Is there a way to trigger ABS actuator to combat spongy breakes? (1 Viewer)

[Bud_Dude]

Curious about all this ABS actuation to get any potential air out of it... It would seem that if actuating the ABS to purge air, that you would need to open the bleeders and pressurize the brake system while doing so in order for the air to have some place to go. Then proceed with a full bleed procedure to ensure you chase any dislodged air bubbles out to the end of each brake line. Seems like a pretty difficult task to bleed do all wheels at the same time. Perhaps a perfect application for speed bleeders though... Or am I missing something here?

 

[cartercd]

My understanding is that air accumulates in the ABS module and cannot be removed via the normal bleeding process. Activating the ABS gets the air out of the ABS module and into the rest of the brake system, where it can then be bled.

I had bled my brakes many times and my brake fluid was relatively clear. After activating the ABS module I saw a lot of dirty (dark) fluid come out when re-bleeding. I think that old brake fluid had been sitting in the ABS module for years.

 

[Bud_Dude]

My understanding is that air accumulates in the ABS module and cannot be removed via the normal bleeding process. Activating the ABS gets the air out of the ABS module and into the rest of the brake system, where it can then be bled.

I had bled my brakes many times and my brake fluid was relatively clear. After activating the ABS module I saw a lot of dirty (dark) fluid come out when re-bleeding. I think that old brake fluid had been sitting in the ABS module for years.

I hear you and will eventually try it here, but probably with speed bleeders installed... And I think exercising the ABS hardware is a good idea, but I remain unclear on why simply activating would dislodge the air or dirty fluid unless the brakes were free to bleed simultaneously. Generally speaking, with the brake system sealed, there is very little 'movement' or flow of brake fluid, applying the brakes mobilizes very little fluid and increases its pressure. Releasing the the brakes allows the small amount of fluid that 'moved' to retreat to its previous 'position'.

 

[bicycleagent003]

To those who bought and used the little vise-grips for their brake fittings, can you explain how/why that tool works better than a flare wrench with a cheater bar? I'm into having the right tool for the job, especially if it's only twelve bucks, I just can't picture why that tool is so helpful. Please enlighten me.
Thanks, and I mean this as a sincere question. I'm not being sarcastic or trying to poke fun at anyone, really just looking for some insight.

*** Edit to my own question: I bought those little Vise-Grips specifically for brake connections and they are indispensable. My rig has very little rust, but getting those brake fittings off is very tough, and flare wrenches want to spread open when you put much force on them. I replaced all my soft lines, and on two fittings in particular, I don't know what I would have done without those little Vise-Grips. Their small size is actually a big benefit because you are in tight quarters down there. It's money well spent, it might save you hours or more of frustration, busted knuckles and cursing. Just get the tool.

 

[smritte]

Curious about all this ABS actuation to get any potential air out of it... It would seem that if actuating the ABS to purge air, that you would need to open the bleeders and pressurize the brake system while doing so in order for the air to have some place to go. Then proceed with a full bleed procedure to ensure you chase any dislodged air bubbles out to the end of each brake line. Seems like a pretty difficult task to bleed do all wheels at the same time. Perhaps a perfect application for speed bleeders though... Or am I missing something here?

My understanding is that air accumulates in the ABS module and cannot be removed via the normal bleeding process. Activating the ABS gets the air out of the ABS module and into the rest of the brake system, where it can then be bled.

When I do ABS bleeding at work, almost all of the manufacturer's want you to install a pressure bleeder. With a scan tool installed, select the ABS bleed function and open whatever bleeder screw or screws it tells you to. On most cars the lines are in diagonal pairs (LF/RR). The scan tool fires off the pump for a few seconds and opens the dump valve. This allows the pump to pull the air from the chamber. next it closes the valve and the pressure bleeder pushes the air out. The pump is cycled on and off with the dump valve over about 60 seconds per line pair. Different manufactures have different combos of which lines to open when, but their all pretty much similar. I think ours is LF-RF- rears are tied together. Haven't looked it up in a long time though.
What their doing here is firing off the pump and valves without a scan tool.

