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Thread: 57 power-guild back flow valve in line

  1. #1
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    57 power-guild back flow valve in line

    Soon it will be time to have the 1957 Power-guild re-built in my Nomad. I once read in an article in Hemmings classic car magazine about making sure that it has the vent breather , and then I read somewhere that if you install a back flow valve in the correct one of the two transmission lines it won't constantly pee transmission oil into your catch pan, or all over your garage floor. Be sure to wear a welder's glove ever time you check the transmission on these cars or it will burn your arm off. Not fun . If anyone knows about this back flow valve please help . Domenic

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    Registered Member BamaNomad's Avatar
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    I'd like to know any/all details for preventing the PG 'bleeding/peeing' on the floor while sitting also!..

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    Hello Bama, the last time I had a 1957 cast iron power-guild re-built by a professional local shop it leaked like crazy. I wish I had saved the article about the back flow valve . Over the years I have heard that when they sit for a few months, the tranny oil goes back into the converter? or somewhere, and they it over flows poss. out the dip stick tube. The one that I had re-built did not have to sit before it would leak. In plumbing a back flow valve only allows the fluid to pass one way. P.S> watch out for the exhaust manifold.Domenic

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    My x took my original 55 HT when she left, and I was a little glad that she took that one, because it use to puke on the floor every winter. Thirty years later my daughter ask me to sell it for her, so I brought it home and did what ever it needed---including topping off the trans fluid. After taking pictures of it for ebay, I returned it to her, and asked her if she had cleaned up the mess, because I didn't see the fluid on the floor where it had been sitting for a couple years. She said "No, it never leaks on the floor."

    She only put a few thousand miles on it in 30 years, but from what she said I must conclude that it probably did puke the first winter she had it, and she never refilled the trans. I used a trailer to bring it to my house, but I asked her if the trans ever slipped, and she said no.
    Last edited by LEE T; 09-02-2019 at 04:21 PM.

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    Registered Member BamaNomad's Avatar
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    Maybe they puke because they are overfilled and the fluid in the torque converter leaks back; I think that was a theory back in the old days. But the service procedures call for checking level when 'running in park or neutral', which means the fluid is in the torque converter. Maybe this 'backflow' valve prevents the fluid from leaking back from the torque converter??

  6. #6
    Administrator 567chevys's Avatar
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    Hello All,

    I sell Transmission Adapter Plates and been selling many to a Guy back east that Has a Transmission Place
    I asked Him why These Transmission lose fluid, Here is what email me

    This is from a company that makes excellent upgrade parts and problem solutions for automatic transmissions.

    Here is a link to a technical discussion about the Cast Iron Powerglide leaking issue.

    https://www.sonnax.com/tech_resource...werglide-leaks



    Here is their explanation of the cause, and the proper fix for the pre-’58 Cast Iron Powerglide:

    Before 1958, the only vent for the transmission was the opening at the top of the fill tube. The dipstick did not have a positive seal, and was designed to allow air to enter and exit the transmission.

    The Hydra-matic™ transmission of that day had a similar dipstick, but it entered the transmission at the top of the case and vented the entire main case and extension housing cavity equally. Since all of the cavities of the Hydro-matic were well vented, leaks were not an issue. By comparison, on the C.I Powerglide, the dipstick tube enters the case at a lower level. This means that - when the fluid is at its proper level - this area is isolated from the rest of the main case cavity. When all of the area inside a transmission case is not vented equally, pockets of pressure are allowed to build up. The vented area of the main transmission case and the extension housing are connected by an orifice in the 11 O'clock position in the rear pump.

    This orifice was restricted by a small pin. Veteran C.I. Powerglide rebuilders learned the hard way that leaving the pin out of the orifice in the rear pump would cause the transmission to burp oil out of the dipstick. Before the vent was added to the main case in 1958, this burping action was the only way that a pressure build up could be exhausted from the main case. This pressure build-up also explains the numerous stubborn leaks.

    To retrofit a vent to the earlier transmissions, a 90° brass fitting was added to the extension housing. A length of fuel line hose with a plastic vent (from a 350 transmission) was attached to the fitting. The end of the hose with the vent was then attached near the top of the dipstick tube.

    Unfortunately, this root cause analysis was started more than 50 years too late for this problem, but hopefully it will help with the way we approach future ones.

    Hope this helps!

    Harrel Lamkin

    1955 2 DR Post
    1937 Chevy Coupe
    2019 Ford Suoer Duty F350
    2018 Ford Explorer
    1955 Chevy Nomad
    1934 Plymouth PE Coupe

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    Registered Member BamaNomad's Avatar
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    That makes absolute sense Sid! Thanks for inquiring with someone knowledgable and passing along their information~ Now all we have to do is pull the transmission and FIX it.... .. and any of us that has removed / installed a C.I. PG trans from under a car KNOWS how much fun that is...

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    This explanation makes plenty of sense to me since the same re-builder that did my leaking 57 power-guild, also did my friends 1958 power-guild and his never leaks.

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