How to: Solve ABS problems on a 1995 Aerostar.

[BrooklynBay]

Check the Delta P switch. There is a lot of information in post # 4.

 

[Jose A.]

ok, post #4 tells me to "To see if the Delta P switch is the cause of the illuminated warning lamp(s), disconnect the two-wire connector (on the Delta P switch) and jump the two wires together."

but there is no 2-wire connector, the only connector has 4 wires, (at the combination valve). Otherwise I don't know where the Delta P switch is, and it is not at the Master Cylinder, mine is a 1997. The only connector at the master cylinder is a 3-wire connector at the bottom center. (for the fluid level switch).

 

[BrooklynBay]

1997 Aerostar RABS schematic diagram.

This schematic was taken from my Ford software.

 

[Jose A.]

where is the Delta P Switch in this diagram? I can't see anything that says "Delta P Switch".

 

[BrooklynBay]

I don't see anything either.

 

[aero-star]

This tread about the RABS is still a bit confusing, special about the naming of certain parts of the RABS system. Even the Haynes ABS techbook is clear in the schematic but lacks proper naming. Ford calls this hydraulic RABS valve.
I got a 1994 Aerostar (given to me) and someone cut out the part after the master brake cylinder and between the combination valve (Combination valve = accumulator+Dump valve+iso valve)
I assume reading this tread; there is a pressure differential valve (with Delta P switch) this must be the one right after the Master Brake Cylinder (Haynes manual calls this combination valve in the schematic) So what is the right name for this valve?

2 lines from the Master go to the top of this valve. Right and Left front brake lines go out.
1 line goes to the combination valve. There is a elec. Switch on top with 2 wires which will operate the red brake light. If this one shorts out; bridge the connector and light will go out. I have a 1996 which has this hole properly capped without a switch maybe Ford idea or some other mechanic.

 

[aero-star]

Just an add on to my message above. Looking at the RABS schematic in this tread the combination valve is called in the schematic; RABS Proportioning Valve Switch this has a 3 wire connector going to it and is fasten to driver side fender cowl.

 

[Jose A.]

wish I could help but I'm still trying to figure it out myself, a total pain, my RABS light is still ON, I've gone through every possible check, no cigar. The brakes are fine, I got tired of throwing parts at the problem.

 

[rv4fun]

While we're the subject of the RABS, it's been a long time since I heard the system kick-in and click like crazy when I stop quickly on wet streets. Maybe I've just slowed down but I don't think that's it. I have no warning lights lit and everything seems normal except the rapid ticking sound when the tires slide. Any ideas how to prove the systems works and where to start looking?

 

[BrooklynBay]

Make sure that there are no metal shavings stuck on the rear sensor.

 

[rv4fun]

Aw man... here in St Louis its dropping into the teens tonight. It'll take me a while to get under there and look at that. My garage is full of all my gold (some people have the nerve to call it junk but they just can't see the value I do in it).

 

[aero-star]

Well it took me the whole day yesterday to figure it out the Aerostar RABS (I will never stop till I do anyway).
Ford calls the first valve after the Master Brake Cylinder (MBC) the Combination Valve. This valve has differential pressure between the front disc and rear brakes. The front disc brake need more pressure than the rear. Has a 2 wire switch on top to activate the red instrument panel light. This switch has a tendency to shorten out to ground (see Jamey Mcfarland story) This valve has different names on EBAY etc. so good for standardisation.

After the Combination Valve comes the Proportioning Valve (Hydraulic RABS Valve) this is for the Rear ABS only (valve with 2 solenoids on it). This valve (the name says it) proportioning between the brake who wants to lock up. When this valve is not functioning proper the orange ABS light comes on. This valve is named by many Combination Valve; yes also in the aftermarket auto parts. Yes confusing. The Haynes ABS Tech-book and the elec. diagram has helped me to figure out the proper diagnostic for this simple RABS brake system.

If your speedometer is working properly then the rear sensor is okay.

Combination Valve sticking (out of center); Red Brake Light will be on. But also when the switch is grounded (for checking ground; bridge wires and light should go out).

Proportioning valve sticking or leaking to accumulator in valve; Orange ABS light will be on.

