Andre The Giant

Hi everyone,

I will try to describe this has good as I can, here goes:
1 - After the car is started the transmission shifts quite smoothly into reverse, but after driving for a bit and I have to put it in reverse to back into a spot, I have to hold the brake real hard since it shifts real hard like if it was revving at higher speed, which it is not.

2 - On smooth driving it shifts nicely, but sometimes, when I mash the accelerator it will lunge into the next gear harshly, not sure which gear that is, but I don't like it.

Last time I tried verifying the level of fluid in the transmission, I was unable to see it properly even on a lift !

What is the order of things to check, correct me if I am wrong:
1- Check level
2- Check modulator pressure ( what should it be at ?)
3- Other stuff I don't know

Much of this will have to be done this spring since it's hibernating right now.
I am just getting organized ahead of time.

Thank you in advance.

Bertrand Daoust

Salut André,

1) Check level. Or an oil change if it hasn't been done recently.
2) Check if the line to the modulator holds vaccum. If this is good, check the modulator. Then check the pressure.

I would start with this.

MainePorsche

Here's a very good document on the transmission. In the troubleshooting section in the front pages it gives a nice symptom approach manner of addressing/testing things.

http://jenniskens.livedsl.nl/Technic...x%20akp722.pdf

For the fluid level, car HAS to be level. Can check on the ground, but easier when it is up (even on jack stands). Clean off well with a rag the front face of the reservoir where the fluid level markings are. The 3 markings are MIN, MAX, and 20deg (or something like that low down). Pay no mind to the 20deg thing - that is level when engine off at room temp. Let car idle to operating temp. When engine nice and warm the level on the reservoir should be between MIN and MAX. I like mine closer to MAX.

Andre The Giant

Merci Bertrand.

I will check when the oil change on transmission has been done, but WTH I will just change it and be done for a while ! ( What is recommended change period ?)

Is it best to check vacuum connected at connection point of modulator or other end ?

I guess to check the pressure, I would need a guage and I am not equipped for this so I might have to go to transmission shop.

MainePorsche

Best to check at both ends of vacuum to modulator. Check at origin to ascertain there is adequate vacuum to this system. Then check at distal end of line to make sure vacuum is reaching the modulator. Also check to see if modulator holds vacuum.

This is a good kit to add to your garage. In a previous thread, Greg Brown says we can check modulator pressure while car is running on stands and not moving (as per trans doc instructions).

Bertrand Daoust

Thanks MainePorsche for the link.

It's something I need/want to buy.

André, maybe we can buy it together?

ihoe

I will recommend this kit for measuring the modulation pressure. It contains all the right fittings to do this properly. The fittings are important, this kit contains a banjo fitting. Worked very well for me.

https://mercedessource.com/store/61x...ssure-test-kit

If I understand you right, it is just when selecting reverse with hot oil you have this problem? What happens when you select Drive?

I have the same issue, car makes a jolt when selecting Drive or Reverse. It only happens with a hot engine. Still working on it.

MainePorsche

Andre/Bertrand,
If you do get, and use, this kit for the modulator pressure you have to use the right angle adapter to the modulator testing port. The straight adapter will leave you no room to attach the gauge hose. All adapters come with the kit in metric and standard.

MainePorsche

From the transmission doc I linked above:

HARSH ENGAGEMENT WHEN SELECTING "D" OR "R"
Idle speed too high. Check pressure receiving (pick-up) piston in valve body for ease of operation and correct installation. Replace valve body (if necessary).
NOTE: Pressure pick-up requires a running period of approximately 2 seconds. Harsh engagement may occur during repeated shifts between "N" and "D". If harshness takes place within 2 seconds, condition is considered normal.

You can give Seafoam Trans Tune Additive first, and see if that loosens up piston movement.

davek9

Also before making any vacuum adjustment, I'd check the cables for proper adjustment first.

And like others have said see if the vacuum line that goes to the trans (located at the firewall) will hold vacuum, you may have a break in the line, if it doesn't hold then trace it back to the modulator, testing the modulator last.

If you don't know when the fluid was last changed, change it, and don't forget to hold on the brakes when shifting gears w/ the wheels off the ground as you can damage the trans.

Andre The Giant

Mine only happens on reverse !

Andre The Giant

Thank you for this info I will peruse this over hibernation period and nights which I'm doing renovations in basement.

Andre The Giant

That is an idea. We can talk offline for that.

Andre The Giant

Thank you Ihoe, That is another one to consider.

Andre The Giant

Noted