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  #1  
Old 07-23-2008, 01:16 PM
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Transmission Vacuum Modulator Adjustment

My 87 300D's transmission shifts too firmly, and I've read that the problem is most likely a vacuum issue. I've checked for any loose vacuum lines in the engine compartment but all seemed connected.

A technical service bulletin mentioned a modified vacuum modulator to reduce the vacuum pressure to the transmission which was made available to address the hard shifting problem. How do I get the modified modulator? And where is the modulator located on the tranny?

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  #2  
Old 07-23-2008, 06:50 PM
compress ignite's Avatar
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"Search" and "Advanced Search" functions

TONS,and Tons of information on this subject.

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  #3  
Old 07-23-2008, 08:04 PM
ForcedInduction
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On the side of the injection pump is the vacuum valve held on with 2 bolts. Loosen the bolts and twist it a little bit each time until you set it where you like.
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  #4  
Old 07-23-2008, 08:16 PM
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Originally Posted by ForcedInduction View Post
On the side of the injection pump is the vacuum valve held on with 2 bolts. Loosen the bolts and twist it a little bit each time until you set it where you like.
Lance, this won't work on a 603. Unless it's set via the factory procedure, it'll flare badly.
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Old 07-23-2008, 09:38 PM
ForcedInduction
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How is it different than the vacuum valve on the 617? Thats how I adjusted the shift firmness on my wagon, I never touched the modulator.
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  #6  
Old 07-23-2008, 09:43 PM
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Originally Posted by ForcedInduction View Post
How is it different than the vacuum valve on the 617? Thats how I adjusted the shift firmness on my wagon, I never touched the modulator.
It doesn't respond properly to adjustments. If you attempt to adjust it as described, for some reason, it results in massive flaring. Dave had the same issue with it. Adjusting it like the 617 doesn't work very well. YMMV.
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  #7  
Old 07-25-2008, 12:22 AM
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Originally Posted by compress ignite View Post
TONS,and Tons of information on this subject.
Thanks. I'll start looking around. I guess I should have known that that would be a popular topic. I'll be careful to do some searching before I post questions again.
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  #8  
Old 07-25-2008, 01:00 AM
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I've read dozens of posts and found the DIY in the Wiki by Continental Imports, and it's pretty confusing. The DIY for some reason suddenly refers to pressure (instead of vaccuum) when describing how to adjust the modulator; and a lot of posts posts contradict each other, so a definitive answer would be greatly appreciated:

Which direction do you turn the modulator to soften shifts?

Thanks

Last edited by theo3000; 07-25-2008 at 01:08 AM.
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  #9  
Old 07-25-2008, 09:59 AM
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Quote:
Originally Posted by theo3000 View Post
I've read dozens of posts and found the DIY in the Wiki by Continental Imports, and it's pretty confusing. The DIY for some reason suddenly refers to pressure (instead of vaccuum) when describing how to adjust the modulator; and a lot of posts posts contradict each other, so a definitive answer would be greatly appreciated:

Which direction do you turn the modulator to soften shifts?

Thanks
I did manage to find this. It's a pdf with instructions on how to adjust the modulator. I'm just not sure how to tell if I have the modified modulator. Anyway, hope this helps. It has good diagrams and text.
Attached Files
File Type: pdf Transmission vacuum modulator adjustment.pdf (69.3 KB, 892 views)
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  #10  
Old 07-25-2008, 10:42 AM
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Way out of my league

I've been reading the posts about the vacuum system on cars like my 87 300D, and MERCY ME! (hence my screen name). I like tinkering, but this is way out of my league. My tranny shifts pretty hard, though it's tolerable.

I'm pretty sure I have vacuum problems, because, for one thing, my rear headrests won't unlock, which I've read is a vacuum issue. I'm still working to solve my "squirrel cage blues", so I'm not sure if I have vent issues or not (just got the car a week ago). But it would not surprise me.

So . . .

Is there anyone close to the Triad (Greensboro) area of North Carolina that would be willing to test my vacuum system? Of course I would not expect this for free. There's no real urgency, but I really don't know who to trust, and as a member of this forum I really feel like a part of a big family.

Thanks for everything.
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Last edited by Merce-Me; 07-25-2008 at 11:00 AM.
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  #11  
Old 07-25-2008, 10:48 AM
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if you need that tranny to work good for a long ammount of time, simply plug up the leaking lines in the engine compartment and run vaccume only to the tranny, that will make your transmission shift correctly.
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  #12  
Old 07-25-2008, 10:58 AM
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Quote:
Originally Posted by Cervan View Post
if you need that tranny to work good for a long ammount of time, simply plug up the leaking lines in the engine compartment and run vaccume only to the tranny, that will make your transmission shift correctly.
20" of vacuum directly to the transmission will cause severe flaring on the 2-3 and 3-4 shifts. It's not good advice.
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  #13  
Old 07-25-2008, 10:59 AM
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Cervan's solution has worked for me. Vaccume to only the transmission and shutoff controllers.

That means disabling("temporarily") EGR, power locks, climate control

Also, It will save you(and others) time if you put your car's year, model, mileage, modification, name, status, etc. in your signature ['User CP' link near the top-left, then scroll down to signature]

EDIT: I'm still hooked up to thingy on the IP that controls vaccume to the transmission
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Last edited by Simpler=Better; 07-25-2008 at 11:05 AM.
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  #14  
Old 07-25-2008, 11:04 AM
mrhills0146
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Quote:
Originally Posted by Cervan View Post
if you need that tranny to work good for a long ammount of time, simply plug up the leaking lines in the engine compartment and run vaccume only to the tranny, that will make your transmission shift correctly.
Whoa, no Sir, bad advice, do not do this! Running full vacuum to transmission will cause flaring and shortened life.

If anything, max life can be achieved from these gearboxes by running absolutely NO vacuum to them, but the shifts will be intolerably hard.
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  #15  
Old 07-25-2008, 10:51 PM
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The jarring shifts from no vacuum will certainly not extend the life of your transmission, nor the flex-disks, engine/trans/diff mounts, suspension bushings, etc. I've driven one with no vacuum, brutal.

If you are having vacuum problems, and it sounds like you are from this and your other thread, the last thing to touch is adjustments. More prudent is finding and fixing the leak(s) and everything will probably operate normally. Messing with the adjustments or re-routing the vacuum will not be a short-cut, just more "un-f___ing" later.

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