Working on the challenge car today, found that I could not bleed the passenger rear brake. Traced back through the hard lines to the ABS pump. Cracked the line to the passenger rear, no fluid when i pump the brake. Cracked the line to the driver's rear, lots of fluid.
Looks to be two lines from the master to the ABS pump (front and rear I assume), and then 4 lines out of the ABS pump to the wheels. No asc+t or some thing else in the way like that.
- Does this behavior mean the ABS pump is boned?
- Can I bench cycle the ABS pump some how to see if that frees it up?
- Whack it with a hammer?
Pull that monstrosity off and put on an adjustable master. Some cars have a stock master with adjustment for the back axles. Or just bypass it.
Is there any hydraulic pressure on the passenger rear at all? If you jack the car up and stand on the brake, is it possible for your helper to turn the wheel by hand?
AFAIK, pretty much all ABS units have internal diagnostic systems and some kind of trouble code reporting mechanism. On a 25 year old car it's probably done by jumpering some pins while keying on and holding the brake pedal and then it blinks them out on the ABS light or something. Do you have access to the FSM? (maybe a PDF?). If so, any such system should be documented in there.
The Miata unit I've played with (10 years newer, but still pretty similar to the original 1990 Miata units) has a separate test mode, where when it boots up it will operate each of the solenoid in turn to test them out. If there are codes stored in it, you may need to clear them before it will run that test, though.
Is this a Bosch unit?
bearmtnmartin wrote:
Pull that monstrosity off and put on an adjustable master. Some cars have a stock master with adjustment for the back axles. Or just bypass it.
Ding ding ding we have a winner!
If whacking it with a hammer doesn't work, I'd just tee the right rear in to the left rear circuit and call it good enough.
Knurled wrote:
If whacking it with a hammer doesn't work, I'd just tee the right rear in to the left rear circuit and call it good enough.
Sounds like a bad idea to me. Consider what the ABS computer might do if it sees a lockup on that wheel, tries to control it with the solenoid, but nothing happens?
Same thing that happens if you lock the wheels with the handbrake while braking. The ABS tries to undo it, and either keeps trying until you let off the handbrake, or it tries for a little while then gives up.
Either way, it would be happening on a circuit to nowhwere.
(You would think that applying the handbrake would disable the ABS, but it doesn't on the vehicles I've tried...)
If it's anything like the ABS "bombs" in Saabs and Audis of the era, the car has to be running or you have to pressure bleed it to give you any movement back there.
Knurled wrote:
Same thing that happens if you lock the wheels with the handbrake while braking. The ABS tries to undo it, and either keeps trying until you let off the handbrake, or it tries for a little while then gives up.
Either way, it would be happening on a circuit to nowhwere.
Perhaps. Or you might confuse the ABS computer and put it into ice mode and have it take away all your brakes.
Converting to non-ABS brakes is a reasonable option, but personally I wouldn't try to fool the ABS computer into being 3-channel instead of 4.
I've never had that happen. The worst that I've had happen was the old ABS IV system that GM used would disable ABS and flash the light at you until you cycled the key. Which was boring, because the fun in dragging the rear tires down a snowy road was making the ABS unit spaz out 
Bosch systems don't give a crap, they keep trying until the brake unlocks.
Well, good news! I will never have to find out what happens if you tee the working wheel to both the rears.
Today I took the cover off the electrical stuff, and located these two relays.
The silver one is the solenoid relay, and the black one (50amp!!!) Is the motor relay. One at a time, I jumpered them, and thus cycled the motor and the solenoid manually. Then, for good measure, I whacked the abs unit with a hammer a couple times.
Cracked the rear passenger line, and BINGO! Got fluid! Bleeding the rest of the brakes went easily.
So, I don't actually know if the hammer or the cycling of the motor and solenoid fixed the issue, but I do know I now have fully functioning brakes on the challenge car! Woot woot!
Thanks all for you help and suggestions!
