6.9 brake problems - getting desperate here....

[TJ 450]

I think it just comes down to luck, and maybe these systems are just very sensitive. I certainly do hope you find a solution, S Class.

If the master cylinder was tested OK, I reckon there must be air trapped in the system somewhere.

Tim

[koan]

I've revisited the brakes several times since rebuilding and replacing everything including hose and master cylinder and still have a soggy pedal.

Buy two (or better four) brake line clamps, should enable you to isolate where the problem is.

Mine is the front calipers and pretty sure it's the pistons retracting more than they should.

koan

[s class]

koan, the clamps are what the brake specialist here advised (well actually, they admitted they use vice-grips, but I don't want to butcher the lines...).  Even with clamps, I'm worried about damaging the lines?

[koan]

Don't think there is a risk of damage to new rubber hoses using the clamps, wouldn't use them on old hoses though.

koan

[WGB]

You can get very cheap hose clamping tools - I have a pair and they only cost about $10.

They look like miniature "G" clamps but the jaws are bevelled to protect the rubber.

Bill

[oscar]

Suppose the lines have rusted inside, how would this actually affect the pedal feel?

Wish I could post you a link with more insight.  When I searched the topic months ago I was under the impression there could be a build up of rust or whatever, some sort of  fixed deposits on the walls of the steel lines akin to blocked arteries that restrict fluid movement in both directions. 

I tried to hypothesise that if the internals of the lines were not smooth that eddies over rough deposits could cause localised mini low pressure spots causing dissolved gases to come out of solution to form very tiny gas bubbles.  A bit fanciful perhaps but prior to last November I'd bleed and bleed and tiny microscopic bubbles seemed to appear even though I thought the fluid was coming through clear.  When we did a two man bleed by slowly applying the pedal there was less or perhaps the bubbles were non evident, but we still had a soft pedal.  I don't know.     

I just think it's plausible most of our lines might have been neglected at some stage over the 30yrs or so through lack of brake fluid changes or a mediocre bleed and some internal corrosion to differeing degrees could be present.   In the case of POVO, it had sludge in rear calipers and leaking front seals.  One site I read last night said the sludge is a combo of oxides formed as the result of old fluid loosing it's anti corrosive properties and those oxides themselves become chemically abbrasive.  The damage is done.  One might clean and reseal the calipers, flush and bleed etc and have clear fluid come through time and time again, but the damage to the lines, if any, will not be obviously evident in the new fluid being bled through.  I still want evidence before I pay for new lines but whatever process is going on, like I said, lines and booster are the two remaining items yet to be replaced in my case. 

[craigb]

my high school physics gives me problems with the line corrosions theory, but by the sounds of things you too Oscar.

But as i'm reading i was thinking. air bubbles must come from somewhere, Just wondered if you took the calipers off, moved them around until the nipple was at the top or trying to imagine how any air pockets could be worked towards it, and of course with a block of wood taped into it so the pistons don't pop out and then bleed again?

Or what about talking to a local old school brake place and see if they will have a go at fixing it, particularly given your evidence. what about John Green? I reckon I would have reached my tether by now and would be ready to do anything!! And of course if one person can sort what this common fault is they will be worshiped for some time no doubt.

And also did calipers, lines etc on my SEC with k750 pads, did about one lap and the pedal went soft. Took it to a place to bleed because I am sick to death of this stuff and they told me the master (which looked new and had a receipt but I have bought another one anyway and about to refit. But I am convinced (after consulting with many) that my problem is a heavy car at Mallala. I have now bought Motul rbf660 brakefluid, which seems to be the highest boiling point fluid available and replacing the k750's with comp3. After that I have one more step that was recommended and thats Ferodo ds (few different compounds) but that will require a pad change at the track. this guy (steve at Manta racing) said that Mallala is the hardest by far on brakes with three hard corners and bugger all time to cool in between, so I think my previous W116 problems and the SEC are all to do with boiling fluid. But mine was always different in that I could bleed up a good pedal, even between runs and it was only going soft after use - also fine on the road indefinitely.

Good luck everybody and try and keep a sense of humour!

[s class]

Oscar, given the neglected state of this car in question, I would have to assume the brake lines are corroded inside.  But then I would als have to assume the same about my trusty rusty that has never given me any grief in this regard. 

craigb - John Green is a little far from Johannesburg... besides, I want to be the one to solve this mystery and be the hero.   

