Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

th 350 automatiC transmission

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by kristoffer, Jun 5, 2001.

  1. kristoffer

    kristoffer Registered Member

    Joined:
    May 21, 2001
    Posts:
    32
    Likes Received:
    0
    Location:
    Norway
    hi, i have a 77 blazer k5 with a th 350. but it will not hold the 3 gear. it drops down, it helps if i put it in N and then down to D then it wil go in 3 for a little wile, but sudenly it drops down.

    Anybody have any ideas??? please help

    Sorry for my bad english.......

    Kristoffer
    1977 blazer k5 cheyene
     
  2. 71RestoRod

    71RestoRod 1/2 ton status

    Joined:
    Mar 7, 2001
    Posts:
    178
    Likes Received:
    1
    Location:
    Evergreen, CO
    Sounds like a problem with the vacuum modulator or the vacuum line leading to it... The modulator can be adjusted, but is cheep enough to just replace if suspect.
     
  3. Steve_Chin

    Steve_Chin 1/2 ton status

    Joined:
    Mar 6, 2001
    Posts:
    1,126
    Likes Received:
    0
    Location:
    Foster City, CA, USA
    I'd guess that the line leading to the modulator is at fault or the TV cable is misadjusted. Either could cause a premature downshift.
     
  4. 2quicK5

    2quicK5 Registered Member

    Joined:
    Apr 18, 2001
    Posts:
    46
    Likes Received:
    0
    Location:
    TN
    It's probably just a vacuum modulator gone bad. Check to make sure that the vacuum line going to it is connected and that the modulator will hold vacuum. If the modulator is OK then the tranny cannot hold line pressure which would require a tranny rebuild to fix. To the best of my knowledge TH 350s have a vacuum modulator and passing kickdown cable, not a TV cable like a 200R4 has which takes the place of a vacuum modulator.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" springs, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     
  5. kristoffer

    kristoffer Registered Member

    Joined:
    May 21, 2001
    Posts:
    32
    Likes Received:
    0
    Location:
    Norway
    how do i adjust the modulator??

    Kristoffer
    1977 blazer k5 cheyene
     
  6. 2quicK5

    2quicK5 Registered Member

    Joined:
    Apr 18, 2001
    Posts:
    46
    Likes Received:
    0
    Location:
    TN
    Some modulators have a set screw that can be adjusted with a small flat blade screwdriver through the vacuum port on the modulator after the hose is removed. Turning the screw clockwise causes the trans to shift later and harder, turning the screw counterclockwise causes the tranny to shift sooner and softer. Check to make sure your modulator can hold vacuum first though. You can use a short piece of rubber hose and suck on it to see if it will hold a vacuum.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" springs, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     

Share This Page