Bench bleed problem

[swamp rat]

Bench bleeding the master cyl today the way a friend taught me, Chuck into a vice, plug the ports on the side, put some fluid in the reservoirs grab a philips screwdriver and start pressing the piston in and out till the air bubbles stop.

I noticed today that every time i press the piston inward brake fluid squirts back thru the rear wheel brake reservoir inlet port about 2" high, however the front wheel reservoir inlet port only push's the fluid up about 1/4 to 3/8" high.

First off I have no idea if pushing fluid back thru the reservoir inlet port is normal.

Secondly, before i removed the master i was having trouble bleeding my brakes, i had plenty of fluid to the rear wheel calipers but next to nothing at the front calipers.

Am i doing anything wrong bench bleeding?

Is it normal for the master to squirt fluid back thru the inlet like that ??

I don't mind saying that this is the first time i have had a master and booster replaced so not a lot of experience with it.

[1blue72]

Should have flexible tubes feeding back into the reservoir when bench bleeding the best way to bleed brakes is with two people start pushing fluid thru those bleeders on the truck don't be afraid to go thru some fluid

[jocko]

If you bench bleed the master cylinder with the ports plugged (the way that most new master cylinder install instructions state to do it), it is important to only push the piston in approximately 3/4"-1", and no more. I put a wide piece of blue or green painter's tape on the screwdriver, insert it into the piston bore (a wooden stick is probably preferred to a screwdriver...), look straight down from above the mc, put a mark with a sharpie even with the rear mounting face of the mc (or any reference point you can repeatedly see clearly) - then mark the tape on the screwdriver again, approx. 1" from the first mark (i.e. UP the screwdriver's shaft). Reinsert and slowly cycle the piston between the two marks, without letting the 2nd mark disappear inside the housing (1st mark is the seated position, 2nd is the 3/4"-1" depression point. Do this until you see no bubbles coming up from inside the mc, and it takes a little while, lotsa air in the passages of a new mc. Works every time.

[cdowns]

i have found bench bleeding way overrated

[Artikgrau325is]

Originally Posted by cdowns

i have found bench bleeding way overrated

Same. By the time I get the plugs and tubes off and hook up the regular lines I'm sure there's a TON of air that gets in anyway.

[LockDoc]

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To answer your question, yes it is normal for fluid to squirt back up from the inlet ports. I think it will only do it when there is back pressure on it (ie: when it is installed or the line ports are plugged) If you had the short bleeder hoses on it I don't think it would do it.

LockDoc

[swamp rat]

Yea i have often questioned the fact that you have to open the ports on install and does some of the air get back in anyway..

I dug around and found the port plugs that you hook hoses to and route them back in the reservoir, so last night i hooked them up and primed till i got all the air out of the lines, then i let it sit till this morning, it had more air in the system so today i went back and forth first raising the front and pumping till no air, then lowering the front down and pumping till no air, did this about 8 times and gonna leave it sit again till after work then try again to see if more air is in the system, if there is more air then i can only conclude its coming in from somewhere ether the plugs or a bad O-ring...

[MLB57]

bench bleed and put it on the truck, also bleed the proportioning valve at the same time you will never get the plastic plugs to seat enough to leave sit. I use old pieces of brake lines to bleed master cylinders.

[swamp rat]

Originally Posted by MLB57

bench bleed and put it on the truck, also bleed the proportioning valve at the same time you will never get the plastic plugs to seat enough to leave sit. I use old pieces of brake lines to bleed master cylinders.

So your saying to leave the Prop valve connected to the master when bench bleeding and run the hoses from the prop valve back to the reservoir?

I didn't even think of bleeding the Proportioning valve at the same time, great idea, it may solve all my problems!

I believe my Prop valve from inline tube needs to be reset, it has no button to press in while bleeding, last attempt i got a tone of fluid to the rear but very little to the front.

[MLB57]

It will center when you install it, yes bleed them both at the same time, gravity bleed the system before you start pumping the pedal

[swamp rat]

Originally Posted by MLB57

It will center when you install it, yes bleed them both at the same time, gravity bleed the system before you start pumping the pedal

I was trying to vacuum bleed the back first, had problem with my bleeder gun, then tried to gravity feed the back, did that then went to the front and got next to nothing.

Hopefully I'll get this figured out pretty soon. I did get the reset procedure from Inline Tube.

[wilbilt]

Yes, fluid will squirt back up into the reservoir when the pedal is released. This occurs through the 'replenishment port'.

If pressurized fluid from the lines was not returned to the reservoir upon removing your foot from the pedal, the brakes would never release.

[swamp rat]

Originally Posted by wilbilt

Yes, fluid will squirt back up into the reservoir when the pedal is released. This occurs through the 'replenishment port'.

If pressurized fluid from the lines was not returned to the reservoir upon removing your foot from the pedal, the brakes would never release.

Makes perfect sense, i just noted that the rear had much more back flow volume. Thank you!!

[jocko]

One note on resetting the prop valve switch - you will normally need to stomp on the pedal once front and rear systems are bled in order to recenter the valve.

[swamp rat]

Originally Posted by jocko

One note on resetting the prop valve switch - you will normally need to stomp on the pedal once front and rear systems are bled in order to recenter the valve.

I missed your post, Thank you! Hope to get back at it tomorrow (actually today now)