Bob K's Hino BC144

[bobk]

Some months ago I noticed brake fluid on the front right hand tyre. Now the bus has been sitting static (and unloved) for a year or so, and I was a bit surprised. Anyway I have replaced the 4 front wheel slave cylinders and adjusted the brakes. Now comes the bleeding. I am in the process of building a pressure bleeder, of which I found an example on a 4wd forum, so I will get around to the bleeding shortly. I have not bled a vacuum/hydraulic system with remote boosters before and I am assuming that it will not be any different to your average small vehicle, ie, start at the furthest wheel etc. However, I just need to be reassured that no other bleeding points need to be looked at, such as the bleeders on the cylinders mounted on the boosters (aft on the chassis rail). Any comments or help would be welcome.
BobK

[T1 Terry]

Is it hydraulic over boosted hydraulic or air over hydraulic? Welcome to a whole world of pain if it is air over hydraulic.
If it is hydraulic over boosted hydraulic, first, bleed between the pedal and the booster.
Bleed method, 2 people that can hear each other, person 1 working the pedal, person 2 operating the bleed nipples.
Person 2 calls to person 1, "pedal down", person 2 confirms, person 1 opens the bleed nipple and keeps I open until person 1 calls "down" confirming the pedal is all the way down. Person 2 closes the bleed nipple and calls up to person 1 "pedal up" they call "up" when the pedal is all the way up. Wait 5 secs and repeat. After 5 cycles, check the brake fluid reservoir.
Do not pump the pedal or any of those antics used in days of old, you will end up with air in the system every time.
Check if the booster hydraulics has its own reservoir. If it does, you will need to cycle that system to get the air out of the booster hydraulics and that will require air/vacuum, depending on the type.
Bleed the pipes going out of the booster first using the system above, then the next point, then the next down the line. If you start with the furthers away you risk pulling air back into the booster hydraulics, you need clean fluid in the lines coming away from the booster hydraulic so any that returns to the booster will not have air in it.
Even using a pressure bleeder, the master cyl at the pedal must be cycled to get the air out of that part and the booster hydraulic cyl must be cycled to get the air out of that part.

If someone has upgraded the system and added a booster after the original equipment booster, start with 2 Valium and adjust as required Then it is part 1, then part 2 as above so you bleed through to the second booster, then the same process as part 2 for the second booster. The brakes are incredible with the booster to second booster upgrade, but bleeding the whole thing requires a lot of patience. The second booster always has its own reservoir, so make sure you keep an eye on that fluid level as well as the other original equipment ones.

T1 Terry

[jon_d]

Be very very quiet..... I'm hunting wabbit.

Be very very careful, don't pump the pedal or push a long way. Unless the master cylinder has been sleeved with stainless steel, the rubber seals tear on the rust at the bottom of the bore.

This was my $350 lesson.

[BernieQ2]

When I done a seal on the left hand rear after renewing the seal I cracked the bleed nipple and put a tube on it into a jar and left it for the night , after making sure the master cylinder was as full as .
Next morning the jar at the wheel was about half full and master cylinder about half full . Done up the bleed screw and all was good .
Whether I was just lucky ....I don't know .. I did in turn check each wheel bleed nipple but got no air from them .
Bernie .

[bobk]

Thank you for the replies, and sorry for the delay. I intend to draw a schematic for myself so that I can fully understand what I am seeing, however for the moment a word picture will have to do..... The (only) reservoir is on the right side of the dashboard under a cover. Two rubber hoses (I suppose front and rear brakes) lead to a cylinder vertically mounted adjacent the steering column. I assume this is the master cylinder. From this vertical cylinder two steel pipes run through the floor then aft to separate cylinders attached to separate vaccuum assemblies. From those cylinders, steel pipes go to tee pieces for left and right, front and rear brake assemblies. Is this info useful?
BobK

[T1 Terry]

Thank you for the replies, and sorry for the delay. I intend to draw a schematic for myself so that I can fully understand what I am seeing, however for the moment a word picture will have to do..... The (only) reservoir is on the right side of the dashboard under a cover. Two rubber hoses (I suppose front and rear brakes) lead to a cylinder vertically mounted adjacent the steering column. I assume this is the master cylinder. From this vertical cylinder two steel pipes run through the floor then aft to separate cylinders attached to separate vaccuum assemblies. From those cylinders, steel pipes go to tee pieces for left and right, front and rear brake assemblies. Is this info useful?
BobK

OK, so it is a hydraulic over vacuum assisted split system between front and rear brakes so there is some redundancy. You do not have a booster over booster brake system so you may not need the ......apparently that calming drug name is also now a dirty word here
As far as the master cyl having rust etc at the end of the stroke, you need to sort that problem first. If you ever have a brake problem that causes the pedal to go to the floor you don't want that to be the total death of the brake system. So, remove the master cyl and either get it rebuilt, rebuild it yourself, or buy a new one and rebuild that one as a spare. If the wheel cyls failed you can be sure that rust pitting is all the way through the system. This is caused by not regularly flushing out the old brake fluid to remove the water it has absorbed from the atmosphere as it heats and cools. That "the pedal just went to the floor half way down the hill" is caused by the water in brake fluid boiling to steam and that just compresses rather than being non compressible when it is in fluid form.

Many moons back you could buy silicon brake fluid that lasted for life, had an extremely high boiling point, was a lubricant and didn't absorb water. The mob that made it seem to have stopped production after the problems they ran into regarding poisoning the Sydney underground water basin

T1 Terry

Strange that I could post it in the previous post yesterday but not today, but it starts with a v

[BruceS]

Trump.... blame Trump!!
That container on the rt side of the dash sounds a lot like Nissan & others have.
It is actually one container that is used for clutch & brake.
Most have a dash warning light that comes on once the level falls so far that a sensor works.

[bobk]

Thank you for the replies. I have said before that I admire the brains displayed on this site. Bobk

[bobk]

Correct Bruce, the reservoir serves front and rear brakes and the clutch. Now the woe is me bit. I tested my pressure bleed device on the bench and all is good (approx 10 psi). I decided not to worry about looking at the master cylinder, it was simply too difficult so I went and bought some brake fluid and filled the reservoir. Had lunch then got into it. I attached the bleeder and gave the pump a half dozen pumps and heard a whooshing sound. You might recall I mentioned earlier that there were rubber feed hoses to the master cylinder. Well you guessed it, those hoses were as old as the bus 1994, and one of em couldn't stand the pressure. What a bloody mess!! Now I know there are 3 hoses cause the dash has had to come to pieces to repair the damage and replace the hoses. This being the case the brake and clutch master cylinders might as well be inspected/fixed. Damn. Clutch appears easy enough but to get the brake master cylinder out has me a bit bothered. There is a removeable pin at the top of the piston shaft where the brake pedal (lever) attaches, but the head of the pin is up against the steering column support structure. I will try removing the hose and pipe connections tomorrow and removing the two bolts that secure the cylinder to the support structure. Once the cylinder is released there may be sufficient space to remove the pin but the pessimist in me says I'd be dreaming.
bobk

[jon_d]

the end of the pin is mushroomed and just pushes down on the piston.

Can the master be removed while leaving the pin in place?