Transmission not shifting properly

Tiny
JALSP
  • MEMBER
  • 1984 MERCEDES BENZ 300D
  • 5 CYL
  • 2WD
  • AUTOMATIC
  • 249,000 MILES
I am having an issue with the transmission not shifting correctly. The transmission will shift into 2nd gear at 20 mph, 3rd gear will shift at 40 mph and no sooner, and it will not shift into 4th gear until I hit 75 mph. If I let up on the throttle down to 65 mph it will shift back down to 3rd gear. It will not shitf back into 4th until I go back up to 75 mph. I have checked all vacuum and put a new modulator valve on the transmission. This did not help. Same result. The transmission always starts off in 1st gear. I have read they should start in 2nd gear but this one does not. Transmission is a 722-315
Saturday, July 11th, 2020 AT 10:39 AM

11 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon,

Is the 4 matic transmission? It was an option in that year.

https://www.2carpros.com/articles/automatic-transmission-problems

I would start by changing the fluid and filter. It sounds like a valve body issue where the valves are not moving smoothly.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Make sure you use the correct fluid as it makes a huge difference in how it shifts.

I attached a picture of the valve body for you as well.

Roy

BB00.40-P-0236-12A Automatic Transmission Fluids (ATF, Sheet 236.12)

Type
Aral Getriebeoel .................... ATF M12
Fuchs .................... Titan ATF 3353
Mobil .................... ATF 3353
Shell .................... ATF 3353
MB 236.12 ATF 3353 .................... A001 989 45 03
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Saturday, July 11th, 2020 AT 11:08 AM
Tiny
JALSP
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I have changed the transmission fluid and this did not help. Not sure on the type of transmission. The number on the transmission is 123 270 59 01 722 315 02 0520386. Not sure if this helps but it is a 4 speed and it does have an electrical connection on the same side as the modulator.
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Saturday, July 11th, 2020 AT 12:23 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Okay, check that main connector and make sure there is no fluid in the connector. If there is, the internal harness will have to be replaced.

https://www.2carpros.com/articles/how-to-check-wiring

Beyond that, it is most likely a valve body issue.

Roy
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Saturday, July 11th, 2020 AT 12:26 PM
Tiny
JALSP
  • MEMBER
  • 6 POSTS
I did take the connector off of the kick down switch and I pulled the Bowden cable off as well and it did not change how it shifted. Still did not shift into 4th until 75 mph and 5,000 rpm's. And the other gears will not shift until 20 mph and 40 mph for 3rd gear and no sooner than that for each.
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Tuesday, July 14th, 2020 AT 4:14 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Okay, this sounds like a valve body issue.

One thing, does the modulator valve have a vacuum hose on it? If it does, measure the vacuum. It need to be around 18-20 inches. That vacuum would come from a vacuum pump.

Roy
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Tuesday, July 14th, 2020 AT 4:39 PM
Tiny
JALSP
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Yes, it has a line down to the modulator valve. It has at least 20 inches of vacuum. I have installed a new one but the same result.
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Tuesday, July 14th, 2020 AT 6:49 PM
Tiny
ASEMASTER6371
  • MECHANIC
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When you accelerate or raise the RPM, does the vacuum drop?

It has to have a signal of being under a load.

Roy
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Wednesday, July 15th, 2020 AT 3:18 AM
Tiny
JALSP
  • MEMBER
  • 6 POSTS
The VCV valve works correctly as you drive. I have had a vacuum gauge on while I drive. As I drive the vacuum goes down accordingly as I push the pedal. Transmission will not shift until it hits the speeds described in earlier post. And it will not shift into the next gear until it hits those speeds.
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Wednesday, July 15th, 2020 AT 3:17 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, good, then we are back to the valve body itself.

Roy
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Wednesday, July 15th, 2020 AT 3:24 PM
Tiny
JALSP
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  • 6 POSTS
Do they rebuild the valve bodies? Would you know if a rebuild kit is available for this?
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Thursday, July 16th, 2020 AT 3:38 AM
Tiny
ASEMASTER6371
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A tech with knowledge can rebuild one. There is not much to them.

I do not have a parts manual to see if it is available separately.

Check around trnamission shops and see if anyone is familiar with this transmission.

Roy
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Thursday, July 16th, 2020 AT 3:54 AM

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