Bled the brakes at 293,957 miles

[FAST4DR]

I intend to perform a second bleed after I have cycled the ABS during our recent rains.

I don't think cycling the ABS pump while driving moves any attributable amount of fluid out of the ABS pump. You need the electronic box that opens the abs valves and keeps them open as you bleed your brakes.

Talked about in this thread.

Will

 

[sdpatt]

Will (FAST4DR), I agree with your statement about the ABS cycling having little effect on moving fluid in the system. On the other hand, The boiling point protection is provided by the new fluid in the calipers. It is the moisture in the old fluid in the ABS pump that is the problem as a corrosion risk to the ABS components.

 

[rangerj]

Just some additional thoughts:

Fast4door is correct. Just cycling the ABS will not "flush" the old brake fluid. The ABS has to be "set" in the mode for bleeding, and then bled in order to get fresh fluid into its components. It is also correct that the brake fluid will absorb moisture through the plastic resevoir over time, as it will through a plastic container.

So, if you are going to store brake fluid, store it in a metal container that is sealed. All one has to do is look inside a caliper or brake wheel cylinder and see the rust to confirm this. (Back in the stone age we used to rebuild wheel cylinders by honing them to remove the pits caused by rust.)

When changing brake fluid buy enough to do the job and avoid storage.

Most "off the shelf" Dot 4 fluid has sufficient heat ranges for normal driving conditions. If your driving conditions include towing, mountanous driving, or a lot of heavy breaking, then higher boiling point brake fluid is recommended.
Note: Road course and other forms of racing, where continuous heavy braking and high temperatures are a factor, requires special brake fluid made for this purpose.

If you store you car for the winter, unless it is stored in a temperature and humidity controlled envoronment, its brake fluid has more opportunity to absorb moisture. So, a brake fluid change should be done more frequently.

The SHO Times web site has a good discussion about brake fluids.

From what I have read it only takes 4% moisture in your brake fluid to render it useless. Food for thought. rangerj

 

[sdpatt]

From what I have read it only takes 4% moisture in your brake fluid to render it useless. Food for thought. rangerj

You eat your old brake fluid?

 

[FordLover]

I typically open the bleeder on the caliper as I push the piston back in. I've heard there could be potential problems when crap/debris in the brake lines are forced back thru the ABS valves. I don't think this would be a problem in Scott's car, since the system had never been opened, but I would think better safe than replacing expensive ABS parts. On my explorer without ABS, I'll not open the bleeder, but on my SHO's I always did, and never had any ABS problems. The calipers are the lowest part in the brake system, so it would be reasonable that eventually any trash in the system would end up in the caliper.
-Martin

 

[sdpatt]

I followed up on my suggestion about a poor man's speed bleeder. I priced the speed bleeder valve products at the local auto parts stores and then examined the cost of a single check valve that I could install in the tubing at each valve that I bleed. The $3 check valve provided all of the benefits of the speed bleeders without the expense.

Since you need to (should) attach a hose to the bleed valve when bleeding a caliper, why not just have the check valve in the hose itself? With the check valve adjacent to the bleed valve, it should provide the same function as the ball bearing check valves in the speed bleeders.

 

[djsSHO]

I need to get out of New York. :cuss:

When I bled my system a year ago with 110k on the clock the fluid had already become a very dark brown color. That honey color is just amazing.

Not to mention the fact that my calipers stopped looking new after 1 winter around here. I paint them just so it's one less thing that can rust off in the winter.

Well, back to replacing broken parts......

 

[Off Road SHO]

You eat your old brake fluid?

:laugh_ti:

 

[TimboSHO]

Incredible! I just can't imagine going that long without replacing lines, master cylinder, calipers, etc.... much less leaving the fluid in there that long. That is simply amazing. I wish my car could have spent most of it's life down there....

 

[rangerj]

Old brake fluid makes an excellent gravy to go with crow!

 

[TimZ]

Fast4door is correct. Just cycling the ABS will not "flush" the old brake fluid. The ABS has to be "set" in the mode for bleeding, and then bled in order to get fresh fluid into its components.

