Suspected brake master issue

[Curtis]

Speed bleeders on there now?

[cbez]

On the wheels yes not on the master.

Shouldn't need it since it can only suck up brake fluid if you run your hose back to the reservoir.

[cbez]

Well still scratching my head on this one.

I've been trying to let it sit overnight and bleed in the morning since that's when the soft pedal is.

Yesterday, firm pedal and solid fluid out of the master bleeder right away.

This morning, 3 pumps of nothing then pressure and fluid coming out of the master bleed. One little pin sized bubble.

[Gregs672000]

Man, this car sure has had its share of mysterious issues. The last thing I can think of would be to rig up something (an extended bar, maybe a weight, or?) that puts constant pressure on the pedal to see if it leaks down or holds pressure over several hours (disconnect battery or fuse for the taillights... dead battery otherwise). The fluid HAS to go somewhere! Are there any places in the system where air could enter without losing fluid? Can't imagine...

[jrusso07]

Crazy problem. One final thought (from me) is to check under all the rubber dust seals/boots for fluid. The seals on the rear cylinder pistons, the seal under the fire wall on the master (although your photo shows no leakage, it might be so minor that it hasn't filled up the boot cavity yet), and lastly, baring fluid on other seals, the dust seals on the front caliper pistons (have to pull the caliper bracket off).

[redroadster]

Which brake fluid do you hate now ?

[cbez]

still hate dot 3 lol.

[JT68]

still hate dot 3 lol.

me too lol, it has ruined a lot of paint.

If the dot 5 fluid itself was a problem, it would always be a problem in every roadster using it.

Hydraulic fluid doesn't work fine & then misbehave "intermittently".

[redroadster]

I'll notify the Automotive Engineers Society of your findings .... If you guys get it working .....for any length of time
of course thats s lot of dot 5 bottles that will have to be changed. you guys are dedicated ...I like that

I was just doing it to the clutch , don't think id risk it brakes wise for one thing ...if you got into a wreck , maybe a dispute about braking & insurance investigator saw it the purple B dot 5 fluid ....
ya done

[Curtis]

If you absolutely can't find any leaks anywhere then you could try a new repro master from Brian at Sin City Datsun. Much most cost effective.

[cbez]

I have a master rebuild kit coming. So we'll see how that goes.

Reasons I suspect the master:

1) When I push, it feels like nothing rather than compressing air.

2) When I push the pedal in the morning with the bleeder open, it doesn't have any pressure even though it has a clear shot out through the bleeder (the fluid should prefer to go out that way rather than compressing any air in the system). No fluid comes out of the bleeder at all until I feel resistance on the pedal.

So I think whatever seal in the master is responsible for holding pressure is compromised, maybe shrinking in the cold and intermittently breaking the seal but then temporarily fixing after being pumped a few times.

[Curtis]

Oh boy, master rebuild. I use the Dremel steel wool type disc to clean them up. Nice surface for seal.

[cbez]

Ok finally got around to it today. I pumped most of the fluid out of the reservoir and I noticed when I'm first pumping with the empty feeling pedal, brake fluid is moving in the reservoir but nothing is coming out of the bleeder until the pedal gets firm again. No air, no dribbles, nothing.

Anyway, everything came apart and went back together fine.

The only real issue I found in the master was what looked like some metallic dust on the seals, and a slightly worn spot in near the rear of the master, that could be felt by hand. I can't really imagine how you would get metal on metal there. Maybe from a previous fix?

Rear of the master was totally dry so no sign that the small amount of wear in the back was causing a leak.

I bled the master and it felt fine, I'll do the lines again tomorrow just in case any got in the lines when I opened the system up.

[cbez]

Firm pedal this morning, and noticeably improved driving feel. We'll see if it stays that way!

[cbez]

hasn't resurfaced since the rebuild...so it was MC related somehow but I'll be damned if I know what it was.