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brake pressure building

Discussion in 'The Hokey Ass Message Board' started by 49_Caddy, Jul 23, 2013.

  1. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    I have only recently started driving my ’49 Cadillac (about 100 miles total, longest trip was 12 miles one way) and have been experiencing some strange behavior by the brake system. All of this driving was done around 30-35 mph (dry rotted tires, have now been replaced) on surface streets, with many traffic light stops.

    As I drive, the hydraulic pressure in the system increases – the pedal becomes increasingly firm and the brakes begin to drag. On two separate occasions, it has gotten to the point where the brake lights stay on (pressure switch on MC) and by the end of the 12 mile trip all four wheels were smoking. :eek: I cooled them down with a garden hose :D and they caused no issue for the return trip.

    Since that experience, I have driven a maximum of about two miles per trip and have had no obvious issues, but I am concerned to drive farther until I can explain why.
    <O:p
    Brake system specs:<O:p
    - stock-type (single channel master cylinder w/ four wheel drums) <O:p
    - entire system was completely redone (all new lines, hoses, wheel cylinders, shoes, springs) by the previous owner<O:p
    - I’m unsure if he rebuilt the MC, but it appears to work perfectly<O:p
    - System has been completely bled<O:p
    - all four wheels turn freely when cold<O:p
    - pedal feels nice when cold<O:p
    <O:p
    This is my first experience with an older car with all drums, but have a pretty good understanding of hydraulics. I’m at a total loss to explain this phenomena and any help or direction would be most appreciated. :confused:<O:p
     
  2. Be sure you have 1/8" clearance between the Master Cylinder push rod and the piston.
     
  3. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    That is a great point, for some reason I never thought about the rod adjustment.

    Anybody have any good tips on getting at the master cylinder in these old GMs (other than making friends with somebody that has a lift)? Just topping up the fluid when I was bleeding it about killed me.
     
  4. Moon Rocket
    Joined: Dec 26, 2012
    Posts: 540

    Moon Rocket
    BANNED
    from GA

    I'll bet that's your problem!
     

  5. Has to be the rod adjustment.
     
  6. dtracy
    Joined: May 8, 2012
    Posts: 223

    dtracy
    Member

    If the return spring is missing or broken it will cause the same symtoms. Either way, you're going to be working on your back with the car on safety stands.

    Dave.
     
  7. daliant
    Joined: Nov 25, 2009
    Posts: 684

    daliant
    Member

    Either a mis-adjusted push rod whitch is causing the relief port in the master cyl to be blocked by the piston or the relief port is blocked by rust or debris. The relief port must be unobstructed to allow the hydraulic pressure to be relieved when the brake pedal is at rest. look in the master cyl, you should see two holes, the smaller one is the relief port.
     
  8. fsae0607
    Joined: Apr 3, 2012
    Posts: 871

    fsae0607
    Member

    Adjust your pushrod. Should have about 1/8" - 1/4" of pedal freeplay before your pedal/pushrod starts pressing on the MC.
     
  9. 2racer
    Joined: Sep 1, 2011
    Posts: 960

    2racer
    Member

    if it has a power booster that could be the problem, defective booster is applying the brakes
     
  10. jmpowie
    Joined: Dec 2, 2006
    Posts: 202

    jmpowie
    Member

    I had the same problem, back off the push rod a little.
     
  11. Dane
    Joined: May 6, 2010
    Posts: 1,351

    Dane
    Member
    from Soquel, CA

    An easy way to check is to crack open a bleeder screw. If the shoes/pads let go of the wheel it's a MC problem (setup in your case). It also could be a 50 year old brake hose, but if that's the case you deserve to suffer... :D
     
  12. R35J1S
    Joined: Jul 20, 2012
    Posts: 141

    R35J1S
    Member
    from Missouri

    I would bet that none of the above are your problem. I have had this happen a few times on older cars that sat for a while. The inner linning of the rubber break lines will break down and come loose. It acts as a check valve. Each time you press the break pedal, fluid will go past the flap in the line and press the pads in. When the fluid tries to return up the line, the flap will close off and not let it go back. After a few times of this, there is so much pressure that the breaks will drag harder and harder. Check all of your rubber lines. Sometimes they look great from the outside but have fallen apart inside.
     
  13. slicknapier
    Joined: Sep 29, 2008
    Posts: 100

    slicknapier
    Member
    from Tucson, AZ

    I have had the same issue before and it was a clogged return hole in the master cylinder. Just cleaned it out with a wire and it worked great. Like yours, everything was new I just got a little debris in the master cylinder. All of the above are spot on with what I was told to look for as well. Keep us updated.
     
  14. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    Finally got around to checking it out (I forgot to mention before that I was in Mexico on business until yesterday).

    There is an access panel (kind of), but you have to remove the brake pedal to get it all the way off. Also, I couldn't see down into the MC at all - even with a mirror. I tried to take a picture down into it with my phone, but it was either too dark w/o flash or the too washed out with the flash against the brake fluid. I think the only way to really see the ports in there would be with a colonoscopy type camera.

    Anyway, there is a spec in the manual to adjust the rod until the pedal lever is 3/4" from the floor pan. Mine was at about 1/2", so I did adjust it to the spec (it only took about one revolution to do so).

