90 Olds Trofeo ABS brake question

I've got an Olds Trofeo with a brake problem in the car lot where I work, and I was wondering if someone out there can help me witht his problem.

I understand that when your driving the brakes will just suddenly grad hard. 1 shop thought that it's the calpers, but I can't see that being the cause.

I'm thinking that it's in the ABS, and I'm wondering if there's a way to disable just the ABS part to test my theory.

It's a rather weird looking setup. I don't see any vaccum lines going to the master cylinder so I'm assuming that it's all electronic.
I don't have access to a digital camara so I won't be able to show you a pic of what it looks like

Thanks in advance
Stu