Is second gear supposed to shift at that high of RPM? - PeachParts Mercedes-Benz Forum

RichC · #1 01-28-2006, 01:38 AM

I finally seem to have the vacuum system sorted out in my 81 300D.
But it seems to shift at a much higher RPM from 2nd to 3rd than any of the other gears.

I have a vacuum line from one of the T's in the master line running to a green restrictor orifice. From there it goes into another T with one end leading to the vacuum control valve and the other to the transmission.

I have bypassed the 3/2 valves on the valve cover, under the little black box.

Have I done something incorrectly?
Is there yet another adjustment somewhere?

Thanks for your help.

biopete · #2 01-28-2006, 09:02 AM

I have 81 300D NA. Just added black orifice. Does it shift at a lower RPM when you have less foot on the pedal ? I just did that. See my recent post about "Orifice sensational shifting" . I think it is supposed ot do that. I really dont know what is normal for the tranny yet. Its possible the orifice is wrong size maybe .

RichC · #3 01-28-2006, 04:38 PM

Yes it will shift at a lower RPM with a lighter foot on the pedal. I read your post about the orifice. I will see if mine in backwards.

I think it might be in the wrong place maybe. I will try moving it to just above the VCV so it will only affect the vaccum leak and not vaccum to the whole system.

Thanks for your input.
RichC

Jim H · #4 01-28-2006, 07:18 PM

Quote:

Originally Posted by RichC

Yes it will shift at a lower RPM with a lighter foot on the pedal. ...I will try moving it to just above the VCV so it will only affect the vaccum leak and not vaccum to the whole system.

Before you do this, search for "Bowden Cable" since adjustment of this cable will affect shift rpm...

RichC · #5 01-28-2006, 08:11 PM

Oddly enough the 81 300D did not come with a bowden cable.

Diesel Giant · #6 01-28-2006, 08:25 PM

Hmmm at what RPM do all the different **** points occur at?

RichC · #7 01-28-2006, 11:17 PM

I do not have a tach so I do not know the specific RPM. But I can tell by engine sound that the 2nd to 3rd shift is definatly at a higher RPM.

If I drive wide open throttle the car shifts as it should, at the tick marks on the speedometer. But any other throttle position the 2 3 shift is scewed high.

Thanks
RichC

sailor15015 · #8 01-28-2006, 11:53 PM

So if you're accelerating at partial throttle the engine will still be in second gear after it passes the corresponding shift marker? Are you sure you don't have a bowden cable? Its not unheard of for them to break.

RichC · #9 01-29-2006, 06:12 AM

Yep, there is no bowden cable on the 81 300D's
I found this out by posting questions on the forum here.
I thought maybe it had been removed, like some of the vacuum lines.

#10 01-29-2006, 09:31 AM

You should not be bypassing the gizmo on top of the valve cover. My daughters 81 300D had a vacuum diagram sticker on the core support on the drivers side. Make sure the gizmo on the valve cover is connected and working correctly. Test all of the check valves on the gizmo and make sure they shut on and off when actuated by the cam.

THEN check the valve that is on the back of the injection pump. Make sure the linkage is hooked to it correctly and hope that this valve is okay because it is EXPEN$IVE.

Also make sure the orifice is in place.

You can't really get this thing set up right unless you have a vacuum diagram. If you don't have one, get one somewhere.

Good luck,

RichC · #11 01-29-2006, 08:40 PM

I have replaced the VCV on the IP pump, and adjusted it to provide the best shift possible.

What do the 3/2 valves under the black box on the valve cover do?
If I could figure out what these valves do, I could reverse engineer and make things the way they were. I have tested the valves and they all seem to work correctly, and do not seem to have mutch wear on them or the actuator connected to the linkage.
These valves are still somewhat a mystery to me, even after reading all I could find posted on the forum.

I did turn the modulator adjustment two notches clockwise to achieve a firmer shift.

I will check down by the modulator for any leaks.

The modulator changes the firmness of the shifts, correct?
And the VCV controlls when the shifts happen, correct?
Is there anyting internal in the transmission that may cause the late 2nd to 3rd shift?

Thanks for all your help.
It is mutch appreciated.

PS: I am parting out an 82 300SD. Name your price and part and its yours.

Thanks again
RichC

RichC · #12 01-29-2006, 11:53 PM

Ahhh

dont you just love the extream complexities of some vehicles.

But that is what keeps me interested. I have recently changed from owning american cars to german. ( From Camaros and Mustangs to Volkswagens Porsches and mercedes )

I guess I'm just a sick puppy, but I like the challange. It keeps my mind occupied so Im not working on world domination or something.

There is something I just like about odd systems and fiddley bits. Maybe because I am one.

Any info on the vacuum controll transmission system is appreciated, including the valves under the mysterious black box on the valve cover.

I have also heard others on the board talking about their transmission staying in 2nd gear at stops then shifting to 1st at take off. Should an 81 300D do this also?

Thanks to all, I really like this board.
RichC

Tiredofagasser · #13 01-30-2006, 01:18 AM

Quote:

Originally Posted by RichC

I have also heard others on the board talking about their transmission staying in 2nd gear at stops then shifting to 1st at take off. Should an 81 300D do this also?RichC

I don't think mine does this. Without being rude, I really think it's all in their heads

No harm meant just MHO...

biopete · #14 01-30-2006, 01:20 PM

I posted this here . It is for our 81,s whiche are a little different than any other
year. Mine is an NA btw.

Note flow and orifices. Unfortuneately there isno color/size specified for the orifice. ill check mb for part. There is another diag. for flow under the other condition -- at idle or full throttle. If someone PMs me i will post it faster than not.

transmission vacuum modulator

Im pretty happy with my black box diconnected. Just easier and safer (i broke my 60.00 main vac line cause of it supply T off) to work under there and shifts are good. not saying they could not be better but i do not really nknow. Now, my only complaint now is it revs up a little much if i have anything more than 1/3 foot on it. Since it never reved up and flared like hell before even with black bx (total opposite of what it does now before the orifice), i suspect the orifice is a tad small. and i can find a happy medium.

if i get bored after i have correct size orifice, i may try black box again and post back any differences. I suspect only difference to be downshifting smoother when. you are slowing down

1983/300CD · #15 01-30-2006, 02:53 PM

2nd to 3rd flare could be your K1 spring.

You can get a K1 spring kit from Phil for around $10.