‘85 300D transmission acting weird

[brihawaii]

Following a few months of very light usage, she started acting strange.
From stop, in D, shifts quickly to 2nd and 3rd at ~ 20mph.
From stop in L , shifts quickly to second and I can manually shift to 3rd(S) and manually to 4th(D) it will not kick down but is drivable.
Trans was ‘rebuilt’ a couple years ago and has been working perfectly since.
Fluid level ok.
Bowden cable adjustments either way has no effect.
(Doesn’t loosening the cable cause it to shift sooner?)
I’m hoping the problem will be obvious to someone here.
Some things I can try before bringing it back to the trans guy.
He’s kind of far away now.
Thanks in advance.
I appreciate your knowledge.

[Sugar Bear]

Rapid/early shifts is sometimes called "stacked" shifts as the shifts are "stacked" closely on top of one another. Check the vacuum line to the modulator, had this on an '81 380SE euro, the modulator was bad.

Good luck!!!

[Diesel911]

Originally Posted by Sugar Bear

Rapid/early shifts is sometimes called "stacked" shifts as the shifts are "stacked" closely on top of one another. Check the vacuum line to the modulator, had this on an '81 380SE euro, the modulator was bad.

Good luck!!!

Can he hook up his mighty vac hand held tester and hook it to the Modulator to see if it holds vacuum?

[Diesel911]

People have had the modulator cap crack or fall off.

[Diesel911]

See attachment.

[Diesel911]

Here is some stuff from a Mitchelle's manual:

“Transmission Slips When Starting Off In 1st Or 2nd (ReverseIs Okay)
Band B-2 shift valve sticking. Band B-2 piston worn or
damaged. Band B-2 adjusted incorrectly or worn or damaged. Adjust
brake band B-2 by installing a longer thrust pin (if necessary). If transmission operates properly with selector lever in "2", but not in "3" or "D" position, one-way clutch may be slipping.
Transmission Slips In 2nd Gear Or Shifts From 1st To 3rd Gear Check control valve B-1 for ease of operation. Replace valve body (if necessary). Remove and install brake band piston B-1, check sealing ring and replace (if necessary). Replace brake band B-1 and thrust body for B-1. Command valve binding.Transmission Slips During 2-3 Upshift Or Slips Initially, Then Grabs Hold Check modulating pressure and adjust (if necessary). Check
for temperature throttle installation (if equipped). Valve body worn or damaged. Replace valve body (if necessary). Replace inner plates of clutch K-1 or recondition clutch (if necessary). Check front cover Teflon ring.

WILL NOT UPSHIFT
Incorrect governor pressure. Defective governor assembly.
Check for stuck kickdown solenoid or for constant voltage to solenoid caused by a defective fuel pump relay (You don't have a fuel pump relay) or sticking kickdown switch.
Valve body dirty or valves sticking. Repair or replace valve body.

UPSHIFTS AT HIGHER SPEEDS THAN SPECIFIED
Check pressure control cable engagement, condition and
adjustment. Check for stuck kickdown solenoid or for constant voltage
to solenoid caused by a defective fuel pump relay or sticking kickdown
switch. Check governor pressure. If regulator pressure is too low,
replace centrifugal governor. Ensure control pressure regulating valve is operable.

UPSHIFTS AT LOWER SPEEDS THAN SPECIFIED
Check pressure control cable engagement, condition an adjustment. Check full throttle stop by accelerating engine and ensuring throttle valve rests against full throttle stop. Readjust throttle stop (if necessary). Check governor pressure. If governor pressure is too high, replace centrifugal governor. Repair or replace valve body.

NO KICKDOWN
Check throttle control and pressure control cable engagement, condition and adjustment. Connect kickdown solenoid to battery and check for proper operation. Replace solenoid (if necessary). Check kickdown valve in valve body. Replace valve body (if necessary).
NO 4-3 OR 3-2 DOWNSHIFT Control pressure cable out of adjustment. Leaking vacuum hoses and/or connections. Ensure brake shaft piston is operable.
Replace valve body (if necessary).

Sorry I cannot seem to find anything that is specific to your symptoms.

[Sugar Bear]

Testing the modulator diaphragm with a Mityvac should work.

[Diesel911]

Originally Posted by Sugar Bear

Testing the modulator diaphragm with a Mityvac should work.

Thanks.

[brihawaii]

Thanks Everyone for your help.
I found the vac line to the modulator in very bad shape.
Replaced it to no effect.
Chinesium vacuum tester arrived today.
The modulator isn’t holding any vacuum.
That’s gonna be a dirty job.

Thanks again guys for pointing me in the right direction.
Showing once again that this forum is an awesome resource.

[tyl604]

You might try removing the cap and reseating it to see if it will hold vac. Is the cap black or green?

[HughO]

Originally Posted by brihawaii

Following a few months of very light usage, she started acting strange.
From stop, in D, shifts quickly to 2nd and 3rd at ~ 20mph.
From stop in L , shifts quickly to second and I can manually shift to 3rd(S) and manually to 4th(D) it will not kick down but is drivable.
Trans was ‘rebuilt’ a couple years ago and has been working perfectly since.
Fluid level ok.
Bowden cable adjustments either way has no effect.
(Doesn’t loosening the cable cause it to shift sooner?)
I’m hoping the problem will be obvious to someone here.
Some things I can try before bringing it back to the trans guy.
He’s kind of far away now.
Thanks in advance.
I appreciate your knowledge.

It usually comes down to vacuum or a bad actuator. also check pressures. I had a similar problem on my '85 and it was my cable. Now it shifts properly and even kicks down.

[brihawaii]

Originally Posted by tyl604

You might try removing the cap and reseating it to see if it will hold vac. Is the cap black or green?

It has the black one.
Cap seems ok was full of fluid though.
Re seating didn’t make any difference.
I guess that means modulator.

[brihawaii]

This car is an ‘85 California model.
I think that means it should be 722.4xx ?
I can’t find the number on the passenger side.
I did get a pic of the plate on the drivers side,
I’ll see if I can attach... not

tag says.

teil nr. 123 270 7601
Aggregat? nr. 255957

Does anyone know if this indicates which trans this is?

[JCSC2]

It wouldn't hurt to check and make sure the ATF level is correct.