Manager Forum

Tim I believe thiswas mentioned before but I didnt see you note it. I would remove the calipers and using a c-clamp lock the pistons and see what the pedal drop is. that would isolate the caliper from the bearings.

Jeff @ Able Auto wrote:Tim I believe thiswas mentioned before but I didnt see you note it. I would remove the calipers and using a c-clamp lock the pistons and see what the pedal drop is. that would isolate the caliper from the bearings.

Well, I have not tried that exact approach to isolating the calipers, but if I block off the hose going to the caliper, wouldn't that have the same purpose?
Again, today, we replaced the calipers and hoses.

Blocking the hose isolates it to that area. Clamping the caliper would indicate a loose bearing issue or any problem in the mountings. Hydraulic fault or mechanical fault. Think past the hydraulic side.

You say that either front line is opened and pedal goes to floor, correct? I've been looking around a bit and I'm seeing a lot about a specific brake bleeding procedure. I've been in and out but will try to get a better idea and report back later. It's a two step procedure. I looked it up by creating an order and opening the Mitchell Repair tab. It appears the ABS module needs to be functioning and that's where I would start. Good luck.

steven kiser wrote:You say that either front line is opened and pedal goes to floor, correct? I've been looking around a bit and I'm seeing a lot about a specific brake bleeding procedure. I've been in and out but will try to get a better idea and report back later. It's a two step procedure. I looked it up by creating an order and opening the Mitchell Repair tab. It appears the ABS module needs to be functioning and that's where I would start. Good luck.

I follow what you are saying but if this is only a rear wheel antilock brake system and the problem is on the front system where there is no anti lock function, why does the ABS module need to be functioning?

At this point i would look at the master cly again. When u have the lines clamped off there really is no where for the fluid to go. But when the system is open it still has to push the pads out. So if u have a problem in the master cly farther in the bore it would not show up when u clamp off the lines. I had this on a geo once.

I just deleted a long response so I'm going to downsize it. If there is any and I mean any air in the rear braking system the module will rear the pressure issue and release all pedal pressure until it lands on the brake default making the module apply pressure to the brakes. In the past I've had to pump a gallon or more through with the pressure bleeder trying to remove the air after cycling the module with my scanner. All it takes is just a little piss ant amount of air. You may be watching the bleeder and think you see a small hiccup. That's the amount of air that will screw with you and the brakes. I've had to deal with trucks that some Mamaluke added length to the pedal rod. All I'm saying is that it may take 5 or 6 cycling's to get the air or it may just be one. Good luck and be patient.

I'm gonna say you're problem is somewhere in the front. I wouldn't go back to the master cylinder. If you're clamping off the front brake lines and the issue goes away, all you've eliminated from the system is everything back from the brake lines. That leaves only the front calipers and mounting equipment/bearings. You've already replaced the calipers (hopefully you did the brackets and slide pins with them). I'd follow the advice to install c-clamps and go from there.

Ok. Got this truck back in today. Pulled all four wheels, went over every brake component to be sure everything was there, in the right place and functioning as it should. Checked the front wheel bearings - they are tight, as in no looseness whatsoever. So, we replaced the master cylinder with a new one from OEM. Guess what? No change. If anything, it is worse, in that the brake pedal fades to the floor faster than the previous one did. And, with this one, if I block off all the hoses at each wheel, the pedal still goes to the floor. Now we are really stumped and grasping for answers. Again, once the pedal goes to the floor, if it is released and immediately applied, there is a rock solid pedal that goes in about 2 inches. I'm about to admit defeat on this one.

If all the air is out of the system, I believe the RWAL valve is faulty. We had a bunch of those on Ford's back in the day. It's allowing fluid to bypass and causing the low pedal. The Fords had the same symptom of hitting the pedal again and it would be ok. I think the reason the symptom disappeared when you blocked off the front calipers is you created an unusual condition where the master cylinder didn't deploy enough to engage the secondary circuit. Someone else mentioned this too. With no fluid to the rear brakes the symptom could not occur. If memory serves me the valve was partially exposed on those Fords and you could physically hold it from moving and pressure would hold. Not sure on that as my brain is getting old.

In the instant case, with only rear wheel anti lock brakes, is there a way to test this small ABS valve without replacing it? I have thought of this valve as a possibility but with a cost of over $400.00, thats a little steep for gambling.

Will your scanner read the ABS functions?

steven kiser wrote:Will your scanner read the ABS functions?

It does, however it does not give me bidirectional controls for this application. There is no DTC's and what little is available on this elementary system is precious little. What might I be looking for?

Use a pressure tester.

brianp87 wrote:Use a pressure tester.

And what would I be looking for? I used to have brake system pressure tester but I sold it cause I hardly ever used it.

You can check the pressure at the rear to know if that is were you are losing it.

brianp87 wrote:You can check the pressure at the rear to know if that is were you are losing it.

In searching for a brake pressure number, I find none. Is there a specific number that should be there or do I simply look for a drop in pressure?

Tim Martin wrote:

brianp87 wrote:You can check the pressure at the rear to know if that is were you are losing it.

In searching for a brake pressure number, I find none. Is there a specific number that should be there or do I simply look for a drop in pressure?

Pressure drop. I have seen a 1999 that the rear brakes were barely working and it was the rear abs valve but no pedal issues. Not sure if it is the same brake system. We found it with the pressure testing the pressure was dropping.

Just ran it through one of my diagnostic services and everything points to the hydraulic control unit. Symptoms match, low pedal pump once and its fine.

Ok, got the truck back in the garage. Replaced the RWAL hydaulic unit. We now have a solid pedal and the brakes work fine. Strange that the issue is with the rear brakes system. However, now, after driving the truck, the amber C2202 (Original VIN Mismatch or Missing). Cannot erase code although one time I drive it and the light is out, next time it is on. Now what? If I try with my scan tool to write VIN, I get a message that VIN writing is not allowed. So now what?