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.

BAD MODULATOR?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Russell Keys, Jan 21, 2002.

  1. Russell Keys

    Russell Keys 1/2 ton status

    Joined:
    Mar 16, 2000
    Posts:
    253
    Likes Received:
    0
    Location:
    Huntsville, TX
    The th-350 I have sometimes won't shift into 2nd gear, or if it does and I let off the gas it will quit pulling. Then sometimes when it's put into gear for/rev it won't move right away, kinda like it has a high stall speed. I did replace the detent cable, but do not think I messed that up. I have a new modulator to put in but wanted to get some input before I started to mess with it. Anyways any help is appreciated. Thanks, Russell
     
  2. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

    Joined:
    Sep 17, 2001
    Posts:
    1,962
    Likes Received:
    0
    Location:
    Western CO
    pull the hose off the modulator and if fluid comes out it is no good . it may need a rebuild ..

    pics page
    <a target="_blank" href=http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1>http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1</a>

    always gets me home K10 STEPSIDE
     
  3. RedDwarf

    RedDwarf 1/2 ton status

    Joined:
    May 9, 2001
    Posts:
    816
    Likes Received:
    0
    Location:
    North Central Florida
    If the diaphragm is bad, engine vaccum will cause ATF to be pushed into the engine and white smoke will be spewing from the exhaust.

    Otherwise, check to make sure it is on tight. My friend had a 350 that acted like you describe and the modulator was loose on the case. He replaced it, so I am not sure that was the only thing wrong with it....
     
  4. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

    Joined:
    Sep 17, 2001
    Posts:
    1,962
    Likes Received:
    0
    Location:
    Western CO
    how could the vaccum push when it is a vaccum?? sorry couldnt resist...

    pics page
    <a target="_blank" href=http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1>http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1</a>

    always gets me home K10 STEPSIDE
     
  5. RedDwarf

    RedDwarf 1/2 ton status

    Joined:
    May 9, 2001
    Posts:
    816
    Likes Received:
    0
    Location:
    North Central Florida
    Vaccum doesn't push smarty pants. Vaccum allows a higher pressure to push the fluid into the low pressure of the vaccum. Vaccum doesn't "suck" like most people think.
     
  6. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

    Joined:
    Sep 17, 2001
    Posts:
    1,962
    Likes Received:
    0
    Location:
    Western CO
    yeah thats what i said , whats going to push it ?? if vaccum doesnt suck why does vac hose suck onto my finger when i take it off

    pics page
    <a target="_blank" href=http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1>http://www.imagestation.com/album/pictures.html?id=4292257869&show_all=1&start=1</a>

    always gets me home K10 STEPSIDE
     
  7. kim tate

    kim tate 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    134
    Likes Received:
    0
    Location:
    New Orleans
    Not sure if this will help you or not, but I had problems with transmission shifting into reverse. Another sympton that showed up at the same time was vacumn lines kept slipping off connecting points. The vacumn lines were slick with ATF fluid. This sympton was in the Haynes repair manual trouble shooting tree and suggested a bad modulator. I replaced the modulator and that fixed both problems.
     
  8. Russell Keys

    Russell Keys 1/2 ton status

    Joined:
    Mar 16, 2000
    Posts:
    253
    Likes Received:
    0
    Location:
    Huntsville, TX
    Thanks for the replies. Hopefully tomorrow I'll get a chance to go over and check out the modulator. I bought one for it a while back but never put it on so I might replace it anyway. I bought the same color band mod. that was on it, but my bud at NAPA said that the book didn't list it as an option for the year and model. How important is it and what's the diff. in colored bands?
     

Share This Page