Brake system bleeding w/Rear ABS
 

Hello,

I am trying to help a buddy of mine fix his Ranger. It is a 1994 Ranger XLT, Regular cab, two wheel drive, manual transmission and I think it has rear ABS. A front brake line blew which drain the master cylinder. Also a couple of pieces of brake line at the rear had to be replace along with the rear wheel cylinders. After installing the new brake system components we were trying to bleed the system. After reading the repair manual I had it said that vehicles with rear ABS you are to bleed the ABS module before bleeding the rest of the system. There is a module where the book described it (driver's side inside the frame rail) with brake line running to it. I am assuming this is the rear ABS module? I didn't see anything that looked like a bleeder on the module. Any ideas as to where to look? Also when I open the bleeders on the rear wheel cylinder no brake fluid came out. Any thought on that? Any help is appreciated.

If you've gotten air into the ABS module, you'll need a special scantool that can actuate the ABS module & a tool to apply vacuum at the wheel cyls to evacuate the system in order to get all of the air out of the ABS motor. A Brake shop, or the Dealer can do that.

You can probably get most of the air out of the system with a hand vacuum pump, connected to the RR, LR, RF, then LF wheel cyls in that order. Keep a close watch on the master cyl fluid level so it doesn't get low & induce more air in the system.

But if air has gotten into the ABS motor, you'll need a scantool to actuate it while applying vacuum to the system.

I have gravity bled a system a couple of times, but thats slow & lately use a "one man" bleed system to do it myself, when I didn't have a helper to pump the brake pedal & it works ok, just have to keep an eye on the brake master cyl fluid level & make sure the hose fitting is tight & no air bubbles are in it, or in the bottom of the catch container where the end of the bleed fluid line is.

Motorcraft PM-1 DOT-3 brake fluid is a top notch product & reasonably priced.

Some thoughts for pondering, let us know how it goes.

I bought one of those tanks that you attach to your master brake cylinder in place of the cap and then pump up the tank and it pressurizes the entire braking system. Can't pump it up too much cause you'll blow the brakes :-X03:-X03:-X03
but it makes bleeding brakes a one man job and I love it.
I have abs on my rear and have never done anything special to bleed the rear. I think if you are following the correct procedure for bleeding your rears then it should work but may take some time on your part to get all the air out of the rear system and as pawpaw states you need to do the farthest calipers first and then work towards the master cylinder.

With a 1994 being pre-OBDII would you still need a scan tool to activate the ABS motor? If I am understanding greenpus right there is no bleeder on the ABS valve itself. Right? So I should be able to go right to the right rear and start at that wheel cylinder? Thanks again for the information.

the scantool is used to actuate the ABS motor, in the event air has entered it.
Otherwise if air hasn't entered the ABS valving, a normal system bleed proceedure will suffice.

I am assuming that since the master cylinder was drained air has entered the ABS motor. Is there a scan tool on the market that the home mechanic can buy to actuate the ABS motor? If so which one would be recommended and where can you buy one? I have an OBDI/OBDII scan tool but does not read ABS codes. Will this tool work to actuate the ABS motor on a OBDI vehicle?

I'm not aware of a low cost, over the counter, non professional scan tool that'll actuate the ABS system, but the Dealer & most brake shops have high end scantools that'll do it.

If the master cyl has been opened, consider first doing a bench bleed on it, then try the conventional system bleed routine at each wheel cyl as I noted above & let us know how it goes.

Finally got a chance to work on the brakes again and here is the latest. I took of the master cylinder and bench bleed that. Re-installed it and tried bleeding the wheel cylinder again and nothing. I took the line off coming into the ABS valve to verify that there was fluid getting to the valve and there was. So I took the line off of the output side of the ABS valve and there is nothing coming out. When we pumped the brakes you could hear some air and a little fluid was squirting out but that was it. Something else I should add. When I took the brake drums off they looked like the shoes have not been wearing on them in a while and the shoes were starting to wear but not to the point of being completely gone. Could the ABS valve just be bad and has been for a while? I bleed the front brakes and took the vehicle for a short drive and the brakes feel like they are working fine. The ABS light and the brake light are not on. So I am still really confused?? So I am not sure if it would be wise to just replace the valve or if it still air in the valve that is causing the problem?

Seeing as how it has new rear wheel cylinders & some new brake line installed, why not consider running this puppy by a trusted brake shop & let them have a go at bleeding the system with their scantool & a vacuum source connected to the wheel cylinders.

They'll soon know if the RABS module is faulty.

If you replace the ABS valve, you'll still need a shop to hook up their scantool to actuate & bleed the air out & sometimes this is tricky.

I have a shop manual for 91 Rangers -- which probably use the same system, and it doesn't show any bleed screw on the ABS. ( There is one for F150s from that era).

It does show a diagnostic connector. Of course, they call out their Rotunda scan tool.

I had a 91 Ranger and did the brakes - including a rear line replacement.
I bled them in the normal fashion, and there was no problem.

So, X2 on get a shop to figure out the RABS. Did your buddy ever notice the ABS coming on? -- you know that rapid cycling of the brakes.

Good Luck,

hj

I have a 93 ranger the rest of this post is in the assumption that the 94 has the same system. It is rear wheel abs only. Hence there is no 'motor' in the valve. Only 2 needle valves and no need for a special bleed procedure. One valve closes to isolate the rear brakes from the master cylinder and prevent brake pressure from rising if the rear wheels have or are about to lock. The other valve dumps fluid to an accumulator dropping brake line pressure to allow the rear wheels to keep turing and keep from locking. When both valves are inactive, the RABS valve just passes fluid through.

If you are not getting fluid to the rear brakes, the valve might be blocked with rust or gunk. You could try cleaning it or simply replace it. I would not recommend bypassing it as the system does not have a proportioning valve to balance the front and rear brake pressures. (Ford calls it a 'combination valve'). The RABS II valve performs that function.

I finally got a chance to work on this again. After trying to bleed the brake again with no luck. I finally replaced the rear ABS valve (not sure if that is the proper term) and everything worked great. I was able to bleed the brake with no special tools. Thanks to everyone for the information!

OK, good feedback on fixing your brake bleed problem & to hear your on the road again!!!

got a 1993 ranger and found the bleeder screw is on the top of ABS unit

Rangers had RABS through the 1994 model year. All wheel ABS was introduced on the 1995 models.