Ford and Spongy brakes

Spongy brakes - UPDATE.. HCU fluid routing diagram

Hi all. Just looking for some input/thoughts from other GenII Explorer owners with regards to brakes. Since I purchased my X a year ago it has been plagued by a spongy brake pedal. I have never owned an explorer before, nor driven anyone else’s so I don’t have much to compare to. To date I have done the following maintenance:
-Replaced brake pads with EBC 6000 pads (front and rear disk brakes)
-Front and rear rotors were still within spec and not scored, warped, cracked, etc so I did not replace/turn them.
-Pressure bled the entire system removing all the old brake fluid and filled with new Motomaster Ford DOT3 (288F Wet boiling point). Then gravity bled, then pressure bled again.
-I have not blead the HCU since I do not have the electronic ABS pump/valve cycling tool. However I have braked hard enough that the ABS turns on then bled the brakes again.
-All the rubber lines appear to be in good condition and do not bulge or bubble when the brakes are applied
-Greased all the caliper slider pins with caliper slider lube.
-All the caliper pistons move in and out freely.
-Performed pump up test.. ie pump the brakes with the key off until the pedal gets hard, then keeping pressure on the pedal see if it moves after a minute. It doesn’t..

The one thing I have not replaced is the master cylinder. From what I have read if the brake pedal is depressed and hits the floor it can tear a seal in the master cylinder (ie by extending the pistons beyond there normal operating range). I’m not sure if this is the problem or not. I can say that when I brake hard the tires have never locked up (even with the ABS fuse removed). The most I get is a very very slight voooov sound (I’m sure this is just the rotors that aren’t 100% true), no vibration or pull, to a gradual stop. Don’t get me wrong the truck does brake, but the pedal feels soft the whole time and I can almost make it hit the floor if I push with medium force. I now this sounds like apples to oranges but I had a Nissan Maxima before and the brake pedal was hard as a rock and only moved half an inch. It feels to me like there is a pinhole leak someplace, maybe the master cylinder, but I don’t seem to be loosing any brake fluid. Or that I have air in the system somewhere but like I said I have gravity bled, used a vacuum pump to bleed and pressure bled the brakes 4 or 5 different times now. I don’t know what to do, it just doesn’t feel safe towing a boat with a truck that has such mushy brakes. Any one experience the same problem or feeling.. Is there a rebuild kit for the master cylinder? Thanks for the help.

It sounds to me like air in the ABS pump. For reference, I have two 95 Crown Vics, and I added ABS to one, and the pedal has felt soft ever since. I know that air got into that ABS pump, and I have learned that it cannot be bled without a special tool.

I had EBC rotors and pads on my Mountaineer for 45,000 miles, and the brakes were very good, relatively.

I suggest that you look into having the brakes bled again, using the special tool which manually cycles the ABS pump while bleeding. It sounds like you have done all of the other proper remedies. I would bet that someone has allowed air to get into or above the ABS pump. That would cause air to get into the pump, etc. Good luck,

I agree, bleed the ABS. IF it's the master cyclinder, you should be able to make the pedal go completely to the floor by hitting the pedal, letting up slightly, hitting the pedal, letting up slightly ... etc. If this happens, then suspect the master cylinder.

Looks like I will have to get the dealer to bleed the ABS with thier fancy tools and widgets. Thanks for the help. .

I would check the vacumm booster lines and connections.

unclemeat can you elaborate a little. I hadn’t thought to check the brake booster per say. I didn’t think it could cause the sponginess. ie if there was a leak in the vacuum line, or a tear in the BB diaphragm I think that would lead to an extra amount of pedal pressure required, similar to when the engine is off and you try to break. I did check the check valve and it seems to be working properly.

I can sort of understand what you are saying though.. For instance, if there was a tear in the brake booster diaphragm then I would have to apply more pressure on the brake pedal to get the same amount of stopping power. ie instead of, lets say, 10% foot / 90% BB I now need to apply 50% foot (the pedal should still end up in the same place regardless) / 50% BB.

On the other hand when the engine is off, 3 or 4 strokes and the pedal is hard as a rock and remains hard until I start the engine. This would lead me to believe that there are no vacuum leaks.

Just had another idea... What if the gasket between the brake booster and master cylinder is leaking? What would happen then? Would air get sucked into the BB and make its way to the intake manifold. How would that affect brake performance?

UPDATE.. there is no gasket between the MC and BB.

marragtop I tried "hitting" the pedal a few times (while the truck was parked and running) and I was able to get it to hit the floor, the pedal slowly made its way back to its up most position. What is happening here? Is brake fluid quickly getting past one of the two pistons when I "hit" the brake, then slowly getting sucked back when the pedal returns? I know for sure it is a dual piston MC since there are two break lines coming out of it. If as suspected one piston is faulty then I would only get max pressure on one of the lines. I think this would greatly reduce breaking as only 2 out of 4 brakes is receiving proper pressure. Or berceuse of the ABS valving, maybe all 4 breaks see the reduced pressure.

I am really starting to suspect the MC. The truck does have 230 000Km on the original MC and BB. Is there a rebuild kit for the MC (poor student can’t afford 199.74 for new MC).