What I haven't seen anyone post here was the symptom for a worn out dump valve. When you first drive your car (after starting) the pump and valves do a self test. This fires off the pump and opens/closes the valve's. Over time the sealing surface of the valves can wear. If you never change your fluid, acid build up will eat the seal also. The symptom is the same as a worn master cylinder or air you can't seem to get out. When you press on the brake, some of the fluid will go past the dump valve into the ABS chamber. In there is a spring loaded piston called an accumulator. This accumulator moves with the pressure. Now you have a spongy (squishy) pedal. The repair is replacing the ABS unit. I have seen this from 100k miles and up. It's not common but it's not uncommon. I've seen countless threads where people try everything to bleed the air and end up deleting the system. The general response was "you just didn't get the air out".

After the mid 60's brakes no longer magically had air appear in them (drum brake seal design). The only way you get air in is someone put it there. People still bleed the air out of brakes periodically because that's what they were taught. You should be changing the fluid completely (this also removes air). Most brake fluid manufacturers life span of DOT 3 is 2-3 years. That's when you flush the system replacing the fluid. The higher the DOT number or the higher the boiling point, the lower the lifespan. I run a synthetic DOT 4 and my lifespan is about a year. I replace mine before any acid build up can occur. The automotive lifespan is longer. They factor in a percentage of acid into their vehicle brake system lifespan. If you want to see the lifespan, read the brake fluid bottle. The best way to remove old fluid from an ABS chamber is by cycling the pump and valves while bleeding (flushing)

To those who bought and used the little vise-grips for their brake fittings, can you explain how/why that tool works better than a flare wrench with a cheater bar? I'm into having the right tool for the job, especially if it's only twelve bucks, I just can't picture why that tool is so helpful. Please enlighten me.
Thanks, and I mean this as a sincere question. I'm not being sarcastic or trying to poke fun at anyone, really just looking for some insight.

The fittings are soft and will somewhat seize. I've had brake line fittings so bad that I had to cut the brake line and put a 6 point socket on. Even then I thought it was going to shear. With the proper flair wrench, sometimes you can round them. Using good quality round jaw vice grips, the teeth tear into the metal, sometimes making it worse. For me, it's another tool to help with slightly rounded bolts.

 

[bicycleagent003]

Thanks for that, I appreciate your reply.
Another reason not to buy a rusty rig, I'm thinking. My rig has been in CA it's whole life, and I'm going to replace all the soft brake lines this summer.
Fingers crossed...

 

[Bud_Dude]

To those who bought and used the little vise-grips for their brake fittings, can you explain how/why that tool works better than a flare wrench with a cheater bar? I'm into having the right tool for the job, especially if it's only twelve bucks, I just can't picture why that tool is so helpful. Please enlighten me.
Thanks, and I mean this as a sincere question. I'm not being sarcastic or trying to poke fun at anyone, really just looking for some insight.

In my case the hex head of the bleeder valve on the load proportioning valves as extremely rusted. Initially I tried a flare wrench but no luck. So I went to a six point socket which got it to crack open and be able to be removed so I could put a little never-seize on the threads. However when it came time for the actual bleed process and the flare wrench still wouldn't work the little vice grip came to the rescue... It's just another tool in the box to try. Ultimately, I'll replace that bleeder with a new one.

 

[JeepinPete]

Any wrench has to have clearance to fit over a nut. Old rusty brake line fittings will likely be undersized, creating more clearance between the nut and the wrench. The vice grip pliers I posted locks down on the nut, no clearance. It really does work wonders on these things.

 

[Toph]

I was recently doing the same thing on my '97 80 series LC up on four jack stands in an attempt to document the speed sensor pulses per mile output. Same thing happened, with the truck at idle I put it in gear and the wheels started spinning when I released the brake. When applying the brake to stop the wheels and place it back in Park the ABS went crazy and made wild growling sounds and vibrations. I reckon this happened because with the wheels in the air (therefore not locked to the ground) and with one or more wheels able to slow at a different rate than the others (probably due to variations in brake disk friction) when the ABS sensed different rates from different wheels it went into action. Actually, it seemed like a good test of the ABS system in terms of confirming it really worked in terms of detecting a wheels stopping at different rates.

Now, how to use all this info as part of the brake bleed process? I'm not so sure... Do you really want to be around a spinning wheel or tire and trying to open a bleeder valve? Seems like it's getting in the danger zone a bit there. Were you successful in doing this?

