Do you bleed brake line when pushing caliper in?
Posted by ApprehensiveStock928@reddit | askcarguys | View on Reddit | 55 comments
I’ve recently read that you should do this so debris doesn’t get pushed back into master cylinder. I’ve never done this and I’ve had no issues. Anyone else had issues or do this?
NightKnown405@reddit
You are going to see responses from two groups. Those that have attended training classes in the last ten years and those who have not. While vehicle manufacturers do not state that you need to open the bleeder screws while retracting the pistons we have learned not doing that opens you up to the risk of damaging the ABS controller, not necessarily the master cylinder. Over time debris from seals and wear of other components collects in the lowest parts of the system. When you push the pistons back and push that fluid from the calipers back through the ABS, there is a risk of blocking one of the tiny orifices in the valves. Or it could get stuck and result in holding a valve open. When this happens there is no way to get that debris back out and you end up needing a new controller which can easily be over $1000 for just the part.
Flash-635@reddit
I'd add that it gets rid of the brake fluid that is in the worst condition.
KoalaGrunt0311@reddit
Nobody ever goes to a mechanic and asks them to change their brake fluid.
JCDU@reddit
Yeah they do, lots of modern cars specify intervals for it and good mechanics / service places will do it at service time.
Sideburn_Cookie_Man@reddit
Sure they do.
Flash-635@reddit
They should.
I don't know why you said that though. If you crack the bleeder while pushing the piston back the fluid that's in the worst condition in the system will come out.
I don't see what's hard about that.
cormack_gv@reddit
Interesting, but I've never bled unless I replaced the cylinder, and I'm not about to.
NightKnown405@reddit
So you have never flushed the brake fluid as required by the manufacturers?
cormack_gv@reddit
I dispute your premise, but no I have never flushed brake fluid, unless I replaced a cylinder.
flaginorout@reddit
Even with this said:
It's a business decision. I'll take my chances and keep compressing pistons without opening the bleed valve.
IF (if) 1;1;000 cars comes back with an ABS light, I'll chalk it up to a cost of doing business.
NightKnown405@reddit
Well you can always charge the customer for the ABS repair. After all they wouldn't know you might have caused it.
flaginorout@reddit
Well, the shops I worked at, if the car came back within a few days of service, then we would have covered it.
but yeah, if a month went by.......different story.
But I suspect damage to an ABS controller is pretty rare.
Serialtorrenter@reddit
My 2005 Honda Civic LX doesn't have ABS; is there any advantage of opening the bleeder screws or is it entirely unnecessary in my case?
NightKnown405@reddit
It's very easy to do a fluid exchange if you still open the bleeders.
Lxiflyby@reddit
its always a risk that the junk will get pushed into the master cyl, but it depends if you can even get the bleeder open on something that old, especially in the rust belt
Rwood219@reddit
This is the technically correct answer.
AccidentCommercial71@reddit
30 year GM Master Technician. I have never, nor have I ever seen anyone ever open a bleeder when compressing a caliper. No issues ever.
mopower65@reddit
I typically do a fluid flush when changing pads or shoes, so I open the bleeder when pushing the caliper piston(s) in.
If I don't do a flush, I open the bleeder if the car has abs. It isn't worth the risk to push a bit of dirt or rust backwards through the abs module.
If I can't loosen the screw I loosen the line from the caliper and let the fluid ooze out from there.
EverlastingBastard@reddit
I always do. Takes very little effort.
noreddituser1@reddit
In addition to the comments about pushing contaminants back through the system, opening a bleeder allows you to determine if the piston is sticking.
With the bleeder open, the piston should retract easily. I the piston does not retract easily, there's something wrong and needs checking
bobqzzi@reddit
No, you do not
NightKnown405@reddit
It is a best practice to open the bleeder. That prevents debris that could be in the caliper from getting pushed back into the ABS control valves where it could block the tiny valve ports or cause a valve to stick open.
bobqzzi@reddit
I think the odds of opening the bleeder causing a problem are much greater than any chance there is debris in the caliper let alone that it will travel up the line into the ABS system.
Hersbird@reddit
Has to be a lot of fluid in the caliper and a short line. Otherwise the contamination may move up, but it will then settle back low over time. If it's a common car I'm not doing it, if I have some supercar with massive brakes, then sure.
u3b3rg33k@reddit
odds of what kind of problem? one you imagined?
there's always debris in the caliper cylinders.
Flash-635@reddit
Oh? What could go wrong by cracking the bleeder while pushing the pads back?
