Better Brakes bleeding, Actuate the ABS

[rhyary]

The topic of brake pedal feel, proper bleeding procedure and quality of brakes have been discussed many times. But I would like to add this observation as it rarely been done under controlled environment.

The gist of this post to let you know that, in my experience and observation, activated the ABS after working on the brakes is essential.

I would further say that once in a while activating the ABS is a good and essential preventive maintenance since it circulate brake fluid through a circuit that is not often used. This is an assumption and observation. I don't have a hard fact about how it works. But it makes sense logically. So I like it.

Recently Landtank worked on my brakes. He replaced most of the hard lines and the master cylinder. Completely flushed all the brake fluid and properly bled the brake system. For point of reference my rotors and pads are in excellent shape. I rebuilt the calipers about two years a go. The rear rotors are not in new shape, but the front are new this summer.

So, when Landtank finished his work the brakes were good, with minor improvement. It was mostly preventive maintenance and my brakes were fine before he worked on the car (at idle the brake pedal sank a bit to the floor but not all way and that behavior was fixed)

After about two weeks it finally snowed in Albany. We had almost no snow this year but we now had a nice slippery 1" coating on the road. It was an excellent opportunity to activate the ABS. I can't activate the ABS on dry pavement.

I made few 30mph to a stop runs. The next day I made few more. Conditions were such that I was able to activate the ABS on a long slide and I did it on multiple runs.

The brakes have dramatically improved. The truck now stop as good as it should. The difference is not only that it stop so well, there is a good brake feel. Meaning the brake pedal is applying the brakes in a very linear fashion. The brakes are responding correctly from light pressure (slowing down) all the way to a hard stop.

So my recommendations are to somehow activate the ABS once in a while.

Hope this helps

Rami

 

[Ebag333]

Good post. Thanks for the details.

This is the second post where I've seen someone mention activating the ABS system and improving the brakes.

Did you bleed the system after you activated ABS?

 

[rhyary]

No. It is perfect now.
And, even I don't mess with perfect!

 

[scrowley]

Last snow storm here in ct. I drove around activating the abs....a lot. Pulled right in the garage and bled the brakes with a helper (pump, hold method) This made the MOST improvement on my brakes after countless hours troubleshooting, replacing parts, and even taking to the dealer!...As well as one other master mechanic shop. Overall I think this method is a must if a spongy pedal is present and brake bleeding is taking forever. I couldnt do it until the snow came because there is no dirt roads right around the corner. I pretty much slid into the garage activating the abs then bled them.

 

[excessive]

Theres got to be a way to activate the ABS through the OBDII interface

 

[86tuning]

You can easily activate the abs when driving if you put two tires onto a gravel shoulder and hit the brakes. Then repeat with the other side.

 

[UWdave]

Not sure if you need the wheels & tires mounted, but this sure exercised my ABS.

I was doing a gear break-in and had the front and rear axles in the air. I put it in drive and let the wheels spin. I can't remember the speed I spun at, but it required some throttle to achieve. Once I was done, I hit the brakes to slow down the tires. ABS kicked in like crazy. The tires wouldn't stop. In a slight panic I just turned the engine off. Neutral would have also done the trick.

It was a little scary spinning the tires in the air. I was on a perfectly flat driveway with 4 big jack stands.

 

[LINUS]

Theres got to be a way to activate the ABS through the OBDII interface

IDK how much activation you need to get things excercised - I live in WA where it snows at least a little every winter & so I get to go hit 'em and bounce the brake pedal/activate the ABS either there or on a wet road - the one thing I learned was that my Griot's Garage pnuematic vacuum brake bleeder was invaluable when pulling through some new fluid - I hear it's a PITA if you dran the system dry then introduce fluid as the ABS hardlines end up trapping air & you need to crack the unions to get all the air out that ends up at that .

Using a tool that pulls fluid seems like the best way to get through a brake fluid changeout without causing yourself the headaches of bleeding air out of the ABS unit & hardlines.

Seems like the easiest way to cycle the ABS is to just go out & slam the brakes on a wet/slick road & see where the overall health of your brakes are - just my real world way of seeing what the situation is.

 

[junbug64]

I just recently replaced calipers, rotors, pads, and rebuilt the entire front axle. I bled the brakes before driving. Brakes were a lot better, but I noticed after teaching my daughter how to drive in snow, how much better they are even after bleeding. I wanted her to know what the LC would do if she had to panic stop. So we got up to 30mph on a packed down snow covered road and told her to slam on the brakes. She was scared of the noises she heard the LC make but the ABS functioned very good and it came to a stop in a straight line. We then found an empty parking lot, and I asked her to do the same thing but this time turning slightly to the right, then teaching her how to compensate to not let the rear come around. She did great and so did the LC. The next day, after the roads were cleared, I noticed the brakes functioned so much better even during normal braking. After reading this thread, I agree after bleeding the brakes, another good way to help improve the brakes is to actuate the ABS. I don't know how the brakes adjusted or if more air is bled by actuating the ABS, but it did improve.


Now to work on the exhaust, valve cover gasket, and power steering cooler leaks. Then let my daughter use it for her short commute to school.

