Bloody "bleeding" issue

[Deleted member 21878]

a while back i tried locking the pedal down overnight and i did not see any improvement.

fast forward to a week or so ago when i was replacing the seal and bearing in the left rear wheel. i ended up pulling both drums to make sure there was no oil leaking on the right shoes. nothing but when i put everything back together and adjusted the brakes they felt different. and when i pushed on the pedal it was rock hard (no servo on mine)

i thought maybe i had done something different to the brakes in the way i adjusted them but i could not think of anything. last Friday i noticed the pedal was back to feeling the same way it did before. a little soft on the first push. in fact i had just gotten used to push and release, then push to brake. don't get me wrong it would stop on the first push, it just felt soft.

So over the weekend i tried this propping the pedal thing again. left it over night and most of the next day. (forgot i had the prop in there) anyway when i took it out, again the pedal was much stronger. today was the first day i could take the car out and the brakes felt much better.

So now i am a believer.

 

[trotti]

kkaa - Not sure if this was ever addressed as there hasn't been follow-up in a while, but I had the same issue with a four drum setup. I was able to diagnose the issue using line clamps (needed true line clamps to isolate the individual lines rather than C/wood clamps) and used a method I found on another forum related to MGAs. More detail in linked thread below, but as a summary I used the "stomp" method. Rather than the simple, two-person, pedal push method, I used the enhanced version where my brake buddy stomped on the pedal to surge fluid out of the lines. This resulted in a lot of air and nice, firm brakes after one single adjustment. I had tried every method ten times over. Tried this once and it was done - quite anti-climatic, actually.

If not useful for you, kkaa, perhaps for the next person that reviews this thread!

https://www.britishcarforum.com/bcf/showthread.php?102634-Brake-issues/page2&highlight=bleed

 

[maxwedge5281]

speaking of bleeding brakes.. i just installed all new brake pipes and hoses in my 59 bn6. i also installed a wilwood dual circuit master cylinder and proportioning valve. i bought the fittings and cunifer brake line in bulk and bent my own brake pipes.i purposely put off bleeding the brakes until a couple of days ago fearing "leaks". i gravity bled the brakes to clear most of the air. and then, finished bleeding with a tube and a partial container of brake fluid. using a long stick to depress the brake pedal and placing the fluid container in sight i was able to bleed each wheel and ended up with get a very solid pedal...and i had no leaks. if you work with brake lines be sure to get a good flaring tool....the run of the mill types just do not give the best results...i ended up buying a good eastwood flaring tool.

 

[John Turney]

RE: Novamonte's comment from Apr 2018.
I Rebuilt my front calipers several months ago and had my wife help me bleed the brakes. No matter how many times we did each of the four corners, the pedal always had 2" of free play on the first push before you could feel resistance in the pedal. The brakes worked fine and after several pumps, the resistance came at about 1 inch.
Two days ago, I finally decided to give Movamonte's idea a try. Used a piece of 1"X2" and a reversed clamp to lock the pedal in the depressed position against the seat frame. The next morning, I measured the free travel and it is now 1" and on the second pump, 1/2". I can't for the life of me understand how this works since I never opened the bleeders but it obviously did something to reduce the free play. I haven't noticed any change, good or bad, in the braking, just less free travel of the pedal.
Anyone know why this would work?

Maybe there is a small bubble of air and keeping the pressure on overnight causes the air to dissolve. Once dissolved. it stays that way.

 

[steveg]

Maybe there is a small bubble of air and keeping the pressure on overnight causes the air to dissolve. Once dissolved. it stays that way.

This might be the case. On this forum someone's theorizing that due to pressure the air in the system is dissolved in the brake fluid. More air can dissolve with more pressure.

My thought: then with the normal ebb and flow of the fluid through the MC, much of the fluid with the dissolved air is distributed upstream into the reservoir, where it escapes into the atmosphere.

This phenomenon appears to be widespread.

