Need Lots Of Help With Brakes Issue!!

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by oneslowgt, Aug 30, 2013.

  1. Firstly if I posted this in the wrong thread sorry I did not want to single it only to 5.0 Fox Mustang area, because its a general thing but here it goes!

    My mustang is a 1991 Gt, everything is factory OE except for the exception of an e303 cam, cobra throttle body, and 373 gears. It's a 5.0L v8, 5 Speed with 135k original miles.

    Since I started my project with this car I have had a brake issue for almost a year now that I cannot figure out for the life of me. Maybe the members here at Stangnet have the knowledge I seek!

    ---Now to the issue---
    When I first press down on the brake it is hard, then becomes "soft" but not like a sponge just "softer" then the hard firm pedal is in the beginning, and yes the car slows down but not good at all, If I am driving at 60 mph and I slam the brakes down as hard as I can.. I can't even chirp the tires to skid or anything. When I let off the brake it returns up with a delay and it again becomes stiff to press down, so I can't do stop and go at all. If I am driving normally and I press down the brake and don't wait for that "stiffness" to go away before continuing then I won't know how hard it will bite the brakes so it's really sudden like a DELAY..

    What I have done to correct the problem with no results:
    -replaced rotors and pads in front, shoes and drums in the back.
    -replaced brake booster, and master cylinder, rebled the lines.
    -replaced all vacuum lines on the engine.

    and also there is no leaking of brake fluid anywhere at all.

    THANKS!! for taking the time to read my problem I hope there is lots of feedback, but again thanks for bearing with me on this wall of text I know everyone has better things to do on their own stangs :D
  2. Did the problem start shortly after the cam swap? It could be causing poor vacuum and not allowing the brake booster to work properly. Or you have a big vacuum leak.
  3. When I put the motor in I put it in with the e303 cam, (I know.. why keep the stock heads, but I didn't have the money at the time and the motor was on the stand so it was easy) but I checked the vacuums and there is nothing leaking air!
  4. I'm running a b cam with stock heads so don't worry lol. I'm betting it is the cam causing low vacuum. You could get a vacuum canister. They are fairly cheap and store vacuum for the brakes.
  5. do you have any issues with your brakes? do you run a vacuum canister? i thought bcam was a little more aggressive??
  6. I haven't had any problems so I don't have a vacuum canister. The b cam has a little more duration but the e cam has a little more lift to it. I did a little search and it seems like quite a few people have had braking issues with the e cam.
  7. I will have to try the vacuum canister its only like 50 bucks or so! thanks for recommending that! Do you know if swapping to better heads would alleviate the vacuum
  8. I'm not sure how much that would effect the vacuum. It would however make you haul more ass which isn't good without brakes lol
    oneslowgt likes this.
  9. a tighter LSA (lobe separation angle) can reduce idle vacuum. stock cams are designed around low rpms where you will make good vacuum with more LSA and lift your usable vacuum will move to the higher rpms each engine is different even with the same setup though at higher rpms most vac will be drawn into the cylinders . a vacuum canister is a good choice to help keep the feeling of a vac leak at bay and is a good idea for even stock cars.

    over lap, compression ratio, head volume, header size all make a difference in vacuum.

    to much or to little of any of these things can cause a loss of vacuum or an abundance.

    look for vac pressure in the 16-22 inches range the higher the better for a daily driver.
    #9 David Pepiton, Aug 30, 2013
    Last edited: Aug 30, 2013
  10. You can also swap the fox booster for an SN95 that holds more vacuum and will increase the brake pressure.
  11. update: last night I was looking around my brakes, I noticed the back left was not bleeding with the valve on the pedal was still stiff. The wheel cylinder seemed locked up, I replaced it and my pedal is starting to feel normal??? hmm.. going to bleed the brakes again and see if it becomes softer, but for right now its just stiff all the way through
  12. Usually "double pumping" can indicate an issue with a stuck brake component. Usually with disk brakes, it's a stuck caliper slide pin. The pedal firms up on the second stroke because you are in essence "taking up the slack"

    My suggestion would be to check your caliper slide pins and rear drum brakes for seized components and replace
  13. if it happens to be a caliper slide pin how do i fix that? do i need to replace the entire caliper?
  14. i didnt think before posting lol slide pin.. duh! also figured maybe the caliper piston might be locked up