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1988 Allante
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88 Posts
Discussion Starter #1
I've had hard shift issues since I bought the car. I want to replace the vacuum modulator which may alleviate the problem. With that said, i got a part at the part store that is supposed to be the vacuum modulator but it doesn't look like what is referred to as the transaxle vacuum modulator in the tech manual or the actual device on the car. Instead it looks like I may have the guts to the transaxle vacuum modulator....Any input from anyone on this? Thanks
 

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98 Fleet Limited, 94 Sedan Deville, 78 Fleet, 86 Fleet
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18 Posts
Hey Moose, I just brought one myself yesterday. You have brought the right part for your project, however, the part that you are taking off is the OEM part. This will look different, but it will go on your trans. Be aware that when you take the modulator out; pay close attention to how the clamp is attached the orientation of the part. I reinstalled it wrong and when I started the car up, the modulator flew out of the trans. and fluid poured out like a russian race horse...lol. I was fierious when this happened. You need to use the tubing that come with the part in the box. It will work and if someone will add to this, I would like to know if I need to put the valve back in before putting the modulator back on, or can I leave this valve out?
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,738 Posts
Yes the valve is what depresses the diaphram within the modulator. Moose, have you verified with a vacuum gauge what amount of vacuum you have at the modulator? Alot of times the orfice at the the vacuum source is plugged up with intake residue. My 88 with 40,000 miles had to be cleaned with a drill bit to restore proper vacuum. My 91 with 170,000 miles had its original modulator.
 

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1988 Allante
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88 Posts
Discussion Starter #4
Thanks for the feedback. I swapped the vacuum modulator out tonight and it now shifts like a new transmission. I'm really excited about getting it in for some stuff i can't deal with on Tuesday such as four new spark plugs on the firewall side, new O2 sensors, and who knows what else, Every minor maintenance i have done has made big differences. I think the car appreciates the attention. My goal is to "do no harm"...so far so good! The valve is a MV303 purchased at Autozone.
 

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98 Fleet Limited, 94 Sedan Deville, 78 Fleet, 86 Fleet
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18 Posts
Yes the valve is what depresses the diaphram within the modulator. Moose, have you verified with a vacuum gauge what amount of vacuum you have at the modulator? Alot of times the orfice at the the vacuum source is plugged up with intake residue. My 88 with 40,000 miles had to be cleaned with a drill bit to restore proper vacuum. My 91 with 170,000 miles had its original modulator.
Carnut, I realized that when I traveled 40 mls home and found out that it was supposed to be installed at the modulator. I installed it and the trans. do run much better, but it sometimes hesitate at passing speed. I hope this doesn't require me to replace the TCC selenoid.
 
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