Vacuum Adjustments on '87 300 SDL (6 cyl)

[howardjnl]

Folks,
Anyone aware of where I can get some info on-line about vacuum related adjustments for the '87 6 cylinder diesel? I've seen most of the info about 5 cylinder, but the 6 has a slightly differenct set up and I need sorting out the overall procedure to set it up.
It all begin with troubleshooting the system because of shifting problems. I replaced a badly leaking modulator valve, set the fluid pressure by adjusting the new valve, but need to follow the whole procedure for adjusting everything properly.
John

[howardjnl]

Folks,
Since my first posting on this thread, I have done several things in an attempt to address the shifting problems of my 1987 300 SDL OM603 engine equipped vehicle. But I still am having a problem. Here's the history:

1. Shifting very early and softly. Rapid shifting back and forth between 3rd and 4th at speed.
2. Checked bowden cable adjustments, okay.
3. Checked vacuum from the amplifier to the modulator, found leak in modulator.
4. Replaced modulator and set pressure as described in on-line doc's.
5. Still have problem. If disconnect vacuum from modulator, shifts fine, just too early. Re-connect, bad between 3rd and 4th again.
6. Replaced all old hoses, cleaned ports to intake manifold, etc.
7. Vacuum control valve bleed port clogged. Replaced this valve.
8. For grins, replaced both vacuum switchover valves.
9. With Mity-Vac, I'm getting good vacuum reading when connected to vacuum source line at amplifier. But when connect Mity-Vac to source line with a T-connection to amplifier, I get no vacuum. I plugged off line to modulator on the transmission, and still get no vacuum, just free flow of air when suck on the vacuum source connection on top of the amplifier and the two bottom hoses are connected normally.

Question: does this mean my vacuum amplifier is leaking / broken internally? Or is something connected to the bottom lines leaking? I wish I knew how the vacuum amplifier is constructed internally.

I'd appreciate any help of advice before purchasing a new vacuum amplifier.

John

[md21722]

You need to start with the accelerator linkage and work from there. Throttle position has a lot to do with WHEN the transmission shifts. Vacuum controls the harshness of the shift. I advise the factory shop manual as a source.

Regards,

[psfred]

That vac system is a bit complex.

First, you must verify that you have good vac to both the vac line at the shift control valve AND the amplifier. If you have no vac at the vac port on the amplifier, you will have no vac at the modulator, since the amplifer is actually a switching system.

Second, you will probably need to replace all the rubber connectors in the vac system, they will all be soft or hardend and leaking. Solves a number of problems.

Third, verify that the vac valves for the air recirc and EGR vavle aren't leaking -- mine were, so I got terrible hard shifts and funny AC operation, both fixed when I plugged the lines.

On the bowden cable, it must be all the way out with the throttle completely closed, with just enough tension on the cable to keep the spring from rattling. Any tighter, and it will cause trouble. It retracts into the housing as the throttle is opened.

"Hunting" between 3rd and 4th is probably a governor problem in the tranny rather than an adjustment, though.

Peter

[howardjnl]

Guys,
Thanks for the feedback!
Concerning running through the throttle adjustments: didn't think of that, makes sense. I'll run through this when I get home tonight.
In addition to the components I listed in my first messages, I've replaced all rubber parts, everything holds vacuum with Mity-Vac. Held it too well with the VCV bleed port plugged up. As for the governer: the transmission works fine without the vacuum line attached to the modulator valve.
I'm going to go through the throttle adjustments, and then recheck the bowden cable and vacuum settings for the VCV. I still wonder how to tell if the Vacuum amplifier is bad. I'll re-check the vacuum in and then out to the modulator to see if they fall within spec.
John

[psfred]

Amplifer should give the following signal to the modulator (engine off, of course, unless you want hook the mitvac up while driving):

At closed throttle, 15-17" vac. No kickdown to second on this car, so vac should drop as throttle is opened until near or at atmospheric pressure (0" vac) at full throttle.

you will have to supply appropriate vac with a pump of some sort (not too big, naturally!) or drive the car with the mitivac "t"-ed into the modulator line.

Peter