Can someone clarify a trans vacuum question

[nazrat]

I'm driving my '85 300TD now (317k miles - woohoo). I've checked every vacuum pod, lock, line and hose that I can find. I've replaced a few door lock actuators, BB'd a few unimportant lines (center dash vent pod, etc) and now have what appears to be a leak-free system. I didn't remove any of the transmission related lines, just checked them for leaks. Being an 85 it doesn't have the 2 valves on top of the valve cover, just a small switch and a solenoid on the inner fender.

So here's the issue: when cold at about 1/3 to 2/3 throttle the 2-3 shift has a HUGE flare. If I'm idling up to speed it is fine, or if I hammer it, it shifts fine. Is this an indication of anything vacuum related (like the vacuum valve on the injector pump?)

Thanks,
Tad

[vstech]

flares can be caused by many things. fluid is the easiest to check.
car must be warmed up to 80C, vehicle must be level, engine must be running.
I had 2-3 flare, and 3-4 flare, ended up being complete overhaul of tranny. theese old beasts get stiff and break.
John

[Maroon 300D]

My car will give me what is dangerously close to a flare on the 2-3 shift when the engine is cold on a cool morning. Once it warms up it's fine. Or if the ambient temp. is warm, it will also be fine.

Since you said this happens when it's cold, I assume it works fine once it's warmed up. I would guess this is not a vacuum issue and is instead related to the fluid. I'm pretty sure it is in my case.

My car will also be reluctant to shift into fourth on a cool morning before the engine is warmed up, and the 1-2 shift will be clunky. I think the tranny fluid behaves differently when it's cold.

When I switch out my fluid and filter I think I'll change to synthetic fluid; I hear it behaves better when cold and tends to eliminate the kind of problems I have.

My tranny was rebuilt about 13K ago, BTW, so I would think your problem may not require a rebuild.

[nazrat]

I need to confirm that it was the fluid, but I found that it was about 2 quarts low. I added fluid and at least warm the shifts are more confident. I also found a big leak in the injector return line, so in a week or two once new line arrives I'll find out about the transmission.

-Tad

[Brian Carlton]

The '85 is a beast unto its own so I can't tell you with certainty if the following applies:

The '86 has a temperature switch that functions in conjunction with the vacuum transducer (blue flying saucer) to raise the vacuum and soften the shifts until the temperature switch opens. You'll see an electrically powered vacuum solenoid next to the vacuum transducer.

If the '85 has the same switch and vacuum solenoid, then you'll only need to disable that switch, or unplug the solenoid, to get the same performance from the trans at all temperatures.

Naturally, when brutally cold, the trans will shift harshly because it doesn't have that switch to soften it a bit. But, overall, you'll be more than pleased to eliminate it.

[nazrat]

Originally Posted by Brian Carlton

The '85 is a beast unto its own so I can't tell you with certainty if the following applies:

The '86 has a temperature switch that functions in conjunction with the vacuum transducer (blue flying saucer) to raise the vacuum and soften the shifts until the temperature switch opens. You'll see an electrically powered vacuum solenoid next to the vacuum transducer.

If the '85 has the same switch and vacuum solenoid, then you'll only need to disable that switch, or unplug the solenoid, to get the same performance from the trans at all temperatures.

Naturally, when brutally cold, the trans will shift harshly because it doesn't have that switch to soften it a bit. But, overall, you'll be more than pleased to eliminate it.

That's great info. On mine that solenoid is up above the overboost solenoid. I'll disconnect it right now!

-Tad