A new brake bleeding thread ... what did I do now?
 

... So after a bit of a hiatus due to health issues, I finally got my brake job on the 124 done, including all new rear hard lines. Almost. I went to bleed it using my Motive power bleeder and new MB brake fluid and here's what's happening. I started at the back right and when I open the bleeder, a bit of fluid comes out, then a frothstorm of bubbly fluid ... which I expected of course ... but the froth just keeps on coming. Then nothing comes out at all. I go look at the bleeder and it's lost all its pressure. Pump it back up and try again, same deal. Club soda, then loses pressure. I've used the Motive bleeder several times with no problem ... bleeding is a breeze. This is the first time I've replaced the hard lines though ... should there really be that kind of air coming out for so long or did I mess something up? I.e., a kink in the tube or a leak? I can't find a kink and I don't see fluid coming out anywhere. I had to rush off to work so I had to drop everything, but I'll inspect the bleeder unit again when I get home. Usually I pump it up to 15 PSI and it holds that while I bleed. Thoughts?

Sounds like you have allowed the rear section of the master cylinder's fluid reservoir to run dry. If you don't allready know the reservoir is seperated into two sections and the fluid needs to flow from the front section over the divider and into the rear section. If the level of the front section is not high enough none will flow over the divider into the rear section and you will run it dry. Sounds like you've pushed out both the old fluid and any remaining fluid in the rear section!

The bleeder fills up the front section of the reservoir quite full, though, and I'm pretty sure it's flowing over. I'll give it an extra look and try pouring in fluid by hand to make sure it's flowing back there. It looked full, but since the reservoir is a bit opaque I could definitely be wrong.:o

Good luck! I use a flashlight behind the reservoir to make it easier keep an eye on the level! It is hard to see the clear new fluid level in an old dirty or stained reservoir.

When I've use my MityVac for bleeding brakes I always get bubbles. When you break open the bleeder valve and suck on it with a device it pulls bubbles from around the bleeder and not just fluid. Try having an assistant pump the brakes and drain the bleeder into a container the old fashion way and see if you still get bubbles.

The bleeder I'm using is a pressure bleeder so it just pushes fluid out rather than sucking, so I don't think the air could be sucked in around the screw. Guess if it wouldn't hurt to try it by hand and see if that works ... I don't have an assistant though. Maybe my brother in law will help.

Bodhi,
Expect to have to fill the reservoir several times as you have completely empty lines and calipers.
I wouldnt use 15 psi, too high, it will cause you to make soda!!
Best have a pint of fluid on hand. Slow & gentle is the trick to bleeding brakes.
Using your mity vac may give a better result. Just keep the back part of the reservoir full.

Good Luck !!

My bleeder is supposed to keep refilling the reservoir automatically (you fill the bleeding unit with fluid and it pushes it into the reservoir) but maybe it's just not working, or maybe it doesn't work right with ABS. I'll bet its not keeping the back of the reservoir full, in which case I maybe will have better luck doing it by hand. If I can find an assistant ... :rolleyes:

I would recommend against using the master cylinder as the pressure source for bleeding. Find out why your power bleeder isn't working. Perhaps it's leaking air from the pressurized chamber to the hose.

You're supposed to pressure bleed these things.

Fill the reservoir to the rim before you put the bleeder on, that pinhole between the two reservoirs is annoyingly at the very top.

Thanks for all the tips folks. I'll fiddle around when I get home (or tomorrow ... I won't be home until 2 a.m.:() and will update with my findings.:o

Since this is being such a pain. Find a friend and do it the old fashion way. Open bleeder, press pedal to floor, close bleeder, and release pedal....... Keep the reservoir full and you should be good to go.

If you're losing fluid too and can't find it, it may be leaking into the booster, just a guess.

"the old fashioned way" is not a good practice with ABS, power bleeding is the best way to go.
if you are getting bubbles and air, it's due to air being in the bleeder, or air in the master cylinder.
when you wake up and log on, I bet you'll have no issues once the MC is full by hand, and the power bleeder is verified to have fluid in the reservoir.

