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Technical Ford Flathead vacuum brake question

Discussion in 'The Hokey Ass Message Board' started by Ritzy1, Jul 9, 2019.

  1. Ritzy1
    Joined: Jun 10, 2010
    Posts: 243

    Ritzy1
    Member

    Looking for some advice from anyone who's using a crab distributor on their early Ford flathead with multiple carbs. I installed a Pertronix 1285LS (12 volt) ignition module in the crab distributor for my 59A-B flathead. The engine is fresh and has an Edelbrock Slingshot with new dual Stromberg 97s and an Isky Max-1 cam. Pertronix tech support told me the distributor’s vacuum brake would not work with that combination, so I plugged the vacuum outlet in the front cover. It seems to be running really rich with the standard #45 jets. Should I plumb the vacuum brake to the intake so that it retards the spark under load? What is working for those of you with similar multi-carb early flatheads? Any advice you could lend would be welcomed.

    Thank you in advance and take care of yourself!
     
  2. What did you expect by asking Petronix tech for advice??? worst place to be asking...Do some reading here on the HAMB for true honest answers...
     
  3. blowby
    Joined: Dec 27, 2012
    Posts: 5,921

    blowby
    Member
    from Nicasio Ca

    I have a flathead with crab and Pertronix and have the vacuum brake hooked up. I don't know why it would act any differently than with points.
     
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  4. Automotive Stud
    Joined: Sep 26, 2004
    Posts: 3,894

    Automotive Stud
    Member

    I have two flatheads with dual 97's and the crab distributor. One has the max 1 cam, the other is an Isky 88. Both have the vacuum brake hooked up with the spring tension set very light on the adjustment and run just fine. They both are still running points however. You might want to switch to a #43 jet or so. That would probably help you out.
     
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  5. tubman
    Joined: May 16, 2007
    Posts: 4,363

    tubman
    ALLIANCE MEMBER

    Pertronix? Again?:eek:
     
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  6. nor6304
    Joined: Aug 23, 2009
    Posts: 179

    nor6304
    Member
    from Indiana

    I have a 46 239 cu in bored & 4" crank with the slingshot & 2 Stromberg's with a Pertronix on a crab & have the vacuum line brake hooked up Only about 50 miles so far but it runs really good
     
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  7. Ritzy1
    Joined: Jun 10, 2010
    Posts: 243

    Ritzy1
    Member

    First of all, thanks for all the constructive replies.

    Turns out, the real issue was that there were two open vacuum ports in the manifold that I was not aware of. Funny, because I called Edelbrock tech support about the best place to plumb for vacuum for the brake booster and they never mentioned the manifold had vacuum ports already. Had the machine shop drill and tap a hole in the plenum (that I probably didn't need). Anyway, the guys at Freeman's garage where I took it, found them and plugged them up. What a difference! John sure put a smile on my face when he took me around the block and it actually ran pretty well. First time I've been able to ride in it! Now, he's going to lean it out a bit and change the power valves to make it more responsive. I am so psyched!

    No vacuum brake plumbed yet, either.

    Sent from my SM-G930V using The H.A.M.B. mobile app
     
  8. hfh
    Joined: Oct 22, 2012
    Posts: 221

    hfh
    Member
    from Western MA

    Nice to hear that John Freeman helped you with your project. He's had a lot of experience with old Fords and is good about sharing his knowledge. I hope you get to put some miles on it this summer.
     
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  9. backrodebob
    Joined: Aug 5, 2019
    Posts: 8

    backrodebob
    Member

    I'm new to the group and you just touched on an issue that's driving me "NUTS" Vacuum to the brakes?
    I bought a 29 ford 2door sedan with a 40-53? flathead in it. the most I can get is 15# vacuum a 17 if I run idle up? there is no power assist? any help would be appreciated! by the way I replaced the master and booster.
     
