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Thread: Low fluid pressure

  1. #1
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    Low fluid pressure

    I have seen mention of proportioning valves 'going bad', but after 15 years of working on cars professionally I have never seen such a thing.

    I did a complete brake job on my car (88/9 LXi swap, new calipers, rotors, lines) and in bleeding the brakes the pressure is rather low. It should squirt a stream out but just dribbles. I have not yet changed the master, but their is no indication there is anything wrong with it and the slight diameter difference can't explain this.

    Is this scenario familiar to anyone else? The brakes feel good, but don't have the bite they should with what I assume should be more pressure. Oh, and the rear rotors I took off were rusty after an 1800 mile drive home. The pads were never really in them. It doesn't seem like the calipers/lines changed this much.



  2. #2
    2.0Si User
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    Re: Low fluid pressure

    Quote Originally Posted by night View Post
    I have seen mention of proportioning valves 'going bad', but after 15 years of working on cars professionally I have never seen such a thing.

    I did a complete brake job on my car (88/9 LXi swap, new calipers, rotors, lines) and in bleeding the brakes the pressure is rather low. It should squirt a stream out but just dribbles. I have not yet changed the master, but their is no indication there is anything wrong with it and the slight diameter difference can't explain this.

    Is this scenario familiar to anyone else? The brakes feel good, but don't have the bite they should with what I assume should be more pressure. Oh, and the rear rotors I took off were rusty after an 1800 mile drive home. The pads were never really in them. It doesn't seem like the calipers/lines changed this much.
    I dunno my old scout the prop valve was questionable I swaped it with a old used one with better results all thing being equal.

    Remember Hondas its cross proportional so one front to opposite rear. Possible one end I guess could effect the other. No or little pressure to BOTH rears is unusal?

    I would start with a new master bench bled and see what kinda pressure you actually have...I dunno what that would be maybe 1500 psi. Bypassing at the master would be very possible on low fluid pressure.

    When you went with new lines you went all new metal or just new flex hoses? Possible one bad not crimped correctly? I use a place in town that makes the stainless steel braid ones custom for about 15 years now with great results. I have used a new out of box rubber flex that must have been collapsed inside and would not return pressure just like an old worn one would.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    My Acura Type R front brake thread

    https://www.3geez.com/forum/showthrea...r+brake+option

  3. #3

    Dr_Snooz's Avatar
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    Re: Low fluid pressure

    As far as I've seen, our prop valves fail by leaking.

    I will say that replacing my prop valve with the Wilwood adjustable absolutely transformed my braking for the better. Everything tightened up and the precision and control it added was almost unbelievable. Stuff just wears out after being in service long enough. Bear in mind that your braking system is 30 years old now. It's probably time to replace everything and completely rebuild the entire system, but at the least, it's worth doing a careful inspection of every component and replacing anything that looks suspect.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


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  4. #4
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    Re: Low fluid pressure

    Snooze did you replumb it back to a Front/rear split?
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    My Acura Type R front brake thread

    https://www.3geez.com/forum/showthrea...r+brake+option

  5. #5

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    Re: Low fluid pressure

    Yes I did. Front and Rear split. There wasn't any other way to plumb it as there are only three outlets on the valve. Two are marked Front and one is Rear and has to be split out at the back of the car (like all American cars). The adjustment knob does the rear outlet only so that would make it very interesting if you did it Honda's way. LOL
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

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  6. #6
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    Re: Low fluid pressure

    I'm doing a mini-track day in March and was looking at this again...
    I wish these proportioning valve numbers weren't so cryptic. But, I found strange difference between my '85 carb and the '86 Si.
    The carb has a 3540 valve, while the Si has a 3030 . And I believe the SEi has a 4040?

    These things are called "dual proportioning valve" so.... are they controlling front and rear? Otherwise why are there 3030 and 4040 if not to reduce pressure to both?
    Here, have something more visual...

    Code:
                 Master       Front       Rear      Prop      Weight      Rotor
    Carb  lude    7/8          2"         30mm      3540       2300        9.5"
    Si lude       7/8          2 1/8"     30mm      3030       2400        9.5"
    SEi           15/16        2 1/4"     30mm      4040?      2600       10.3"
    This table could use the F/R weight distribution, but I don't feel like looking it up at the moment...
    Is there anything that can be made to make sense from this? 3540 to 3030 seems like such a big difference on a nearly identical car.
    Last edited by night; 02-15-2019 at 01:00 PM.

  7. #7

    Dr_Snooz's Avatar
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    Re: Low fluid pressure

    I got nothing.
    Last edited by Dr_Snooz; 02-12-2019 at 07:28 PM.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

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  8. #8
    DX User ShiRen's Avatar
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    Re: Low fluid pressure

    I've gotta say, I did new rotors, metallic pads, new master cyl, booster delete, and replaced the rear drum cylinders (its a DX, small rotors, calipers and shoes were still in good shape). the brakes are about as hardcore as I can get them, and for the life of me I cant get the car to even try to lock the old ass econobox tires. The manual brakes arent holding me back either and it still stops ok, but I expect so much more, leads me to believe new lines and a wilwood proportioning valve are almost necessary.

  9. #9

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    Re: Low fluid pressure

    After reading this I wonder if I had this same issue with my DX a while ago. I had replaced everything except the brake lines, prop valve, and the flex lines to the calipers. The car would stop but I could not lock the tires up no matter what and it was hard to hold the car still idleing at a light.

    I ended up upgrading to LXI calipers up front and SEI disk on the rear. I changed the prop valve, booster, and master cylinder. Now my braking is amazing.

    My guess for you is probably a bad prop valve or less likely low vacuume. I don't see anything else that would cause this issue for you.

    1988 Honda Accord LSDX-I

  10. #10
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    Re: Low fluid pressure

    I forgot I came back to this thread... but that is where I'm at with this too. I'm looking for a 4040 to replace it with (and for the variety) and then will open the original to see.

  11. #11

    Dr_Snooz's Avatar
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    Re: Low fluid pressure

    Just run the Wilwood and you can set it any way you want. These prop valves are so old now, I don't trust them. The newest of them is, what, 25 years old? Mine was an unending headache. If they have any issues, you can't get parts, or info. You can only buy another old one and cross your fingers again. The Wilwood will require you to change the lines around some and do some re-flaring (the Honda lines are metric sized flare nuts while the Wilwood is SAE), but it's not a bad idea to do some major brake overhaul work at this age anyway. And the Honda flare nuts are some kind of pot metal crap that rounds over the moment you put any torque on them. If I had the money, and wasn't buried with a million other urgent projects, I'd replace the entire brake system from stem to stern with as much aftermarket stuff as I could figure out how to retrofit in.
    Dr_Snooz

    "I like to take hammers, and just break stuff, just break stuff." - Beavis


    1989 Honda Accord LX-i Coupe, 220k miles, MT swap, rear disc swap

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