Is this a bad brake master?

[tjp]

My initial post:

Bleeding my brakes after new brake master install. I bled the master in the car. Then rear brakes bled just fine. Now I cannot get fluid to flow to the front--am still on the front left. It just looks to me like there is air just bubbling in the reservoir when I pump the pedal with the front left speed bleeder open. If I open the bleeder for the reservoir the fluid drains out by gravity so assume no blockage.

If I did't get all the air of out the master would that cause what I am seeing?
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Postby msampsel » Sun May 29, 2016 1:05 pm

You probably know all this ...

If dual master, which I do not have, one of the circuits is rear and the other front.
It could be the master in that if dual the front and rear are separate.

If so does the fluid flow from master to the (five way going on other posts not expert knowledge on the existence of a 5 way) union?
Do either of the front brakes bleed?

got some of my info here: viewtopic.php?f=3&t=23650&p=211409&hilit=dual+master+line#p211409
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Postby svwilbur » Sun May 29, 2016 2:09 pm

on my 1970 2000 i believe it has two bleed valves on the master. did you bleed them both?
Mine has the little light that tells you when one of the masters has failed or that part of the system is failing, low or no pressure, in one side of the master cylinder. Either the front or the back.

I bleed the rears then the master and then the fronts but I did not have any issues. I did not use speed bleeders just the two person open, down, close, down synchronization method.

Maybe your speed bleeders got some gunk in it and is not closing?

Since this is a new master install is it possible that the front side is not sealing well in the master?
Did you try bleeding that side of the master with pressure instead of gravity to see if it bubbles too?
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svwilbur wrote:
did you bleed them both?
yes. But what are the chances that, if I didn't get all the air out of the reservoir for the rears, that it would cause the reservoir for the front to not pump?

svwilbur wrote:
Maybe your speed bleeders got some gunk in it and is not closing?
I removed the speed bleeder. It didn't change anything.

svwilbur wrote:
Since this is a new master install is it possible that the front side is not sealing well in the master?
If this is the case what are my options? Is this master shot out of the box?

svwilbur wrote:
Did you try bleeding that side of the master with pressure instead of gravity to see if it bubbles too?

I tried gravity and got fluid out of the bleeder for the rear reservoir. I also loosened the hard line fitting under the rear reservoir and got gravity drip. There is no blockage in the system: I was able to blast air through the system all the way to the reservoir.

I'm stumped.
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tjp wrote:
Bleeding my brakes after new brake master install. I bled the master in the car. Then rear brakes bled just fine. Now I cannot get fluid to flow to the front--am still on the front left. It just looks to me like there is air just bubbling in the reservoir when I pump the pedal with the front left speed bleeder open. If I open the bleeder for the reservoir the fluid drains out by gravity so assume no blockage.

If I did't get all the air of out the master would that cause what I am seeing?

^^^Just reading this over again.
This part just sounds really strange:
"It just looks to me like there is air just bubbling in the reservoir when I pump the pedal with the front left speed bleeder open. "

Why would air ever bubble in the reservoir???
It should just push fluid down the brake line and bubbles come out of the caliper bleeder.
Maybe something is wrong with the pistons or the seals when it was assembled?
or it is blocked and just pushing stuff backwards past the seals and piston.
But you say it can drip out and bleed.

I'm stumped. Just does not sound right at all. Blowing air back up the system may not have helped. but i assume you had this problem prior to that.

If you can get an assistant I would try the old way and re-bleed the master and try the fronts again using the old way of bleeding, down pedal, open bleeder, close bleeder, up pedal, repeat. There should be no bubbles in the reservoir. after running a couple reservoirs of fluid out it should be bubble free at the caliper.
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I am waiting for a video of what the rear reservoir is doing. I'll post that in a minute.

[tjp]

We did re-bleed both bleeders on the master--I got some air out of the front and next to nothing from the rear. And then I tried to bleed the front left again. Same results: nothing--no flow to the pipes.

Check this video. It is what the rear reservoir is doing as I pump the pedal. I've never seen this before.

https://youtu.be/gmtMLMwbwmc

[svwilbur]

That definitely does not look too good.
Sounds like maybe your new master is worse than your old one.

Maybe you should consider taking it apart and see if the pistons and seals all looks ok of if there is an imperfection in something?
You could compare the assembly with your old one.

Does that sound like it might make sense to the other contributors to the forum?

[tjp]

Thanks for all your input/feedback today Stacey. I really appreciate it, especially in the middle of a weekend when most are off doing what not else.

The last master was leaking into the foot well so obviously shot. The replacement was a "NOS" part bought a few years ago. Lesson learned. NOS parts with rubber seals are not reliable.

