Need help bleeding the brakes on a W123 240D -- tons of air

[Mölyapina]

I've been trying to bleed the brakes on John's 240D so that I can drive it home. I seem to have no end to the air that seems to be stuck in the lines, and I am wondering if there is an issue I am not detecting either with me or with the system.

Here is the situation: after installing and bleeding the new clutch master, I drove the car around his property and found I had no brakes. I pulled the car back into the shed and my friend and I set about bleeding the brakes. After about 5 minutes of no luck, I realized I was hearing a slight squirting noise and looked over to the front passenger caliper to see fluid spraying out. I went over and found that Purplecomputer (guy John bought it from) had started doing something with that caliper but not finished, and had left the bleeder valve clean open, partially drying out the system. We tightened it and kept working on bleeding the passenger's-side rear. After a while of no luck, John passed by and suggested bench-bleeding the master. Sure enough, the master was pretty dry, so we bled it out until steady fluid was pouring from all three lines back into the reservoir.

After bleeding the master, we set back about the passenger's-side rear. After a while, when we were still having no luck, John passed by again and noticed that I had forgotten that I needed to CLOSE the bleeder valve every time my friend let the brake pedal up, so I was basically purging a bit of air, then sucking it back in, etc. Once we did this, we bled all four and took it for a test drive. The brakes were a bit firmer, but still very wanting. Nonetheless, I felt that we had made progress, and so we wrapped up and left for the day (my friend's mom wanted us home for dinner).

I went back last night, intending to bleed the brakes one more time and then drive it home. However, after 45 minutes of trying to bleed the two rears, we were still out of luck. After an intial pass of clean fluid and then some bubbles coming through on the rear passenger's-side caliper, we all of a sudden got tons of air -- more air than fluid -- coming through. Eventually I switched over to the other side, and was just getting tons of air most of the time. My dad was pumping the pedal for me, and I was closing the bleeder each time I told him to let it up (in fact, before I told him to let it up), so that shouldn't be an issue?

Anyway, at this point, I'm totally befuddled as to what is going on. My thinking is to go splurge on a pressure bleeder and open both bleeder valves on the rear brakes and loop them into a bottle on top of the trunk, thereby eliminating the variables of pedal bleeding and hopefully punch out whatever air is in the lines all at the same time. I could then do the front brakes individually.

What do you guys think? Good idea? What else should I do or look at? The master is pretty definitely bled, and the car doesn't appear to be leaking fluid anywhere else.

[Stretch]

Originally Posted by Mölyapina

I've been trying to bleed the brakes on John's 240D so that I can drive it home. I seem to have no end to the air that seems to be stuck in the lines, and I am wondering if there is an issue I am not detecting either with me or with the system.

Here is the situation: after installing and bleeding the new clutch master, I drove the car around his property and found I had no brakes. I pulled the car back into the shed and my friend and I set about bleeding the brakes. After about 5 minutes of no luck, I realized I was hearing a slight squirting noise and looked over to the front passenger caliper to see fluid spraying out. I went over and found that Purplecomputer (guy John bought it from) had started doing something with that caliper but not finished, and had left the bleeder valve clean open. We tightened it and kept working on bleeding the passenger's-side rear. After a while of no luck, John passed by and suggested bench-bleeding the master. Sure enough, the master was pretty dry, so we bled it out until steady fluid was pouring from all three lines back into the reservoir.

After bleeding the master, we set back about the passenger's-side rear. After a while, when we were still having no luck, John passed by again and noticed that I had forgotten that I needed to CLOSE the bleeder valve every time my friend let the brake pedal up, so I was basically purging a bit of air, then sucking it back in, etc. Once we did this, we bled all four and took it for a test drive. The brakes were a bit firmer, but still very wanting. Nonetheless, I felt that we had made progress, and so we wrapped up and left for the day (my friend's mom wanted us home for dinner).

I went back last night, intending to bleed the brakes one more time and then drive it home. However, after 45 minutes of trying to bleed the two rears, we were still out of luck. After an intial pass of clean fluid and then some bubbles coming through on the rear passenger's-side caliper, we all of a sudden got tons of air -- more air than fluid -- coming through. Eventually I switched over to the other side, and was just getting tons of air most of the time. My dad was pumping the pedal for me, and I was closing the bleeder each time I told him to let it up (in fact, before I told him to let it up), so that shouldn't be an issue?

