The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > General Truck Forums > Engine & Drivetrain

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 03-31-2018, 10:46 PM   #1
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
TH400 help

I have a TH 400 that I just got in my truck and, it's not shifting right. Could it have to do with this (see pic below) is this supposed to be hooked up to a vacuum line?
Attached Images
 
'65 chevy lover is offline   Reply With Quote
Old 03-31-2018, 10:50 PM   #2
B. W.
Registered User
 
B. W.'s Avatar
 
Join Date: Nov 2014
Location: Bigfork, Montana
Posts: 1,137
Re: TH400 help

Yes, vacuum modulator. Hook it to vacuum & see if it shifts better.
B. W. is offline   Reply With Quote
Old 03-31-2018, 11:05 PM   #3
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,246
Re: TH400 help

Just to clarify, it needs to be connected to manifold vacuum.
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 04-01-2018, 12:03 AM   #4
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Quote:
Originally Posted by B. W. View Post
Yes, vacuum modulator. Hook it to vacuum & see if it shifts better.
Thanks, will do.
'65 chevy lover is offline   Reply With Quote
Old 04-01-2018, 12:05 AM   #5
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Quote:
Originally Posted by Captainfab View Post
Just to clarify, it needs to be connected to manifold vacuum.
Thanks, Captain, I'll check it out.
'65 chevy lover is offline   Reply With Quote
Old 04-01-2018, 10:45 PM   #6
YoungPup1977
Account Suspended
 
Join Date: Jun 2015
Location: No longer here
Posts: 1,000
Re: TH400 help

Just some additional tidbits.......From the pic, I believe the modulator maybe adjustable as well....so you can take a small screw driver and adjust the set screw in the modulator....turn the screw clockwise will firm up the shift (later) and counter clockwise with soften the shifts (earlier) ....
YoungPup1977 is offline   Reply With Quote
Old 04-02-2018, 12:23 AM   #7
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Quote:
Originally Posted by YoungPup1977 View Post
Just some additional tidbits.......From the pic, I believe the modulator maybe adjustable as well....so you can take a small screw driver and adjust the set screw in the modulator....turn the screw clockwise will firm up the shift (later) and counter clockwise with soften the shifts (earlier) ....
Thanks, I'll check it out.
'65 chevy lover is offline   Reply With Quote
Old 04-05-2018, 11:39 PM   #8
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Hooking up to vacuum fixed the problem. It shifts good now. I felt and looked around on the valve body, but didn't see or feel a screw to adjust how it shifts. Thanks to all for the help!
'65 chevy lover is offline   Reply With Quote
Old 04-06-2018, 12:37 AM   #9
Captainfab
60-66 Nut

 
Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 23,246
Re: TH400 help

The adjustment screw on a vacuum modulator is inside and accessed thru the port for the vacuum hose.
__________________
Power Steering Box Adapter Plates For Sale HERE
Power Brake Booster Adapter Brackets For Sale '63-'66 HERE and '67-'72 HERE and '60-'62 HERE and "60-'62 with clutch HERE
Rear Disc Brake Brackets For Sale. Impala SS calipers HERE Camaro Calipers HERE D52 Calipers HERE 6 Lug HERE
Hydroboost Mounting Plates HERE
Captainfab is offline   Reply With Quote
Old 04-06-2018, 10:22 AM   #10
Alex V.
Registered User
 
Alex V.'s Avatar
 
Join Date: Mar 2013
Location: Campbellsville, KY
Posts: 888
Re: TH400 help

Quote:
Originally Posted by Captainfab View Post
The adjustment screw on a vacuum modulator is inside and accessed thru the port for the vacuum hose.
This. And on a Turbo 400 the modulator is the sole control of shift points and firmness, except for the electric switch for WOT downshifts which most, but not all have.
__________________
Alex V.
------
1967 C10 Suburban, 350/NP435, Green/Green, PS, PB, HD cooling, charging, shocks, and springs.

1985 GMC C3500 SRW, Sierra Classic, 454/TH400, white/blue.
Alex V. is offline   Reply With Quote
Old 04-06-2018, 03:24 PM   #11
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Quote:
Originally Posted by Captainfab View Post
The adjustment screw on a vacuum modulator is inside and accessed thru the port for the vacuum hose.
Ah, I'll check it out. It shifts fairly quick from 1st to 2nd, but from 2nd to 3rd takes a bit longer. I'll have to drive it more to see if I need to adjust it. Thanks for the info.
'65 chevy lover is offline   Reply With Quote
Old 04-06-2018, 03:33 PM   #12
mattfranklin
Senior Member
 
mattfranklin's Avatar
 
Join Date: Dec 2011
Location: Moraga, CA
Posts: 797
Re: TH400 help

Quote:
Originally Posted by '65 chevy lover View Post
Ah, I'll check it out. It shifts fairly quick from 1st to 2nd, but from 2nd to 3rd takes a bit longer. I'll have to drive it more to see if I need to adjust it. Thanks for the info.
Glad you got to the root of it. I'll bet it revved way up and then slammed the 1-2 shift. I had that vacuum hose fail once because the PO put the exhaust too close to it and burned the hose until it was extremely brittle.
__________________
(Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1

http://67-72chevytrucks.com/vboard/s...d.php?t=567340
mattfranklin is offline   Reply With Quote
Old 04-06-2018, 03:42 PM   #13
DieselSJ
Registered User
 
Join Date: Jun 2016
Location: Phoenix, AZ
Posts: 574
Re: TH400 help

Quote:
Originally Posted by Captainfab View Post
The adjustment screw on a vacuum modulator is inside and accessed thru the port for the vacuum hose.
Be very careful and make changes 1/4 to 1/2 turn at a time. You can puncture the diaphragm in them if you crank it in too far. As me how I know...
__________________
87 R30 CC Dually, TBI 454, NV4500, zero rust barn find
87 Jeep Grand Wagoneer, 6.5 turbodiesel, 700R4
DieselSJ is offline   Reply With Quote
Old 04-06-2018, 08:48 PM   #14
GASoline71
"I ain't nobody, dork."
 
GASoline71's Avatar
 
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,921
Re: TH400 help

Also there was a steel line that ran down there from the factory. Attached at the intake behind the carb and to the modulator with a 4" piece of rubber hose. A long rubber vacuum hose going all the way down there can weaken and colapse.

Gary
__________________
'cuz chicks dig scars...

My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread.

The Rebuild of Creeping Death after the wreck

Quote:
Originally Posted by LONGHAIR View Post
I would never rebuild a 305.
Quote:
Originally Posted by prostreetC-10 View Post
I love using vacuum gauges as part of the carb tuning process. I hook the gauge to the inside of my garbage can and leave it there.
Quote:
Originally Posted by Marv D View Post
Remember Murphys 2nd law of mechanical relationships... "OPPOSING COMPONENTS ATTEMPTING TO OCCUPY THE SAME SPACE, AT THE SAME TIME, GENERALLY END UP OCCUPYING ADJOINING SPACE AT THE BOTTOM OF THE OIL PAN"
Quote:
Originally Posted by cableguy0 View Post
Its cheaper to listen to advice given when you ask for help than it is to ignore everyone and wait for carnage.
GASoline71 is offline   Reply With Quote
Old 04-08-2018, 12:21 AM   #15
'65 chevy lover
Registered User
 
Join Date: Apr 2011
Location: Ft. Worth, Tx
Posts: 536
Re: TH400 help

Thanks to everyone for the information, it is very appreciated!
'65 chevy lover is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 03:22 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com