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Thread: 1990 SC brakes have me concerned

  1. #1
    Join Date
    Nov 2012
    Location
    Canton, GA
    Posts
    247

    1990 SC brakes have me concerned

    Hey,

    A couple days ago, I had been running several errands in my 1990 SC 5-speed. After I stopped for dinner, I started up the car, but the brakes were hard. I drove around the parking lot and realized my accumulator ball was not charging and I had no power brakes (it was actually pretty hard to stop the car at less than 10 MPH). I Googled the forums on my iPhone and suspected that the problem was either the 40 Amp fuse that goes to the "Anti-Lock Motor" and/or the 10 AMP Anti-Lock fuse of the Primary Junction Box. I bought both from a nearby Autozone and installed them. I was frustrated that neither fuse I was replacing looked blown. After replacing the 40 amp and the 10 amp fuse anyways, I re-plugged in the car battery and turned on the car (engine off). I was disappointed and kept turning the key on and off. When I left the key in the On position for about a minute, I suddenly heard the accumulator motor working. I'm a little concerned because my system WAS working all day up until this point AND it didn't seem to work again until after I replaced the fuses BUT not immediately (The car had the new fuses for like 5 minutes before the car would recharge).

    I was able to safely drive it to our workshop without issues. I even plugged in the battery yesterday and turned the key to the on position; the brake accumulator was charging and I didn't need to wait. Since it seems to be working, I decided to leave the fresh fuses in place in case the old ones had corrosion or a lot of resistance. My parents aren't convinced the problem is solved, however. I won't know for sure unless I drive it again or if there is some kind of test I can do.

    Background info: My ABS brakes actuator assembly was sent of to Super Coupe performance in the summer of 2015 (when I first got the car) to get rebuilt, so the system basically works like new and had a very thorough brake fluid flush at the time.

    However, I did park on a slight hill at the restaurant and might have turned off the car while it was in the middle of charging (because I was constantly applying the brakes up until the moment I parked). Can these systems get freaked out if you turn them off in the middle of their job?

    Slightly unrelated: My car has a power drain I haven't identified yet (I've known about it for perhaps 3-weeks). I have to unplug the battery if I don't plan on driving within a few hours because it will totally kill the battery in LESS than 12 hours (the interior lights won't even come on if I wait that long). So the car's battery is unplugged and re-plugged in every day. However, I did not unplug it at the restaurant until after I tried to leave and noticed the brakes weren't working. I can hear a faint clicking sound all the time even when the car is off and there is no key in the ignition. I think some switch or relay could be flipping on-and-off for no reason (I think somewhere on the passenger side).

    Maybe the car is fine, but I thought I should say something in case it's serious and I caught it early. My car's E-brake does not work and the brake pads/rotors have not been changed since I've owned it, so if I lose power brakes, I would probably get into an accident without any hope of stopping in time (I can only downshift so fast). A part of me is tempted to buy the best rotors and brake pads I can and to fix my E-brake so that if I DO lose all power brakes while driving, I have a chance of slowing down in time; especially on Georgia roads where you don't always have more than 2 seconds to react to something.

  2. #2
    Join Date
    Dec 2007
    Location
    Salem OR
    Posts
    7,124
    Quote Originally Posted by Rick_Leuce View Post
    After replacing the 40 amp and the 10 amp fuse anyways

    For all the fun I've had keeping the ABS working on my '90 SC, I've never gone near the fuses.

    Main suspects your example are: accumulator, pump, relays/wiring

    If your unit was 'rebuilt' as recently as 2015, I'd put relays & wiring at the top of the list given your current issue.

    If the pump runs but the accumulator won't hold a charge, you'll know because the pump won't stop...don't run it any longer than necessary. If you come out first thing in the morning and turn the key on, the pump should run around 30~40 seconds. With a fully charged and good condition accumulator, you should see several pumps before the pressure drops and the motor kicks on and the light come on in the cluster. Don't worry if you see that light come on for a moment with a charged accumulator and key on...it's just the system doing a circuit test.

    ABS relays are near the self-test connector, pass. side firewall. See the Component Locator PDF (search here), or use your EVTM. I'd start there, investing in a new relay if age unknown, and doing a close visual on it's connector. Clean/replace as needed. Be very patient with the lock tangs on the connector, and don't be surprised if it puts up a fight trying to get it off the relay. Effort to buy a new ABS relay, not just anything that fits. Be careful working with that circuit....the hot is always on.

