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Author Topic: Bleeding the Miata's ABS brakes  (Read 18038 times)
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Scotty
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« on: September 20, 2012, 12:50:55 AM »

A while ago, I determined that my ABS block was leaking fluid out when the pump would engage.  I waited forever, but I finally got around to sourcing and installing a salvaged unit from The Parts Group.  It doesn't leak, and my problems have been solved!

Of course, I had to bleed the system, and I really had to get fluid into the ABS's magical chambers.  Some people have no trouble bleeding their ABS, and have a high, hard pedal all the time.  For the rest of us, my internet searching revealed the following recommended techniques:

1) Bleed the brakes, go for an ABS-engaging spin around the block or on some sandy/wet/leafy/snowy/slippery road and then re-bleed the system to get a good pedal.
2) While the car securely supported on stands, start it, put it in gear, spin up the wheels, and apply the brake to get the ABS to engage (that's how I verified my leak initially, but it requires that you get the wheels going pretty quickly or judiciously applying the throttle while you do it -- plus, the unloaded drivetrain does all kinds of interesting things).
3) Pretend that ABS in a Miata makes the pedal feel terrible, and the fix is to remove the ABS.

1 and 2 are great, and they work, since they get the pump to cycle but they do take some time and/or involve some risk.  3 is also great, because now you're frustrated by a deficient system that should be changed, not a broken one that could be fixed.  

There is another option, which I didn't find on the internet but in the tech manual:

Jumper the GND and TBS pins in the DLC.  Step on the brake.  Key on.  This puts the ABS into diagnostic mode (without a special tool), and the pump cycles once on each channel.  Repeat that a couple of times, as you bleed each caliper, for best results.

I had to do it a few times to get all the air out after installing a dry ABS block, but it did work.  If you're just doing a normal bleed, you should feel a difference pretty quickly.

The only other thing I'd mention is that, on our cars, the line from the MC goes to the ABS block and, from there, back to the driver's side caliper.  This makes it a longer line, and "farther away" from the MC than the passenger's side caliper.  I'd been bleeding my brakes the traditional way (LR, RR, RF, LF) since I got the car, but I tried reversing the order for the fronts and can't say I notice a difference.

Hopefully, this post will help someone who heads to Google before they head to Mitchell's.  Oh, and for anybody thinking, "I've heard of GND but what's TBS???"



This is a 99-00 DLC pinout, but the positions of GND and TBS are the same on my car.
« Last Edit: September 20, 2012, 02:06:27 AM by SilverMiataRacer » Logged

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SilverMiataRacer
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« Reply #1 on: September 20, 2012, 01:04:50 AM »

Great write up Scotty.  Thanks for the great work!
« Last Edit: September 25, 2012, 10:52:50 AM by SilverMiataRacer » Logged

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