Another 603 vacuum adjustment/shifting thread... help Brian, Dave, etc.!

[AlexTheSeal]

Hi guys,

I have a hard-shifting transmission on my '87 300D. I've been doing a lot of diagnostic work and parts replacement and have read just about every thread here on the issue, but my symptoms aren't quite the same as any I've read about.

My vacuum pump, vacuum control valve, and transmission vacuum modulator are all new. I have been through literally every vacuum line and connector on the car and replaced quite a few that tested bad; there are no leaks to speak of. In particular, the lines to the EGR and ARV are capped, and the ACC vacuum subsystem is tight (tested at the manifold behind the glove compartment). The ALDA could stand a tweak, but off-the-line performance is adequate so I haven't done it yet. The transmission fluid and filter are fairly new (10K mi or so) and I think the level is correct, although I always have a hard time reading the dipstick.

The new vacuum pump is putting out a steady 25 inches of mercury. When I replaced the VCV, I adjusted it to output 14 inches at idle. I have a tranny pressure test gauge, and I adjusted the new modulator correctly (with the vacuum line disconnected, and to the pressure from the TDM [I forget what the spec is now]).

I've been driving the car with my MityVac teed into the line from the top of the vacuum amplifier to the transmission modulator, and am seeing pretty consistent behavior:

• At a warm start, the vacuum amp puts out about 5 in. If I leave the car idling, this slowly (over the course of a few minutes) rises to about 12-13 in.
  
• Any accelerator input, even a very light touch, drops the output back to 5 in. For example, the amount of "throttle" needed to keep the car going a steady 25 mph on a flat road puts the vacuum amp output at a steady 5 in.
  
• Pushing the accelerator down any further causes the MityVac gauge to drop to zero almost immediately. When I let up on the pedal, it slowly (over ten seconds or so) rises back to 5 (or higher if the car is just sitting and idling).

From my reading of how the vacuum amp is supposed to work, this doesn't seem right. I expected output at idle to be nearly as high as the reading directly from the VCV (even allowing for the MityVac bleeding off some vacuum). And output above idle, I think, should be inversely proportional to accelerator position, in other words gradually tending towards zero as the pedal goes down. Last, I would think that response to letting off the accelerator would be quicker, so as (for example) to smooth out an upshift after accelerating to cruising speed and letting off the pedal.

Any thoughts here? If it's just that the vacuum amp is bad, that's fine---I've replaced practically everything else, and I wouldn't be surprised if the flying saucer were bad too! But I want to make sure there isn't anything else I'm overlooking.

[aersloat]

If you think that your ALDA needs a tweak then start there. My shifting changed dramatically when I adjusted the ALDA. Where in Portland are you? Removing and adjusting the ALDA only takes half an hour or so (including removing the windshield wiper reservoir) once you have done it a few times, which I have. Drop by some time-- we could probably adjust it pretty quickly.

[AlexTheSeal]

I understand how cranking up the ALDA could affect part-throttle shifting, but it shouldn't have any effect on vacuum coming from the amplifier at idle, as I understand it.

[gsxr]

1) The ALDA has a significant effect on part throttle shifting - I would definitely adjust the ALDA. It has no effect on full-throttle (redline) shifts.

2) The VCV (on the side of the IP) is not adjusted with a vacuum gauge. This MUST be adjusted per the factory procedure. It's a black/white, zero/one, yes/no, binary adjustment. It's either correct or it's not, there is no gray area. I've tried to adjust shifting softer/firmer by moving it a little one way or the other in the slots, and all it does is make the tranny shift screwy. I can't explain it, I don't understand it, I just know that on several '87 300D's it's done the same thing. The factory procedure is at this link (200kb PDF file). Note that the adjustment is done with the engine off and there is no mention of setting to a particular vacuum reading. Usually it will end up right in the middle of the adjuting slots.

3) The modulator pressure should be set with the gauge as a rough guide, but otherwise it's set by seat of the pants. Basically you want it so there is zero flare at full throttle shifts, and no firmer. This is not always where the pressure gauge says it should be. There's even a note in the WIS about ignoring the gauge when the shifts are off. You might want to check out the 722.3 diagnostics at this link (1.5MB PDF file).

4) Make sure the pressure line from the ALDA to the BFS (blue flying saucer) is clean and all the lines (both vacuum AND pressure) in that area have solid rubber connectors... sometimes the ones underneath, out of sight, can crack and leak. (Don't ask how I know!)

[AlexTheSeal]

So, an afternoon's work and a few test drives later...

1. I R&Rd the ALDA, which wasn't hard at all---I don't know why I was so scared of it all this time. Did the requisite one-and-a-quarter turn counterclockwise. Wow, what a difference! I wish I hadn't broken the nipple off the top of the shutoff valve with the Channel-locks, though.