Anyway, at this point, I'm totally befuddled as to what is going on. My thinking is to go splurge on a pressure bleeder and open both bleeder valves on the rear brakes and loop them into a bottle on top of the trunk, thereby eliminating the variables of pedal bleeding and hopefully punch out whatever air is in the lines all at the same time. I could then do the front brakes individually.

What do you guys think? Good idea? What else should I do or look at? The master is pretty definitely bled, and the car doesn't appear to be leaking fluid anywhere else.

There seems to be a fair amount of user error going on - either yours or someone else...

...so if you're going to splurge on a pressure bleeder that's one way out. The other way which is better if the cap of the reservoir of the brake master cylinder is going to leak on you is to consider a cheap (or expensive!) vacuum gauge set.

Using these vacuum gauges (with the little bottle to capture fluid) is a nice way to bleed brakes by yourself. You have all of the control. Watch the gauge - pump as far is goes - open the bleed screw - watch the bubbles come out - close the bleed screw before the gauge goes back to atmospheric pressure.

(Tip for vacuum brake bleeding - wrap the bleed screws with PTFE tape to help stop air from being sucked down the side of the bleed screw - that confuses the process somewhat! Don't put PTFE tape on the sealing tip of the bleed screw though)

[vtmbz]

Plenty of people know more than me, but what I do is use a mity vac at the passenger rear caliper and suck out 12 oz of fluid. Switch to drivers rear and repeat. Switch to passenger front and repeat removing 8oz. Finish at drivers front, also 8oz. Be very careful to fill the master with a like amount of new brake fluid as you go. When done, you will have pulled all the fluid out of the system along with any air.

The rear chamber is hard to see and hard to fill,so pay attention to it.

[toomany MBZ]

Bleeding these things, clutch, can be an issue.

I'll recommend a power bleeder, this is a one person operation.

[MagicBus]

JL - I seem to recall you mentioning that you'd worked on the clutch hydraulics. Is that so, and if so, is everything properly buttoned-up and tightened in the clutch hydraulic circuit?

I highly recommend a power bleeder, but I wouldn't necessarily splurge for one. I built my own from these plans (authored by a friend of mine):
The DIY $20 brake bleeder

If you were closer, I'd be willing to loan you mine.

Are you topping off the MC with fluid throughout this process? If the fluid level drops too much in the reservoir/MC, then you'll be pushing air through the system, and will need to start again.

I don't recommend leaving both rear bleeders open at the same time. It might very well work, but less margin for error if you work one line at a time.

Also, are you sure all bleeder screws are working properly? Sometimes they get gummed up and fluid won't flow through them properly. You end up loosening the screw enough so that fluid exits through the threaded hole in the caliper, but not the bleeder screw itself, complicating matters.

[Zulfiqar]

as mentioned above, remove and wirewheel the bleeder nipples and then do a simple one man flush old school way.

use a jar/bottle and route your clear hose into it so its dipped in liquid at the bottom of the container, hang the setup so its above bleeder level but lower than master cylinder level but make sure the bleed hose is going upwards from the bleeder, crack the bleeder open only half a turn and push the brake pedal, the weight of the liquid will keep the system submerged even at the threads and the liquid in the container will prevent air being sucked back in.

I use this technique on every car of mine and never had any sort of bleeding issue.

[Mölyapina]

@Stretch: Yes, I definitely feel like user error is at the root of the problem here. PTFE tape is a good idea -- I will take some along.

Do you mind elaborating on the vacuum gauges idea or providing a link? Not 100% sure what you're talking about.

@vtmbz: John did drop off his MityVac for me to use -- I'll give that a shot tomorrow. I have been making sure that the master is full; in fact, the level was dropping very little at the end, which should have been a huge hint for me that air was entering the system from the outside.

@toomany_MBZ: Ha, we actually bled the clutch very quickly and got it driving just fine. I'm going to see if it works for me to borrow Rick's (MagicBus'), since I actually pass by pretty close to where he lives when I head down to John's (JB3's).

