Sorry, I need a clarification here... What rack and how do I open it? Are you talking about something on the white plastic valve?

The rack controls the injectors. Just move the "throttle" linkage from idle toward maximum power and the rack will move to provide more fuel to the engine. We don't call it "throttle" because a diesel engine is not throttled.

I am thrilled you started this thread--I have the EXACT same issues. Low load clunking.

Which MityVac did you get?

Question for others--What mode of MityVac is suited to do this job? Would this one do it or do you have to have the 0400 model? Is there a recommended place to get one? Thanks in advance!

http://www.amazon.com/Mityvac-7000-Automotive-Tune-Up-Bleeding/dp/B000BPFB3A/ref=pd_bbs_sr_1/104-9001271-1222314?ie=UTF8&s=automotive&qid=1188520535&sr=1-1

The plastic one seemed kind of flimsy when I was shopping for one. I ended up buying the metal one.

Brian - When the Mityvac is fully pumped up, I get about 12.0 mm Hg to start. Then,

in 20 sec - it is down to 11.0 mm Hg
in 1 min - down to 10.0
in 1 min 45 sec - down to 9.0
in 2 min 35 sec - down to 8.0
in 4 min - down to 7.0

I did do this test nonetheless, and it behaves exactly like you described it should - losing vacuum in-sync with the rack movement.

The modulator has a slight leak.........nothing serious. The VCV is modulating the vacuum signal properly.

So, if the transmission is still exhibiting the characteristic clunking and very firm shifts.........we need to see if an adjustment to the VCV or the modulator is in order.

Disconnect the vacuum line to the transmission and connect the Mityvac. Run the hose into the cabin. Pump up the Mityvac to 15" and keep it there (give it a squeeze every so often as it falls).

Now drive the vehicle and see if the hard shifts disappear. Make sure the Mityvac stays between 12" and 15" during this test.

Brian - you mean bypass the T-junction on top of the green damper and pump the tranny line directly with Mityvac? But then I don't understand how the shifting will be controlled with the gas pedal, if we're bypassing the modulator... Could you please explain.

I believe he means connect as it is in this pic (but run the mityvac into the car so you can see it while driving):
http://img252.imageshack.us/img252/2...uum3ay7.th.jpg

You are using mity vac instead of the car's vacuum system to feed the trann'y modulator. This is only for testing. If the tranny shift nice and smooth through all gears, then the problem lies elswhere.

That's what I assumed and did - I connected the Mityvac into the T-junction, in place of the line from the vacuum pump. I ran the line into the cab.

Wow, I had to pump the Mityvac hard, pretty much all the time to keep up with the modulator during accelerations and such. The shifts did feel a good bit smoother, although not seamless - probably because my hand couldn't keep up with the demand for vacuum all the time. I didn't hear clunking, but I didn't drive around a whole lot like this either - my hand was about to kill me.

Also a thing to keep in mind - my shifts are generally much smoother on hot engine/tranny than during the first drive in the morning.

That's not the setup that I want. I want the Mityvac to go directly to the modulator valve........bypassing the T junction.........so that the VCV doesn't leak vacuum while you drive.

The test failed because the VCV leaks far more vacuum than you can possibly pump with your hand. The modulator doesn't.

So, repeat the test with the proper connections..........I want to see if the modulator will respond with higher vacuum levels.

In the pic, the mityvac is not connected to the T junction, it's connected to the line which goes into the T junction.

I'm following .....
 

...... this too. thanks, BC.

Thnks for this Brian, I have the same problem and this step by step troubleshootig guide your creating is going to be very helpful.

Maybe this can be turned into a step by step diagnosis with pics for the DIY Articles section?

Scott