Well, it turns out the rear of the master cylinder was indeed empty! BenzGirl got it on the first shot. :o It was hard to see because my MC is a big foggy, but when I shined the flashlight on it I could see it was fluidless. So I filled it up, but the pressure bleeder back on (I also tightened the hose clasp on the power bleeder) and everything worked!:) Aside from hitting my face on the underside of the car, it went smoothly from there. Thanks guys!

I'm still having a couple issues, though ... one being a chuff chuff chuff sound when the car is rolling slowly (goes away when the wheel is turned left) that I'm guess might be dust shield. The other is that the left front wheel gets hotter faster than the others and smells a bit burning. It doesn't really drag when I turn it by hand but it has me worried. That was the wheel that seized on me on the highway and almost caught fire, which is what prompted this brake job. I replaced the calipers, rotors, pads, hoses and wheel bearings, so i don't know what would still be wrong. Maybe I made the bearings too tight.:(

Answer
 

Did you remove/inspect the wheel bearings and re-pack them with fresh grease?

Extreme heat will cook the grease into TAR...

Yes I replaced the bearings with new ones including the races in the hub, and packed them with MB grease, exactly the amount specified in the FSM. And I set the play using a dial gauge ... but had a little trouble getting consistent readings at first. I did finally find a position for the gauge that got consistent readings and set it as exactly as I could. Both hubs seemed to spin comfortably and evenly.

Both front wheels are definitely HOT. I drove it for a few errands to see what transpired and it felt OK. Just super hot when I touch the wheel ... I can even feel heat coming off. No smell anymore though. It is pretty hot out today (95 maybe?), and I know brakes do get hot, but ... :(. I'm driving the Jeep to work and I'll see what the Benz does tomorrow. I replaced a lot of things, so lots of room for error ...

After doing my homework and using the search feature I'm leaning toward a bad master cylinder. Both fronts seem to have the problem, though the left side a bit more (might just be my perception). Ugh. I don't have the energy ...

How are your rotors?

Question
 

Are the pads and caliper pistons free?
Have you replaced the rubber brake hoses?

If the answers are yes = a bad master cylinder.

Brand new, OE rotors.
whunter ... yes, all four reman calipers and new pads w/ light MB brake paste on specified surfaces and replaced all four rubber hoses.
Guess I'll do some MC testing/replacing research; I'm sure there's many threads on it. I have an MC from a 124 that's been sitting in my parents' garage but maybe for all the effort to install it I'll just get a new one.

I may just wimp out and take it to my indy, at the risk of losing my street cred as a DIYer.;)

FYI
 

The used one on the shelf should still be good, try it.. :)

It is an easy DIY, not a major PIA. :D

Thanks. Now that I've read the FSM description it doesn't look that bad. I thought I would have to bench bleed it but the FSM just says install then fill the reservoir?
The one on my shelf is from an 88 300E ... that will work on the 300D, right?

Answer
 

Both 1988 300E and 1987 300DT have the same part numbers listed.

MB# 004 430 34 01 superseded

MB# 005 430 24 01 superseded

MB# 005 430 39 01

Yes it will work.

If you are lucky & fill the master with fluid before you fit it & provided fluid has not drained back out of the lines, you can get away with out re-bleeding the system. I have done it many times. You are probably getting tired of bleeding brakes & have a big supply of spent fluid !!

Yes, I am definitely tired of bleeding and buying new fluid.:P Doesn't the fluid have to be drained out of the lines? Or can you drain it where the lines attach to the cylinder so it stays in the calipers/lines?

Thank you whunter for the parts numbers! My computer will not open the EPC anymore, it doesn't like the Java application.:mad:

re EPC, you may need to adjust security seetings on your browser, I have trouble with Chrome doing this, I have to allow the app every time I run it? Due to 'unsafe components'...the notification in the top bar is too fast to hit!

The EPC used to work on Macs, but the vendor who writes it for MB made some changes a while ago and although it uses java it requires Windows (or at least did the last time I accessed it.) Don't know if BodhiBenz1987 uses a Mac, but I have to fire up a virtual machine to access the EPC now.

