Greetings, haven’t been here for a while, my 92 aero hasn’t had any strange problems for a while either. Here is one for the books. Yesterday, the ABS light came on. The brakes felt fine, so I checked all four wheels. No leaks. Then I checked the Master Cylinder. It was way down. I filled it and the ABS light went out. When I got home, I checked around for leaks. I found an item the shop manual refers to as a combination brake valve. It is just below the MC. It has a small opening on one side and that is where the fluid was leaking. Not much though, just a drop or two per day. I cleaned it up and sure enough it was wet after a day. The dealer here wanted $200.00 for a new one and didn’t have any in stock as they say these valves never fail. I went to the bone yard and got one for $10.00 and it worked perfect. The strange thing is that I didn’t have to bleed the brakes. I put it together, took off all the wheels and got ready to bleed the brakes. I started it tried to pump the brake pedal a little only to find it went down about an inch and was rock solid. I put it together and when for a drive. The Brakes work perfectly. I have never worked on the brakes before where I didn’t have to bleed them. This is the strangest experience I have ever had with brakes.

 

Sometimes the brakes will clear themselves of air particularly when the opened part is near and below the mc. This is likely what happened in your case. I have changed many mcs without bleeding the brakes. If your pedal is fine, do not worry.

Your problem is not strange, that is exactly what I would expect.

Ken

 

I went through the same deal on my 94. I would recommend a full bleed and total change of fluid. The brake fluid seems to hold water, and it causes rust in the valves and wheel cylinders. I think if I had done a full bleed every couple of years, it would have saved me a grand.

 

A full brake bleed is always good.

ken

 

One other common problem is corrosion forming in the chamber containing the shuttle valve. There is a switch screwed into the front of the combination valve that detects the shuttle valve shuttling from either a leaking circuit or aggressive bleeding. But it doesn't seem to be very waterproof, so moisture gets in. The corrosion that forms will short out the switch, triggering a brake system failure, which causes the ABS system to stop working (light comes on).

 

I will probably still do a complete bleed of the system, but It works so well right now I don't want to mess with it for a while. It's spring break here and I promised the family a full week of fun.

I think this valve must have been defective for a long time. For years the van behaved strangely during heavy braking. If I had to do a fast stop, the brakes seemed to grab nicely for a few seconds and then they felt like they let go. The dealer said this was normal for this van. I didn't like it, but I thought the dealer knew what they were talking about. Now with this replacement valve, the brakes grab and don't let go. It's a nice change.

One other thing about this valve. the new one has a type of rubber plug in the front of it while the old one just had this tiny hole where the fluid started to come out I think the plug must have come off at some point.

 

That is the way the crappy rabs system is supposed to work. It scared the heck out of me on a hard stop once. The rabs system keeps decreasing rear brakes until they are not there. I replaced my rabs system with an adjustable proportioning valve and never had better brakes. see other posts on the subject. rabs sucks.

Ken

 

By chance, do you have a step-by-step instruction and part numbers for the valve? I wouldn't mind having real brakes again.

 

Search my previous posts on the rabs subject. It is easy to install an adjustable proportioning valve. It works very well.

ken