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joe0508's avatar
joe0508
Explorer
Nov 25, 2015

hydroboost diagnosis test

I have been having a problem with my brakes here lately and i am in the process of taking it in for a diagnosis.The problem is the brakes doesnt seem to have the stopping power they should have and they are spongy.They seem to go the better part of the way to the floor before i get any response.If i hit them hard the brake light will ficker on the dash.One time it came on and stayed on and wouldnt go off untill one day i was missing around and while it was idling i pumped the brake very lightly a couple of times and it went out i thought that was strange.I have checked the fluid in the master cylinder and it is full almost to full.The power steering fluid is good.The belts and dont see any leaks.I have tryed a diagnosis test on the hydrobooster that i found on the net and when i turn the engine off and pump the brakes to discharge the accumulator it says the pedal should harden noticeably but it doesnt make a difference although when the motor is running it will pump up.At least when im going down the road.Havnt tryed it at a stand still yet.Anybody have any ideas?I dont wont to replace the booster if it is the master cylinder.
  • westend's avatar
    westend
    Explorer
    Nov 25, 2015
    Sounds to me like you have air in the brake lines. Have you ever had the brake system bled?
  • joe0508's avatar
    joe0508
    Explorer
    Nov 25, 2015
    I hope that is all it is and to aswer your question i havent done anything to the brakes since i got it except turn the front rotors and change the front pads.I had problems before i did these items with the brakes but the light light is recent.I dont think the items i had repaired had anything to do with it because the light issue started happening long after.
  • joe0508's avatar
    joe0508
    Explorer
    Nov 25, 2015
    joe0508 wrote:
    I hope that is all it is and to aswer your question i havent done anything to the brakes since i got it except turn the front rotors and change the front pads.I had problems before i did these items with the brakes but the light is recent.I dont think the items i had repaired had anything to do with it because the light issue started happening long after.
  • darsben's avatar
    darsben
    Explorer II
    Nov 25, 2015
    westend wrote:
    Sounds to me like you have air in the brake lines. Have you ever had the brake system bled?

    or
    Brake Fluid Contamination

    Over time, brake fluid will absorb moisture and this can also cause spongy pedal problems. Water can get into the system through the rubber brake lines. It will lower the boiling point of the fluid so that, under heavy braking, the heat forms bubbles of gas in the fluid itself. This gas is compressible (whereas brake fluid is not); hence the spongy feel in the brakes.

    Brake fluid needs to be changed every so often. It was news to me when m mechanic told me but he was right. MAKES A Difference
  • joe0508's avatar
    joe0508
    Explorer
    Nov 25, 2015
    darsben wrote:
    westend wrote:
    Sounds to me like you have air in the brake lines. Have you ever had the brake system bled?

    or
    Brake Fluid Contamination

    Over time, brake fluid will absorb moisture and this can also cause spongy pedal problems. Water can get into the system through the rubber brake lines. It will lower the boiling point of the fluid so that, under heavy braking, the heat forms bubbles of gas in the fluid itself. This gas is compressible (whereas brake fluid is not); hence the spongy feel in the brakes.

    Brake fluid needs to be changed every so often. It was news to me when m mechanic told me but he was right. MAKES A Difference
    Thanks for the info.The fluid does seem to look pretty dark.Those two items will be on my top list bleed all for corners and change the fluid.Do you know on the hydrobooster when you change the brake fluid do you have to change the power steering fluid also?I know the two work together.I hope not because i here their is a special technique for bleeding the power steering system and im not sure if most techs is gonna know this.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Nov 25, 2015
    What model year is the RV?

    WHat brand?

    Do you have GM or Ford chassis?

    Have you changed the brake fluid recently? Or ever?

    Is there a front caliper flex line with a bubble on it when the brake pedal is pressed really hard? That can cause really spongy brakes. Normally once the RV is over 20 years old, the front flex lines should be replaced, regardless of how 'great' they look.. .

