i don't even know what gravity bleed is unless it's refering to the vacume pump bleeders, apparently you're over my head now
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| Bleeding ABS Brakes http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=1&t=40139 |
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| Author: | dirt pig [ Thu Feb 12, 2009 2:55 am ] |
| Post subject: | Bleeding ABS Brakes |
I here that there is a special way to bleed Brakes with ABS. Apparently if you pump the brakes on an ABS equipped vehicle, you risk damaging the master cylinder. Is this true? Can some-one enlighten me? Does anyone know the correct procedure? |
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| Author: | KJ 119 [ Fri Feb 13, 2009 7:49 pm ] |
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Haven't heard anything about pumping ABS brakes. I'll be changing my brakes sometime this weekend. Anyone know if this is an urban legend? |
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| Author: | JeepinJarhead03 [ Fri Feb 13, 2009 10:21 pm ] |
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there's nothing special with bleeding abs, make sure bleeders closed before pedal is fully depressed i think the danger of working with abs that you're remembering is depressing the brake caliper with the bleeder closed, ie: when depressing the caliper you have to open the bleeder so that fluid isn't forcibly backfed across the dohicky sensor that I can't recall the name of at the moment but you get what I'm saying I think bleed them as you usually would, when you get done give it a few pumps, advanced abs systems typically pump firm with 2 pumps pumping them while driving, whole different story, it disrupts the abs system which perhaps that's what you were recalling hope this helps clarify things if i'm in error i'm sure someone will correct me |
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| Author: | KJ 119 [ Sat Feb 14, 2009 9:02 pm ] |
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Did a brake job today,but didn't need to bleed.Used a C-clamp and piece of wood.All went smooth. |
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| Author: | JeepinJarhead03 [ Sat Feb 14, 2009 9:26 pm ] |
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yeah you can squeeze the pistons in without bleeding during compression, however it can and will damage some components if you don't bleed during compression it cost me over 700 bucks on my z34 by not bleeding during compression perhaps theyve changed the way the abs systems work now days, i'd still bleed during compression to prevent stressing anything, the cost of adding a little brake fluid is cheep in comparason |
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| Author: | dirt pig [ Sat Feb 14, 2009 10:36 pm ] |
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The reason I ask is that I intend on installing extended, braided lines when I do my lift. Which means that when I remove/replace lines, I will definitely need to bleed air out of the system. On a footnote, I spoke to a mechanic friend of mine and he said that ABS works on a seperate although linked system. He said if you need to bleed an ABS equipped vehicle, the safest way to bleed is gravity bleed.Takes a lot longer but extremely safe. |
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| Author: | JeepinJarhead03 [ Sat Feb 14, 2009 10:40 pm ] |
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i don't even know what gravity bleed is unless it's refering to the vacume pump bleeders, apparently you're over my head now
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| Author: | dirt pig [ Sat Feb 14, 2009 10:45 pm ] |
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Gravity bleed is the same as vacuum bleed without the vacuum. Let nature (Gravity) do the work. So, are you saying that what KJ119 did with the C-clamp and wood was risky? Is this how you destroyed your system? |
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| Author: | JeepinJarhead03 [ Sat Feb 14, 2009 11:09 pm ] |
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i may have misunderstood what he was saying, and my method may be outdated with the newer abs systems pre abs, could just flip the pad over and use a clamp to compress the pistons in, wasn't a great idea but was widely practiced late 80s-90s abs, you needed to crack open the bleeders while compressing hte pistons in (could still use the reversed pad (block of wood) and a clamp or a pry bar to pull the caliper towards you while still on the vehicle but to fully answer your question, yes, by compressing the pistons without cracking the bleeder open to expell the fluid instead of pressuring it back through the system it trashed my abs the pedal was almost impossible to press, extremely stiff, as if the brake booster didn't exist. stopping in a short distance was impossible without standing on the brake with both feet, and if you hit the brake hard and fast enough with both feet it would start to stop and then