@MagicBus: Yes, I believe so. No leaks and the clutch works beautifully (granted I've only used it about 15 times since bleeding).

If you don't mind, I actually drive down 495 on my way to John's, and could stop by and pick it up tomorrow morning if you're around? I would probably be heading back sometime in the early afternoon and could drop it off then. I was reading the plans, but unfortunately don't have much time tonight to build my own -- plus, this way, I'd have a known good one to use.

Def. topping it off. Like I mentioned above, it's actually not changing much, which says to me that air is getting in somewhere in my bleeding process.

The reason I was thinking of leaving both bleeders open was in case there was an air bubble at a junction point or something that was messing me up -- is that unlikely/silly?

I'll thoroughly check and clean the bleeder screws, plus use plumber's tape on the threads, like Stretch suggested.

@Zulfiqar: I'll try that too. Are there advantages to that over pressure bleeding? It seems to me like pressure bleeding makes it harder for me to screw up, so I was thinking of trying it first.

[greazzer]

Invest $30 or so smackers and get one of these. You will need an extra fluid cap for the reservoir. Well worth the investment. Motive Products #1 Selling DIY Brake Bleeder

[Mölyapina]

Originally Posted by greazzer

Invest $30 or so smackers and get one of these. You will need an extra fluid cap for the reservoir. Well worth the investment. Motive Products #1 Selling DIY Brake Bleeder

I was thinking of that, but the problem is that I would really like it by tomorrow morning.

[Stretch]

Originally Posted by Mölyapina

@Stretch: Yes, I definitely feel like user error is at the root of the problem here. PTFE tape is a good idea -- I will take some along.

Do you mind elaborating on the vacuum gauges idea or providing a link? Not 100% sure what you're talking about.

...

Just the cheapo version of the decent brand that has already been mentioned



I've seen a kit like this for 20 euros - but usually they cost a bit more then 30 - I don't expect these kits to last but for not much money it should do OK for a little while. If you like this method of brake bleeding (and it works out for you) then I'd invest in a decent kit. Otherwise try the pressure bleeders that pressurise the reservoir

[Mölyapina]

Originally Posted by Stretch

Just the cheapo version of the decent brand that has already been mentioned



I've seen a kit like this for 20 euros - but usually they cost a bit more then 30 - I don't expect these kits to last but for not much money it should do OK for a little while. If you like this method of brake bleeding (and it works out for you) then I'd invest in a decent kit. Otherwise try the pressure bleeders that pressurise the reservoir

Oh yeah, that's JB3 left in the garage for me to use. I'll give that a shot tomorrow. Thanks!

[Stretch]

Originally Posted by Mölyapina

Oh yeah, that's JB3 left in the garage for me to use. I'll give that a shot tomorrow. Thanks!

Remember the vacuum hand pump just sucks air and not brake fluid!

The long hose in the collecting bottle goes to the hose you connect to the bleed nipple.

The hose to the hand pump just fits to the hole in the top of the collecting bottle.

As mentioned above - keep an eye on the fluid level in the reservoir.

Also keep an eye on the gauge - close the bleed nipple in time.

Also make sure you're not about to suck brake fluid into the hand pump.

(Don't re-use old fluid)

Get a few extra bottles of new brake fluid before you start - better to have more fluid than you need - you should be able to get your money back on unopened bottles if you buy from a decent place.

[Ceristimo]

I replaced three calipers on my DD Mazda a few years back and ran out of time half-way through the job. Stored the car for a few days with no rear brake caliper, and obviously the whole system drained through the open brake line (did not realize at the time that that would happen). So I ended up with a completely dry brake system.

Anyway, long story short:
It took me and a buddy about a frikkin' hour of pumping the pedal, to get all of the air out, since the whole system was drained and full of air. I just used a jar and piece of flexible brake line on the bleeder. Half way through we almost wanted to give up too, it felt like we were going nowhere, but we kept going.

