1987 300TDT Transmission shifting issue

[1987-300TD]

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]

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

[1987-300TD]

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]

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]

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]

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!

[Mxfrank]

Vac at 18 is fine. But your trans line isn't being modulated. Shift your gauge to the VCV line, which should be on the bottom of the BUFO, to the right. You can also test the turbo sense, which is the center connection. This should show manifold pressure (not vacuum).

If you have modulated vacuum at the VCV line, then the BUFO isn't working correctly. If you don't have vacuum at all, then the line is open, track it back to the break. If it doesn't modulate, the line is either clogged or the VCV is bad or misadjusted.

[1987-300TD]

Does this sound like a vacuum problem?

I had the opportunity to test tonight. I tapped into the VCV line under the BUFO. Vacuum moved from 12" down to around 2". If I let off the accelerator, it would move up. Depressing the accelerator would move it down.

I had another BUFO I had grabbed from pic-a-part. I just put it on but did not measure any vacuum. My shift from 1st gear to 2nd gear seems smoother.

My shift from 2nd gear to 3rd gear revs all the way to 4K before shifting. If I let off the accelerator as I get close to 4K, she slips completely out of gear! I have to drop the gear shifter to 2 in order to get her back in gear. Get her to 4th and no problems.

I am bringing my MityVac with me tomorrow to test each of the lines again with the new BUFO.

Thank You for your Insights!

[Mxfrank]

You have good modulation at the VCV, the problem has to be at the transmission modulator side. Try drawing on the line with your mityvac. It could be that there's a bad connector or the modulator is damaged.

Not to be pessimistic, but your 3/4 problem sounds like a bad clutch pack. I had a similar problem with my 190DT...I'd get well into third, and then it would shift to neutral. Required a teardown and rebuild. The friction plates and the clutch drum itself were worn out. But I could never get 4th to engage, so maybe you have a shot at it being a simpler problem. Getting into fourth places the greatest load on the hydraulic system, since both clutch packs have to be engaged. So there's a shot that it's related to insufficient working pressure. I assume your fluid level is correct?

[1987-300TD]

Thanks for sticking with me MXFrank!

I checked my fluid level today as a matter of fact. It was low so I added. Unfortunately, no difference.

When you refer to "the problem has to be at the transmission modulator side", which item is the Transmission Modulator? Is that one of those devices connecting to the wall next to the washer fluid reservoir? If so, I believe 1 is completely disconnected. Not sure if the second is functional.

I will report back with more info later...

Again, Thank You!!!

[vstech]

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

[biopete]

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

[Mxfrank]

Originally Posted by 1987-300TD

When you refer to "the problem has to be at the transmission modulator side", which item is the Transmission Modulator? Is that one of those devices connecting to the wall next to the washer fluid reservoir? If so, I believe 1 is completely disconnected. Not sure if the second is functional.

Find the BUFO hose labeled "trans" (you had this before). Plug a mityvac into the hose and draw on it. This hose leads all the way to the transmission modulator. It should hold vacuum. If not , follow it along and see if you can find a leak.

[1987-300TD]

Thank You All for the added insight!

MXFrank - I plugged the MityVac into the line leading to the trans. She took 20" and after 1 minute was holding steady at 19".

What can I check next?


MXFrank and BioPete - Approximately how much does a transmission rebuild cost? Probably not a DIY.?. :-)

[biopete]

We paid 900 each and r&r ourselves