Newport 1967 brake problem...

Brakes, Suspension, Rims and Tires

  1. surfmaxx

    surfmaxx New Member

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    Hello everyone,
    I have a problem with my braking system.
    The first thing to say is that the brake system (except the brake booster) has been replaced. The car brakes perfectly on the brake test bench. But when I brake from medium or higher speed to a standstill, the brake no longer releases automatically. The car only d again when I accelerate slightly. Then the brake pedal comes back up a little bit. This does not occur on the brake test bench.
    Does anyone have any idea what I could consider.
    (Drum brake front/rear, midland brake booster)
    Thx
     
  2. shooter65

    shooter65 Senior Member FCBO Gold Member

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    Welcome to the site.

    I just tinker and am not a mechanic so others will be able to help you better then I can. The assumptions I'll make is that all or most of the brake fluid has been replaced when you reworked the system and that you don't have any leaks. So the first possibility is that there is a vacuum leak in the booster so it's not building pressure properly when under a heavy load. The second is if it works the first few times but after you do several hard stops, that's when the you experience the problem, it could be the fluid is overheating and loosing viscosity which will reduce the pressure in the system. If this is the case, synthetic brake fluid will help but if you're braking this way, you probably should upgrade to discs as drums aren't the best design for this type of braking.

    I'll defer to other real mechanics to give you better answers but I hope this gives you a few ideas.
     
  3. surfmaxx

    surfmaxx New Member

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    Hi,
    i only drive slowly and brake carefully :)). I dont think ist a overheating problem.
    Does anybody know where to find a new or rebuild one? Rockauto etc are all sold out...
     
  4. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    First thing is to be sure the brakes are assembled correctly. Longer shoe goes towards the back and shorter shoe goes to the front.

    From there, I'm thinking that the push rod going into the master cylinder needs to be shortened slightly. What often happens is the gasket behind the master cylinder is left off and that effectively lengthens the push rod. There's a length that it sticks out from the brake booster listed in the service manual.

    If you don't have a service manual, download one here: MyMopar - Mopar Forums & Information - Service Manuals Since they don't show a '67, download a 67 Dodge. It will be close enough for now, but try to get one.

    If you want the booster rebuilt, and I strongly suggest you rebuild the original rather than replace it, have Booster Dewey do it Power Brake Booster Exchange | Providing Parts for Classic Cars These guys are the best... That said, that is probably not your problem.
     
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  5. detmatt

    detmatt Old Man with a Hat FCBO Gold Member

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    Brake hoses new too?
     
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  6. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    I assumed that the brake hoses had been replaced too, but if they haven't been, that could cause exactly what it happening.
     
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  7. rkrochen

    rkrochen Well-Known Member

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    Is this a 4 wheel drum brake system or front disc rear drum. If it has disc brakes the calipers can seize up causing locking brakes and or the caliper slides aren’t moving which will create a lockup or dragging brake.
     
  8. CBODY67

    CBODY67 Senior Member

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    Considering the servo action of the particular-design of the brakes, the release when barely accelerating tends to make me believe that it's more of a pedal return issue than an issue with the hoses or at the wheels. Which would relate to weak return springs at various locations in the system. Upstream of the wheels, not at them.

    I believe there are some springs in the master cylinder, but mainly to ensure the pistons are positioned correctly, generally. Possibly a spring related to the reaction valve in the booster? But what I'm suspecting is the PEDAL return spring under the instrument panel, OR some frictional resistance in the pedal's pivot bushings. Maybe a bit in the seal/bellows where the pedal push rod goes through the cowl to the booster itself?

    IF the pedal returns and the brakes release when moving forward a bit, that's engaging the servo action to help apply the brake shoes to the drum frictional surface, which is stretching the return springs at the individual wheels. IF the pedal returns when moving rearward a bit first, that would do the opposite, helping weaker brake shoe springs to further release, I suspect.

    So, "easy things first". I'd suggest you look under the instrument panel at the brake pedal pivots, pushrod mechanisms, AND return spring for the pedal itself. Make sure all of that is working free and with no resistance in the pedal return mode.

