1987 300TDT Transmission shifting issue - PeachParts Mercedes-Benz Forum

1987-300TD · #1 10-15-2014, 02:27 AM

Good Day All!

My wagon has been shifting "funky" for a week or 2. The funky shifting could be described as such:
* poor performance off the line with white'ish smoke
* not shifting between gears until ~4000 RPMs
* slipping out of 3rd gear if my foot was removed from the accelerator

I finally buried my head under the hood this past weekend. After all the research I had done, I believed I was troubleshooting a vacuum problem. After replacing several of the black connector hoses around the blue saucer, I thought I had the problem licked!

Alas,several of the symptoms were fixed but not all.

* She is now much quicker off the line and the smoke is gone except if I go hard on the accelerator.
* She shifts more smoothly between gears and does not need to hit ~4000 RPMs. 2nd to 3rd is the exception. She still seems to want to hit ~4K before shifting but the shift is smooth.
* I thought she was staying in 3rd gear but sporadically, if I take my foot off the accelerator, she will slip out of gear. If I move the gear shifter to 2 and give a little fuel, she goes back into gear and I can shift back to D.

I did not check my Trans Fluid level this past week but it was good approximately 2 months ago (I have not had any trans fluid puddles in that time.)

Any thoughts would be greatly appreciated!!!

Thank You!

glenn

Diesel911 · #2 10-15-2014, 11:38 AM

"it was good approximately 2 months ago"
is a long time.

1987-300TD · #3 01-18-2015, 06:50 PM

Good Day All!

I am resurrecting this post as I have not been able to rectify the problem but I have more data. :-)

1st off, I did not realize I have had this issue since October of 2014...

I checked the tranny fluid level per Diesel911. It was a little on the low side but still above Min. (Thanks for the advice Diesel911!)

Today, I drove it with my Mityvac connected to the vacuum system. I specifically put a "Y" in the line going from the BFS (Blue Flying Saucer) to the transmission. Although the level would fluctuate, it never went below 10".
As I understand it, the vacuum level should decrease all the way to 0. I did not even get close to that. Does that mean my BFS is shot? If not the BFS, where should I troubleshoot next?
Thank You All!

PS - Cruise Control is no longer working either. Is this related?

Mxfrank · #4 01-18-2015, 09:02 PM

A few thoughts:

- Sporadically not shifting out of third. This is probably the downshift switch, which is located under the accelerator pedal. You need to lift the carpet mat for access. Because of where it is, not unusual for it to be fouled with dirt and fluids. Mostly, you can clean them, but it may need replacing.

- Harsh 2-3 shifts. Try replacing the K1 spring in the valve body...search for more info.

- Vacuum amplifier(BUFO). There are four or five hoses terminating on the Bufo. The one for the transmission is the one on the top right side. This vacuum signal is a modulated signal based on the position of the vacuum control valve. If you move your Y to the bottom right connection, you can read the source signal. If the source signal isn't variable, check the connections on the VCV, which is on the right side of the injection pump. There is also a feed from the turbo, and a feed from the vacuum pump.

1987-300TD · #5 01-18-2015, 11:16 PM

Thanks for the reply MXFrank!

- I will check my downshift switch probably next weekend. Is there a procedure on how to test it?

- I was thinking about a K1 spring kit. Also thinking about the superior shift kit. Thoughts?

- My BUFO has 3 vacuum ports, 2 on top and 1 on bottom. The top are labelled TRA and VAC. I transferred the Y to the VAC and was getting a consistent 18" or so. It did not move at all. Should this be where I am seeing vacuum fluctuations?

Thank You!!!

1987-300TD · #6 01-20-2015, 02:07 AM

Wanted to bump this thread back to the top as my problem still exists...

I have read several more threads about transmission problems. Alas, most refer to funky shifts. Mine is most noticeable in the fact that I have very little fluctuation in the vacuum going to my trans. Is the fluctuation controlled by the VCV?

I get a consistent 18" to the BFS and 15" to 10" to the trans. Never saw the trans vacuum drop below 10". If not the VCV, what controls the actual vacuum changes to the BFS?

Thank You!

vstech · #7 01-22-2015, 09:48 PM

The modulator is at the transmission itself follow the vacuum line to the trans...

biopete · #8 01-22-2015, 10:33 PM

If you are getting 2 or less hg at full throttle to the Tranny your vcv is ok. You can adjust the vcv to start with less vacuum. They are supposed to go to 0. And sometimes they need to be replaced if they won't go to zero. But I got one to go down to 4 hg and it worked good enough. But I'm going to try a replacement vcv now I have one. This is on a 240d though

I had an 87 Tdt a few years back that had similar problems. Slipped out of gear in third and wouldn't go. It was first noticeable when hot on the freeway. I tried everything and a superior shift kit. Finally it wouldn't go. Had to get a rebuild. Sorry to say that's probably what you are looking art as someone said. You can fiddle and try all you want but they all go out eventually.we did three in one year on my friends and my cars. All from w124s. The good thing it's the trannies are awesome when they are fresh rebuilds. So don't feel bad about doing it sooner rather than later. It just means more time for you to enjoy it.

Good luck

biopete · #9 01-23-2015, 09:04 AM

We paid 900 each and r&r ourselves