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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: flips87c30 on January 28, 2013, 06:05:05 pm

Title: th400 not shifting soon enough
Post by: flips87c30 on January 28, 2013, 06:05:05 pm
I have an 87 v30 with a 454 and a th400. the issue is when going from first gear to second it seems to shift late. it revs too high then shifts kinda hard. Not as bad when going from second to third. I looked under the truck and noticed that the modulator line is not hooked up to the modulator valve(broken rubber piece). Is this my problem or should I be looking for something else?   Thanks in advance
Title: Re: th400 not shifting soon enough
Post by: Sartobuilt on January 28, 2013, 07:32:59 pm
Yes, that should fix it. Might want to replace the hose, they get squishy from trans fluid.
Title: Re: th400 not shifting soon enough
Post by: flips87c30 on January 28, 2013, 07:39:55 pm
Thanks I live about 45 minutes from the nearest autoparts place. Just wanted to make sure there wasnt something I was overlooking before I made the drive.
Title: Re: th400 not shifting soon enough
Post by: bd on January 28, 2013, 08:14:04 pm
If there is evidence of any trans fluid oozing from the nipple of the modulator valve, replace the modulator valve and install a new vacuum hose.
Title: Re: th400 not shifting soon enough
Post by: Engineer on January 29, 2013, 08:30:07 pm
Yes, that should fix it. Might want to replace the hose, they get squishy from trans fluid.


If there is evidence of any trans fluid oozing from the nipple of the modulator valve, replace the modulator valve and install a new vacuum hose.

I'll ditto both of these posts.

If your modulator valve has a broken diaphragm (leaking fluid) make sure you match the color bands on the out side of the valve when buying a replacement.
Title: Re: th400 not shifting soon enough
Post by: DnStClr on February 07, 2013, 09:53:57 am
And, don't forget, expect trans fluid to come out when you replace the valve!