    Then I took the family for a drive to check it out. Everything was feeling fine, I even did a couple of pretty firm stops to test. Then, I ended up having to do a full-on panic stop when the car in front of me decided to stop for a yellow light - after that the pedal became increasingly firm and I started to smell that distinctive aroma.

    The pedal is not just firm, it's totally solid. There was no way to pull it back, the lever was against the floorboard.

    I ended up pulling over and waiting for it to cool down (it is Friday night on Woodward avenue, might as well take in the sights). After 45 minutes, the pedal was still solid and the brake lights were still on. After that, I crawled under the LF and was able to open that bleeder to relieve the pressure. Driving home after that went fine, but I was very careful.

    I'll adjust it out some more tomorrow, if that is still no good I'll dig deeper.


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    Last edited: Jul 26, 2013
  15. rustyangels
    Joined: Sep 28, 2010
    Posts: 178

    rustyangels
    Member

    That happened to me, I did everything possible to prior to replacing master, but that cured it.
     
  16. R35J1S
    Joined: Jul 20, 2012
    Posts: 141

    R35J1S
    Member
    from Missouri

    Not true, if it is brake hose that has broken down then opening a bleeder will also release enough pressure to release that shoe or pad. If your brake lines don't cost too much, just change them for good measures.



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  17. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    OP says all of the lines were replaced. All three hoses would have to be bad to cause all 4 wheels to heat up. The most likely culprit is a lack of freeplay on the pushrod. Even if the master cylinder piston is stuck all of the way out, there should be some freeplay in the pedal. Shorten the rod a little more.
     
  18. dtracy
    Joined: May 8, 2012
    Posts: 223

    dtracy
    Member

    I aggree, you need to adjust the rod the other way, less distance between the pedal and the floor, not more. Making it less shortens the pushrod and will give you more freeplay, and that's what we think you need.

    Dave.

    P.S. Make sure you have a return spring on the pedal as not having one will have the same affect as the pushrod being too long. The weight of the pedal will push against the piston and cause it to move inward enough to close the return hole which stops the fluid from returning from the wheels to the master cylinder, same as having too long a pushrod.
     
    Last edited: Jul 28, 2013
  19. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    The 3/4" spec is to the back side of the floorboard.

    [​IMG]
     
  20. dadseh
    Joined: May 13, 2001
    Posts: 526

    dadseh
    Member

    honestly...learning how to fix brake problems on the internet should not be your first choice if you have no clue how your system operates. The previous owner told you he put a new brake system on it and the car still had dry rotted tires under it!!??. Are the pigs all gassed up and ready to fly as well??
    Take it to a brake shop and have it inspected.
     
    Last edited: Jul 28, 2013
  21. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    Um, yeah. Thanks for your contribution.

    All the parts are new, he sold it before getting it fully to drivable condition and therefore did not need tires yet.

    I have plenty of experience with cars, but this is my first with single channel, non-power drum brakes.

    Just forget I asked anything if you are that offended.



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  22. dadseh
    Joined: May 13, 2001
    Posts: 526

    dadseh
    Member

    we are not offended at all. Just dont like to see a fellow HAMBer have an accident tinkering with brakes.
     
  23. buckbuc
    Joined: Jul 20, 2013
    Posts: 2

    buckbuc
    Member
    from maryland

    more than likely the releif port in the master cylinder is clogg
    ed
     
  24. Roger Walling
    Joined: Sep 26, 2010
    Posts: 1,146

    Roger Walling
    Member

    A friend has a 300 Chrysler with the ram charge intakes on it. Same problem. I shortened the brake pedal rod and no change.

    He sold the car, next owner noticed an exhaust leak onto the brake line. He fixed that and the brakes worked fine ever since.
     
  25. Pontmerc
    Joined: Jul 13, 2013
    Posts: 122

    Pontmerc
    Member
    from Finland

    Just making full repair my catalinas brakes.After new brake wheel cylinders, hoses and shoes i bleeded the brakes and test the pedal fee all seems to be just fine.Try to spin each wheel.They seems have little drag, more than when i adjust the shoes.Well, taking bleeder screw loose in one wheel make it and the rest spin freely so mallfunctioned item has to be master cylinder.Short piece of mig welder wire solve the problem as i open the glogged hole in master cylinders bore.
     
  26. GassersGarage
    Joined: Jul 1, 2007
    Posts: 4,728

    GassersGarage
    Member

    You might also check the exhaust system. How close is the M/C to any exhaust component? If the M/C is heating up, it will cause the same symptoms.
     
  27. 49_Caddy
    Joined: Mar 29, 2013
    Posts: 51

    49_Caddy
    Member
    1. GMB

    Hmmm, that is an interesting point (about the heat from exhaust). Although I'm pretty sure the exhaust is ok, there is a long stretch of steel brake line the runs under the radiator, right where the overflow tube goes.

    Since the timing of the brake problems also seem to correlate with the car getting up to about 220-225, I wonder if that length of line is floating in boiling coolant and acting as a reverse heat sink.

    Seems far-fetched to me, since the brakes didn't unlock themselves after cooling off for 45 minutes, but I've been meaning to put some sort of overflow reservoir on there anyway.

    I've also ordered some parts from Rock Auto, including an M/C rebuild kit. I'm going to have to take the M/C off to inspect the vent holes, so I might as well through a new piston and seals in the while I've got it off.


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