basically coast at a much lessened brake force speed. i don't know 100% but by not bleeding when compressing i basically forced trash into the hydrolic system of the ABS and trashed the unit or damaged other components, I didn't perform the repairs, i refused to do anything other than light maintence on that vehicle due to the design of the engine compartment, friend of mines dad who owned a nice race shop did it for me and basically charged me for parts only some abs units have an actuator that can be bled as well, i am rather ignorant of what specific type of abs units are on our jeeps and whether or not they have bleedable actuators (some abs actuators you have to have a scanner to cycle the abs to bleed it specifically and separately from the actual brake lines- had to use it on some saab box trucks) it's very safe advice to let it bleed it during piston compression, much safer that way and the only way i'd bleed it -- in theory this gravity bleeding sounds solid, as long as the master cyl is above the level of the calipers it would work as long as you dont go touching the pedal and keep the resovior full would imagine it would take awhile though? 30mins, hour? i've never done it in that method |
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| Author: | JeepinJarhead03 [ Sat Feb 14, 2009 11:10 pm ] |
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let me reinterate, im not sayin 119 trashed his by doing it in that method, just saying that doing it in that way is as you put it, risky, and yes that is how i trashed mine was a mistake that i won't make again! |
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| Author: | tjkj2002 [ Tue Feb 17, 2009 11:46 pm ] |
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JeepinJarhead03 wrote: there's nothing special with bleeding abs, make sure bleeders closed before pedal is fully depressed Sorry but that is 100% wrong.You can compress the pistons back into there bores without opening the bleeder screws on ABS equipped vehicles with no damage being done.You got unlucky and had a bad pump to begin with,GM pumps(older ones) are known for massive failures.They make fancy tools now to push the pistons back into the bores also.
i think the danger of working with abs that you're remembering is depressing the brake caliper with the bleeder closed, ie: when depressing the caliper you have to open the bleeder so that fluid isn't forcibly backfed across the dohicky sensor that I can't recall the name of at the moment but you get what I'm saying I think bleed them as you usually would, when you get done give it a few pumps, advanced abs systems typically pump firm with 2 pumps pumping them while driving, whole different story, it disrupts the abs system which perhaps that's what you were recalling hope this helps clarify things if i'm in error i'm sure someone will correct me As far as bleeding ABS brakes there is no special procedures for the KJ or the KK,now GM and some Fords need there specific scan tools to be able to bleed the brakes but that's only if the ABS pump is replaced or the master cylinder.Just don't let the master cylinder run dry,then you need to remove it and bench bleed it,not fun. |
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| Author: | JeepinJarhead03 [ Wed Feb 18, 2009 12:00 am ] |
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K not going to argue it, won't argue the bulletins that went along with that experience or information either not sure it's that much of an extra effort to bleed in the process in the instance that i was only 99% wrong and actually damage abs selenoid or force trash into the hydrolic unit as for our line of jeeps, mopar says you don't have to so with our's youd be right toyota and gm on the other hand strongly advise the bleed, perhaps a difference in the selenoids i'll keep bleeding, it isn't that big of an inconvienence |
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| Author: | LMWatBullRun [ Sun Jan 15, 2012 10:09 am ] |
| Post subject: | Re: Bleeding ABS Brakes |
one of the things I have learned through experience is that brake fluid absorbs moisture while in the system. regular dot-3 or dot-4 fluid probably should be changed yearly to avoid rusting of the cylinders, which is why I went to ATE SuperBlue, which is less sensitive to moisture and can go a couple of years typically between changes. I strongly recommend that you change brake fluids regularly. Always bleed and replace the fluid BEFORE you do any brake work. That way you reduce the likelihood of getting contaminated fluid with trash in it in your new brakes. When the cost of parts and time are considered, an extra liter of brake fluid is cheap. |
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| Author: | sota [ Sun Jan 15, 2012 6:29 pm ] |
| Post subject: | Re: Bleeding ABS Brakes |
I was taught to crack the bleeder open when pushing the piston(s) back in so as to remove the fluid that was in the cylinder bore, where it's been exposed to the most heat. you really don't want to push "dirty" fluid back up the line, into the ABS module and possibly back into the master cylinder, especially if you're not replacing all the fluid at that time. |