I had a similar problem with my brakes. It turns out it was the rubber gramet in the vacumm booster had degraded and was leaking. It is easy to check, A visual will do most of it and a mechanics stethiscope will also let you know if there is a leak.

I asked this a while back but and never got a reply so I figure I'll ask now as we are on the topic of brakes.

I know there has been a lot of discussion on this topic in the past so stick with me here. I need to bleed the HCU and I don’t have the fancy Ford T90P-50-ALA tool to do it. Now the T90P-50-ALA works by running the pump for 60 seconds. After 20 seconds you hold the "valve" button for 20 seconds then release it, the pump continues to run for the remaining 20 seconds. You can now bleed the brakes like normal. I would like to know if anyone that has used one of the tools or has access to one and can tell me which valves it activates. There a 6 valve in total. L. ISO valve, R ISO valve, Rear ISO valve, L. Dump valve, R. Dump valve and Rear Dump valve. I imagine that when you hit the "valve" button it activates either the ISO valves or the Dump valves the 20 seconds or some combination. If anyone has had one of these HCU's apart before and can tell me how the brake fluid is routed through the unit that would be a good place to start. Or if I could get a picture of the T90P-50-ALA unit itself, specifically the harness portion (so I can see the contacts) that could also help.


I am going to make an educated guess and say that the ISO valves are normally closed removing the ABS pump from the hydraulic loop when the ABS is not engaged. When the ABS is triggered the ISO valves open/close according to which tire needs/does not need brakes. During this time the ABS pump is running providing the required pressure to operate the brakes (ie a predictable, regulated pressure that does not depend on your foot). The Dump valves are used to reduce pressure/help control the flow of fluid or act as a reservoir. Now I imagine that air in the HCU unit gets trapped behind the Dump valves (in the reservoirs) and the only way to get the air out is to open the Dump valves along with the ISO Valves and run the motor. And via some magic the air will find its way past the ISO valves, and can be bled out using the traditional methods.

If there is anyone that has used one of these tools before can you describe the sounds made by the HCU.. ie the motor is running, I hear valves cycle on and off every xx seconds… or maybe the valves simply open then close 20 seconds later..

I plan on putting together a electronics watchamacallit to simulate the very expensive Ford tool. Ill post the results.

Hello, contact Glacier here. He has some experience with the ABS diagnostic tools. He may be able to steer you to a workable tool. Good luck,

UPDATE: I am on crack.. I have come across a hydraulic fluid routing diagram for the HCU and I can now explain in detail exactly what happens when the ABS is activated (well a heck of a lot better than I could before). A picture is worth a 1000 words so I won’t even attempt to explain in detail what happens. Email me for the pic since I can’t seem to post it.

It is also worth mentioning that the DUMP valves seals can fail and allow brake fluid to enter the accumulator. This IS VERY OFTEN confused with a failing MC since they give the same spongy pedal feeling.

I was just wondering if your vehicle has a brake proportioning valve like the older models before ABS was introduced? It's not too common for them to go bad, but any part could break after a while. This balances the pressure of the fluid in the front, and back.

With 4WABS the HCU controls proportioning under normal and ABS braking.
Please correct me if I am wrong.

Some vehicles used RABS, and had rear wheel cylinders. Do you have that or calipers? I know you mentioned that you have 4WABS.

He has 4wabs, and 4 wheel disc brakes. RABS were just for the 91-92 I think. I think that in 93-94 you could get 4wabs. 95+are all 4wabs, with 4 discs.

I was thinking that if he had rear wheel cylinders, the cylinder/s, and/or return springs might be bad.

I have never seen a modern vehicle without a proportioning valve. The factory proportioning valve in all vehicles is not called a proportioning valve.

As far as I know, all Ford vehicles have a combination valve, which contains the "proportioning valve." All vehicles need it, including ABS vehicles, because ABS does absolutely nothing under normal operation. ABS only functions when adequate pressure is applied to stop a wheel from turning. BTW, that is the cause of some ABS malfunctions; if you never use it, it becomes attriphied.

These later Ford vehicles have the proportioning valve function built into the master cylinders by design. Regards,

So where is the combination valve? Is it built into the MC or is it part of the HCU assembly. I would tend to think that it is integral to the dual outlet MC's. But then again it could just as esily be part of the HCU.. I dont know....

Do you have a repair manual, or CD of your vehicle? If not, maybe you could get a diagram from the dealer. They usually give you a free printout if you ask them (usually, but not always). I would also suggest downloading the Ford CD from WWW.Fordcds.Com.

I have a copy of Hanes, the Ford CD and a copy of Mitchel OnDemand. None go into the detail I am looking for. Its kinda like asking for the schematic of the Anti-theft (RAP) module. I can find out which wires plug into it but I cant see whats inside the box.

I think the only 2 options are to either get a copy of your brake system from the dealer, or just trace all of the steel brake lines until you find that proportioning valve. You could also call the dealer, and ask them how much one of them is. If they have one in stock, you could go there to take a look at it. It will give you an idea as what to look for.