I have a 1978 300D with a non-vacuum system transmission. It has a shift flair on 3rd and 4th gear. I was told at the MB dealer to adjust the modulator valve in with a 3 MM allen wrench about 1/2 to a full turn in, dirve it and make another adjustment if needed.
I am trying to locate the modulator valve and more clear instructions on the adjustment process. Photos would be a good thing. Any help?
Dave Thompson
d2t@nwnatural.com

That transmission DOESN'T have a modulator! Modulator pressure is PRE-SET by spring pressure. Should be 2.8 BAR!

Adjustment for shift is done by changing the length of the control pressure rod from the trans to the accelerator bellcrank. Making the rod shorter will stiffen the shift.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

The early diesel mechanical modulator can be deceptive. On the passenger side, rear of the car in the tail section just after the transmissions case you will find the mechanical modulator. Remove the nut, I do not remember the size; inside of that hole is a Allen screw 3 or 4 mm. that is the adjustment for the pressure spring, turn cw to raise working pressure.

My 1975 300D has a sever 2-3 shift flare. 1-2 and 3-4 shift will flare occasionally. I just got the car. The origianl owner replaced the transmission 40K miles back. Bands and clutchs seem good because once engaged things are tight.

So what is the deal with these non-vac modulated shift trannys. Is there a modulator adjustment or not ??

I dont understand that a modulator would be mounted on the tail of the car. Wouldnt it have to be on the transmission?

If someone can explain shift control adjustement on this car I will appreciate it.

__________________
JMF

The fixed modulators on early diesels are have a straight screwdriver adjustment under the 17mm cap nut (think its 17). As with movable modulators the key to the proper pressure is the eventual protruding length the device imparts on nthe valve inside the trans that it applies. A significant flair or soft shift can arise from putting a sealing washer under the device when screwing it into the trans. As the total length is the criteria adding the washer messes it all up. Move it in for harder shifts and out for softer. This trans is designed to have control presure control shift pressure and if no one has screwed the mod up then the proper mechanism for increasing shift strength is to make it shift later.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Can you please, post a picture of the passage side of your transmssions
tail section.

Thank you all very much. I think it is all starting to make sense. There is a modulator adjustment access at the tail of the transmission housing on the passenger side just like C32AMG said. It has a 17mm cap.

The origianl owner who replaced the transmission with a rebuilt one almost certainly did not adjust the transmission properly. So I think I will do this:

1) change the ATF and filter (7 years old).

2) set the shift points according to the maintenance manual.

3) If it still flares, crank the modulator adjust screw in.

I paid the original owner $400 for this car, It is in excellent condition. The body and paint are really fine. He couldn'y get it started the last time he performed maintenance. After I got it home and replaced 3 siezed injectors and the starter it fired right up and it runs good. The starter was weak and was straining against the force of compression.

I will report back on the modulator.

Meanwhile I want to start a thred on horse hair.

__________________
JMF

I have screwed the modulator adjust all the way in. It has no effect. Shift flares are guaranteed on 2-3 shift unless light throttle is used. Shift flares on 1-2 and 3-4 occur sometimes.

The car shifts fine if I release the throttle at shift points and let it go into gear.

I think I will take the modulator adjuster out and see what I can see.

As a last resort I suppose I can take it to someone who knows what they are doing, but where is the fun in that. Next thing you know I will be asking strangers on street corners for directions when I'm lost.

__________________
JMF

The hydraulic operation of the 722.0, 722.1 722.2 is different then that of the 722.3 722.4 and 722.5. The modulator and control pressure (TV rod) controls shift timing and shift feel. You have low throttle control pressure. Adjust the TV rod, you need more pressure. Adjust the rod shorter, more throw.

Hope you can help with my 1976 300D. 114/115.
As you know they start out in 2nd gear. The first shift from 2 to 3 is always at around 20mph (the hash lines on the speedo). But when it does this the RPM's are pretty high. So naturally it just wacks into 3rd gear.
Hot or cold it doesn't matter...same effect. The shift from 3 to 4 is smoother and good.
There is one rod from the valve cover down to the belcrank. Then two rods from the belcrank to the transmission.
A) Can I adjust this transmission to shift at a lower RPM and mitigate the wack?
B) Is the answer in just adjusting the horizontal rods or the vertical rod?
ANy advice would be very very much appreciated. I just want to prevent my transmission and drive line from being damaged by this harsh shift.

I'm kinda curious about this adjustment as well. Do I just use the point on the end of the rod? It doesn't seem that there's a whole lot of thread to make a difference in the shift point from there.

nevermind, figured it out.

In keeping with the shifting problems. I've got an 85-300 turbo diesel which shifts hard when cold but when it warms up a bit it shifts nicely. Usually shifts at 2500 rpms. Is that the right shift point for all gears? Would the hard shifting suggest that the fluid and filter need changing? 215K miles. Also what is flaring referred to in this initial post? Hard or soft shifting? Or something else?
Mike