Seriously, though, In my case I doubt boiling brake fluid is the issue, as I haven't even got the car up to operating temp since the last bleed, and I have the problems. 

I think the only thing I can do now is clamp the brake lines.  My local specialist shop said this is what they would do in any case if I brought the car to them. 

[WGB]

At least clamping the brake lines should put the master cylinder to the test.

Bill

PS I assume there are no loose hub bearings front or rear.

[s class]

WGB, I did the front bearings, and I have looked at the rears, which seem to be in order.  I did 10 minutes-worth of phoning around for brake-pipe clamps today, and so far nothing.  I will have another try tomorrow.

[Papalangi]

s class, what you want is either hose pinch off pliers like these,
http://www.sjdiscounttools.com/lis34660.html

or the C clamp (G clamp) style,
http://www.sjdiscounttools.com/lis22850.html

They won't be listed specifically as brake line clamps but may be listed as fuel line clamps.

Michael

[WGB]

Those second ones are the ones I have

Bill

[s class]

Thanks guys.  They are available online no problem, but will take a month to get to me.  I was hoping to find something local in the interests of getting the job finished. 

[Papalangi]

If you don't mind paying a premium, there must be the equivalent of Snap-on, Matco or Cornwell in your area.  Great big trucks packed full of tool porn.  You'll see them parked outside repair shops every now and then.  I paid $75USD for an 8 or 9 piece 1/4 inch drive metric socket set and $45 for the ratchet but I will likely never have to replace them in my life time.

In most auto parts stores, we have a section with a big "help" sign on top.  It's loaded with cheap specialty tools like these.  I also have a shop near me called Kent Tool Town.  I never go in there when I have money or am tired, it costs too much.

When calling around, you may have to use terms like "heater hose", "radiator hose" or "fuel line" combined with "pinch", "clamp", or "shut off".

Worst case, fold a 3 or 4 inch long piece of 1/4 inch copper tubing in half over the brake line and very carefully clamp it with locking pliers.

Michael

[oscar]

craigb - John Green is a little far from Johannesburg... besides, I want to be the one to solve this mystery and be the hero.   

I'm gunning for you sclass.  You'll be our saviour, the John Connor of brakes!  Sry, just watched the last Terminator movie with the kids.

FWIW, craig and sclass, I sought pro help/advice from my mech in Wagga plus our work workshop guys and MBSpares where I ended up getting the new MC from.  All said it was the MC when I described the sinking pedal.  Yet if I clamped hoses (with those Lisle clamps) or plugged the MC outlets with crimped and soldered salvaged lines, the pedal remained solid with and without engine running and standing on the pedal.  No sinking at all.  I made similar plugs for the end of flexible lines to make sure the flex hoses weren't bulging, or the steel lines if that's possible.  Same result, solid pedal.  Boiling fluid making vapour can be a problem but I agree it's not yours sclass nor mine when the problems exist with cold brakes right after a bleed.  I haven't tried angling the calipers in a way to help air out, but I spent ages tapping with a hammer to encourage trapped air out.  Don't know if that helped or not.

Although I've wondered about replacing the steel lines, when I think about those things I did above, you'd think the problem lies squarely within the calipers.  But having taken off the first set, resealed with no improvement, then resealing and trying a second set with still no improvement, I was left scratching my head.  Can we blame the reseal kits?  Are those big O rings bulging under pressure or is it just my method of resealing? 

But then, one more thing deserves mentioning re the MC.  If I think back to what I might have done wrong, Carl Jones once said something in a thread about not putting the pedal to the floor as the MC's lip seals will be damaged.   I've read it elsewhere too but at one stage or another, all of my MCs went to the floor before I read any of that advice.  I haven't tested any of my four MCs with the pedal say a quarter or half way depressed before applying clamps, then pressing the pedal further in without it lifting back to rest.  The seals might be fine at the start but not mid bore.  I'd be a brave, or perhaps foolish, bloke to doubt Carl's word but I admit I did.  Maybe I didn't want to admit I did the wrong thing four times over and certainly didn't want to shell out for another new MC.  I pulled the original one apart and from what I could tell on close inspection, each lip looked fine, but who knows what happens under pressure and halfway in the bore.  In the end, he's resealed his calipers with the same kits, hasn't pushed the pedal to the floor and has a solid brake.  So although I am/was a bit 50/50 about the possible damage to the MC, is it possible at any stage that your pedal hit the floor and fully compressed the MC?