Auto Transmission problem
Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Auto Transmission problem
The auto trans is a Turbo 400 with almost 60000 miles on it. Based on advice from this forum a couple of months ago, I solved a HUGE problem, with it eating all of the transmission fluid, by changing the vacuum modulator valve. Now I have another question. If I am cruising along at anything under 40-45 mph, the car won't shift into third gear unless I let off of the gas completely. As soon as I add some throttle, the car is no longer in third. Now, I know nothing about auto transmissions and don't know where to start on this one. Advance Auto couldn't find the Turbo 400 in their computer but said the vacuum modulator was the same for the 350 and 400. Any ideas guys?
Gary
Gary
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Re: Auto Transmission problem (GaryS)
See if it was assembled with an adjustable mod valve. If it was, then you can adjust the speed with a small pocket screwdriver.
Pull the vac hose off the valve and stick the screwdriver in it. Clockwise brings the upshift speed HIGHer and obviously, counter-clockwise brings it lower.
If it was not assemebled with an adjustable valve, have one put in.
Pull the vac hose off the valve and stick the screwdriver in it. Clockwise brings the upshift speed HIGHer and obviously, counter-clockwise brings it lower.
If it was not assemebled with an adjustable valve, have one put in.
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Auto Transmission problem (mapman)
Gary. Look inside the modulator nipple. That would be where the adjusting screw is, it there is one. Also make sure that the pin that the modulator moves is in place and in good condition. When you take the modulator off you should see it sticking out of the trans. I have seen these fall out un-noticed and the new modulator put in without the pin.. TH400 modulators ARE available. Try a GM dealer. I went to auto trans school a number of years back and hev rebuilt a few TH400's. So.... if I can be of any help.....Please ask. :thumbs:
Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Re: Auto Transmission problem (silvervetteman)
Well, I will take a look at the nipple to see if it is possible that there is an adjustment in there. This nipple can't have an ID of more than 1/4" but I will check it out tomorrow. Can't look at it today - too much Super Bowl prep.
I will also put my vacuum gauge on the intake manifold to see if there is a vacuum leak.
Can anyone confirm that the Turbo 350 and 400 take the same vacuum modulator?
Gary
I will also put my vacuum gauge on the intake manifold to see if there is a vacuum leak.
Can anyone confirm that the Turbo 350 and 400 take the same vacuum modulator?
Gary
Melting Slicks
Joined: Aug 2001
Posts: 3,046
Likes: 124
From: Wichita KS
Re: Auto Transmission problem (GaryS)
GaryS,
I did a quick search for transmission modulators at www(dot)autozone(dot)com for 1972 Corvette. They list both a 400 and a 350 transmission. The modulator part number is the same. There are several choices to identify the application under search, I was guessing about your 1972, but it looks like they may be the same.
I did a quick search for transmission modulators at www(dot)autozone(dot)com for 1972 Corvette. They list both a 400 and a 350 transmission. The modulator part number is the same. There are several choices to identify the application under search, I was guessing about your 1972, but it looks like they may be the same.
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Thread Starter
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Re: Auto Transmission problem (mapman)
Whoa Mapman! I didn't even think to try that route. Oh well. I learn new things each day. I will be doing a vacuum check and then pulling the VM to see if the installation is correct and to see if perhaps my new one is leaking. It only has 3000 miles on it.
News at 11.
Gary
News at 11.
Gary