Motive clear Vinyl Hose
 

These Motive pressure brake bleeders are a great unit. I bought one about 5-6 yrs ago, then didn`t use it until last yr for the first time when I did my 4-spd trans swap. works great.

Then last week I decided to flush out the old fluid, (can`t have dingy looking fluid going to the GTG) Iam under the R/R wheel and all is going well, then hear bubbles gurgling through the line. then it clears up and flows clear? HMMM.
then go over to the L/R and start on that one.

suddenly I hear liquid dripping up front, look under the car and it is pouring down from the engine :confused:.

Zoom up to the front of the car, and the clear vinyl hose where it clamps onto the Motive, has split and I have a sprinkler of brake fluid shooting up to the hood liner and all over the engine:mad:.

I wipe up the mess, spray Marine Clean (degreaser) and hose off everything and all is well. cut 4in off the hose, reconnect and finish the next day.

SOOO, if your clear vinyl hose is a little stiff, replace it. :o

Charlie

I built my own pressure bleeder and the instructions said to not go over 14psi. I didn't want to have to crawl out from under the car so many times so I figured 20psi would give me a longer interval, plus maybe drive the old fluid out with a little more force taking more crud with it.

While under the car I noticed fluid dripping out near the engine bay and I found that the rubber grommets that fit the reservoir to the master cylinder cannot take that kind of pressure without leaking.

Lesson learned.

Bodhi
Sometimes when you have new rotors and pads they will have a tendency to get hotter than normal when new. That will go away after they brake in. There are a couple of test to try. Jack up the wheel you suspect. Spin it. Get in the car and depress the peddle firmly. Go back to the wheel and spin it again. If it was the same both times and not to hard to spin then everything is AOK. If the wheel is hard to spin, loosen the bleeder and re tighten. then try to spin again. If it is easer this time, then you do have a problem. Press the peddle again, but this time loosen the brake line at the master cylinder that goes to that end of the car. Spin again. If it spins easily, then there may be a problem with the master cyl. You can also try at the anti lock unit. I think you get the idea. You are looking for something holding pressure on the caliper.
Have a SALT sandwich, get the BP up a little and have a GREAT DAY.
Paul

Answer
 

Brake bleeder - power bleeder Homemade
http://www.peachparts.com/shopforum/diesel-discussion/117258-brake-bleeder-power-bleeder-homemade.html

The critical factor is keeping the bleeder fluid level full enough that only pure fluid reaches the pickup.
The bleeder fluid maintains the reservoir fluid level, preventing air entering system.
Most systems bleed just fine at 2 - 5 PSI.
Some systems I have connected to and popped the reservoir off the master cylinder at 3 PSI, the mount grommets where junk.

Thanks Paul.:) I had been starting to drive myself crazy second-guessing whether or not the brakes actually still have a problem. I just stayed away from the car for a day to "recalibrate" my perspective and fiddled with it more today. I don't think the brakes are really dragging very much ... for comparison I checked the wheels on my Jeep, and they actually drag a LOT more than the 300D's. Not that that proves anything, since the Jeep could need brakework too (have not noticed any problems). I wish I had a better perspective of what normal drag feels like vs. bad drag. They certainly don't drag like the wheel did when the caliper seized! I did try cracking the lines on the MC and it didn't change the feel of any of the wheels. When I just pump the brakes a few times and go to spin each each wheel, there's a light resistance at first but once it's in motion it goes back to the way it felt prior to pumping the pedal. I drove the car a bit today and didn't think the brakes got horrendously hot ... again, it's really hard for me to judge what's too hot and what's normal hot. I did notice that when I get the car to about 30 and just let it coast on flat road, it keeps rolling easily for quite a while. I took it out on the highway, and the only thing I noticed abnormal was a slight steering wheel vibration at 80 mph (prior to the brake job I had vibrations at 50, 60,70, etc.). Also, no smells ... maybe I got a bit of stray grease on the rotor on that first test drive.

So ... I have the doner MC and ordered the seal that goes between it and the booster ... but I'm torn as to whether I need to replace it, or if I'm just making a big to-do about totally normal behavior.

For some reason I thought in an ABS-equipped vehicle you needed higher PSI?:confused:

Answer
 

There are some out there.
Rule of thumb:
Use 2-5 psi, if it fails you can raise the pressure by increments of five, up to 20 psi.

