Hi All, First, let me say I really have been looking for posts for what I am sure is a very well documented problem, but I can not seem to get the info I need, and I am posting a thread that I hope will not annoy the senior members. Please excuse my ignorance, as I am new to all of this stuff - but I mean well. With that said:

I have a recently aquired 1991 350SDL with 205K miles in what seems to be amazing overall condition. I have just converted it to run on Veg oil, and it all is working great so far.

Just the other day, I noticed that the trnasmission is shifting hard. It seems to happen in all gears, especially first to second, but they all seem pretty hard. I checked the trannsmission fluid and it seems fine.

The wierd thing is that the problem, while always worse when the car is cold, is nontheless seemingly intermittent. Sometimes it seems to ride just fine, and then in an hour or two, it starts shifting hard again.

I fear am facing either catstrophic and expensive transmission failure (isn't 205K miles a lot for a transmission?) or some simple vacuum issue that I do not really understand.

I am not a complete mechanical moron, but I am near that side of the fence. Still, I did the conversion myslef and I have access to a lift and nice tools. Can anyone point me to a thread where I can troubleshoot some basic transmission hard shift diagnosis?

Also, is there anything I can premptively do to avoid bending a rod, blowing a timing chain and other stuff that I hear I should be suspect of in the 350 SDL? Having invested a great deal of time and money into my veggie conversion, I really want to maintain this great car as best as I can.

Thanks for all your consideration.

BTW, here are some pics of the WVO installation

http://www.steveadler.com/wvo.htm

A two-word hint:

Vacuum Leak

There is a valve on the transmission that modulates shift pressure in response to applied vacuum.

More vacuum = softer shift (signals light pedal pressure and low power)
Less vacuum = harder shift (signals heavy pedal pressure and high power)

Mity-Vac or any other vacuum gauge could be a most helpful diagnostic tool.

There seems to be no documented, proven cause for this. Take the Fatalistic approach, if it happens, it was meant to happen...
I have never heard of an OM603 engine timing chain 'blowing' on this board.

You can measure chain wear, commonly called 'stretch' and replace the chain when required. As it wears, the timing retards until performance drops off. With the OM603 I suspect you could lose quite a bit of performance before it became something you would notice daily.

So maybe it is a vacuum issue? This is prefereable to expensive, catastrophic transmission failure. Are there any threads that detail what I should do?
I will get a vacuum gauge, if anyone can reccomend one, but once I have it, what do I need to check?

Are there any manuals that discuss basic MB 126 diesel vacuum systems and how to troubleshoot them?

Thx!

You bet! My late 300SDL transmission was still going at 264k+ so they can be long-lived.

Oh, only about 1 million! This article below is good general reading on how M-B transmissions are controlled.

http://www.continentalimports.com/ser_ic20242.html

While any vacuum gauge will work, the "MityVac" also has a hand pump and will function as a vacuum source. This can be invaluable to check leak-down of suspected items, such as vacuum modulator diaphragm on the transmission.

Sorry, forgot to mention also...

1. Come visit the Diesel Discussion forum. There are 'stickies' on DIY hints...
2. Experiment with the "Search" function, 3rd from the right in the blue banner above. "MityVac" will pull up good sources.