----------
'93 Green, 2"OME lift, 315 Kumhos with stock gears, 204,xxx miles

 

[Tools R Us]

Just drive a dirt road. On the wheeling trip last weekend I didn't lock the center, the ABS was banging away all day.

 

[Ebag333]

After reading this thread, I agree after bleeding the brakes, another good way to help improve the brakes is to actuate the ABS. I don't know how the brakes adjusted or if more air is bled by actuating the ABS, but it did improve.

The way air bubbles work, a large bubble will compress a large amount, but the same amount of air distributed and broken up won't compress as much.

If there is air in the ABS system, it's likely collected into a large bubble as the ABS system isn't used much, is a high point in the braking system, so will collect air but air won't be moved out of it.

Once you activate ABS, you're breaking up that bubble into small bits and distributing it though your brake lines. This improves your braking feel, but doesn't eliminate the problem.

I think that bleeding during or after activating ABS is the key here, which matches with what Toyota (and other manufacturers) say to do with other vehicles that have similar ABS systems when bleeding brakes. Activating ABS gets the air bubble out of the ABS system...but not out of the brake lines. I bet if you activated ABS a bunch and then bled, you'd be surprised at how much air is in your lines (even if you just bled).

 

[86tuning]

Pumping the brake pedal will ebb the brake fluid back and forth will move bubbles to the highest point and trap them.
1 brake master
2 abs pump/accumulator
3 lspv

Activating the abs will discharge fluid from the accumulator back into the brake system. Bubbles near the accumulator could also be pushed back up into the brake master and then out of the system.

On cars with spongy brakes the first thing we look for is taper worn pads and seized calipers, then air in the hydraulics. The trick is to find all the air in the system. And prevent introduction of air into the system when the hydraulics are opened up.

 

[Stevesnj]

Bought new rotors, pads, caliper rebuild kit and found this Pneumatic bleeder for $30. It should pull fluid out from the ABS system too. I think I should have awesome brakes after all this!

 

[SUMOTOY]

ABS Brake bleeding

I go through a couple gallons of brake fluid a month, mostly bleeding german cars. The newer (2000>) cars actually have an OBD access to activate the ABS solenoids to get the bubbles out. This is done while using a pressure bleeder. In the new cars I use 2 bar pressure and several liters to get entrapped air out out of the ABS controller.

Vacuum bleeders aren't used as often as pressure bleeders. IME with vacuum bleeders, they can actually cause more braking problems than they solve. In lieu of a pressure bleeder, the best way to release entrapped air is to activate the abs on low cf conditions, then rebleed. ABS is not an 'unused' circuit, it is part of the hydraulic system - you bleed your brakes, by definition, you bleed the ABS circuit.

Trapped air in the ABS solenoid is usually caused by the ABS pintle valves tendency to trap and hold air bubbles. Cycling these pintle valves releases the bubbles, allowing the air to be bled thru the bleeder screws.

A couple of tips I found helpful when working on 80 brakes. First, don't let the fluid go dry in the reservoir. Second, allow the brakes to gravity bleed first, as this reduces the risk of air bubbles sticking in the ABS pintles valves. If pedal is still spongy, drive to a grassy knoll and activate the ABS. Once the bubbles are released from the pintles, they will bleed pretty easily.

Lastly, if replacing the brake master, bench bleed it first, then fill the reservoir and crack open the lines at the master before the ABS solenoid. This reduces the chance of sending bubbles to the ABS solenoid from the get-go.

HTH and my .02

Scott J

 

[PoorHouse]

After reading this I was curious to try it as my truck just got new rotors, caliper rebuilds and new fluid.
Mechanic uses a pressure bleeder. My brake pedal has always felt good and there was no change after the brake work.

Cycled the abs a few times on our icy driveway last night. Pedal feels the same as before.
Maybe as ebag pointed out if you have a large bubble trapped activating the abs breaks it up into smaller bubbles giving a firmer pedal, if no air is in the system, no change.

 

[Itchy Sides]

Subscribed, with thanks!

 

[warpdriv]

Is there a way to activate the ABS without having to drive it? Maybe activating it by jumping a connection...

 

[Itchy Sides]

^ That was asked in another thread, IIRC. And, no, not on our 80's, unlike some newer cars. Would be convenient!

 

[Hoosier Daddy]

Actually, it is possible, and I've done it.

Unfortunately this was a while back and I don't remember the exact process. It involved studying the wiring diagram for the ABS, and then applying a ground and a 12V source to certain pins on the ABS wiring harness. I used this method to cycle the solenoids and the pump.

If you search "Sumotoy and" "ABS", you'll see a thread where Sumotoy talked about how he would do it. My procedure was similar to Sumotoy's but different in that I used a different part of the wiring harness. If I had any common sense I would have made some notes at the time I did it.

 

[Alexbv]

Awesome !
My brakes have always been so so. On the street they could bring me to a stop but couldn't lock up the tires or activate the ABS. I just had the fluid flushed completely and refilled while getting the lift done and the brakes where exactly the same.

I just read this thread and took the cruiser to a dirt shoulder nearby and hit the brakes activating the ABS. After about six times I drove home, hit the brakes on the asphalt and amazingly locked the tires chirping while activating the ABS !

Thank you for this post.