Hey did some searching this morning and am striking out.

1994 Grand Cherokee 4 wheel disc w/ABS 4.0L 180,000 miles bone stock.

A month ago I came to a normal stop on wet pavement @ a red light, and it felt like the ABS kicked in pedal dropped?? First time since I've owned the jeep (10+ years) Pedal sank as did my stomach...Pedal was fine for days, but it has a tendency now, mostly in parking lots, to sink just before coming to a complete stop. I cannot make it happen. I have not done any brake work on this for several years. Jeep is driven in the winter and once in a while during the warmer months. Last thing done was changing front and rear pads about 20,000-30,000 miles ago.

When I did these I opened the bleeder on the calipers and then pressed the pistons back in removing some of the old fluid. After I installed the new pads I refilled the MC and and slowly pumped the pedal to get the pistons to seat the pads against the rotors. After test driving checked and topped MC as needed. Been successful with this method for years...MC still has ample fluid but is dark....

I'm wondering if; over time, since I have never bleed the brakes, if when the ABS activated the other day (if it did) it somehow got air trapped maybe dirty fluid? I've read I need a DRBII scan tool to bleed the ABS. I followed a few threads that had someone saying that you should be able to activate the ABS by placing 12v to certain pins? Didn't say which pins. I'm curious what you guys think? Is it air in the ABS? will some hard stops from 20-30MPH in gravel be enough to activate the ABS so I can bleed at the wheels? Is there an alternative to buying the DRBII (besides taking it to the dealer/service center) by placing power to the ABS control?

Thanks in advance

 

This reply shows the DRB II tool.

My process is to use the Motive Products Power Bleeder for one-man bleeding.

 

Thanks I'll give power bleeding a try and see if it helps. I've a pressure bleeder for another car hope I can just buy the adapter and make it work...

 

A full system bleed-flush is always a good thing but I'm betting your master cylinder is on its way out.

 

How come? What makes you think the master cylinder is on its way out? I'm just generally curious about that, and wondered why?

 

The internet is actually amazing! It took less than 10 seconds to find out more about the master cylinder, and had this information:


(copied & pasted)
Over time, with constant use, the seals inside of the cylinder can wear out and form internal leaks. A bad brake master cylinder may result in a pedal that feels mushy, spongy, or that slowly sinks to the floor when depressed.

(me)
I imagine the only way to fix something like this is by replacing it the master cylinder?

I remember reading about mushy brake-feel. Some people were saying also the line or hoses going to the calipers can also cause the brakes to feel mushy, even if after a good brake fluid change/bleed is done, when they are older and worn out too.

Would the master cylinder going out cause more of the pedal dropping and sinking to the floor thing? Verses.. maybe having more of just a mushy feel alone, with no real noticable pedal-drop when applying the brakes.. if the system only needed to be bled with new fresh fluid, or had worn out caliper hoses?

 

No, you can buy a rebuild kit and do it yourself. It's not a difficult job.

 

Brake fluid is hygroscopic, meaning it will absorb moisture. After a period of time, this moisture will cause rust and corrosion inside the piston bores of calipers, master cylinders, and drum brake cylinders. (AND ABS UNITS) Any time you replace a caliper or other cylinder, it's a good idea to completely change all the brake fluid, completely purging the system when you bleed it, especially if it has changed color.

 

Yes sir! Excellent!

 

Hygroscopic. You know.