Persistent brake problems: air trapped somewhere?

[Gäst W-J-M]

Are the flexible brake lines on the Volvo compatible with some other

 

brand, in the context of correct fittings/screw-thread?

 

 

 

Background: I have a 'two-stage' pedal/brake interaction, as if there

 

is air in the lines (first push only half the brake performance,

 

second push full performance, lasting a dozen seconds), yet dozens of

 

hours research by Volvo experts, testing/exchanging nearly every

 

crucial part/component (new slave cylinders, replaced master, booster-

 

surgery/inspection), haven't solved the problem....including exotic

 

methods as bleeding at the slave cylinders (military tip #1) and

 

reverse bleeding (military tip #2).

 

And 5 consulted military-workshop experts said that they too have

 

faced C3-series with this exact problem, and that they too couldn't

 

solve it....it just happened sometimes after service #XY, and even

 

rebuilding the entire system didn't do it.

 

(Volvo itself apparently rebuild the entire system in glass once,

 

just to analyse whether they could *see* a section/spot that trapped

 

air-bubbles)

 

 

 

Last remaining alternatives:

 

 

 

- inserting a few more bleed-nipples at strategic points.

 

- replacing all the rubber flexible lines with stainless steel, if

 

only to improve the first stage to a more acceptable level

 

(I can't imagine the original rubber lines being the cause of this

 

two-stage problem, as that would imply that there is a weak spot in

 

the rubber, bulging out at the first push, only contracting after a

 

dozen seconds)

 

 

 

Btw, two bleeding methods I came up with, but were not embraced by

 

any of the shops, is 1) high-pressure/pedal bleeding with engine

 

running (boosters active), and 2) using a more viscous fluid, in a

 

different color (learned that color-thing from someone who bled his

 

brakes with milk, so that he could see when the old brake fluid was

 

out.

 

 

 

Any thoughts about any of these points?

 

W-J-M2007-05-27 23:07:38

[Gäst ErikC304]

Hello Willem-Jan! I dont know who posted here, but some time ago one member meant that it helped letting the piston nearly put out of the cylinder, that one person pressed pedal softly and second person held piston to its position and in that way let air and liquid out of the upper part och cylinder. I find it strange that cylinder could be designed with bad bleeder screw position, but according to the poster it worked. Could be worth testing, I have myself no experiance to this wizard way bleeding.

[Gäst s-os]

They even locked the bottom brake-shoe with a hammer against the floor so that the bottom cylinder piston would not jump out... it worked for them... a lot of air came out from the upper cylinder and the brakes became very stiff and precise.

 

this was done by "lövviksbon" who also replies in swedish below... i tried to translate and edited above according to his remarks.

s-os2007-05-28 10:14:25

[Gäst lövviksbon]

Japp, det var dom övre cylindrarna på framhjulen som det fastnat luft i för oss. Hammaren satte vi mot golvet och det nedre bromsbelägget, för att den nedre cylindern inte skulle hoppa ut när vi tvingade ut den övre.

 

Jag skulle gärna svara själv men min stavning är nog så dålig på svenska så han skulle inte förstå vad jag skrev.

[Gäst W-J-M]

Hello Willem-Jan! I dont know who posted here' date=' but some time ago one member meant that it helped letting the piston nearly put out of the cylinder, that one person pressed pedal softly and second person held piston to its position and in that way let air and liquid out of the upper part och cylinder. I find it strange that cylinder could be designed with bad bleeder screw position, but according to the poster it worked. Could be worth testing, I have myself no experiance to this wizard way bleeding.[/quote']

 

 

 

Hmm....you mean the master-cylinder, correct?

 

Your description sounds similar to what is known as 'bench-bleeding', bleeding the unit on the bench, removed from the vehicle.

 

(in Land Cruiser context, I never understood why this might be necessary, since you can avoid 'bleeding-by-pedal/piston' alltogether with an external bleeding-vessel/tank (brake-fluid under air-pressure), connected to the brake-reservoir(s), refilling automatically).

 

 

 

And such an external unit (more common when servicing trucks) is what was used in my case too.

 

(for those who want a cheaper consumer-grade unit, check the PowerBleeder, made in the USA; that is what I used myself in the past)

 

(but the shop used a professional truck-style unit of course)

 

 

 

Note that this also avoids the problem of taking care of both front shoes at once, since you can pressurize (and refill) one reservoir/circuit at a time, not both toghether as when you press the pedal.

 

 

 

Add reverse bleeding (pressurizing & filling upwards, from the slave-cylinders, at the wheel, back into the reservoir), and there simply can't be any air left in the master-cylinder, unless they specially designed an air-trapping dead-end cavity somewhere in the top....8-))

 

 

 

Btw, spoke with another guy in Sweden today; he mentioned the trick to raise the *nose* of the vehicle into the air, to overcome this air-trapping.

 

(only a mild hill, which suggests that it can't be a large/complex air-trap either, hence it should have been solved by other means as well)

 

(we did *lower* the nose in one of the first sessions, which still sounds more logical to me, in the context of air-traps further down the line....but perhaps for air-traps near the master-cylinder, nose up might be better)

 

 

 

PS, two interesting side notes/questions:

 

 

 

1) has anyone ever figured out why our Volvo's originally had a second, smaller, brake-shoe return-spring as well?

 

(which is impossible to put back in place after service)

 

 

 

2) current replacement brake-shoes from Altyco are remanufactured, resulting in a 1mm thicker brake lining than original....for most brake drums, this is okay, since they have been worn, especially when driving in mud, as is typical for most military & utility trucks....however, firefighters hardly saw any mud, so their brake drums are in much better condition....even *too* good to fit the thicker brake-linings, impossible to get them on, no matter what....so in the end, my shop got an older set of original brake-shoes, the only solution.

 

 

 

Conclusion: for this kind of 'near-new' drums, either find a set of original shoes, or have the old shoes relined yourself at a brake shop, to a less thick specification.

 

(custom relining is also something I want to do one day with my old civil clutch....a guy in the USA had his relined with Kevlar....sounds as if I could do that with brake-lining as well....)

 

 

 

 

 

 

 

 

 

 

 

 

 

W-J-M2007-05-28 19:09:45

[Gäst s-os]

It´s NOT done on the master-cylinder, it´s done at the wheel with the brake-drum removed... you must have the piston in the brake cylinder almost out of its place (jumping out of the cylinder)...thats why you need to be two, one pressing the brake pedal very gently... fixing the bottom brake-shoe with an e.g. hammer against the floor will keep that piston in place (easier if you do not have to worry about it also)... this is how I understod it was done. s-os2007-05-28 19:25:44

[Gäst W-J-M]

It´s NOT done on the master-cylinder' date=' it´s done at the wheel with the brake-drum removed... you must have the piston in the brake cylinder almost out of its place (jumping out of the cylinder)...thats why you need to be two, one pressing the brake pedal very gently... fixing the bottom brake-shoe with an e.g. hammer against the floor will keep that piston in place (easier if you do not have to worry about it also)... this is how I understod it was done. [/quote']

 

 

 

 

 

Hmm....the only remaining mystery:

 

The exact same slave-cylinders were used in Land Rovers, correct?

 

How come they never suffered from all this?

 

Or were the slave-cylinders in a different orientation, vertical vs horizontal, or upside-down compared to Volvo?

 

 

 

And is your method identical or at least congruent with the method I mentioned earlier, bleeding at the cylinders, instead of the usual bleeding at the nipple?

 

(apparently the tube section between cylinder and bleeding nipple wasn't designed/configured properly either, still allowing trapped air)