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Technical disc brake swap issue..still got a soft pedal

Discussion in 'The Hokey Ass Message Board' started by Vincentnova, Dec 2, 2018.

  1. jcwilliamsj
    Joined: Feb 17, 2018
    Posts: 11

    jcwilliamsj

    may as well hook the rear line directly to the mc. if your pedal is still good drive the car. when you stop hard the rear should try to lock up. if that happens the pv is likely the culprit or you could buy the test kit and check the pressures.
     
  2. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova


    yes i did
    with only the front line connected to the master cylinder
    no proportioning vavle
    with this pressure gage i get 1300 to 1400psi ( hard push )
    car on wheel car dont stop
    i would like to do a pressure test with the wheels on floor but i cant...the bleeder is very close to the spindle
     
  3. If you get that pressure at the caliper then you have a friction problem between pads and rotors.


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  4. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova


    what are your suggestion ? what should i do? or test?
     
  5. Make sure the rotors are surfaced properly, and try different pads, make sure everything is clean.


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  6. AHotRod
    Joined: Jul 27, 2001
    Posts: 10,353

    AHotRod
    Member

    I to have witnessed this as allot of these "kits" have extremely poor quality brake pads and shoes.
    We have had to remove them and we replace them with Wagner premium brake pads and or shoes.
     
    Jimhu and Vincentnova like this.
  7. Yeah no shit!
    Should be bouncing you off the windshield.
    Friction surface problem
     
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  8. 54vicky
    Joined: Dec 13, 2011
    Posts: 1,118

    54vicky
    Member

    he is trying to scrape his face off windshield after putting real brake pads on.
     
  9. Jimhu
    Joined: May 23, 2016
    Posts: 13

    Jimhu
    Member

    Something no one has mentioned, unless I missed it, is to check the engine vacuum at the brake booster; if low due to blockage, camshaft profile, or vacuum leak (not likely), or cam not installed correctly, clear/ repair vacuum line to booster, ck cam timing, put in a milder cam to get vacuum back, or add a vacuum motor to get the vacuum needed at the booster. A decent vacuum motor is going to run you anywhere from around $300 and up. They are noisey, you get used to it. This is the best fix when due to cam profile. You'll have to decide the approach depending on what you find for low vacuum.
    Without correct vacuum, you can barely get the vehicle to stop even STANDING on that pedal with both feet. Ask me how I know.... when you're approaching that whatever it is in front of you fast and not stopping although you're standing on it, you feel it in strange places!!!!

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  10. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova

    well i must have the oldest tread going on in here....at least im good at that ahahah
    wwell well well
    i went with other pads i did get from the local autoparts stors duralast MKD154..wich are semi metallic..and nothing change ----------->do you think i will really feel a difference with wagner pad? again my car is rolling and not stopping
    only the rear breaks works...Im really far away from the felling to go trough the windshield with these breaks

    also an other story that Im dealing with now..and wont go much in detail about it because it bugs me so much..
    I had the system checked and tested by a shop ( its what they do---breaks---)
    the system is good.....no leaks ..pressure test ok etc.....( because the car has no tags they didnt really test it)
     
  11. 54vicky
    Joined: Dec 13, 2011
    Posts: 1,118

    54vicky
    Member

    probably better to take it to a shop that deals in brakes.rather than a fracture clinic
     
    31Vicky with a hemi likes this.
  12. Since I can’t remember details and am too lazy to read it all again, what calipers do you have? I remember you had good pressure at the caliper I think.


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  13. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova

    Its what i did...
     
  14. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova


    Metric caliper
    The one that can be find in the 80's gm cars . pre 79 to be exact ( no low drag caliper )
     
  15. The calipers slide freely on the mounts? There are force gauges that replace one of the pads to read actual caliper force during brake application as well.
     
  16. Happydaze
    Joined: Aug 21, 2009
    Posts: 818

    Happydaze
    ALLIANCE MEMBER

    As others have said with that kind of psi at the caliper you should be stopping fine. I'm not rereading the thread, sorry, but if it's not the friction material it must be the piston(s) being seized in the caliper. Don't care if they're new. Get the pistons out and checked, cleaned up, reinstalled with rubber grease, ideally new seals. Destruction test - remove pads and stand on the brakes. Protect paint first. Expect a huge mess. If no mess, establish why! If one comes out, put it back in, clamp it in and get the other(s) out. Suggest one wheel at a time.

