'94 ABS problem

[cyazee]

120k on pushrod XLT. Intermittant ABS light on about 2 weeks . Got a scan tools that does ABS.. It showed 3 codes for right front sensor.. Took the rotor off, fins inside rotor and sensor were very dirty. I cleaned them and went to Boston, no problems.
On the way back intermittant abs light ,right wheel heats up caused by caliper not releasing. Put new caliper, brake line, set of pads (old one were burned)on front. Bled fronts, on my merry way.
20 miles later same lockup is happening. R/f wheel is hotter than left, left is hot, both calipers are not releasing.
Spoke to mechanic he states abs is problem. I removed the two cube ABS relays and two ABS 30 amp fuses from power box and drive.. Calipers are released, wheels cool and "ABS" light in dash on.Mechanic says brake fluid is very dark.
The XLT is running good save abs. What should I do?

 

[dogfriend]

I was looking at my factory manual for 97.

They have a symptom chart for ABS problems. If one wheel locks without the others (similar but not exactly your problem) you should first verify that there are no kinks or restrictions in the brake line going to that wheel. If that is okay, they have two tests to determine if HCU (hydraulic control unit) is the problem. Both tests require a breakout box to monitor voltages sent to HCU. So, it is very possible that your mechanic is correct.

Looking at the description of the system, it uses solenoids to control pressure applied to each wheel. Normally solenoids are open to allow master cylinder pressure to reach each wheel. If locking (or potential locking) is detected, the solenoid (s) close to block pressure from master cylinder. If sensors detect that wheel is now moving, the solenoid opens again to allow master cylinder pressure.

Total speculation: If the solenoid for right front were partially sticking, it may not release pressure when it should. The solenoid is part of the HCU.

I would double check the caliper you replaced to make sure it is okay and all brake lines on that side are okay. Check to make sure that the caliper pins are lubed and the caliper slides correctly. If all this is okay, then it is probably the HCU. I don't know if the wrecking yard would sell this (liability) but I can imagine that it is $$$ from the dealer.

Only you can decide if it is worth the risk to run without ABS. I probably wouldn't. You can always get more money, but you only have one life.

 

[VOATMJ1]

Originally posted by dogfriend
Only you can decide if it is worth the risk to run without ABS. I probably wouldn't. You can always get more money, but you only have one life.

I find that living in Iowa in winter, that my ABS does more antilocking than braking, in both my Caddy and my Sport 4x4.

True enough, ABS is far superior in rain, gravel, dry pavement, etc, but snow/ice????? I wonder.

 

[94EBexplorer]

screw it leave the fuse out... first gen x ABS sucks!!!!

 

[dogfriend]

just my opinion

like I said, he has to decide for himself

my system works well, I've never had a problem with it.

I drove an Aerostar on ice with ABS and I almost hit the car in front at 1mph because the brakes wouldn't engage

Another time in a rental, ABS saved me from broadsiding a 16 yr old who pulled in front of me without looking

I think in general you are better off with it because you maintain steering control in a panic stop if the system is working correctly.

But that's just my opinion.

The only other issue to consider is if the brake system will continue to work correctly because the HCU is still plumbed into the brake line but is not getting power. I don't think this is a problem, but there could be some effect on braking performance compared to a system which doesn't have a non-functional HCU.

Oh yeah, I would have the brakes bled in either case because the dark color is an indication that the fluid has absorbed moisture and it can reduce performance and cause corrosion of the brake system.

 

[JWood]

Break fluid flush maybe...

could be some sludge build up in the fluid if it's real old, hampering the calipers a bit...just a thought.

 

[dogfriend]

Re: Break fluid flush maybe...

Originally posted by JWood
could be some sludge build up in the fluid if it's real old, hampering the calipers a bit...just a thought.

Yeah, I second this. It might fix your problem, but even if it doesn't you need to replace that old brake fluid anyway.

 

[Rhett]

What is the best way to change brake fluid? Use a turkey baster to suck out the old fluid at the reservoir?

 

[JWood]

I'm not sure about the

"do it yourself" way, but shops charge $50 - $75 for the service. It takes them about on hour or so, but they drain the whole system - master cylinder and all. I think there are several different places they have to drain from.

 

[dogfriend]

newer way

I think the best way to bleed is to use a pressure bleeder which attaches to the master cylinder and forces the old fluid out of the system thru the wheel bleeder screws. This way theoretically avoids getting any air in the system. I have not done it this way myself (don't have the bleeder)

This is an example, but I haven't used it http://www.ontool.com/store/product/10403 There are also cheaper alternatives for home use http://www.ontool.com/store/product/21181

The other method (besides the two person pump the brake pedal) is to use a hand vacuum pump to draw fluid from the bleeder screws on each wheel. I have done it this way, and it does work but it is difficult to avoid sucking some air thru the threads of the bleeder screws (you are supposed to apply silicone grease to avoid this but it didn't work for me) You can get the old fluid out this way, then have a helper pump the pedal to get the air out at the wheel cylinders/ caliper.

If you have a newer Explorer with ABS, be careful. The Haynes and Chilton manuals warn that if you get air in the HCU (hyd control unit) you will need to hook up a special scan tool to bleed the system. It is not clear to me whether you can do a normal system bleed without the scan tool; I am trying to research this now because I would like to replace the fluid in my truck now with 80k miles.