Losing brake pressure when applying the brakes

Discussion in 'Engine/Fuel/Exhaust' started by undertakerman, Feb 23, 2017.

  1. undertakerman

    undertakerman Member

    I have a 65 Plymouth Sport Fury that I built 15 years ago that ran great up until a couple of years ago. But after some major engine repairs last year has ran great ever since. But the last couple of times I have driven it I have noticed that when I applied the brakes the car does show down and then it gets to the stopping point the brake pressure goes away and the peddle goes to the floor but the car does stop. But a time or two I have had to use the parking brake to stop the car. Now the engine does have a vacuum recovery system for the brakes. Due to the cam that is in the engine the vacuum pressure is a little lower then it should be and the vacuum recovery system stored the vacuum for the brake system. What could the problem be. HelpHelpHelp
     
  2. mrmopartech

    mrmopartech Moderator Staff Member

    First I would buy a electric assist vacuum pump,and remove the hose to the manifold.do a complete fluid change and bleeding of the whole system.At worst the master cylinder could be on the way out.If you need more help,call me at 514 659 0445 cell or 450 424 0445 home mrmopartech -scott
     
  3. Bob Hogan

    Bob Hogan Well-Known Member

    I'm In..... That its the master cylinder if nothing else is leaking.....
     
  4. mrmopartech

    mrmopartech Moderator Staff Member

    I agree,but you need to try the simple cheapest things first,before condeming the MC,which over decades go south real fast,and with old brake fluid that abzorbes moisture,and then turns the fluid to crap,low pedal is sure bet,mrmopartech
     
  5. Bob Hogan

    Bob Hogan Well-Known Member

    Agreed... It never hurts to make sure what the issue/problem is... And all the other stuff never hurts one bit to do..The simplest things cat be over looked.. :)
     
  6. undertakerman

    undertakerman Member

    Gentleman. I totally agree. I_Agree My first thought was to change the brake fluid and rebleeding the entire system. Now at times I have had to add brake fluid. I always check my fluid levels before driving the car. Now mrmopartech you said "buy a electric assist vacuum pump, and remove the hose to the manifold". I agree on buying a vacuum pump. What I don't understand is you said "remove the hose from the manifold". I_Dont_Get_It Could you please clarify that statement. And what happens to the vacuum recovery system. Does the vacuum pump tie into that system or does that system need to be removed. Help
     
  7. undertakerman

    undertakerman Member

    Hello Bob. As I said earlier I have had to add fluid to the master cylinder the last couple times I had driven it. This morning I found brake fluid on the inside of the master cylinder on the engine side and down on the frame. Can the master cylinder cap seal be leaking? The lines where they come out of the master cylinder are clean no leaks found there. I cannot locate any other leaks without pulling the wheels and rear drums. I don't have time to start doing that today. But will soon.. Michael S.
     
  8. Bob Hogan

    Bob Hogan Well-Known Member

    Yes, the cap can leak if the seal gets in bad shape or the cap Bail Wire that hold the cap gets weak. But if your adding fluid, you know its going somewhere?
    You might even need to loosen the master cylinder from the booster and see if its leaking back into the booster. If that winds up being the case, then you will need to replace both the master and the booster units. But check all the other stuff first and make sure its all in good working order.
    Just my 2 cents.... Good to see you Mike.. :)
     
  9. undertakerman

    undertakerman Member

    Hello Bob. The bail wire is still pretty strong and I believe that the seal is bad because I noticed what looks like rust stains on the engine side of that seal. I do place on replacing the cap during this maintenance period if not the master cylinder itself.. Mike
     
  10. Bob Hogan

    Bob Hogan Well-Known Member

    I see... Brake fluid is a good stripper. And yes if its seeping you will see rust and or the rust/crust buildup.... Mr.Mopartech pointed out the Moisture in the system, and that moisture will compromise the system for sure.
     
  11. undertakerman

    undertakerman Member

    mrmopartech. I'm going to install a electric assist vacuum pump and I'm not sure which one to buy. I have at all different brands. I have looked at the ones that Summit offers and on Ebay. I'm trying to stay around 150.00. The one that I'm interested is the is on Ebay for 145.00 plus shipping and handling. It's made by Auto City Classic 12VVAC producing 18-22 inches of constant vacuum. What electric Vacuum assist pump that would cost around 150.00 that could be tied into my existing vacuum recovery system do you subject... Mike
     

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