    I've just cleaned up a set of Wilwood calipers that I found were sticking. Probably only one out of 4 were free. Took some work to get them all out. Tremendous difference to the braking! I thought the reducing brake effectiveness over a number of years was just me getting older or something, but thankfully not! No, just racing calipers with no dust seals being used on the street and getting mucked up - only seen about 20 years use! Wasn't noted as an issue as such until I came to replace the pads. Immediately knew there was a problem when the pistons didn't retract wilfully. Simple brake job became a little more complicated, but the results were spectacular!

    Chris
     
    AHotRod likes this.
  17. o_Oo_O
     
  18. As I said, there are gauges for measuring output force of a caliper. Way smarter than a "destruction" test.
     
    Happydaze likes this.
  19. IMG_1498.JPG

    Notice the line on the manual.


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  20. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova

    Yeah i was looking at one of those..but they kind pricey...do they work with the wheel on rotor?
     
  21. Happydaze
    Joined: Aug 21, 2009
    Posts: 818

    Happydaze
    ALLIANCE MEMBER

    Saw your reference to that but wasn't aware of such things, which being a bit of a tool whore is quite an admission. Neat. But if you have the pressure gauge and can also detect if the calipers are seized then it's kinda redundant. Still want one though, but unlikely to get one!

    Not exactly sure what's occurring in this pic though. Replace the disc? Why have two then?
    [​IMG]

    32v - car isn't moving anywhere. The mess is fluid on the floor, should the piston come out! I don't recall ever having successfully extracting the pistons from the caliper (when they're well stuck) with anything other than the hydraulic pressure from the brake system, although I guess there's a pro tool for that too! :) I've damaged a few dust seal retaining grooves (on the piston) though by prying / levering on them, which has resulted in purchasing new calipers :(.

    Anyway, the problem on hand seems to be cornered with little escape?

    Chris
     
  22. One for each side, as far as removing caliper pistons, use air


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    Last edited: Dec 3, 2019
    Happydaze likes this.
  23. I also cannot understand how removing the caliper and popping the piston and fluid on the floor give any sort of valuable information on how much force the caliper is putting out


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  24. 6sally6
    Joined: Feb 16, 2014
    Posts: 803

    6sally6
    Member

    You guyz are an absolute riot!!!!:p
    I learned (on here!) when using GM caliphers you need a GM stepped MC. I had so-so brakes on my hot rod because I had a Maverick MC pushing the GM caliphers. Change made a huge difference.
    I use the cheapest pads the store has!! They are the softest material and grip the hardest. Don't last as long but...........we don't drive'em as much as the DD. (normally)
    6sally6
     
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  25. Vincentnova
    Joined: Nov 6, 2015
    Posts: 63

    Vincentnova

    My problen with the stepbore is the booster...it doesnt fit , Not enough space with the engine. Unless if there is a small booster for stepbore ?
     
  26. Happydaze
    Joined: Aug 21, 2009
    Posts: 818

    Happydaze
    ALLIANCE MEMBER

    I'd suggest that having conclusive proof that a piston is not seized has value. Of course similar can be achieved without popping out, as you know :).

    I'm sure compressed air will push pistons out which aren't seized, but I've experienced needing as much or probably force (my unmeasured estimate!) as a panic stop to get some out. I wouldn't fancy trying that with air, and certainly haven't got an air source that could deliver that. Who has?? I dunno.

    Anyway, Vincentnova just needs to do whatever it takes to prove that the pistons aren't seized, because it sounds as if they could well be (imho) :).

    Chris
     
  27. This is your problem they couldn’t road test it not theirs. However they could have done more based on your complaints and concerns without driving it. EVERYTHING THAT you are going to do from this point forward will not require driving until you’ve completed.

    Happydaze thoughts are correct although I’d question and avoid some of his methods. You’ve proven the pressure on the fluid side of the caliper piston, yet the brAKES are not functioning. It’s a simple matter of finding the mechanical issues.
    Remove caliper, put a block thinner than the rotor between the pads and prove the piston is moving.
     
    54vicky likes this.
  28. The caliper pistons should come out easy enough, take them off the car, blow them out with compressed air, leave the pads in place or use a block of wood. You'll need new caliper kits if you take them apart. But you'll know right off if you have a stuck one. I think it is something else, but good to rule out a stuck piston just to get it out of the way.
     
  29. The riot part is the stepped bore master is for low drag calipers which the op says his are not, that’s all I can go off. Anyways there is more than enough good information here to allow him to find his problem so I will step aside now because like most threads on brakes, it’s now heading downhill.

    Oh and if they are low drag calipers it will have a low pedal.


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    firstinsteele likes this.
  30. Because I can’t leave well enough alone....I understand where you are going here and don’t necessarily disagree with the train of thought but as 31vickey said put a block of wood in and watch, no mess. If they are moving now it’s a matter of why they are not applying enough force to stop the car.


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