    Next, check the 4-pin pump power/ground connector on the side of the master cylinder...it's the one resting in a shiny metal 1/2 hoop on the driver's side. Being especially careful to not break the lock tangs on the plastic connector, open it up and inspect/clean the contacts on both halves as needed.

    If you can duplicate a no-run condition with the pump, reach in with a probe and lightly tap on it (don't go nuts or you can damage the pump magnets, etc.) to see if it wakes up...if not, move the harness around at the power connector on the side of the master cylinder, then at the relays.

    Note the grounds for that circuit are in the ganged ground connector on the header panel, front, driver side of the radiator opening. Inspect and clean, confirming the bolt that holds the assembly to the header panel is tight.

    Still no joy, search here on pulling ABS codes...that connector is in the trunk, pass side. Don't forget there is an ABS module in the carrier under the rear deck, behind the seat.


    As for improving the brakes just-in-case, good luck. These things are a handfull without power assist, so I'd keep my expectations fairly low that you can rely on any upgrades (short of being able to press 700lbs w/your legs) to help without it, just make sure the brakes are in good condition all around, as they should be regardless. The system is designed to hold surplus pressure in the event of a fail, just don't waste braking applications getting the car out of traffic.
    Last edited by KMT; 08-25-2019 at 11:32 AM.

  3. #3
    Join Date
    Nov 2012
    Location
    Canton, GA
    Posts
    247
    Thanks for the fast reply.

    The pump does stop after 30 or so seconds (we had it rebuilt years ago because it would not stop) and the accumulator does hold a charge (replaced at same time system was rebuilt) The concern was that the pump did not come on when the key was on AND the brakes were hard/brake fluid was above the “fill with charged accumulator” line. But it eventually did charge and I got it to our shop. I’ll try doing a test later on; I imagine it could be a worn relay or wiring that has a loose connection. I will be a little reluctant to drive it until I can find/fix the problem.
    Last edited by Rick_Leuce; 08-25-2019 at 12:16 PM.

  4. #4
    Join Date
    Nov 2012
    Location
    Canton, GA
    Posts
    247
    Just took a look at the 1990 SC, there is a little bit of corrosion around the ABS system. The bolt holding in the negative wire had a thin coating of rust all over (even in the threads). I stuck the bolt in a drill and held a wire brush to it, I also brushed the loop connector and filled the hole/covered the bolt in dielectric grease. I also unplugged the 2-wire plug facing the front of the car and put some dielectric grease in it (as a preventative measure). Its really hard to access the 4 or 5-wire plug at the base of the reservoir, or the thick black plug behind the reservoir, so I decided to look at that later. I plugged in the battery and turned the key on, it took about 5-10 seconds of being on before it began to charge.

    Unless the car needs a minute to ďthinkĒ after plugging the battery in before it will charge the brakes, I think it could be an old relay that doesn't always turn on when itís supposed to. The high-beam headlights in the same car dont always come on either when I push the turn signal stalk forwards (because it has auto-dimmers). Since you mentioned the relay could be the problem and it feels very similar in nature to a different relay issue I have; Iím going to plan on replacing the relay next and see if that changes anything.

  5. #5
    Join Date
    Aug 2005
    Location
    Paoli Indiana
    Posts
    4,824
    The abs relay can cause battery drain it did on my sons 35th sometimes the relay would stick and the pump would stay on! Also same deal with the fuel pump relay!
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  6. #6
    Join Date
    Nov 2012
    Location
    Canton, GA
    Posts
    247
    Quote Originally Posted by Jacob_Royer View Post
    The abs relay can cause battery drain it did on my sons 35th sometimes the relay would stick and the pump would stay on! Also same deal with the fuel pump relay!
    I'll look into it. I stuck my head around the car (with battery plugged in but car off) and I thought I heard clicking from around/under the passenger seat. At first I thought it could of been the metal spring somehow making the sound, but it went away when I unplugged the battery. I can't hear the random clicking from in the trunk, but I can easily hear it in the cabin and I can barely hear it with my head in the engine compartment.

    On a slightly unrelated note, I replaced the E-brake handle in my 1990 SC. The one it had wouldn't stay locked (and would sometimes shoot the button off) so I finally removed my center console and swapped it with one I pulled from another 1990 SC. It'll be nice to not have to keep using a block of wood everywhere I go (especially when I want the engine running while I am out of the car). One small victory.

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