FYI:
Some of the newer vehicles require a diagnostic tool to bleed the brakes by cycling the ABS and reset the system.


Brake:
--------------------------------------------------------------
Some Facts About Brake Hoses:
#1. The average life of a brake hose is six years.
#2. Brake hoses deteriorate from the inside as well as the outside.
#3. Moisture is absorbed into brake fluid systems through brake hoses.
#4. Contaminants in brake fluid act abrasively on the inner wall of brake hoses.
#5. The brake hose reinforcing fabric deteriorates through expansion and moisture.
#6. High operating temperatures contribute to the deterioration of hoses.
#7. Brake hoses swell with age and restrict flow.
#8. Generally all brake hoses on a vehicle deteriorate at the same rate, So all hoses should be replaced if one is found to be faulty!

Brake hose failure mode:

#A. Rupture (burst hose) = age, exercise (too many miles) or impact are the typical cause.

*B. Partial internal collapse = the inner ply becomes damaged/detached acting as a partial restriction and/or one way valve.

#C. Full internal Blockage = the inner ply becomes damaged/detached acting as a plug = brake pedal still feels good but there is no brake application.

http://www.peachparts.com/shopforum/diy-links-parts-category/142411-brake.html

Thanks for the info on bleeder pressure, Whunter. My grommets were new and they still leaked at 20psi.

Regarding brake drag, after experiencing (and repairing) a seized rear caliper, I always check the brake drag while coming to a stop. I release the brakes at the very last moment of travel to see how the car moves those last few inches. Easy to see if it stops abruptly/tightly or free. Also on a very slight incline, the car should roll upon brake release.

So I've put about 300 miles on since the brake job. Everything works great, and I can't detect any drag when riding on the highway, accelerating, or when I jack up and spin the wheel including after firmly depressing pedal and letting off). But they still get blazing hot, especially on the front, after stop and go traffic. Too hot to hold a hand on for more than a second or two, and though it doesn't have a burning smell per se, it smells kind of toasty. They don't seem to get this way after highway drive and cruising to a stop.:confused::( My dad test drove it and says stop obsessing and just drive it ... I guess he's right. I do have two fire extinguishers on board after all.

One thing I have done to make the pressure bleeding go easier is use the ATE super Blue. When I do them again in 18 months i will use the ATE amber. The color change is a great visual indicater.

Darn. I was hoping you'd have some sort of result. I've got more/less the same thing: rebuilt my calipers, replaced the lines, repacked the bearings (with gauge), no drag on spinning, reasonable MPG = inexplicably hot front wheels.

I was about ready to re-re-build my calipers and see if the "whiskers" on the gasket that the FSM says is responsible for retracting the pads are working or installed correctly.

stop and go is very harsh on the front breaks. lots of friction heating them up, and very little airflow cooling them off. it's the nature of the beast. to see if the heat is a problem, with a cold car, drive 100 feet, stop normally, then drive another 100 feet, and check the temps. if still cold to the touch, you are fine, if they are very warm, investigate the caliper release system again.

Even so hot you can barely touch them? I don't feel like my Jeep or 240D gets as hot, although certainly wheel design may have to do with that (240 has hubbies and the Jeep has different material wheels and bigger holes in them). I'll give the 100-ft test a try. After a short bit of driving (i.e., I drive to the grocery store) they don't get very hot. But usually when I drive around a lot, or drive to work and hit a lot of lights, it gets ferociously hot.
I can't really compare whether it's gotten hotter than before the brake issues and repairs, because before I knew of brake issues, I didn't obsessively feel my wheels.:o

Bodhi,
If it will make you feel any better, I just drove about 10 miles with 1/2 city type driving and 1/2 slow highway (45 mph). I just went back out and the front wheels were so hot I couldn't hold my hand on them for very long. The ambiant temp is about 96 deg here and I was driving my 500SEL.
In the morning we are making a 400 mile trip to the Outer Banks for the week, and I am not at all concerned about the brakes. Relax and enjoy that FINE car. ;););)
Paul