2. I adjusted the VCV according to the PDF above, and while I had the ALDA out and access was improved I also followed the procedure in the FSM to set the length of the linkage rods, the Bowden cable, etc... everything was messed up there. How could the vertical rod that goes roughly from the end of the accelerator cable down near the kickdown switch be two centimeters shorter than spec? (You do measure them between the centers of the sockets, right? That's the only way that made sense to me.) I guess somebody tweaked the linkage to improve shifting and didn't know what they were doing.

3. I have crisp but not clunky shifting in all gears now at part throttle, very light shifting at idle, and, at full throttle, a little bit of flare on the 1-2 shift but not on the others. Guess I need to adjust the modulator one direction or the other.

4. I went over the system again for vacuum and pressure leaks and did indeed find them in the connections under the BFS. In fact, I replaced every soft air line under the hood and tested all the hard lines individually with the Mity-Vac (none needed to be replaced). I still have a slight vacuum leak somewhere, I believe, based on the Mity-Vac readings on the line coming off the BFS to the modulator:

• I'm now seeing about 15 inches at idle, 10 at part throttle, and 5 at full throttle.
• However, the vacuum at idle only reaches 15 inches after the car's been sitting for a minute or so. Whenever it drops (i.e. with accelerator operation) it takes a LONG time to come back up.
• Also, the reading doesn't seem to be affected at all by whether the turbo is spinning or not. I don't have a boost gauge yet, but I am pretty sure I'm getting decent boost, and isn't the change in manifold pressure when the turbo comes online supposed to influence the BFS?
• Nor does adjusting the hidden plastic adjustment nut on the bottom of the BFS seem to affect its output at all. (I was afraid to turn it more than a complete turn in either direction, though.)

So it seems like there must still be a problem somewhere. But I have no idea how to test the BFS independently for proper operation, nor the two pressure switches next to it. The lines to and between them are clear and tight, I know that---but how do I know that those components are working and not leaking? In particular, the BFS and the switch next to it both connect pretty directly to the vacuum pump, so if they're leaking I fear all my other adjustments are in vain.

[justinperkins]

I don't have anything to offer this thread, but I am watching it closely as I need to do the same thing to my wagon as I am experiencing flaring at full throttle between 3-4 and sometimes 2-3.

I am very thankful at the knowledge shown in this thread by Dave and Alex. Thanks guys

[gsxr]

Originally Posted by AlexTheSeal

3. I have crisp but not clunky shifting in all gears now at part throttle, very light shifting at idle, and, at full throttle, a little bit of flare on the 1-2 shift but not on the others. Guess I need to adjust the modulator one direction or the other.

Yes - for a full-throttle flare, tweak the modulator *slightly*. You want it just at the point where flare is zero. Probably won't be more than 1 turn, maybe less.

Originally Posted by AlexTheSeal

• I'm now seeing about 15 inches at idle, 10 at part throttle, and 5 at full throttle.
• However, the vacuum at idle only reaches 15 inches after the car's been sitting for a minute or so. Whenever it drops (i.e. with accelerator operation) it takes a LONG time to come back up.
• Also, the reading doesn't seem to be affected at all by whether the turbo is spinning or not. I don't have a boost gauge yet, but I am pretty sure I'm getting decent boost, and isn't the change in manifold pressure when the turbo comes online supposed to influence the BFS?
• Nor does adjusting the hidden plastic adjustment nut on the bottom of the BFS seem to affect its output at all. (I was afraid to turn it more than a complete turn in either direction, though.)

15" is normal... the VCV drops the vac pump feed of 25" down to 15". The function of the BFS is, mainly, to prevent "full hard" shifts unless boost is present. However you need to have the engine under significant load to build boost. It helps if you have a boost gauge to watch. Usually, the BFS doesn't fail, and never requires adjustment, unless you're really picky about shifting. I only know one guy (Justin Dobbs, aka 'JRD') who adjusted the BFS and improved shifting a little bit. I've never touched mine.

Originally Posted by AlexTheSeal

So it seems like there must still be a problem somewhere. But I have no idea how to test the BFS independently for proper operation, nor the two pressure switches next to it. The lines to and between them are clear and tight, I know that---but how do I know that those components are working and not leaking? In particular, the BFS and the switch next to it both connect pretty directly to the vacuum pump, so if they're leaking I fear all my other adjustments are in vain.

I don't think there's still a problem, other than removing the slight full-throttle flare. You do want to make sure the boost signal tubes (and fittings) to the BFS are clean, and make sure the switchover valves near it are not plugged. One is the overboost protection, the other is the "cold shift softener", which disconnects the boost signal to the BFS when the engine temp is below 50°C. (The 50°C switch is directly above the thermostat, btw.) I disconnected this on my car because it would cause a FLARE when the engine was cold! I intend to remove the valve and change the plumbing too, but I haven't had time. If there is a third solenoid, your car has the "cruise surge fix" installed... I also removed this, because it reduces part-throttle power, by adding a restriction in the line from the manifold to the ALDA except at WOT. Killing the EGR and ARV cured the cruise surge. Here's photos from my old white '87:

Before:


After: