1991 ABS "burp"

[KDirk]

Ok, a strange problem on the 91 'vert. I had an ABS light on the dash when purchased. Pulled codes with Tech 1 tool, indicated main pump relay problem. Checked relay, was ok. Then discovered someone (prior to my ownership) had rather sneakily disconnected the harness under the air cleaner box leading to the ABS valve block near the radiator essentially taking it offline. Had normal brakes but no ABS. Reconnected harness, started car and ABS light was gone. OK.

Not so fast. Every time I apply the brakes now, just before the vehicle come to a complete stop (say 90-95% to full braking) the system noticeably "burps", which is kinds of the sound it makes. Also gives a quick pulse of odd feedback to the pedal, so is rather noticeable to both hear and feel. No codes set now, and the basics seem to check out (fluid, wiring, etc.). Any brilliant suggestions on this one? Keep in mind this is the Bosch system (not Teves) as it is a 91. Standard brakes are working, but have not tried to lock them up to verify whether ABS is functional or not as I don't want to find out they aren't the hard way.

KDirk

[Ronnie]

Ok, a strange problem on the 91 'vert. I had an ABS light on the dash when purchased. Pulled codes with Tech 1 tool, indicated main pump relay problem. Checked relay, was ok.

I know very little about a '91 but I wasn't aware of the '91 having a pump. What does it do?

[KDirk]

Oops. Should be main solenoid relay. Had 88 on the brain tonight as I was working on Threatta. Anyway, other than a terminology screwup, the rest of my original post stands as is.

KDirk

[D-a-n-i-e-l]

Inspect and clean the abs sensors and rings. Also check for loose or freed abs leads.

[DAVES89]

I would check the rubber brake lines. They may look good but be collapsed on the inside. The sensor leads on a '91 are basically like vacuum cleaner cords, so even if the outer jacket is frayed the inner leads have another jacket. So if the ABS light is out I would think the sensor leads and brake system is good.

One additional thought is that there may be air in the lines.

[KDirk]

Yeah, so far electrical diagnosis renders no apparent problem. Will be checking the hoses and probably changing the brake fluid anyway shortly as a PM so will bleed the system for air. If it is still doing it after that, I will do futher troubleshooting.

KDirk

[Guest Mc_Reatta]

This sounds like a sticky valve and seal to me. Sounds like valve doesn't open properly then opens very slowly letting pressure free making the noise.

I think you're on the right track with a fluid flush. Can you try to pin down whether the noise is coming from the master cylinder or the box up front?

[KDirk]

Mc-

Will try to make that determination this weekend. Car is in storage today due to periodic rain storms. Will report back if I can figure out which part is making the unusual sound.

KDirk

[Larry W]

For what it's worth, I don't own a Buick, but on my '99 Chrysler Town & Country, you're better have equal tire pressure and wear at all four corners or the ABS ain't happy. Not only will it burp but it wil puke and fart also. It's an easy check.