Transmission doesn't shift
Thread Starter
Intermediate
Joined: Nov 2012
Posts: 39
Likes: 0
From: Dallas Texas
Transmission doesn't shift
I bought a disassembled 69. 350 with automatic. Both the motor and transmission were rebuilt, but not installed. I have it all running. Motor is good. The transmission works when shifting the gears manuallly, but does not shift on its own. I klnow NOTHING about transmissions. I connected the vacuum line to the modulator. Is there something else to do? Any suggestions on where to check?
Race Director
Joined: May 2006
Posts: 18,785
Likes: 2,598
You state you connected the vacuum line to the modulator but make no mention to where the other end is connected. It should be connected to manifold vacuum, constant vacuum when engine is running even at idle. Are you sure the previous owner didnt install a manual valve body in the transmission?
Thread Starter
Intermediate
Joined: Nov 2012
Posts: 39
Likes: 0
From: Dallas Texas
The vacuum is connected to the manifold. Is there an easy way to tell if it was modified to manual shift. I googled it and it seems like there are a lot of modification required internally in the transmission.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
How fast have you driven it in drive to say it wont shift ?
Make sure the detent cable is free and not stuck
make sure the modulator has its pin installed into the valve body
make sure the modulator is connected and good.. Good can be checked by driving car and then taking hose off modulator to see if trans oil is present on its vac connection
Make sure the detent cable is free and not stuck
make sure the modulator has its pin installed into the valve body
make sure the modulator is connected and good.. Good can be checked by driving car and then taking hose off modulator to see if trans oil is present on its vac connection
Drifting
Joined: Jun 2010
Posts: 1,781
Likes: 15
From: Oxford Ohio
Some folks increase the shift pressures in a 350 by removing the check ***** in the valve body. When you go that, you have to leave the check ball in the line from the vacuume modulator valve for the trans to shift. The only way to tell is to drop the pan and open the valve body. It's a messy job, but not difficult.
Race Director
Joined: May 2006
Posts: 18,785
Likes: 2,598
Your post is confusing some people as to what transmission you have, I assumed you have a 69 with 350 cid engine and a 400 Turbo Hydramatic, others are interpreting your post that you have a 350 Turbo Hydramatic. In either case it sounds like you have to drop the pan and possibly the valve body.
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Melting Slicks
Joined: May 2011
Posts: 2,753
Likes: 119
From: Springfield Missouri
the new vacuum modulators have an internal adjustment screw where the hose hooks up. Ask me how I know??? Mine would not shift except manually until I found out about this, now it is sweet!!!
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,630
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From: New Or-leens Loo-z-anna
AAAAAha......this rookie needs to check out THAT adjustment (been 40 years since I needed a vacuum modulator)
Last edited by doorgunner; Oct 27, 2013 at 12:02 AM.
Thread Starter
Intermediate
Joined: Nov 2012
Posts: 39
Likes: 0
From: Dallas Texas
The transmission is a 400. I ordered a new valve from Summit Racing. I will install it this weekend. If that doesn't work, I'll keep shifting. BTW.... I am not a rookie. I'm still in the minor leagues
Pro
Joined: Jul 2012
Posts: 707
Likes: 147
From: St. Petersburg Florida
Do you have an update on your tranny? I have the same issue on a TH350 in a 1979 I just bought. It shifts great. Just have to do it manually. I just assumed the previous owner put a manual valve body in it.
It does downshift on its own though. Can someone tell me if a manual valve body is supposed to downshift on its own or if its full manual up and down?
It does downshift on its own though. Can someone tell me if a manual valve body is supposed to downshift on its own or if its full manual up and down?