Gunk_Olgidar@reddit
See my reply with the easy solo DIY bleed method that makes this concern moot.
NightKnown405@reddit
And in that thought you are setting yourself up to learn something you really don't want to know. ABS controller hydraulic failures are often caused by debris that collects in the lowest portion of the system being pushed upstream when the pistons are pushed home in the caliper.
There are two ways to learn about stuff like this. You can find out about it in a training class based on the lesson someone else learned the hard way, or you can deal with the results of learning it first hand. You are free to choose.
H0SS_AGAINST@reddit
I recently had an ABS module failure not long after doing pads and rotors. I'm not saying me not cracking the bleeder caused this, because I've never had an issue before, but it is quite the coincidence.
NightKnown405@reddit
This would be the typical scenario. The vehicle behavior might be similar to what this instructor explains in this video. Tundra ABS Controller Hydraulic Failure
Viking2151@reddit
I don't, the only time I bleed brakes if I have to fix something like a brake line or replacing a caliper or master cylinder. I do how ever crack the lid of the master cylinder to allow fluid to escape when I press the caliper back, I live in the rust belt, so I never touch the bleeders unless I have to.
I recently blew a line on my 94 suburban and my driver's side caliper wasn't great anyway but I was going to try to get the bleeder loose, wasn't even there anymore, rotted off. Lucky the caliper was like $40 with the core, wasn't worth trying to extract it anyway. Rust belt sucks lol.
Appropriate_Cow94@reddit
I personally don't. I've also fought long battles solo trying to get a firm pedal again after opening them that way.
Ive done uncountable brake jobs since for decades and not opened them with zero issues.
u3b3rg33k@reddit
I open the bleed screws because it makes pressing the cylinders in super easy. like quick clamp easy, not c clamp easy. bonus is that you don't push old fluid back into the system, so bleeding is faster.
why work harder than necessary? seems like a no brainer to me.
RickySlayer9@reddit
You only need to bleed a brake system when there is air within the system.
The ways air gets in:
If none of these issues are present you likely don’t need to bleed your brakes, however brake bleeding is very easy and nearly free. When in doubt, bleed them bitches
ac5450@reddit
We were taught in school that it was best practice to do so to avoid pushing contaminants back up into the abs unit. In practice when I worked in a shop no one ever did that, myself included. For my own personal cars I do pinch off the brake hose and push back the piston with the bleeder open, but then I also flush and bleed the system whenever i do brakes.
NightKnown405@reddit
Do not pinch off a brake hose. A better practice is to use the brake holding tool to lightly apply the brake pedal.
ac5450@reddit
Im taking about using the plastic hose pincher with a wing nut. They were marketed for use on brake hoses when they came out. Im not using any sort of pliers or vice grips.
NightKnown405@reddit
There is a Teflon inner liner inside of the hose than can crack when the hose is pinched shut. This is also something that has been presented in up-to-date classes.
ac5450@reddit
Did not know that. My information is unsurprisingly out of date. Was in tech school in the early 2000s and we literally had instructors pinching off brake lines with needle nose vice grips with fuel line on the jaws.
ThatsJustMorrowind@reddit
There wasn’t a better way or tool to do it back then. Also most of the guys teaching back in the 2000s were working on non abs vehicles(for their actual wrenching career) that this wouldn’t apply to.
NuclearHateLizard@reddit
You technically should. I learned this in school. But nobody does, and no, it doesn't cause any immediate issues on a car that's had even semi-regular servicing. I learned that from real life once I actually started working on vehicles.
Did you hear about copper content in brake fluid? Apparently it's really bad, but we never knew this for the over 100 years we've been using copper washers in brake fluid systems. And it hasn't caused any issue that I've ever heard of to this day. Food for thought
Funny_Car9256@reddit
I wiped out my gen IV Jetta MC by not cracking open the bleeder, so for the last 20 years I always open the bleeder.
supern8ural@reddit
I was taught to do it this way when I worked for a brake manufacturer years ago. The theory was to not push debris into the HCU, not the MC.
Of course we were working on prototypes with shiny new parts so this was not an issue.
Thinkfaster1@reddit
In 40 years I’ve only had it mess the master cylinder up twice and both times it was a Toyota. So when I do Toyotas now I crack the caliper bleeder screw.
FloridaMan_Inc@reddit
If you never open the system (never remove a line, loosen a fitting, open a bleed valve, etc.) then you don't need to bleed it. You only have to bleed it if the system was exposed to atmosphere and air entered the lines.
If all you did was compress the piston and nothing else, no air could have entered the line so bleeding isn't necessary.
