Weak brakes

Digitalchaos

Registered User
I have been enjoying my SC more now since the weather has eliminated the necessity for salt, and an old problem has resurfaced which has existed since I bought the car.

On my '93 (no mark II accumulator), my brakes are simply weak. The pedal travels significantly when stopping, and bottoms out during hard stops. It is, and has been, pretty consistant. The fluid was changed once.

I am aware that these cars have a hydralic brake control unit which needs to be bled in a special manner with a computer device to remove trapped air, but I wouldn't think air could be this bad.

The resevoir loses no fluid, over any period of time.

I have also researched a brake booster with few results. Does our car have one of these? If so, how does it operate on these cars? Could it cause this behavior if it were bad and show no other symptoms?

Thanks for any input, this problem is illusive!
 
Haven't found much literature on the TEVES IV. However, what I have seen so far states that the bleeding procedure is normal, with the hydraulic unit depressurized (sounds like a key off procedure), then the hydraulic unit itself is bled (sorry, don't know how this happens), and then the baseline brakes are rebled. You might check the members section on brakes to see if anything shows up.
To me, it sounds like you still have air trapped in the system somewhere.
 
Wait a sec...

How does one properly bleed a 93-95 Supercoupe?

I've changed the fluid and bled from each caliper. I've noticed about an 1" or so travel since then and when I nail ABS, I feel the pedal not just pulsating, but pulsating UP.

Is there more to bleeding the system?
 
Deep6, according to everything I have encountered thus far there is. This includes the Chilton manual, several mechanics, a shop manual from the library, Autozone, and the dealer. Apparently a special 'breaker box' is necessary to activate the hydralic control unit so that trapped air can be released. From what I can tell, this is an electrical device which plugs into the ABS wiring harness and opens the HCU. W/O it, air inside the HCU never gets out during a normal bleed. Apparently

I was going to have the dealer bleed my brakes w/ this tool just to see if it was air, but the dealer wanted 90 dollars for a bleed and the brakes are performing in such a poor manner as to make me think its more that air that the price simply wasn't worth finding out. I was hoping to know for sure before giving that much to the dealer :eek: .


TbirdSCFan, Literature does seem limited about our braking system. Apparently the one used specifically for these years SCs was not used on very many cars.

I still think there may be a brake booster apparatus...
 
We've bled the brakes on my 95 several times using the conventional method, when doing the various brake upgrades over the years ... never had any problems afterward.

I think Pat DiPersia had issues similar to yours, you may want to try contacting him.


cheers,
Ed Nicholson
SCCoO
 
Digitalchaos said:
.. Apparently a special 'breaker box' is necessary to activate the hydralic control unit so that trapped air can be released. From what I can tell, this is an electrical device which plugs into the ABS wiring harness and opens the HCU.
I'm fairly certain there's a way to rig it so that you don't need the tool. If you can find a wiring diagram for that unit, I can take a look if you'd like. I only have a Teves II schematic.
 
TbirdSCFan; thats what I was thinking. Probably the breakout box doesn't do anything but connect a circuit with two wires in that harness for a period of time.. hence if I can find which wires and how long to connect them it should work. A late model diagram would be necessary.

fast Ed N, thanks for the info. Perhaps I'll have to find him and see what he found out..
 
Ok something even more unusual today. After having driven in water/melted snow last night, today the brakes feel almost normal.. they are more firm with significantly less pedal travel.

Odd. Thoughts?
 
Yes.. you probably activated the ABS in the wet somewhere a few times which relocated some air bubbles. If I were you, I'd do a normal bleed of the lines quickly before the bubbles have a chance to find their way back into the pump. Shoot, you may have just made a discovery. I mean, you were trying to figure out how to get the pump to run... and guess what... just mash down on the brakes hard when its slippery... that makes the pump run.
 
if you noticed...

I mentioned in my post earlier that When I activate the ABS I've noticed the pedal pulsating, but pulsating UP toward the driver.

As if the pedal is getting much firmer and more reactive.

However, the effect only lasts as long as the ABS is activated. After that, the pedal doesn't feel soft but seems to have more travel that I originally remember it having.

At any rate, I would like to find out if there is in fact a way to activate the pump to pump out the remaining air should some get trapped up in there.

I remember when I was bleeding my brakes, I let the master cylinder get too low and I'm sure I sucked air right in. I seemed to get it all out of the rear caliper but like I said before, it never felt quite the same as it did before.

Now that I'm considering upgrading the brake hoses and possibly the brakes themselves, I'd like to make sure that I can flush all of the air out.

This question specifically pertains to Teves IV systems with a straight up master cylinder rather than the hydraulic pump/accumulator combo which were on the 89-92 Sc's Not the Teves II system. I want to know about the later trouble-free 93-95 Teves IV system. How can we get the pump to run when we are bleeding the brakes?
 
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