    If it is a class C, is there transmission fluid behind the drivers side carpet on the inside? This would indicate a bad hydroboost, and they can be really expensive. Mine cost $950 from a truck supply place in Long Beach where I used to work, and they gave me the fleet price - back in 1994 or something, so with inflation, they probably run $1,500 or more now. . .


    What fluid is dark? power steering or brake fluid? Both can get dark when they are older.

    While at it, check out the transmission fluid. If that is dark too, then start saving for a new $3000 transmission. .. Change the transmission fluid as soon as possible if it is dark or smells bad. You will still be leaving about 1 gallon of fluid in the torque converter. Then only way to get all out is flush it, but still some will remain, say 15% or 10%. The only true way to get rid of most all of it is to change it twice in a row. Then 75% or more is replaced the first time, and the additional 3 gallons of fluid will dilute anything that remains. Changing it again within say 1,000 miles will get ride of most of the old stuff, leaving the new stuff to 'dilute' some not so dirty transmission fluid. . .

    Fred.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Nov 25, 2015
    For my power steering fluid, I used a turkey baster, drew out what fluid I could from the power steering resivoir (it is pretty small inlet diameter, check it before getting one with a opening to large) and then add new fluid. After a couple of times, then much of the fluid has been replaced.

    From what I have heard, to 'Purge" any air from the power steering lines, you turn the wheel to hard left, wait for it to stop making noise (about 20 seconds at full lock to the left, then right) and it will be ready for use.

    Make sure that you do not overfill the power steering resivoir, the fluid expands a lot LOT when you warm up the engine, and can cause problems if overfilled.

    Good luck,


    Fred.
  • joe0508's avatar
    joe0508
    Explorer
    Nov 25, 2015
    Golden_HVAC wrote:
    What model year is the RV?

    WHat brand?

    Do you have GM or Ford chassis?

    Have you changed the brake fluid recently? Or ever?

    Is there a front caliper flex line with a bubble on it when the brake pedal is pressed really hard? That can cause really spongy brakes. Normally once the RV is over 20 years old, the front flex lines should be replaced, regardless of how 'great' they look.. .

    If it is a class C, is there transmission fluid behind the drivers side carpet on the inside? This would indicate a bad hydroboost, and they can be really expensive. Mine cost $950 from a truck supply place in Long Beach where I used to work, and they gave me the fleet price - back in 1994 or something, so with inflation, they probably run $1,500 or more now. . .


    What fluid is dark? power steering or brake fluid? Both can get dark when they are older.

    While at it, check out the transmission fluid. If that is dark too, then start saving for a new $3000 transmission. .. Change the transmission fluid as soon as possible if it is dark or smells bad. You will still be leaving about 1 gallon of fluid in the torque converter. Then only way to get all out is flush it, but still some will remain, say 15% or 10%. The only true way to get rid of most all of it is to change it twice in a row. Then 75% or more is replaced the first time, and the additional 3 gallons of fluid will dilute anything that remains. Changing it again within say 1,000 miles will get ride of most of the old stuff, leaving the new stuff to 'dilute' some not so dirty transmission fluid. . .

    Fred.
    It is a class a gm 92 thor pinnacle.I have never changed the brake fluid but i have recently changed the power steering pump because i was getting a lot of noise from it and that cured that but i have always had a problem with the brakes that seem to take a lot of effort to stop and a lot of travel before getting any feel.I have not really been to worried about it untill the light started coming on which to me indicates a problem.Not sure if it should come on when there is air in the system?I am not sure what a flex line with a bubble on it is or if i have ever seen one but sounds like something i should check for.
  • darsben's avatar
    darsben
    Explorer II
    Nov 25, 2015
    hydroboost is for the power on the power brakes.
    Brake fluid an entirely different system. No interconnect. You can change bake fluid without worrying about the hydroboost
  • _40Fan's avatar
    _40Fan
    Explorer
    Nov 25, 2015
    You either have a rear wheel cylinder leaking, rear shoes that need adjusted or a failing master cylinder. The light coming on under a hard brake press is telling you that the differential switch is seeing more pressure in the front than the rear at that moment. Brakes are set up to have the rears apply just before the fronts do.

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