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Old 03-28-2010, 02:48 PM
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Transmission Modulator Question

Hey everyone,

So yesterday after doing a valve adjustment I noticed that my shifting had gotten considerably bad and late. Well after troubleshooting it for an hour or so Tyler adjusted the transmission modulator (forgive me if that's not what this is) near the ip on my car. During the adjustment, the adjusting nut snapped off and is nowhere to be found.

However this was not the problem, there was a vacuum line that had cracked and repairing it cured the shifting problem.

The shifting was MUCH better, incredibly smooth actually, after the adjustment on the modulator. However the car was hot, and had been driven 200 miles (for the gtg) so this morning it shifted a little rougher.

Anyways I'm wondering what can be done to fix this and what this part consists of. Is it NA specific, meaning I couldn't go tear one off a turbo model in a junkyard? Or can I easily repair it?

Here are pictures of what I'm talking about:







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Old 03-28-2010, 03:38 PM
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That is the vacuum control valve. It controls how much vacuum is going to the transmission modulator on the trans. The amount of vacuum going to the trans is related to the engine rpm. They aren't NA specific. I actually thought they were only on the turbos, but I was wrong once, so I goes it could happen again. You should be able to find one on just about any auto trans 123. The early models were all mechanical. They had linkages that controled shift quality and timing and a mechanical modulator. Some time around 79 they must have switched to the vac controlled trans.
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Old 03-28-2010, 06:05 PM
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Quote:
Originally Posted by colincoon View Post
However this was not the problem, there was a vacuum line that had cracked and repairing it cured the shifting problem.

The shifting was MUCH better, incredibly smooth actually, after the adjustment............
You're referring to the vacuum control valve, and, clearly it's functioning properly.

Your photo shows the locknut in the proper position, therefore it's not clear that anything needs to be replaced at this time.
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Old 03-28-2010, 06:19 PM
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^No, something definitely broke off of there during the adjustment last night. Whatever we were turning last night is no longer there. It was a 7mm nut.
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Old 03-29-2010, 01:32 PM
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Okay I need a new one of these. I'm having terrible shifting yet again, and a bit of flaring at low rpm in 1st gear. It shifts something awful.

Not sure how all of it happened in the first place, all I did was a valve adjustment :/

EDIT: Just threw the old piece of vacuum tubing on to the place it came from, and it shifted okay again. This piece of tubing was leaking, so I'm guessing that I have too much or too little vacuum going to this valve. However I can not adjust it because of the missing nut.


Last edited by colincoon; 03-29-2010 at 01:51 PM.
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