Why do brake systems fail; simply lack of maintenance. The cause is usual moisture and other contaminants. Cleaning the rear sensor is important (black metal residue will interfere with this sensor or also the solenoids in automatic transmissions. Recommended by Mfg. is every 2 or 3 years replace the fluid. If you are a DIY why not every year? You probably will never have any problems with the BRAKE SYSTEM except for pad/shoe wear. Get a vacuum brake bleeder or automatic one (which fill the MCB automatic) and enjoy loosening in the right sequence the bleeding screws.
When I accumulate a new vehicle first thing on my agenda is; All Fluid Replacements.

 

[rv4fun]

aero-star, Thanks for the great run down on the components and operation of the RABS.

Like I mentioned in my earlier post, I know when the RABS is triggered, you'll hear a rapid ticking sound which is actuating some valve that prevents the rear wheels from locking up so that you can maintain full control of the vehicle while it's stopping - I'm not sure which component that is. It's a great safety feature.

On Aerostars I've driven in the past, it was normal to hear/feel it kick in at least a couple times a year. I haven't had that happen on any of the Aerostars I own now.

Can you tell me what condition causes the RABS to actuate and any guess as to why it wouldn't? I've never had any warning lights on (other than when turning on the key before starting the engine) and the brakes work great. Any idea how to test them to prove the RABS is ready and functional if needed? :scratch:

 

[aero-star]

A clean hydraulic brake system seldom fails, moisture which create corrosion in the hydraulic brake system will cause the valves to stick. Change the brake fluid every year, and you will never have problems.

 

[rv4fun]

I know it's good practice to change brake fluid and annually wouldn't be too often around the midwest because of the terrible humidity during our summers. The rule of thumb I go by is if it's dark, it's time to change. It's a shame there isn't a way to flush the wheel cylinders and get all the brake fluid out. I recently replaced the front rotors and pads on my "new" (to me) Aerostar and while the calipers were compressed, I sucked the master cylinder out and refilled it with new fluid so the calipers had fresh fluid in them when I pumped the brakes back up. I should have crawled under the back and bled them too while I was at it.

There are stories about motorhomes brakes failing while going down the mountains because the brake fluid was so contaminated with moisture it boiled! The bubbles prevent the brakes from working (bad timing - it could ruin your whole day). I know Ford recommends changing fluid at least every two years.

 

[CLTuna]

Dash RABS and dim brake lights staying on;

1. Cleaned and lubricated ebrake switch. Dash Brake light illuminates bright when set. Dim when not set.
2. Was able to pull the top connector from the shuttle switch. Jumpered the shuttle valve switch connector. RABS light and dim brake dash lights remain on.
3. Checked rear wheel cylinders, no leaks.
4. Brake fluid level fine, pumped brakes several times, could not find a line leak either.
5. Checked all brake and vehicle lights, all fine.
6. Depressed steering column red hazard switch, only works on all four corners if I have on turn right signal. No clue why this is.
7. After driving van for a few miles RABS light would go off then reappear if I set the e-brake.

Will check brake pedal switch and fuse block next.

 

[CLTuna]

8. Brake pedal switch fine.
9. Pulled RABS fuse #7 (20a) Lights stayed on.

 

[aaron.aerostar]

I do have my own thread going, but I thought I'd maybe post here for some help also.

Had a little SUNDAY FUNDAY with the van yesterday...

• Cleaned my parking brake switch, now the BRAKE light gets slightly dimmer / brighter when I love move the handbrake. Proof a cleaning was needed, it didn't do that before.
• Took apart the cluster, and discovered the REAR ABS light bulb was burnt out
• Replaced the bulb
• Started the van
• BRAKE and REAR ABS lights are both constantly lit, like I though they would be
• Replaced the REAR ABS sensor / no change. Drove around and still no change.
• I am going to do the test on the delta P / rear ABS proportioning valve and see if that makes the light turn off. I really hope that's the cause of this issue. Then it would just be a proportioning valve replacement, right?

Also, when I got the cluster back (and dash back together) now anything over 45 MPH, the speedometer needle dances around like crazy! I'm hoping I bumped something loose, going to open her back up and make sure all the connections are tight? Or could this have something to do with the rear sensor that I replaced?

 

[don-ohio]

Mine dances a bit before 60mph...……...don't know why,but it's no bother and cruise control works fine.

 

[aaron.aerostar]

Mine dances a bit before 60mph...……...don't know why,but it's no bother and cruise control works fine.

Replaced the rear speed sensor with a FORD one, speedometer stopped dancing.

Lights are still on though.