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  1. #1
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    Kubota L-35

    Default small dump truck brake problem

    Ive got a GMC 6000 dump truck that the brakes stopped working.
    It has a hydrolic master cylinder on the fire wall and a vacuum booster under the cab.
    The pedal goes to the floor, no leaks anywhere and the fluid level stays up.
    I'm thinking master cylinder?
    Any suggestions?
    Thanks, Tim

  2. #2
    Veteran Member Bob Rooks's Avatar
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    Yuchai Bulldozer

    Default Re: small dump truck brake problem

    Sounds like a master cylinder to me too - by-passing. Does the fluid bubble if you depress the brake pedal slowly? What year is the truck? How old is the brake fluid?
    Yuchai 306R dozer, Mustang 2040 skid steer, Mitsubishi MS035 Mini-Ex with four buckets and a rake, 7' Dual Dozer with dual Trimble GCR-2 laser receivers.

  3. #3
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    Kubota L-35

    Default Re: small dump truck brake problem

    1978, cant see cylinder while pumping, I'm by myself.
    Fluid about 3 years old.
    Thanks

  4. #4
    Veteran Member Bob Rooks's Avatar
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    Default Re: small dump truck brake problem

    Make sure all of your vacuum line connections are good and tight.
    Are there brake lines going to the booster?
    Yuchai 306R dozer, Mustang 2040 skid steer, Mitsubishi MS035 Mini-Ex with four buckets and a rake, 7' Dual Dozer with dual Trimble GCR-2 laser receivers.

  5. #5
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    Ottawa, Ont
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    Ariens

    Default Re: small dump truck brake problem

    to the floor and no leaks = master

    rebuild or replace , bench prime and install ... then bleed brake system

  6. #6
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    Kubota L-35

    Default Re: small dump truck brake problem

    Quote Originally Posted by Bob Rooks View Post
    Make sure all of your vacuum line connections are good and tight.
    Are there brake lines going to the booster?
    Yes. lines to booster.
    Any chance the booster cylinder is bad?

  7. #7
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    Ontario
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    CT235

    Default Re: small dump truck brake problem

    might just be the pushrod between the pedal and the booster. not unheard of.
    Tim.

  8. #8
    Veteran Member Bob Rooks's Avatar
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    Default Re: small dump truck brake problem

    Quote Originally Posted by GT2 View Post
    Yes. lines to booster.
    Any chance the booster cylinder is bad?
    Yep, that's the usual suspect, and the most expensive unfortunately.
    Yuchai 306R dozer, Mustang 2040 skid steer, Mitsubishi MS035 Mini-Ex with four buckets and a rake, 7' Dual Dozer with dual Trimble GCR-2 laser receivers.

  9. #9
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    Mt Crawford Va
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    massey GC 2400 JD LA 145

    Default Re: small dump truck brake problem

    I am told that some years of GM trucks had a problem with trapped air in the master cylinder. Knew one guy that drilled and taped a vent hole in his and vented it as he added fluid, He said it worked.

  10. #10
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    Kubota L-35

    Default Re: small dump truck brake problem

    I got the old master cyl off and was able to see the problem, there was rust on the backside of the cylinder bore that was preventing the piston from returning all the way.
    New master cylinder on and back to work!
    Thanks for everyone's help.
    Tim

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