While it is easier and more effective to do the bleed with the proper diagnostic controller, cycling the ABS can and will shuttle the old fluid out of the HCU. The main difference with using the diagnostic tool is that it guarantees that you have cycled the build and dump valves for all four wheels. If you want to acheive this with an ABS stop, you will need to do it several times, and each time it needs to be a high effort ABS stop, so that you are more likely to get ABS action at all of the wheels and you will be moving more fluid through each valve.

 

[rangerj]

Timz,

When you "shuttle the old fluid" out of the HCU (ABS), where is it shuttled to? Where does the fluid go? Does the brake fluid circulate?

Assuming the disk brake pads are within a few thousanths of an inch away from the disk, how much fluid is actually going to move, and how far does it move?

Granted, the fluid moves over time as the disk pads wear, but this may take several years. So, how many "high effort" ABS stops will it take to refresh the fluid in the ABS components, and how many years will it take before the fluid is completely refreshed in the ABS.

I'm not trying to be a wise guy. In fact I agree with you. Cycling the ABS is a good thing. It helps prevent the pistons and valves in the unit from freezing up. It also will at least mix some of the new fluid with the old.

There is a chance that when the brakes are bled that at least one of the ABS pistons or valves are open and fluid will flow through in the bleeding process.

Again, I am not intending to be disrespectful to you. I usually try to recommend the "best practice", or the OEM specified practice or procedure. But, as you surely know, there are always alternative ways to accomplish the same task. The above is mostly intended for the less experienced. rangerj

 

[TimZ]

Timz,

When you "shuttle the old fluid" out of the HCU (ABS), where is it shuttled to? Where does the fluid go? Does the brake fluid circulate?

Assuming the disk brake pads are within a few thousanths of an inch away from the disk, how much fluid is actually going to move, and how far does it move?

Granted, the fluid moves over time as the disk pads wear, but this may take several years. So, how many "high effort" ABS stops will it take to refresh the fluid in the ABS components, and how many years will it take before the fluid is completely refreshed in the ABS.

I'm not trying to be a wise guy. In fact I agree with you. Cycling the ABS is a good thing. It helps prevent the pistons and valves in the unit from freezing up. It also will at least mix some of the new fluid with the old.

There is a chance that when the brakes are bled that at least one of the ABS pistons or valves are open and fluid will flow through in the bleeding process.

Again, I am not intending to be disrespectful to you. I usually try to recommend the "best practice", or the OEM specified practice or procedure. But, as you surely know, there are always alternative ways to accomplish the same task. The above is mostly intended for the less experienced. rangerj

No offense taken, rangerj. It's an interesting subject, and I don't mind explaining my statements further. I do appreciate the civil discourse.

The main purpose for doing the ABS stops is to move the fluid that was trapped in the HCU behind the control valves back into the main hydraulic system, where it can then be flushed out with a conventional bleed. During an ABS stop, you will move more than enough fluid to accomplish this. The passages in the HCU that we are talking about here are not more than an inch or two long. This is the same thing that the diagnostic tool does.

You are moving more than the amount of fluid that it takes to back the pads off a few thousanths of an inch when the ABS is cycling. The build and dump valves actually operate as a pressure regulator for each caliper, in much the same way as the fuel pressure regulator operates in you EFI system. The build valve lets fluid in from the pump/master cylinder. When the pressure gets high enough that the wheel locks, the dump valve opens until it starts to spin again. This process repeats over and over very quickly during the entire stop (i.e., it's not a one-shot affair). This is what all of the brake pedal pulsations are from.

Just to put this into perspective, the pump's job in the ABS system is to maintain system pressure though all of this. If the pump were not in the system, you could still have ABS function from the master cylinder pressure alone, but the amount of fluid that is moved during the stop would cause the pedal to go to the floor, usually before the stop is over. That should give you a rough idea of how much fluid is moved.

Clearly, you will need to re-bleed after the ABS stops to clear the fluid out again.

As to how many you should do, I'd SWAG that somewhere in the neighborhood of 5 stops should be enough. It would be best to do this on a wet/slippery surface, just to keep the wear and tear on the tires down. Obviously you should pick a safe place to do this, also.