See: https://forums.noria.com/topic/brake-fluid-will-it-absorb-air

 

[Legal Bill]

Air gets stuck in funny places. Try bleeding at each juncture and fitting. Caution...this can get brake fluid on your paint. Protect the area first. Have a helper pump. Open the fitting, wherever it is (master cylinder, juntion or caliper or wheel cylinder) and close it while the fluid is running out.

The other option is a pressure bleeder, but even those sometimes can't chase out every last bubble.

 

[steveg]

Following up on the "stick" phenomenon: today several Healeys drove the Angeles Crest Highway up to about 7000 ft. Two of us had done the stick thing and started off with a hard pedal. In the course of driving downhill about 40 miles using the brakes a good deal, we both noticed the pedal became spongy with about 2 or 3" travel.
The weird thing is having arrived at lower altitude (1500 ft), the pedal became hard again as before. My buddy said the same thing happened. I'm using DOT 5, he's using DOT 4.

Maybe the lessened air pressure at altitude causes the air to escape from solution to be re-dissolved at lower altitudes.

Mysteries on top of mysteries!

 

[Novamonte]

Darth Vader - Can this be because of water in the brake fluid evaporates because of the heat generated from the brakes when going downhill and using the brakes a lot? If the fluid is not chaged regularly the content of water in the fluid will increase gradually over time. Once the brakes cool off the steam bubbles disappear.

 

[steveg]

Darth Vader - Can this be because of water in the brake fluid evaporates because of the heat generated from the brakes when going downhill and using the brakes a lot? If the fluid is not chaged regularly the content of water in the fluid will increase gradually over time. Once the brakes cool off the steam bubbles disappear.

Sounds reasonable. However my system underwent a complete overhaul in summer of 2016 as I changed to DOT 5 - including all new rubber on all 4 calipers and flushing the system with brake parts cleaner and compressed air. Maybe the compressor introduced moisture into the system.

 

[Bob_Spidell]

Following up on the "stick" phenomenon: today several Healeys drove the Angeles Crest Highway up to about 7000 ft. Two of us had done the stick thing and started off with a hard pedal. In the course of driving downhill about 40 miles using the brakes a good deal, we both noticed the pedal became spongy with about 2 or 3" travel.
...

Sounds like fade to me (I forget, Steve, do you have 4-wheel disks?).

 

[steveg]

Wasn't riding my brakes, but it does sound like fade. I have 4 wheel disks. The whole thing is a mystery to me.

 

[John Turney]

DOT 5 absorbs air and DOT 4 absorbs water. Either one coming out of solution can cause that.

Weekend before last a group of us did four of the Sierra passes: Tioga, Sonora, Ebbits and Carson. Yes, don't ride the brakes.

 

[steveg]

DOT 5 absorbs air and DOT 4 absorbs water. Either one coming out of solution can cause that.

Weekend before last a group of us did four of the Sierra passes: Tioga, Sonora, Ebbits and Carson. Yes, don't ride the brakes.

So John, did you get any fade?

If I've got air dissolved in my system (sounds likely) I wonder if there's a way I could minimize it when installing new fluid - such as supercooling it in the freezer.

 

[Bob_Spidell]

Hmmmmm ... this is a stretch, but nitrogen gets dissolved in the blood under pressure--when diving--and when the pressure is released the nitrogen forms bubbles ('the bends'). Maybe put the BF in a vacuum chamber?

 

[John Turney]

So John, did you get any fade?

If I've got air dissolved in my system (sounds likely) I wonder if there's a way I could minimize it when installing new fluid - such as supercooling it in the freezer.

Steve,

No fade on my part; I minimized my brake use by downshifting. I didn't hear anyone else complain, either. Maybe we weren't going as fast, especially after meeting a semi head-on on the single lane portion of Ebbetts Pass. Exciting!

Supercooling it would likely make it worse. Heating it would be better: less air dissolves and the viscosity is lowered, making any bubbles rise faster. If you have a Mityvac, put some brake fluid in the little jar and apply vacuum; you'll see the air bubbles come out.

 

[steveg]

It's now been 2 weeks since I did the "stick" on my brake pedal and it's still high and hard. Evidently the process does make a permanent change.