I'm fixing to install a set of Slee stainless steel brake hoses in a day or three here and have been considering how to do the best brake flush and bleed I can when done.

yup.
bleed, actuate, bleed.
I wouldn't be caught dead next to those wheels while running

 

[kenavt]

Wyatt Pine - sorry did not see your request in post #29 until today. Below is how I activated my ABS. I did this several times in short bursts (5 secs) and then bled.

I manually ran my ABS actuators today, to flush out the remaining fluid and air, to try and get rid of my soft pedal. Unfortunately my pedal is still soft after bleeding at all five points, so my hunt for bubbles will continue. But I did it a bit differently then @cartercd based on the FSM. It looks to me that you want to attach +12V to the same pins he indicated, but on the six-pin connector actually connect pins 1, 3, 4 to ground (not 1, 2, 3).

Pin 1 is "SPR" which I figure is "right" as in front right
Pin 2 is "AST", which is shown as being a solenoid in the overall vehicle wiring diagram below. But the ABS-specific wiring diagram shows "AST" with a resistor. I did not close the circuit on this pin... not sure what it is. Does anyone know what it is?
Pin 3 is "SRR" which I figure is "rear"
Pin 4 is "SPL" which I figure is "left" as in front left

 

[kenavt]

Finally answered my own question by finding this random Lexus technical training doc on ABS for vehicles of the era (notably not the LC/LX): the AST pin is a status pin. If the ECU sees abnormal voltages at that pin, it will throw error codes (described in the FSM). So not needed for jumping the ABS actuator.

http://www.autoshop101.com/forms/brake10.pdf

 

[jpoole]

@kenavt

What would you change about this connection strategy after your recent reading?

 

[kenavt]

@kenavt

What would you change about this connection strategy after your recent reading?
View attachment 3476689

I don’t know what you’re getting at here… so here’s a couple of attempts:

• I didn’t mention this, but I was also running the pump on the 4-pin connector.
• The correction I had was the difference between the words and drawing in the original picture: the drawing shows 6-pin connector pins 1,2,3 shorted to GND, but the text says pins 1,3,4 (which I think is right).

 

[jpoole]

Thanks @kenavt

I was trying to tie your recent observations back to the images from @cartercd that he shared in post #19 and #35 in this thread. I've used the post #35 image to actuate the ABS pump on my '97 80 during a brake fluid flush with good results. I'm up to changing the approach if there is more/better info available but I'm not sure that your observations indicate a change of approach for the goal of activating ABS while flushing brake fluid. Given the overall focus of the thread I thought I'd ask for a little clarification.

 

[Malleus]

LEAK.. yikes.. that would be ticky on the trail!

So I got under there with two vise grips, which gave me more control. By pulling very hard as I twisted I pulled it off. Like I thought, the flare nut lip had rolled. No doubt from being over torquing at the factory. Funny I can't find a torque spec, in any FSM hard cory or TIS for these brake hose to pipe flare connection. I only find pipe flare to master spec of 11ft-lbf.

Flare nut end was rolled (enlarge) and hung up in female end, it also was cracked. The male flare nut, deposited metal into threads of female end. So I cut off tip and re-flared the pipe with a new flare nut in place.
View attachment 1693458 View attachment 1693460 View attachment 1693459
I didn't like the looks of my first flare so cut off and did a second. Any more cut off and I'd not gotten flare tool on, due to bend.
View attachment 1693461
New SS braided brake hose installed with aftermarket flare nut.
View attachment 1693462

After I've bleed and confirmed no leaks, I'll paint pipe and grease to protect from rusting where I damage paint.

Thanks @kenavt

I was trying to tie your recent observations back to the images from @cartercd that he shared in post #19 and #35 in this thread. I've used the post #35 image to actuate the ABS pump on my '97 80 during a brake fluid flush with good results. I'm up to changing the approach if there is more/better info available but I'm not sure that your observations indicate a change of approach for the goal of activating ABS while flushing brake fluid. Given the overall focus of the thread I thought I'd ask for a little clarification.

Did you flush the ABS into a container, or into the closed brake system?

 

[jpoole]

Hey @Malleus

I wasn't sure what would be best so I did it a few different ways. Here's a summary of my brake fluid change process:

• fill the garden sprayer based flush tool with brake fluid, connect to master cylinder reservoir and pressurize to 20psi
• open bleeder ports one at a time and while open give the brake pedal a few pumps to have "higher flow" bleeding moments
• after all 4 wheels and lspv are running clean run the remaining new fluid out of the flush tool reservoir by loosening each fitting on the ABS system that sits atop the driver front wheel well. I rinse the area regularly with water when I bleed these line fittings so that brake fluid doesn't stay on paint/etc.