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| Author: | tjkj2002 [ Sun Jan 15, 2012 8:32 pm ] |
| Post subject: | Re: Bleeding ABS Brakes |
sota wrote: I was taught to crack the bleeder open when pushing the piston(s) back in so as to remove the fluid that was in the cylinder bore, where it's been exposed to the most heat. you really don't want to push "dirty" fluid back up the line, into the ABS module and possibly back into the master cylinder, especially if you're not replacing all the fluid at that time. It all cycles through the whole system anyways.What's in the caliper does not stay there for very long. |
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| Author: | sota [ Mon Jan 16, 2012 10:24 pm ] |
| Post subject: | Re: Bleeding ABS Brakes |
curious how that's the case, given that it's a single-path circuit from the proportioning valve (or ABS module in this case) down to the caliper. it's not a loop, just a straight line. |
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| Author: | tjkj2002 [ Mon Jan 16, 2012 10:29 pm ] |
| Post subject: | Re: Bleeding ABS Brakes |
sota wrote: curious how that's the case, given that it's a single-path circuit from the proportioning valve (or ABS module in this case) down to the caliper. it's not a loop, just a straight line. Had to go to a class about brakes a few months ago and was presented by Carquest.They did a test where they ground up a master cylinder cup into fine powder(the rubber ones) and put it in a caliper that they rebuilt.Installed that caliper and tested the fluid everyday and 14 days later some of that powdered cup was in the master.They took apart the whole system and found traces in the other 3 calipers also. I didn't think it would travel like that either but it does. |
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| Author: | fratichelli [ Tue Jan 17, 2012 6:22 am ] |
| Post subject: | Re: Bleeding ABS Brakes |
Brownian motion, or just simply the vibration stirring up the fluid. If you ground up lead or even steel it might take a while to "circulate." |
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| Author: | sota [ Tue Jan 17, 2012 8:48 am ] |
| Post subject: | Re: Bleeding ABS Brakes |
interesting. I guess on one hand the emperical evidence was always there... brake fluid IN the reservoir always gets discolored over time, so it has be migrating from someplace. I always figured it might be something to do with water absorbtion and specific gravities. either way i'll stick with changing ALL the fluid every time I replace the pads. 
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| Author: | LMWatBullRun [ Sun Mar 04, 2012 1:01 pm ] |
| Post subject: | Re: Bleeding ABS Brakes |
finally got down the priority list to the brake fluid replacement. I had 4 new speed bleeder screws ready to replace the existing ones, and all went well except for the LR, where the PO had replaced the caliper with a non compliant part with different (metric) thread on the bleed screw. I really love speed bleed screws, they change brake bleeding from an arduous PITA 2 person chore into a half hour routine one person job. I've tried vacuum, I've tried pressurizing caps, and this is the best and easiest way bar none. Quick, neat, no fluid drips, and nothing that will upset ABS systems. It makes it easy to do your yearly brake bleeding. I usually do my vehicles in the spring, after the winter and before the heat and stress of long summer trips, usually towing something heavy, but I knew that the Jeep had not seen new brake fluid in a long time, so I did this while it was still cold. Based on what I saw, I suspect that the PO NEVER changed the brake fluid, even after replacing the caliper. I know no self-respecting professional mechanic would have done that, so my expectation is that the PO never read the maintenance schedule, or simply did not care. I am probably going to order replacement calipers all around and replace them when I do the pads and rotors later in the spring, because I have no confidence in the condition of the existing calipers, and I am planning on mountain towing. I like vehicles to go as they should, but as I get older, I've begun to value STOPPING power more. The old fluid was so saturated that it floated on top of the ATE Super Blue fluid I used, which I have never seen to this extent before. Then again, I have never run brake fluid for 7 years, either.  Before I started using ATE, I changed brake fluid yearly. Now, I change it every 2 years or 30K miles, or prior to component replacement. When I factor in my time and the increased service life, I think the ATE is cheaper over the life of the vehicle and performs better to boot. I don't own any stock and have no financial stake in either of these firms, but I really like both the speed bleeders and the ATE fluid. Highly recommended. |
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