Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by artificer » Thu Mar 14, 2019 8:46 pm

How about the possibility that you are pulling air around the slave cylinder cups...they are designed to expand against the cylinder walls under pressure. Pulling a vacuum on the system will induce air pressure in the opposite direction of the cylinder cup design.
Not so!
It is brake fluid under the application of atmospheric air pressure on the reservoir that pushes the brake fluid to the lower pressure source i.e. vacuum @ wheel cylinder bleeders.

This vacuum has absolutely no influence whatsoever on wheel cylinder rubbers/seals that are held squarely in position by pistons that near completely fill the wheel cylinder recess. The seals/rubbers are separated by a spring & on occasion/some applications expanders.

One achieves gravity bleeding due to the same atmospheric process/function if the master cylinder is high enough....it is just that vacuum makes bleeding more controlled & just so much quicker.

Often reverse bleeding offers a good solution to problem brake bleeds.
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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by sixbysix » Fri Mar 15, 2019 12:16 am

So have disconnected one of the brake lines - going to the front brakes a couple of feet from the master cylinder and pumped the brake a little (with vehicle off) - and only a drip or two of brake fluid came out the end of the line - so seems likely to be master cylinder i would think unless there is excessive air in the master cylinder - can this happen ? I haven't seen anything in my manual about bleeding the master cylinder .....
Thoughts?

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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by W. Winget » Fri Mar 15, 2019 4:35 am

Artificer
If there is a blockage (as the next post appears to indicate) the vacuum will be placing a negative pressure on the lines and air could be introduced past the slave cylinder cup seals. Is this not physically possible or have some scientific laws been violated I'm not aware of? although when new they seal pretty darn good, they are still angled toward the flow of fluid for a reason and if the flow of liquid or air (pressure) is opposite of the seals design..... :?:

Air can only be introduced in so many ways:
- Shaken fluid entrapping it and poured into the system
- Leak in a rubber line due to cracking or damage
- Mechanical leak due to a loose or corroded fitting or ruptured line
- Blockage at some point which induces cavitation in the liquid when passing a pinched point
- leakage past a seal
- oh...low fluid in Master cylinder while bleeding opening up the port to air

Where did my Mom go wrong?
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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by Ben Dover » Fri Mar 15, 2019 5:02 am

None of the above efforts have worked, the time tested method of just pumping up the master cylinder and bleeding each cylinder starting with the most distant has been a time tested method for both mechanic and "do it your selfer" for over 80 years. Find a lelper who has bled brakes before and give it a go.
No need to get fancy and bleed into a bottle, keep it simple.
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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by sixbysix » Fri Mar 15, 2019 5:51 am

ok I seem to have generated some interest :0) but no arguments please

so to sum up so far - springy soft brake pedal going to floor - goes to floor even easier when vehicle is running

no obvious brake fluid leaks from any position, master cylinder full/normal level.

have tried a standard manual bleed (pedal pumping) at all wheel cylinders - getting nothing out of wheel bleed nipples except on one wheel
so then tried vacuum bleeding - recovered fluid and lots of air bubbles from all wheels regardless of how long i kept going.

detached brake line to front wheels about 2 feet from master cylinder - pumped brakes, no fluid produced (about 2 drips) - meaning? Master cylinder not working properly??

Thoughts: air leak some where either through the master cylinder - if this is possible if rubber perished (remembering though that master cylinder is not leaking brake fluid) OR possibly through rubber brake lines adjacent to wheels if they (or one) is cracked (again noting no brake fluid leaks detected).
OR vacuum sucking through wheel cylinders ...?
OR internal collapse of rubber brake lines adjacent to wheels - though this doesn't seem to explain the air bubbles i get - or does it?

any other suggestions? - i am still thinking master cylinder as I haven't had high pressure fluid pumping out of brake line when it was disconnected suggesting to me that there is a seal problem on the master cylinder.
however do the master cylinders normally leak if they have perished seals ... ? (given this one isn't leaking).
awaiting your comments
- and thank you


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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by Ben Dover » Fri Mar 15, 2019 6:05 am

The reason the pedal goes to the floor when running is the assist from the Vacuum Power Cylinder.
My suggestion is to get an assistant and start trying to get some resistance feeling from the master cylinder (however little) and then see if you can start some flow from the rear bleeders.

Is there any dirt and sludge in the master Cylinder reservoir> It would not hurt to clean it up and install a kit.
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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by johnwaz » Fri Mar 15, 2019 8:59 am

It sounds to me that your problem is indeed in the Master Cylinder. Fluid can push past a blown internal seal and not have an external leak.

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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by sixbysix » Fri Mar 15, 2019 6:14 pm

Thank you johnwaz and ben and artificer ( i was hoping to hear a little ore from you)

Ben - yes there was a little black "silty' material in reservoir - not heaps of it but enough to discolour the walls and floor of the reservoir
i was wondering if it might be perished rubber 'dust' -?

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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by Ben Dover » Fri Mar 15, 2019 9:37 pm

Good thinking, and If you do install a kit, use alcohol or a non petroleum solvent to clean the cylinder.
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Re: Studebaker US6 always get air bubbles when vacuum bleed wheel cylinders

Post by Ben Dover » Sat Mar 16, 2019 6:48 am

Sometimes the master cylinder will get a touch of air that is difficult to get rid of. There are little tricks some have learned to get around that, one is "burping" the master cylinder by just nudging the pedal, when you do it just right there will be a ripple of return fluid and a bubble will surface.
Remember not to let the reservoir go dry.
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