HT4100 Brake Loss
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HT4100 4.1, 4.5, 4.9 Discussion, HT4100 Brake Loss in Cadillac Engine Technical Discussion; Oh my god when will this end. So I'll start at the beginning. My dad and I bought a 1984 ...
  1. #1
    miningmanpwn is offline Cadillac Owners Member
    Automobile(s): 1986 Fleetwood Brougham 5.0L, 1984 Sedan DeVille 4.1L
    Join Date
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    HT4100 Brake Loss

    Oh my god when will this end. So I'll start at the beginning. My dad and I bought a 1984 DeVille to do a quick flip on. The trans in it had died, so we swapped it with one we had laying around for our Fleetwood. But thats not my issue. The trans is in there and the car runs and drives fine. Except theres no brakes.

    We first noticed a loud tapping coming from the vacuum pump that disappeared as soon as we took the belt off. So we figured the cause of our brake booster problem and tapping was a bad vacuum pump, so we went to the junkyard and picked up a new one. We installed it and started it, and the tapping returned with a continued loss of brakes.

    We have absolutely no idea whats going on, and we want to get this thing out of our garage. The way this vacuum pump works is like this. It has a belt driven cam lobe that turns and pushes a rod back and forth. This rod is connected to a diaphram that creates suction when pulled on. We thought the knocking came from this diaphram not moving due to backpressure and the cam smashing against the rod.

    Right now I'm attempting to figure out the source of the back pressure, but I'm striking out. Looking at the emissions routing on the HT4100 gives me a migraine anyways.

    So if anyone out there knows whats going on, I desperatley need help. This thing needs to go, we absolutley hate the thing.

    Thanks, Bryce

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  3. #2
    carnut is offline Cadillac Owners Master
    Automobile(s): 1988 Allante' (sold), 1984 Eldorado, 84 Sedan DeVille
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    Re: HT4100 Brake Loss

    I think you've gotten another faulty vacuum pump. I would verify the pump is putting out 1st! Should pump out at least 18 in. vacuum steady. That pump helps the vacuum booster. Is the pedal rock hard or does it sink to the floor? There is a filter just in front of the booster in the line of the large vacuum hose to the booster, that could be plugged. You should be able to blow thru it in either direction.

  4. #3
    miningmanpwn is offline Cadillac Owners Member
    Automobile(s): 1986 Fleetwood Brougham 5.0L, 1984 Sedan DeVille 4.1L
    Join Date
    Oct 2013
    Age
    24
    Posts
    3
    Thanks for your input.

    I can definitely feel the suction on the hose that connects to the outlet, but the air that the pump is blowing out the outlet doesn't feel near as strong as the suction in the hose. The brake pedal will move, but it takes a lot of force to push down and the pedal doesn't go down all the way (basicly it feels like the assist in the power brakes isn't working).


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  5. #4
    carnut is offline Cadillac Owners Master
    Automobile(s): 1988 Allante' (sold), 1984 Eldorado, 84 Sedan DeVille
    Join Date
    Feb 2003
    Location
    california
    Age
    66
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    5,702

    Re: HT4100 Brake Loss

    Take the hose off the booster, remove its check valve and put a vacuum gauge in that hose. Whats the reading? at idle.

  6. #5
    miningmanpwn is offline Cadillac Owners Member
    Automobile(s): 1986 Fleetwood Brougham 5.0L, 1984 Sedan DeVille 4.1L
    Join Date
    Oct 2013
    Age
    24
    Posts
    3
    Found my issue! It was the hose from the brake booster to the back of the TVS. The hose wasn't connected right. Thanks!


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