ApprehensiveStock928@reddit (OP)
Thank you. Is it necessary to pop the reservoir lid to “relieve pressure “ while compressing piston? I did do this 😬
FloridaMan_Inc@reddit
Not necessarily. If you opened the lid then you have to bleed the lines though.
ProJoe@reddit
That is absolutely wrong.
Majestic_Two_3985@reddit
Sorry, no you don’t.
Ok-Office1370@reddit
Asterisk - also check the fluid, and do bleed the lines if you have a helper. Too many words in case search necro:
Brake fluid turns black when exposed to contaminants including water. So you can just look in the reservoir. If it's not clear, bleed the lines. Doesn't matter the cause. If it happens more than every several months, you need to look into the cause.
Reddit always assumes they're omniscient. Problems come from things you DON'T see. Like for all you know your brake reservoir cap has a problem and it's letting moisture in 24/7. Or you did get air in the system for whatever reason.
If you're solo and need a quick fix. And you don't own a self bleed kit by chance. You can turkey baste the old fluid out of the reservoir to replace it with fresh. Pump the brakes a bit. Check if the reservoir is dirty. Repeat. This does not get at the riskiest bits so it is not a proper replacement. But it's better than nothing if you're a college kid trying to limp it home to dad to work on. If you're very very lucky, as you're doing this, any air bubble will decide to head north and "pop" itself. Or you'll feel a spongy problem when you push the pedal hard and know you must bleed regardless.
Bulocoo@reddit
50 years a (hobby) mechanic. Done dozens of brake jobs.
If you have access to a bleeding system and know how to do it. Cracking the bleeder and purging some fluid works. However doing that requires you know how not to get air in. You will also have to refil up top.
Having said that I have pressed the calipers in with no bleed most of the time. Never had an ABS failure - low risk.
NightKnown405@reddit
I have done thousands of brake jobs through the years. I haven't had a failure of an ABS controller either, but I open the bleeders after I learned about this happening from other technicians who shared their experiences. I have however diagnosed and replaced dozens of ABS controllers for complaints of pedals dropping or traveling too far or for brakes slow to engage/release. (It usually causes a pull or wheel lock-up). We have gone as far as cutting the assemblies open and visually confirmed the debris that was trapped in the hydraulic assembly of the ABS.
ConclusionFlat1843@reddit
No, but then if I'm working on the brakes it's a pretty old shitty vehicle. Anything I own that's not old goes to my mechanic.
Gunk_Olgidar@reddit
Not required, but it is a best practice to do so with modern ABS systems.
Because you do not want particulates (precipitates, rust, etc.) being pushed up stream into the ABS pump. Such things can foul the ABS valves and ruin it, turning a hundred $ repair into a potentially thousand+ $ repair. The MC is not typically the victim, but the ABS unit often is.
Plenty of folks will pooh-pooh a bleed during a brake job, and say "I've been doing this for decades without issue." But we also see posts in here from time to time where folks take their car for a simple brake job and end up suddenly with a bad ABS. It's not random happenstance.
Here's an easy no-mess method for solo DIY bleed that only takes an extra minute or two per wheel:
Source a 3 to 4 foot long piece of 1/4" tygon tubing.
Connect the tubing to the bleeder, and drape it up a foot and over the coil spring and then hang down over/into a catch pan.
Leave the cap on the brake fluid reservoir. Open the bleeder screw and then push back the piston. The fluid old (likely yellow or brown, possibly with particulates) will come out of the bleeder along with any solid contaminants, flow up to the top of the loop and down into the pan. The loop will act as an air block, with the fluid in the up-hill side of the tubing preventing air from getting into the caliper.
(optional, and recommended) You can then solo-bleed the caliper if you wish, in which case you will want to open up the brake fluid reservoir and add fresh fluid as appropriate to keep the level topped up. Again the loop allows single-person operation without risk of air entry during the bleed. And you can use the clear tubing to visually inspect the fluid that is exiting the caliper. When it runs clear, replenish fluid in the reservoir and move on to the next wheel.
When complete, close the bleeder and bring the tubing down off the coil so it's hanging straight down off the bleeder nipple and let it drain into the catch pan. Remove the empty tubing from the nipple with paper towel in hand for a no-drip finish.
Repeat for each wheel/caliper as appropriate.
LankyNihilist@reddit
Since brake fluid is hygroscopic I usually flush the fluid if I'm doing the brakes, and here in N. MI there's a good chance if your pads are worn out your calipers are sticky too.