  10. Dak Rat
    Joined: Mar 8, 2006
    Posts: 352

    Dak Rat
    Member

    Pretty sure you would be happier with 43 or 44 jets with that set up.
     
  11. tubman
    Joined: May 16, 2007
    Posts: 4,363

    tubman
    ALLIANCE MEMBER

    They are talking about the "Vacuum Brake" which is part of the distributor, which is a completely different deal than vacuum assisted power brakes. First of all to be of any help, we need the basic type of engine you are running. '40-'53 covers a lot of territory. Does your engine have the distributor mounted on the front of the engine on the timing cover (between the water pumps, or is it mounted to the side and attached to the passenger side head? If you have the latter, you have an 8BA type engine, which does not have the vacuum brake. They are only on the earlier (pre-'49) engines.

    On your other problem, even if you can increase the vacuum from 15 to 17 by raising the idle, you are just masking the problem. Better you should first check for a vacuum leak. This was the O/P's problem, and when solved, resulted in a smooth running engine. (See post #7 above).
     
    Last edited: Aug 6, 2019
  12. This is a carburetor VACUUM BRAKE (a.k.a. choke pull-off). It is used to slightly open the choke valve on the carburetor during cold starts to prevent flooding.

    VACBRAKE.png

    This is a distributor VACUUM ADVANCE (or sometimes retard) canister. It alters ignition timing by the application engine manifold or ported vacuum.

    VACADVANCE.jpg

    This is a VACUUM POWER BRAKE BOOSTER. It reduces brake pedal effort by the application of engine manifold vacuum.

    BRKBOOSTER.jpg
     
  13. tubman
    Joined: May 16, 2007
    Posts: 4,363

    tubman
    ALLIANCE MEMBER

    Close, but no cigar (two outta three ain't bad). Here is a picture of a Ford "Crab" distributor. The "Vacuum Brake" is the cylindrical thing sticking out of the top of the distributor body (The silver part in the picture.) A vacuum line runs from the intake manifold to a port on it. The tension on the brake can be adjusted by turning the screw sticking out of it. (Sorry for the tiny picture; it was all I could find at short notice.)
    crab.jpg
     
    Last edited: Aug 6, 2019
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  14. KenC
    Joined: Sep 14, 2006
    Posts: 271

    KenC
    Member

    Actually the choke thingy is a 'pull off' or 'choke break' in every manual I've seen. Not a 'brake'.
     
  15. backrodebob
    Joined: Aug 5, 2019
    Posts: 8

    backrodebob
    Member

    sorry I goofed! 49-53 distributor on right side and yes I ck’ed for leaks but I’ll go back and re-check. Go’na install hei and add a elector vac pump any thoughts?
     
  16. tubman
    Joined: May 16, 2007
    Posts: 4,363

    tubman
    ALLIANCE MEMBER

    Yeah, a couple. First, is your car 6 or 12 volts? 6 volt electronic ignitions are notoriously flaky for several reasons, the primary one being electronic noise.. I would recommend keeping the points and learning how to keep your ignition system in tip-top shape; at the number of miles we put on these cars each year, a points system will last for 15-20 years, where an electronic system can "die" at any time leaving you stranded. Points will give you plenty of notice they are going bad, allowing you to get home and fix the problem. Also, parts for point ignitions are cheaper than new electronic modules.

    Why a vacuum pump? It may increase the vacuum shown on your gauge, but again, it would mask the real problem. Sounds to me like a bad idea.
     
  17. backrodebob
    Joined: Aug 5, 2019
    Posts: 8

    backrodebob
    Member

    12V I appreciate your feed back! go'na be honest, never had experience with a flathead, learning as I go.
     
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  18. backrodebob
    Joined: Aug 5, 2019
    Posts: 8

    backrodebob
    Member

    changed my mind and added a vacuum canister, went from 15 # to 21 brakes work great! also decided against hei, like I said learning as I go!!
     
    Ritzy1 likes this.

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