    Just some thoughts,
    CBODY67
     
  9. CBODY67

    CBODY67 Senior Member

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    When the hoses de-laminate internally, it makes a one-way valve of sorts that restricts brake fluid flow, in which ever direction it happens in. Usually, it happens when the fluid flows TO the brakes, which means the brakes don't fully release, no matter what, until the particular brake line is removed to release the pent-up pressure. Then the wheel-brake releases and can work fine until the next brake application.

    Just some thoughts,
    CBODY67
     
  10. twostick

    twostick Senior Member

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    Do they release if you pull the pedal up with your toe?

    There is a valve in the booster that can get gummed up and keep the vacuum applied and hold the brakes on. The one on my 66 was so bad that when you touched the pedal, the brakes would fully apply by themselves. The pedal would just drop from under your foot.

    Mine had a leaking master cylinder that put brake fluid in the booster. I fixed a return spring to the pedal and it eventually cleared itself after a few doses of brake clean were run through the booster.

    Kevin
     
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  11. surfmaxx

    surfmaxx New Member

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    Oh, so many answers...Thanks

    The brakes are assembled correctly. I am sure, the shorter shoe goes to the front.
    The brake hoses are new too.
    The push rod going into the master cylinder was adjusted so, that there is a little air between the booster and the master cylinder when you are not braking.
    If i pull the pedal up, nothing happends, the car dont move....

    I think i will remove tho booster again and try to clean it. There is anything against using wd 40 creep oil?
    And i will check the whole pedal system. I think i will assemble a stronger spring.
     
    Last edited: May 24, 2020 at 4:15 AM
  12. swisherred

    swisherred Senior Member

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    I have a 67 newport and mine doesnt have a return spring under the dash for the pedal....not sure if mine is missing or if his shouldnt be there...
     
  13. Davea Lux

    Davea Lux Old Man with a Hat FCBO Gold Member

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    If you old master cylinder was leaking, usually this causes the fluid to get ingested into the booster. When you remove the booster, shake it to see if you can hear fluid sloshing about, if so have the unit rebuilt. Brake fluid degrades the internal components of the booster and it will fail if it has not done so already.

    Dave
     
  14. CBODY67

    CBODY67 Senior Member

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    I don't think that I'd use wd-40 to CLEAN anything in a power brake booster, period. The many types of rubber in there might not like being doused in it. It's a lubricant, not a cleaner, per se.

    CBODY67
     
  15. surfmaxx

    surfmaxx New Member

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    I had already opened the booster. It looks like new. No break fluid in it.
     
  16. Big_John

    Big_John Illegitimi non carborundum FCBO Gold Member

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    There is no spring on the brake pedal.
     
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  17. surfmaxx

    surfmaxx New Member

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    Good to know... i had one...
    My previous owner was an expert, i found a lot of botch in this car.
     
  18. shooter65

    shooter65 Senior Member FCBO Gold Member

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    Previous owner probably added the spring because they had the same issue and didn't bother to fix it right.
     
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  19. 68NewportDDD

    68NewportDDD New Member

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    Welcome to the site!

    Hey hey hey! Doing the same thing to my 68 Newport. Wheel cylinders and booster were both shot. I went all of the way around and replaced just about EVERYTHING. New wheel cylinders (Dorman), the shoes (oddly enough) were in good shape, new brake hardware kit for each axle (also Dorman), new flex hoses (NAPA)(in the front). The booster was compromised; a lot of fluid leaking out on the bottom of the booster: I replaced both the booster and the Master Cylinder. Leeds Brakes sent me a custom set up (not specifically for a Newport but it fits). Those guys were great, incredibly helpful, and the kit came completely assembled. The booster even came with a custom bracket in order to get it to match up to the original brake line locations on the Master Cylinder and also to match the mounting locations on the firewall. I have not tested it yet but looking good so far. I still want to get the original booster rebuilt though - will send that off to Booster Dewey.

    This was my first foray into messing with a brake pedal. I did not see any springs under the instrument panel. The rod going from the brake pedal to the booster may need to be cut down a little more though. All in all a pretty simple job. The biggest problem I am encountering right now is getting the brake line fitting threaded back in to the brake line block for the passenger side rear; it is acting like the threads on the block are gone.

    I will keep everyone posted.

    Best of luck SurfMaxx!
     
    Last edited: May 24, 2020 at 7:49 AM
  20. 68NewportDDD

    68NewportDDD New Member

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    Twostick - Gives a new meaning to Power Assist? LoL