'91 c4 abs locking up

[HU*LT5]

THANKS FOR ACCEPTING ME TO UR GROUP.A MEMBER OF MY VETTE GROUP '91 C4 COUPE ABS LOCKS UP THE FRT BRAKES.THINGS HE HAS DONE :BRK BOOSTER(NEW),MAS.CYL.(NEW),PWR BLEED W/ABS CYCLE FLUSH.THE LOCK UP OCCURS ABOUT 5-10 MIN.DRIVE.HE THEN SHUTS CAR DOWN FOR APPROX 5 MIN,THEN STARTS TO DRIVE & THE CAR MAY NOT DO IT AGAIN FOR FEW HOURS OF DRIVING.STRANGE,NO CODES WHEN USING MY SNAP-ON SCANNER AT REST OR ON A DRIVE.ANY IDEAS NEEDED.THANKS,GE.:ugh

 

[BigKahunaFL]

THANKS FOR ACCEPTING ME TO UR GROUP.A MEMBER OF MY VETTE GROUP '91 C4 COUPE ABS LOCKS UP THE FRT BRAKES.THINGS HE HAS DONE :BRK BOOSTER(NEW),MAS.CYL.(NEW),PWR BLEED W/ABS CYCLE FLUSH.THE LOCK UP OCCURS ABOUT 5-10 MIN.DRIVE.HE THENView attachment 25165 SHUTS CAR DOWN FOR APPROX 5 MIN,THEN STARTS TO DRIVE & THE CAR MAY NOT DO IT AGAIN FOR FEW HOURS OF DRIVING.STRANGE,NO CODES WHEN USING MY SNAP-ON SCANNER AT REST OR ON A DRIVE.ANY IDEAS NEEDED.THANKS,GE.:ugh

Yeah. How ' bout ya quit SHOUTING at us!?!

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[echo4golf]

THANKS FOR ACCEPTING ME TO UR GROUP.A MEMBER OF MY VETTE GROUP '91 C4 COUPE ABS LOCKS UP THE FRT BRAKES.THINGS HE HAS DONE :BRK BOOSTER(NEW),MAS.CYL.(NEW),PWR BLEED W/ABS CYCLE FLUSH.THE LOCK UP OCCURS ABOUT 5-10 MIN.DRIVE.HE THENView attachment 25165 SHUTS CAR DOWN FOR APPROX 5 MIN,THEN STARTS TO DRIVE & THE CAR MAY NOT DO IT AGAIN FOR FEW HOURS OF DRIVING.STRANGE,NO CODES WHEN USING MY SNAP-ON SCANNER AT REST OR ON A DRIVE.ANY IDEAS NEEDED.THANKS,GE.:ugh

Are you sure the Snapon scanner will pull ODB1 codes? Might do better to pull them from the DIC.

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[HU*LT5]

Snap-on scanner type

Are you sure the Snapon scanner will pull ODB1 codes? Might do better to pull them from the DIC.

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[Hot Rod Roy]

The pushrod between the power booster and the m/c may be a little bit too long. This pushrod is adjustable. If it is too long, the piston in the m/c will block the vent port, which is supposed to relieve the pressure in the brake lines as the fluid warms up. The fluid will expand as it gets warm.

You should be able to see this little port by removing the m/c reservoir cap. As you gently push the brake pedal (engine off), watch for a small jet of brake fluid from this port. You may be able to see the piston in the port if the fluid is clean.

This pushrod can be adjusted by separating the m/c from the booster without removing the brake lines from the m/c. Gently pull the pushrod out of the booster just far enough to grab the rod and twist the adjusting nut on the end of the pushrod.

 

[Hib Halverson]

It's unlikely that ABS is causing this problem as ABS-2S in 1991 does not have the capability to increase brake pressure above what the driver is creating with the master cylinder.

Take a look at the pushrod discussed above but, admittedly, since only the front brakes are affected, that might not be an issue.

Do the front brakes lock or just drag?

Pull the ABS fuse then road test. Post whether or not the problem occurs.

You said you read no codes. Has the ABS Service light been on?