 

[rangerj]

TIMZ,

YES! Thanks. This is indeed what this forum is all about, i.e. the learning process regarding the various systems. Your explanation is greatly appreciated. rangerj

 

[sdpatt]

Well, I believe that I have adequately cycled the ABS pump on my car. Last weekend, the Lone Star SHO Club (LSSHOC) had the annual Winter Run on Saturday and a visit to the MotorSport Ranch (MSR) on Sunday. I didn't use the ABS on Saturday (that poor cat wish I had at 100 mph), but the many trips around the 1.7-mile, 11-turn MSR road course on Sunday allowed for dozens of ABS-assisted stops on racing tarmac.

When I get a chance, I will perform the feed and bleed operation again to purge another quart of fluid.

I still find it amazing with all the discussion of brake upgrades that the OEM system on the Gen I can still spend 20-minute sessions racing near the limits of acceleration, cornering and braking traction. The tires are the limiting factor on the road race course as the speeds were limited by the ultimate traction with the road. The little 10.2 inch rotors and Performance Friction Carbon Metallic pads were able to easily inflict ABS even at the end of the 20-minute open sessions.

Fade was not a problem, but deposition of carbon on the rotors caused brake pulsations during the (slightly) milder lead and follow laps. With the heavier usage during the subsequent open sessions, the brakes smoothed out and worked well when hot.

I had sanded the front rotor's surface about a week before the event and had apparently failed to adequately bed the pads and rotors before the heavy use event. It is quite important to properly embed the carbon pad material into the rotor's surface with easier application before race conditions are attempted. Lesson learned. Joy ensued.

In first two images below, I am ready for my group's turn on the track. I passed that red Vette, but only because he had traction problems and could not hang in the corners with speed. The thrid image is a partial of the cars lined up in preparation for the day on the track. We had 27 cars participating.

 

[k_mesaros]

All my tech school training material says that the proper term is Hygroscopic. I have also read a lot about DOT 3 and DOT 4 brake fluids. DOT 4 does have a higher boiling point, UNTIL it absorbs any amount of water, then it degrades much quicker than the DOT 3.

 

[k_mesaros]

Ok, here are some numbers.

Boiling point minimum when dry: 3=401 f 4=446 f
Moisture absorption rate after 18 months= 3% (DOT 4 is a little slower, but nobody has numbers with regards to how much)
Boiling point with 3% moisture contamination: 3=301 f 4=223 f
that is a 25% drop for DOT 3 and a 50% drop for DOT 4
Flash point: 3=272 f 4=250 f

Kevin

 

[rangerj]

Kevin,

Thank you. I think you make the point for refreshing brake fluid every few years, or so, say something less than every 14 years .

As for the correct technical term for brake fluid absorbing moisture, Hygroscopic vrs. hydroscopic, the issue is still being debated among the organic chemistry folks, and the chemical engineering folks.

The several engineers and chemists I have spoken with, who are long time experienced folks working in the field of automotive chemicals, say that the argument is like the one concerning the pronunciation of the word tomato. Is it pronounced tow-maw-tow, or tow may-tow?

The majority opinion says hygroscopic is correct.

It is also recommended that the ABS be activated periodically to prevent the internal components from siezing. So, if you store your SHO it would be advisable to activate the ABS before storage, and immediatly after you bring it out in the spring. It would not hurt to activate it at least once a month when it is not in storage. rangerj

 

[platoribs]

With all the snow we've gotten here in the great white north, cycling the ABS has become routine instead of the exception.

Scott, I assume your haven't experienced the dreaded rear brake line keeper squashing that causes the rear brakes to hang on after releasing the calipre?

Might be something to check, however it's mostly for us poor salted street SHOwners.


Your fine specimine really should be featured on some follow up story about SHO's. Not only did it deliver the goods in 1989, but 300,000 miles later it's still spanking the new LS and others too. Congratulations!

 

[sdpatt]

I have experienced a rear brake caliper hanging only after the torn slider pin boot allowed the pin to rust. I have inspected the boots more often since that occurence back when my car was still a young pup.

No, the brakes are working quite well. Even after the fast weekend with the Winter Run and MotorSport Ranch. The embedded carbon has been brushed away by normal brake usage and the brakes are still smooth and strong with no warpage in evidence.

I will use my home-made speed bleeder as soon as I can get a few spare minutes. I haven't even had time to take some used oil to AutoZone for recycling.

I want the '96 upgrade, but I still can't financially justify the need to my (thankfully) very money-conscious (non-working) wife.