Can someone tell me the proper procedure for bleeding the ABS unit on my 94 with standard brakes. Is the ABS unit behind the drivers seat?
Thanks

 

I believe it takes a tech 1 or tech 2 to reset it so you can bleed...Maybe an expert will pipe in with some solid facts. From what I understand there is a solenoid/actuator valve that needs to be opened in order to bleed it. Most Ive talked to said there is no need to bleed the ABS if it is in good working order.

Dont take this to heart, I am by no means 100% positive, just food for thought.
Brake problem?

 

Bobmarshall,

Cusinartvette is correct that some years require a tech-1 or 2.

HOWEVER, it is not required for our 1994 C4's (presume yours is an LT1).

Bleeding the ABS/ASR (anti-lock/anti-slip) unit (which IS behind the driver seat, in the bolt-locked compartment) requires both bleeding the unit itself, and bleeding each wheel in a specific sequence. I have also read it then requires a test drive where you slam on the brakes to engage the ABS, and then re-bleed the wheels one more time.

The procedure is as follows (assuming no air in Master Cylinder bores, which would otherwise require bleeding the Master cylinder first):

1. Deplete vacuum reserve by depressing brakes several times with the engine off.
2. open and line with paper towels and place a container in the storage compartment behind the driver's seat where the ABS/ASR unit is located.
3. bleed the 'master cylinder prime pipe', via the 'modulator valve' on the ABS/ASR unit (looks like a normal bleed screw on the top rear of the unit -- just protect the interior from the brake fluid). This does not require any brake pedal movement, just open bleeder and close when fluid clear with no bubbles.
4. bleed each wheel in the following sequence (requires typical 2-person brake bleeding procedure -- press and hold pedal down, open bleeder, close bleeder before pedal hits floor, let pedal come up, repeat until fluid is clear and has no bubbles):

4a. Right Rear.
4b. Left Rear
4c. Right Front
4d. Left Front

FYI, I use one of those plastic bleeding containers (e.g. Leslee ? brand) and connect the hose directly to the bleeder -- not using the adapters that come with it as they leak).

Also, remember that all brake fluids are not the same. Further, DOT-4 brake fluid is not necessarily better, and is not recommended for our C4's on purpose (contains a slightly corrosive agent to aid in the increased boiling point, actually absorbs more water over time than DOT-3, is thicker which can slow-down the response time of the wheel calipers to the brake pedal).

However, that said, DOT-3 is getting hard to find, aside of directly from the dealer, and many on the forum use/swear by certain brands. Do a search and consider carefully which you wish to use.

 

with the Admiral.

Sometimes when you try to bleed the rear wheels you will notice that you can not get any fluid, that is because a solenoid in the ABS system is in the closed position.
If you had a Tech 1 o 2 scanner you could bleed the system with help of the scanner.
Do not worry, if you do not have a Tech scanner just drive very carefully for a few meters, you should reach 10mph so the system will cycle itself just as you would with the tech 1.
Drive home and bleed the system, now you should be able to do it.
Remember that you do not have to drive a long distance, just reach 10 MPH, so you do not have to expose yourself to harm, and remember that while you drive you will have inefficient brakes until you bleed in the correct sequence The Admiral described.

Good luck!

 

Question...If you had the car on stands, and "drove" for that proverbial 10 feet forward or reverse would that activate the ABS for you or is it based on a certain mph?

 

Yeah mate

 

As Kinkajou said (btw, good info), it is based on MPH, not distance.

However, per the FSM, it is only 4 MPH.

And on our 94, that's about right, as I hear it (sounds almost like something is wrong with brakes) just starting to go forward in the parking area behind the garage (say within about 20 feet).

But remember as Kinkajou said, ONLY need to do this IF no brake fluid comes out during the caliper bleeding. If it does, just bleed as normal.

 

If its a 94 in question here you wont need to invoke an ABS test in order to bleed the brakes anyway.

 

Sorry for the 'jack, but do the front or rear tires determine the speed to the computer? could one just spin the wheel(s) on stands to activate it? Wonder if one was spinning if that would freak it out -Just curious

 

Neither of them, the transmission does, cause the VSS is located in the output shaft housing.

 

 

If a shop bled the breaks on my 89 (RR, LR, RF, LF) normally, would that also flush the ABS unit?

I talked with a shop today, and the guy said the above method would also bleed the ABS system as well. ???

 

Yours is OBD1, so this process isnt necessary. Just bleed away