Determining if vacuum modulator is good?

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   This is off a 64 classic with the M8 transmission. Has the kick down wire and a metal vacuum line going in the rear. I rebuilt the trans and have run it about 200 miles. Seems to work fine, shifts fine, kicks down fine so I'm not seeing any trouble. Problem is it leaks like crazy. I replaced the o ring when installing the modulator and used some trim adhesive to put the bellows on. Now that I have it back off I can see that there is probably some leakage around the bellows where it contacts the pushrod. I probably didn't get enough stickum around it. I also found that the o-ring had moved down into the threads and had gotten chewed up during install. I'm really not sure how you keep that from happening with the o-ring?
Now that it's out I've tried blowing in both ends and there is leakage. I would think that if I suck on the vacuum end there should not be any leakage. Would this be correct? I can put my finger over the end where the rod goes and the vacuum still leaks. 

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dogbone Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Mar/13/2008 Location: TN Status: Offline Points: 702	Post Options Post Reply Quote dogbone Report Post Thanks(0) Quote Reply Topic: Determining if vacuum modulator is good? Posted: Sep/30/2016 at 9:33pm
	This is off a 64 classic with the M8 transmission. Has the kick down wire and a metal vacuum line going in the rear. I rebuilt the trans and have run it about 200 miles. Seems to work fine, shifts fine, kicks down fine so I'm not seeing any trouble. Problem is it leaks like crazy. I replaced the o ring when installing the modulator and used some trim adhesive to put the bellows on. Now that I have it back off I can see that there is probably some leakage around the bellows where it contacts the pushrod. I probably didn't get enough stickum around it. I also found that the o-ring had moved down into the threads and had gotten chewed up during install. I'm really not sure how you keep that from happening with the o-ring? Now that it's out I've tried blowing in both ends and there is leakage. I would think that if I suck on the vacuum end there should not be any leakage. Would this be correct? I can put my finger over the end where the rod goes and the vacuum still leaks.
	64 Cross Country Wagon 770, 79 VW Scirocco, 70 Porsche 914-6, 82 Subaru Brat, 1991 Autozam