Suspected brake master issue

[unklpat]

speedbleeders are your friend. I think part# 3824 fits our cars. Make sure to remove the ball bearing on front. Pat

[DAC21]

speedbleeders are your friend. I think part# 3824 fits our cars. Make sure to remove the ball bearing on front. Pat

Yep, Goodrich SB3824, it's a Harley Application which fits the Roadster front and back if original cylinders. The pack in my hand actually has P/N 817-02252, but sold as SB3284. I believe Speed Bleeder the original Company making these assigned P/N SB3284. Either the patent expired or they have licensed out to Goodrich and Dorman whom assigned their own P/N. Here is the best deal I found for a pair. $12.35 shipped add tax. Size to look for if shopping a different brand is 3/8-24, 1.29 inches long

https://www.ebay.com/itm/234171745645

[unklpat]

I'm holding a package in my hand, Speedbleeder brand. Part# SB3824HD, the part# reflects the size and pitch of the bleeder threads. I've put several in, and know this to be correct. Pat

[DAC21]

I'm holding a package in my hand, Speedbleeder brand. Part# SB3824HD, the part# reflects the size and pitch of the bleeder threads. I've put several in, and know this to be correct. Pat

That P/N should also work for the Brake Master Cylinder as well 1964-67 as Rallye shows the rear Bleeders and Master cylinder as being the same part.

[unklpat]

Again, remove ball bearings in front caliper bleeder holes. The cool thing about this product, you can do it yourself, it is more accurate than opening and closing the bleeder, and you can force the fluid thru, sort of purging your lines. Pat

[cbez]

I'm sure the info will be good for society but I already have speed bleeders guys and bled everything thoroughly a few hundred miles ago. It's a new issue but I guess it's possible I have air getting into the system somewhere.

[DAC21]

I'm sure the info will be good for society but I already have speed bleeders guys and bled everything thoroughly a few hundred miles ago. It's a new issue but I guess it's possible I have air getting into the system somewhere.

One would think if air is getting in, fluid is getting out. Yet no signs of drips?

[Curtis]

I found it hard to see any fluid when my front caliper failed.

[redroadster]

Did you bench bleed the mc ? Or do it on car before hooking lines up , you take $ 1ft brake lines and hook up then curve them into the mc tank , pump until no air bubbles are present .
It doesnt return to that same condition in the vid until morning ? Thats strange cant say Ive ever seen that in 4 decades of auto work if tge caliper pistons aren't parallel to the rotor it can spring back , you need a pumper while you watch the brake action

[cbez]

it will return like that after a long sit (the longer, the softer it seems..) or occasionally during traffic ill get a longer brake press but not fully soft.

reservoir is still high and I checked fittings recently so if it is leaking it's microscopic somewhere.

[redroadster]

My recollection from a 311s post was when bleeding the brakes, go very slow when depressing the pedal for bleeding. I believe it was to take 10 seconds to go through one pedal press. That worked for me. Depending where the air is, it can take a while. Also, I would focus on on the front brakes as that is likely where the issue resides.

Those darn front calipers.

The rear brake master cyl pressurizes 1st 80% then the frt

[cbez]

Bled the fronts and topped off the master, did it solo so I couldn't look for bubbles. 20 mile test drive felt fine, after sitting 5-6 hours took another several pumps to get a firm pedal again. No perceptible drop in the reservoir level at all.

Confusing for me as generally air has always given me an overall shitty pedal, not one that pumps up and then feels perfect. I'll try to bleed the rears and master just in case but I think I have a master rebuild in my future. Thinking perhaps the check valve went bad?

symptoms:

long sit: 1-4 presses of a totally soft pedal to get a firm pedal
driving: occasional slightly softer press, which is immediately firm on a followup press

[JT68]

cbez, What you are describing is classic "air in the system/micro leak behavior".

For micro leaks, go around to every fitting and wipe it with your fingers. If your fingers come up even barely damp, that is your leak. Tiny leaks may not be noticeable in the reservoir immediately, but over time (days/weeks), will show up. They also may not leak at all unless the system is under pressure.

If ALL the fittings come up totally dry, there is still most likely air in the system unless you find a damp cylinder.

Did you bench bleed the master very thoroughly? If not, bleed it VERY slowly until ALL bubbles are gone. You can do it on the car with two people. If there is a bubble trapped in the master, you may NEVER get it out by bleeding the wheel cylinders.

The reason the pedal feels better with a few pumps (whether a micro leak or air) is you are pressurizing the system and/or compressing the trapped air. A few seconds/minutes later, that all bleeds off and you have a semi-limp pedal again.


ps. unless it is a micro leak at the cylinders, this isn't the fault of a specific cylinder design. The same behavior will occur whether stock brakes, volvo wilwood or z32. Anything.

Pitted&rebuilt cylinders can behave like this too, but eventually you will find a small amount of leaked fluid somewhere. (sometimes they ooze)

[cbez]

Well, I went to get a video for you guys this morning and of course the pedal was fine and firm on the first press (ebrake released). I hate intermittent issues.

I am not ruling out microleaks it's just hard to wrap my head around a leak being significant enough to take 4~ full pumps to repressurize the system, but also not drop the master cylinder level at all, and have no pedal drop while under pressure.

I never bench bled the master but I did bleed it thoroughly with the bleed screw on it and the car jacked up in various positions trying to work any bubbles out.

Just to double check I bled the master again today, a couple tiny bubbles but that's it.

[jrusso07]

This is a long shot but I had it happened on my 69 SRL clutch hydraulics. The rubber hose to the slave was old and worn. When I first got in the car the clutch pedal was soft and after a few pumps it was firm and held the firm pressure for the drive. The next day, soft again (repeatedly). I wasn't until I tried to bleed the slave that I noted the hose was blown up like a balloon in one 1" area of the hose. Replaced the hose and bled, good to this day. So, check all three of the rubber hoses for damage where the sidewall of the hose is weak and can balloon. Look at them when the pedal is firm