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Old 02-09-2019, 11:17 AM   #1
Mini-Skoolie
 
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Year: 2005
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Brake bleeding 2005 thomas

I have a 2005 thomas safe t liner that I recently replaced the hydromax booster and master cylinder because it was leaking between the 2 pieces so I pulled one that was good off of an international 3800 bus I owne because they use the same units and now I can't seem to bleed the darn thing to get it to work
Just to be certain I even swapped the old one back on and it won't bleed either .the problem is that it won't build pressure to push the fluid out at the wheel cylinders . so tried to use a vacuum bleeder and it doesn't hardly pull fluid either it's as if there was a restriction.
Now using the vacuum pump on the line going into the and unit pulls a lot more fluid than at the wheel cylinders. So I'm thinking it has something to do with the abs but it was working fine before the swap.
One other thing is that the electric pump on the hydromax booster is also no longer getting power and my brakes aren't working either
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Old 02-09-2019, 03:37 PM   #2
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What kind of shape are the brake lines in, front to back to be sure it isn't that creating your situation?


How old and rusty are they if at all?


Get some pics of bad spots in your mind.
Lots of brake help on here.


John
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Old 02-09-2019, 03:59 PM   #3
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Don't know your bus? And John has a good point.
The rubber flex lines at each wheel over time can and will collapse the internal lining and not be visible on the outside. Most hydraulic systems have a distributionblock (manifold with sized orifices) after the line/lines leaving the master cylinder to distribute the fluid to front/back at the required pressures.
On an older system the distribution block can and will collect rust particles and block the orifice openings.
Brake fluid flows both ways as the peddle is pressed.
If the master cylinder cap and or rubber seal is bad then you have contaminated fluid injected into the entire brake system? Rust for anything steel/iron.
The rubber lines could be the issue?
As far as power to the pump? I would start with the fuse? A lot of old connectors that are wore out only takes a little bump or a not disconnecting the battery before starting to pull plugs/wires.
Good luck
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Old 02-09-2019, 08:11 PM   #4
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Thank you fellas as for the lines they look to be in good condition and without leaks I blocked off the lines ports coming out of the master cylinder with plugs and the pedal still went to the floor even after trying to bleed it by pressing the pedal and cracking the plugs to bleed out the air still no pressure so I'm thinking that the master cylinder is bad .
Should have one in tommorow
As for the motor I found the moniter/controller for it unfortunately it doesn't match the number of wires it's supposed to have according to the bosch info I found on the hydromax system if I could find a diagram of it I could check the wires but I've given up on that after calling the manufacturer and being sent to the dealership being told they would get me one and nothing .
Such is typically my experience with dealerships .
But I figure I can take care of wiring after the brake pressure is solved
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Old 02-09-2019, 08:39 PM   #5
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It could be that the master cylinder is air locked. If I remember correctly, I have had to resort to pressure bleeding on a stubborn unit. Other times I have left all the bleeders open and just kept adding fluid to the reservoir, however that may not work on a bus with the distance the fluid has to travel.
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Old 02-09-2019, 08:58 PM   #6
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Quote:
Originally Posted by one_eyed_jack View Post
It could be that the master cylinder is air locked. If I remember correctly, I have had to resort to pressure bleeding on a stubborn unit. Other times I have left all the bleeders open and just kept adding fluid to the reservoir, however that may not work on a bus with the distance the fluid has to travel.
Sounds like good possibility.
I have an idea about rigging up a pressure feed deal using a spare cap .
How much air pressure did you use ?
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Old 02-09-2019, 09:14 PM   #7
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Quote:
Originally Posted by Doe69936 View Post
Sounds like good possibility.
I have an idea about rigging up a pressure feed deal using a spare cap .
How much air pressure did you use ?
You know I can't remember, couldn't have been more than a couple psi., think I just held a section of heavy tractor inner tube with valve stem attached over the reservoir. I didn't have a spare cover to make a proper set-up with.
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Old 02-09-2019, 09:19 PM   #8
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Quote:
Originally Posted by one_eyed_jack View Post
You know I can't remember, couldn't have been more than a couple psi., think I just held a section of heavy tractor inner tube with valve stem attached over the reservoir. I didn't have a spare cover to make a proper set-up with.
If you have a cap it would be real easy, just drill and tap it to 1/8 pipe and get a valve stem that has 1/8 pipe thread on the other end.
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Old 02-09-2019, 09:19 PM   #9
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wires and hydromax

There are two ways the bosch/bendix hydro max can be wired.

1) more basic low level system, has fewer wires and parts.

2) more woop dee doo level system has more parts and a kind of diagnostic module

The electric pump runs all the time if there is some sort of fault or a problem in the system. The pump is a back up to the power steering pump.

on the work bench, you should have a fitting in the master cylinder outlet ports. then on the fittings you have some sort of pipe or tube going back to the reservoir. brake master sitting up right ..fill reservoir with brake fluid, now with some sort of tool push in - full stroke - on the plunger of the master brake cylinder..... you should see brake fluid and air bubbles going out the tubes into the reservoir. after several strokes, you should see pretty much just brake fluid. This is called "bench bleeding"

Now that this is done... wait...... Is the plunger -- the little rod thingy sticking out of the end of the booster? this part is going to be the thing that pushes in on the brake master cylinder when you step on the brake pedal.

okay, now that we know the push plunger thing is there. bolt the master cylinder in place, loosely. those tubes and fitting things should still be in place.

take out one of those fittings... and as quickly as you can thread in by hand the brake fitting/pipe of the bus into the hole... get at least two turns by hand, tighten fitting. care full how tight, you can crack or split the end of the brake line if you tighten too much. err on loose, you can tighten a bit more if we have a leak there. now do the other pipes to the master cylinder.

now that all brake pipes are connected and tight, tighten the master cylinder.

now you are ready to bleed brakes.... maybe.

you should be able to gravity bleed brakes.....

fill to the top the brake master cylinder. leave the lid off the reservoir, unless there is dirt, dust, rain hail or snow able to get into reservoir. In that case just set the cap on the top, do not screw it on.

now go down to the front right wheel and open the bleeder screws. you should have fluid run out with air bubbles after a minute or two.....

If you do not have fluid leaking out after a couple of minutes, your rubber brake lines are likely in need of replacing..... The bummer thing is.

in order to check your rubber brake lines, you will destroy the part in the process. if the fluid is not flowing..... loosen the top end of the right front brake hose where it connects to the brake pipe...... I would then expect the fluid to weep or leak here after a minute or two. if you have fluid at the top of the rubber hose, but not down low at the caliper/brake drum. Then it is highly likely your rubber hose is shot.

cut the rubber hose in the middle, use some thing very sharp to get a good clean cut.... I expect you find the center closed up, like a millimeter or less.

you need new rubber brake hoses... replace them all.

fill the master again, attempt to bleed.

william
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Old 02-09-2019, 09:21 PM   #10
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Well I just watched a video on building one out of a bugsprayer said don't go over 20psi so there's a range to not go over .
"Smacks head" innertube brilliant thanks
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