Register now to get rid of these ads!

Technical Vacuum advance question

Discussion in 'The Hokey Ass Message Board' started by Mark Wahlster, Mar 18, 2021.

  1. Mark Wahlster
    Joined: May 21, 2016
    Posts: 76

    Mark Wahlster
    Member

    I have a Prestolite IAT-4405 Distributor I got it NOS. I also found what I believe are some NOS vacuum advance cans for it. Standard VC-110 the vacuum advance cans showed up today. And they both have no travel? the stop on the arm is right up against the stop. If I add vacuum to the can the arm does not move. What am I missing here? There is no obvious way to adjust them like with a 68 Mustang 200 6L distributor where you turn a screw inside the can to adjust. Are both of these made incorrectly or what. One of the arms has 3.5 stamped on it the other has 7.5 on it.

    Any of you old school distributor guys got a clue?
     
  2. Look real close and see if they were locked for shipping. I am just guessing on this but that is what I would look for.
     
  3. garyf
    Joined: Aug 11, 2006
    Posts: 283

    garyf
    Member

    Some prestolite s had an allen screw adj. inside the vac. port
     
  4. egads
    Joined: Aug 23, 2011
    Posts: 1,419

    egads
    Member

    Can you move the arm by hand? Depending on the age , the diaphragm may have gotten stiff ? Picture.
     

  5. Mark Wahlster
    Joined: May 21, 2016
    Posts: 76

    Mark Wahlster
    Member

    [​IMG]

    [​IMG]

    [​IMG]

    Nothing inside which looks to be an adjustment.

    The advance that is in the distributor the stop is about 1/4"" away from the stop. The arm is in the orientation it fits into the distributor with. I car with a pair pf pliers pull the stop away about 1/16th inch on the one marked 7.5 and maybe 3/32" on the one marked 3.5
     
    Last edited: Mar 18, 2021
  6. garyf
    Joined: Aug 11, 2006
    Posts: 283

    garyf
    Member

    If mounted on the dist. with the arm hooked on the breaker plate,does this then move the arm off its stop & is it then able to move the arm or plate w/ vac applied ?
     
    Last edited: Mar 18, 2021
    pprather likes this.
  7. speedshifter
    Joined: Mar 3, 2008
    Posts: 312

    speedshifter
    Member

    Arm has to travel toward the diaphram when vacuum is applied. I think they are faulty. The exact amount of advance & the inches of vac needed is, in my opinion, not as critical as the centrifical advance. Vac advance helps mileage when cruising. When you floor it there is almost no vac so it does not effect acceleration. Greg
     
  8. saltflats
    Joined: Aug 14, 2007
    Posts: 12,594

    saltflats
    Member
    from Missouri

    Boost retard?
     
  9. Mark Wahlster
    Joined: May 21, 2016
    Posts: 76

    Mark Wahlster
    Member

    For a Distributor thats OEM application is a 1961 Willys FC-150 with a 134F I don't think so.
     
    egads likes this.
  10. Mark Wahlster
    Joined: May 21, 2016
    Posts: 76

    Mark Wahlster
    Member

    Not Sure but I can't pull the arm out even if I use pliers to get a solid grip on it. they both have at best 3/32" of movement. I checked another new spare I have and its only got maybe 1/8" of movement. I think I am going to unweld the little mounting bracket so I can grind the stop back a bunch then weld a little tab on the arm with a set screw I can adjust the amount of travel with. I have four of these now that are all new. SO I can risk experimenting.

    I tried mounting one to a spare IAT-4405 distributor I have any yes it moves the plate MAYBE enough to change the timing 2 degrees.
     
  11. saltflats
    Joined: Aug 14, 2007
    Posts: 12,594

    saltflats
    Member
    from Missouri

    Corvair ?
    Have you tried to apply pressure to it?
     
  12. Mark Wahlster
    Joined: May 21, 2016
    Posts: 76

    Mark Wahlster
    Member

    The diaphragm is pretty much right against the back of the can so no.
     
  13. saltflats
    Joined: Aug 14, 2007
    Posts: 12,594

    saltflats
    Member
    from Missouri

    Got it, sounds like a improper built part.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.