So the next question should be how reliable are "NOS" rebuild kits?

I'd still like to hear if any one else has ever seen what I am getting from this brake master.

[Linda]

My understanding is rebuild kits are only as good as the bore they are going into.... Or you could do a stainless sleeve and only have to worry about the seal bits.
Or get the 510 master with line adapter and warranty.
Linda

[fj20spl311]

a NOS cylinder should have a "NEW" bore and therefore the perfect candidate for a rebuild.

[tjp]

My understanding is rebuild kits are only as good as the bore they are going into

Very true but please let's keep this about WTF is wrong with my "new" master.

Or you could do a stainless sleeve and only have to worry about the seal bits

not going to go here yet.

Or get the 510 master with line adapter and warranty.

someone save me time and give me this part number as the money I spent on a "NOS" master was wasted.

[svwilbur]

I would think that if the NOS part has failed it most likely failed from the rubber seals decomposing over 40 years or sitting on a shielf.

if you inspect it maybe you could confirm what has failed and verify that the bore still looks good and that there is not any corrosion in the bore.

if it is just the "rubber" seals you could purchase a new ( NOT NOS) rebuild kit to make it functional again with the new seals.

That may not be your problem but if it was me I would go that route, check for a failure and try to repair with new parts.

good luck. let us know what you discover.

[Linda]

Tech Wiki, Parts Interchange has info on 510 master and adapter per Karl Payne.
Read the Parts Interchange for cost savings!
However price listed is higher than some sources.. Cardone rebuilt 11-1538 avail via RockAuto, Oreilley's and other sources for an early 510 master(68-72) no reservoirs around $50-60. Core may be required.
Must use adapter, multiple parts # in Parts Interchange.
Not sure if vendors carry any of these parts.

Linda

[C.Costine]

We did re-bleed both bleeders on the master--I got some air out of the front and next to nothing from the rear. And then I tried to bleed the front left again. Same results: nothing--no flow to the pipes.

Check this video. It is what the rear reservoir is doing as I pump the pedal. I've never seen this before.

https://youtu.be/gmtMLMwbwmc

Whenever I have bled brakes they have pushed fluid as your video shows, with air mixed in. With the cover on of course you can't tell if there is air coming up with the fluid.

[Datrock]

Before posting that NOS parts are bad, I would unassemble the cylinder, post some pics of what is bad with it, something maybe obvious wrong, never know it might just need a cleaning with brake fluid and reassembled.

[GeoffM]

If the U-cups aren't bad, their installed backwards.

[dbrick]

If the U-cups aren't bad, their installed backwards.

That makes sense. Messy, but easy enough to disassemble and look.
On a dual master, the piston and cups or seals on the rear master section do 2 things. They push fluid to the front brakes and another set of cups push the front piston to actuate it. If the rear section blows out, then a spring loaded rod, after compressing a bit, pushes the front piston.

Odd possibility, not sure if it happens on Datsuns, is that the brake safety warning switch in the junction block is jammed. There is a shuttle valve between the 2 sections and if pushed either way by unbalanced brake pressure, it activates the switch but can also block the passage on the side that failed if it sticks or jams on the switch.


Last thought is the rod is not coming back all the way, happened to me when the clip and washer that hold the rod were too thick. You must have clearance between the round end of the rod and the recess in the piston. the hole in the bottom of the reservior is only able to let fluid into the piston area with the piston fully back. As little as 3/16" can make the cylinder not be able to fill. This could explain the bubbles.You can see the cup pass the hole as you look down into the reservoir with a light just as the brake pedal comes fully up, that's when it should either bubble or squirt a bit of fluid up.

If you can, try to bench bleed it, short lines right back into the reservoir, see if it pumps at all, and/or borrow or buy a Motiv power bleeder, they work like a charm.

[tjp]

1 is a random one from a box of parts
2 is the "NOS" one
3 came off the car

I've not yet dissembled the NOS one to see if I can figure out what is wrong with it. What is jumping out at me are the bolts under the rear reservoir on 1 & 2. The master that failed last early winter does not have this bolt. Also, the tops where the plastic part of the reservoirs mount are smooth on the top two and ridged on the one that failed on me.

Thoughts on these differences?

Thanks
tim

[msampsel]

The smooth ones desire a hose clamp for the fluid reservoir.
I think one of my old time reservoirs actually screwed on and did not need a clamp.
Yes I lived in the 60's and 70's as a young adult so I do not remember everything!

The extra bolt there at the front of the MC is present on all the ones for sale.
Might have helped in the manufacturing process and or centering of the rod.
Does not seem to be high enough to be for bleeding.

My ramblings ...