So here are some tips perhaps that might be helpful:
- Put a piece of wood under the brake pedal so you can't push it all the way to the floor. Pushing the brake pedal all the way to the floor could potentially mess up the master brake cylinder.
-The proper technique is: open bleeder a bit, have helper push pedal, close bleeder, then have helper release pedal. (this is the part that took an hour to get the air out)
- Check the brake fluid level often, as you don't want it to run too low. This will cause it to suck air in again, which will only make it harder...
- Bleed one brake at a time, working your way from furthest to closest caliper, measured from the master brake cylinder. Basically, start rear right, then rear left, then front right, then front left.

I don't necessarily think you might be doing something wrong, it's just that in a system where a lot of air has been introduced, it can take forever for the bubbles to disappear, and using the wrong technique at first might have even introduced more air than what you started with.

Persistence will most likely pay off though...

Or yeah...get a pressure bleeder. Never worked with those, but I'm sure it's a lot less frustrating...

[97 SL320]

This is getting more difficult than it needs to be.

After an intial pass of clean fluid and then some bubbles coming through on the rear passenger's-side caliper, we all of a sudden got tons of air -- more air than fluid -- coming through. Eventually I switched over to the other side, and was just getting tons of air most of the time.

The master cylinder reservoir has a internal dam ( 2 when there is a clutch master cylinder port ) to prevent one circuit from draining all the fluid if another leaks. You probably ran out of fluid on the side you are bleeding.

My dad was pumping the pedal for me, and I was closing the bleeder each time I told him to let it up (in fact, before I told him to let it up), so that shouldn't be an issue?

Closing the bleeder ( lightly ) before the pedal is released is the proper method.

Here is the easy way to bleed brakes , half of it will even work with one person and generally produces good results.

Gravity bleeding

Fill the master cyl to the normal level , leave the cap loose but sitting on the MC to prevent splashing.

Slide a ~ 18" long piece of vacuum hose on the bleeder screw, direct this into a pan. The end does not need to be in or on the bottom of the pan. The hose creates a siphon effect and keeps fluid from making a mess.

Open the bleeder screw. if fluid comes out let it drip for a bit. If no fluid, leave it open and pump the pedal a few times until you get some fluid but do not press more than 1/2 travel. ( more than 1/2 travel can damage seals as they ride across dirt if the MC is old )

Let the fluid drip until you don't get any bubbles coming out. ( the bubbles will look sort of like soap bubbles / discontinuity in the stream. )

Close the bleeder and move to the next brake.

The above works fine with one person and produces good results most of the time especially if the MC was not run out of fluid. Even then it works well enough to move the car around.

A trick to getting more fluid out is to finger tighten the bleeder so it acts like a check valve allowing a bit of fluid / air to come out but won't draw fluid when the pedal is raised. With this , a single person can operate the brake pedal.

A step above this is the 2 person bleed. Do the vacuum hose trick and let fluid flow. Lightly tighten ( just over finger tight ) have the person in the car press the pedal _SLOWLY , ONLY ONCE and NOT WITH HIGH PRESSURE_ ( hand pressure would do ) , once they have pressed the pedal, open the bleeder then close it once you get a spurt of fluid and / or air. When the fluid runs clear, tighten the screw. The bleeder seat is tapered so it does not take much to generate a seal.

This technique will surge fluid through the system bringing trapped air with it that didn't come out during gravity bleeding.

If the brake pedal is pumped rapidly, that can aerate the fluid causing more difficulty in clearing the system.

Lastly, in a real pinch, do the gravity bleed, close the screw then compress the caliper pistons, this will force air to the top of the system and out the MC. This works better with worn pads or careful observation of piston position with a pad removed and brakes pumped to extend the piston.

A modified method is to leave the brake line loose , compress the piston, re tighten and pump the pedal to extend. Sometimes the bleeder screw is stuck and the above 2 are the only way to get air out.

[Mxfrank]

Originally Posted by 97 SL320

The master cylinder reservoir has a internal dam ( 2 when there is a clutch master cylinder port ) to prevent one circuit from draining all the fluid if another leaks. You probably ran out of fluid on the side you are bleeding.

Right answer. There is indeed an internal separator in the reservoir. If the fluid runs low while you're pumping out the rear brake, the reservoir will LOOK full, but it isn't. After a few strokes, you'll be pumping air. When I'm bleeding rear brakes I keep the reservoir filled to the brim, then suction out any excess after I'm done.