manual!

[ja17]

Hello Coops,

I looked at a couple of valve bodies and did not find any with holes.  I am still not sure that yours may be a production variation? I will take a look at one or two more tomorrow and get back with you.

[ja17]

Hello Coops,

I looked at another valve body today and it did have the hole, the same as yours !

[Coops]

Damn! damn! damn! I was sure that the little hole was at the origin of my late 3 to 4 shifts. Does anyone know where I might obtain a valve body? and how much it would cost?

[nikopu]

Sounds like JA has a whole pile of them 

BTW Ja17, you don't happen to have a spare AT oil pan in decent shape, do you? message me ...

[Coops]

Joe,

You never said if any of the valve-bodies that you have are available?

Regards, Coops

[ja17]

Hello Coop,

I have a stack of them and no way to test them. 

[Coops]

Joe,

If you had one with the same part number ie. = 112 277 23 01, but without the pin hole, I would be prepared to take the risk of it being a good one or not. I would simply try it out in the box as it is a 4hour swap out. It would also enable me to build one good one out of two dodgy ones. I am just a little dubious about the cost and shipping costs to France.

Here is a photo of the part number casting.

Regards, Coops

[ja17]

Hello Coops,

Very risky trying to use a valve body witch has no history.  For instance, if it came out of a trans which was bad, it could have metal particles or other containments inside it. It then could damage your transmission itself. I would not suggest that you take the risk. Better to find a used one with history.

[Coops]

Joe,

I am disappointed; I was quite exited by the idea that I could get my hands on a complete valve body.

I cannot see any other way of finding out what is wrong with mine apart from doing a side by side comparison between two parts with exactly the same number. The german workshop manual does not give specifications, and findig someone with a test rig in europe will be impossible.

The only thing that is on offer over here, in France, is a complete box (without history @ 2,500$!) as I have already paid a transmission "expert" 4000$ to rebuild my box and it is all starting to be "silly money".

I guess I will have to live with the fault even if it spoils the pleasure of driving an otherwise nice car.

Regards, Coops

[nikopu]

I also think it would be  a worthwhile exercise, if you have tried all the other routes. Have you figured out the pressure test points etc as indicated in the service/repair manual? Perhaps, these could be done using standard modern pressure measuring meter and home made tubing/connections etc.?

If you can get your hands on another valve body, the full gasket set costs about 70€. Takes a day or two to rip it apart, thoroughly clean it and reassemble. Trying this as an replacement valve body on your car could give some indication of where the problem may be.

[ja17]

Hello Coop,

I tend to think the problem may still be in the rear pump or governor. If you think it may be in the valve body, you may just want to try a lighter spring on that particular slide valve. There are good used transmissions over here for less than $500, but sometimes you have to wait for them to pop up. 

If seeing another valve body opened up could help you, we could do an on- line dissection  and documentation with one of the units I have here.

Take care,
Joe

[Coops]

Joe,

Thanks for all the time you are spending helping me on this topic.

When I had the transmission rebuilt, they changed the the rear pump and calibrated the centrifugal governor, changed all the friction plates and bands. But the trans came back with exactly the same fault as it went with. I will have to find some where to get hold of a valve body (or "shifting sleeve housing" BBB) to be able to compare them side by side.

I do promise that I will update the technical manual when I find the problem!

Rgds, Martin