This year I added ABS pump actuation per the photo above in a few different places. After running brake fluid through the front, driver caliper bleeder until clean I then closed all bleeders and ran the pump for 6 seconds and moved to the rear wheels/lspv. I ran the abs pump for 6 seconds in between changing from one bleeder to another since I go check the flush tool pressure and keep it at 20 psi between bleeder changes anyway. A few times I also ran the ABS pump for 6 seconds while a bleeder port was open and fluid was being pushed out of the bleeder port.

I wasn't setup to observe if dirty fluid came out after the ABS pump was run and I don't know if my approach above is ideal, it's just where I've landed after doing this every few years (and multiple times after changing brake components). In the past I would activate ABS on gravel before/after brake fluid flushes so I don't think the fluid was super old though it does seem like a little air may have been knocked out of the system this last fluid flush, that previous flushes without running the ABS had not gotten. Of course, running the ABS pump may not have made a difference and/or there may have been a better way to do it. It was an easy addition to the whole process though and I don't think it hurt anything.

I've flushed the brakes on my 80 many times at this point and have changed all parts of the system out, except the hard lines, in the last few years and the brakes felt a little better after this last flush than they had previously. No other changes were made during the last flush besides the fluid change process listed above.

 

[Malleus]

Good to know. Thanks.

I have just changed the fluid in my son's 80 and am planning to do the same to mine. We also used the brake pedal flush method to get the fluid out faster. It worked well for us. What didn't work well was that since I was manipulating bleed screws and couldn't watch the brake master cylinder reservoir, it ran dry, so we had to bench bleed it.

This is one of the few areas I was disappointed in the FSM writers. Using bleed screws and hoses from the Napa kit is far less messy. There's just no way to follow the FSM and not wash the fender and intake with brake fluid. What irked me about that kit was that there's only one of each size fitting in the kit, so you have to buy two.

I wrote all that to say I was hoping to catch the ABS fluid using those same fittings, and was curious if you had done something similar. It would obviously require a source of fluid, since the ABS pump would be disconnected from the brake master cylinder.

I didn't want to flush the fluid and then contaminate it with the old fluid from the ABS pump.

 

[jpoole]

Unless required I would not want to isolate the ABS pump or do anything to introduce air into the system, ever. I only open bleeders or line fittings when there is plenty of fluid and pressure on the system (I keep it around 20 psi). I also don't bleed/flush with the brake pedal primarily and instead the pressurized feed bottle connected to the master reservoir does most of the work. I only pump the brakes a few times per bleeder to surge fluid out and push extra debris/bubbles (possibly).

Given how much it can take to bleed these things I think it's a bad idea to remove the ABS pump for flushing unless you already have the system open at that point. It seems to me like fluid will circulate in/out of the abs pump via attached lines one way or another so simply operating the ABS pump while fluid is already being pushed through the system seems like it could be "good enough" without necessarily being perfect. This is why I bumped the ABS pump for 6 seconds as I worked through the 5 different bleeder ports (but after at least having clean fluid to a front and rear wheel circuit) since each different circuit being opened may influence where fluid goes when the pump cycles. This seemed to be the easiest way to hopefully flush stuff out of the ABS side of the system without actually learning how the system works in more detail or developing a perfect plan.

I share all of that to open my process up to criticism too, especially if there are ideas for ways to make the process easier.

 

[Malleus]

It baffles me how difficult the brake system is on this truck. It's the only Land Cruiser I have problems with; none of the other models have the problems the 80 series has.

The system was open at one time, when they were installed on the line, so emptying any given component shouldn't be any different. It's essentially what happens when you replace a caliper. Yes, I realize they had a pressurized system for filling, but it's really no different than the ones we use to perform maintenance.

 

[jpoole]

Yeah, I agree on that. Granted, once all is well it stays that way and a fluid change following my process above is quick, easy and clean.

I've considered studying the system more closely to see if I could figure out why it's hard to bleed but haven't as it seems unlikely that it would change much about my current bleed process since I don't want to modify the system from stock.