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Brake Fluid

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Guido36 said:
Brake pedal went to floor with no warning and no brakes - luckily I was doing less than 10 mph at a show and managed to stop with the parking brake before nearly taking out the NSRA Safety Inspection tent! This was in a car I had recently purchased and hadn’t thought to check the brake fluid type. There can be incompatibility issues between certain rubber seals and DOT 5. The attached article gives more insight on seals and seal material types....

http://www.adlersantiqueautos.com/articles/brake1.html
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So, what did you determine was the cause of the problem? Gelled fluid won't typically cause this, but a damaged foot valve could (happened to me).
 
Brake pedal went to floor with no warning and no brakes - luckily I was doing less than 10 mph at a show and managed to stop with the parking brake before nearly taking out the NSRA Safety Inspection tent! This was in a car I had recently purchased and hadn’t thought to check the brake fluid type. There can be incompatibility issues between certain rubber seals and DOT 5. The attached article gives more insight on seals and seal material types....

http://www.adlersantiqueautos.com/articles/brake1.html
 
With respect, hat does not seem like a positive explanation.
 
Bob
what do you mean by a damaged foot valve? what are you referring to?

Guido36
did the pedal pump back up after failure? or just did not work after that? if the seals were an issue, did you not have leaks?

i use DOT5 but i replaced everything when rebuilding the car. then started out with DOT5. also use in the clutch. but same thing. all new lines, cylinders and hoses from the start.
 
Drone Dog said:
Bob
what do you mean by a damaged foot valve? what are you referring to?
...
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It's the spring-loaded valve with a tiny seal at the left side of the repair kit; #29 in this photo: https://mossmotors.com/brake-pedals-master-cylinders-bn4-to-bj8

I've heard it called the 'foot valve;' it also has other names. It allows fluid to flow into the MC when the pedal is released then, when you apply brakes it seals up the orifice so that all pressure goes to the brakes. If it leaks your brakes, obviously, will not function properly. Once, on a long road trip mine failed and I had to double/triple pump the pedal to get good braking (for over 1,000 miles). I don't generally tailgate, and it was a major annoyance, but if it failed suddenly you might have a problem. When people describe similar symptoms, I suggest they watch the fluid in the reservoir when someone pumps the brakes for them; you can usually see the fluid in the reservoir rise a little if the valve has failed. When I tore down the MC I saw that the seal had a nick on it, but was otherwise OK. I have no idea how the seal got damaged, but I can't attribute the damage to DoT5 ('correlation isn't causation'); I've used it for tens of thousands of miles before and after that episode and not had any issues. I've heard early formulations of DoT5 had issues due to the fact the silicone fluid is inert, and doesn't cause seals to expand like glycol-based BF; supposedly, agents that cause seal expansion were added to DoT5 later on.

Unlike glycol-based fluids DoT5 is not flammable; there are instances of glycol fluids leaking after collisions, with the resultant fires causing injuries and deaths. This site used to have some reports, but I can't find them now: https://automec.co.uk/products/silicone-brake-fluid-dot-5
 
After the pedal went to the floor the brakes did come back up but failed a second time. At this point I did find some seepage and opted to replace and upgrade the entire brake system which I intended to do anyway. I upgraded to Wilwood discs all round. Wilwood sells their own brake fluid. Their comments on DOT 5 silicone based brake fluid can be seen here....

https://www.wilwood.com/BrakeFluid/BrakeFluidProd?itemno=290-0632
 
Bob
thanks for the info. reason i asked was i had an instance a good while back. one day driving in town, i had gone maybe 5 miles. nothing over 35mph. was going to stop at the third stop light that morning. the brake pedal went right to the floor. pumped them once and i had half a pedal, pumped again and there was a full pedal. naturally i drove slow to my destination and hit the brakes quite a few times with my hand on the hand brake at the ready. but they were fine. like i say that was a long while ago and it has never happened since. always had a good pedal before then and after.
at one point i thought maybe i just hit the clutch instead of the brake but i would have felt that because the spring is different. i took the car out quite a few times after that on back roads to see if it would happen again but nope. has been fine ever since.
 
This may not apply to the problem that introduced this discussion, but maybe it does. I went through a lot of tom-foolery years ago trying to diagnose a severe one-wheel rear lock up. I won't go into the details, but Steve G (response precedes this) suggested I change my rear brake shoes that looked good but had a bit of brake fluid contamination. New shoes were the answer. Over the years I have replaced almost everything in the brake system, including upgraded soft lines front and rear, pads, front wheel pistons, etc. Our Healey club members have been successfully using the pressurization system Bob S mentions to combat the issue Steve mentions above, air bubbles in brake lines. The addition of a hand-crafted silicone sealing ring in the reservoir cap has been helpful in this technique.
 
FWIW, I once had rear hubs leak on one of my Healeys. The shoes were almost brand new, so I tried to 'save' them by cleaning/soaking with brake cleaner, sanding, rinse and repeat. Although it appeared there was no trace of diff oil on the shoes when I was done, the shoes would not bind properly. Get even a drop of oil on shoes and you can (should) pretty much write them off.
 
John Turney said:
Racing brake fluid has to be bled very often and is not recommended for street cars.
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That's news to me. Basically, racing brake fluid has a higher boiling point so it's better for racing. But it still degrades from the tremendous heat caused by racing. That why we bleed the system frequently so fresh fluid is constantly added. This is not necessary with street cars. The only reason I can think of for not using it in street cars is because it is more expensive. DOT 3 is fine for most street cars.
 
Richard--


Perhaps it could be restated "Racing brake fluid is bled/changed often and its expense is not justified for street cars".
I like Wilwood 570.


​
 
I thought this forum was about street cars, not motorsports. Therefore, racing brake fluid does not have to be bled/changed often in a street car. That was the point I was trying to make. John's post that racing brake fluid had to be bled/changed frequently suggested to me that racing brake fluid was a different kind of animal than regular brake fluid. It is not.
 
Martinld123 said:
My problem was left rear brake locking up. Went to replace wheel cylinder and noticed dark fluid in reservoir. So I believe my only option is to replace all of the brake fluid. So how crazy should this get?

Replace all new wheel cylinders or just some kind some kind of fluid flush? I replaced cylinders and fluid 8 years ago. All I remember is I hate doing it, lol. Can I get away with just running new DOT 3 fluid through all of system until runs clear? I hate brake jobs on BN2, 1956.

Thanks, Marty
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I finally get around to replace my reservoir with one from Moss and also left rear wheel cylinder from Moss. When I started to bleed the wheel cylinder I noticed that the bleed screw is a course thread and leaks air when I open it only half turn or so. I think I read that some people use Teflon tape. Does that sound like a good idea? Then I noticed there was some black spots on surface of brake fluid in reservoir and around the lip there was some black residue that rubs off. It could also be rubber seal going bad?Not sure but looks like they might have over sprayed black on lid area? I will call Moss Motors tomorrow to see what they suggest I do.
 
I recently installed new bleed screws which I bought at the auto parts store. They're 3/8-24 threads. I wrapped the threads on each with a 5" piece of teflon tape.

They still leak a little air when bleeding. In my recent experience, actual air in the lines comes out as big bubbles the same diameter as the clear tube; bleed screw leakage is a tiny stream of perrier-fizz sized bubbles. Once you've got the big bubbles out, you're good.
 
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Steve, thanks for that explanation of bubble size. I can never seem to get rid of those tiny bubbles. Now I understand they are probably fron the bleeder threads and not internal to the system.
 
steveg said:
I recently installed new bleed screws which I bought at the auto parts store. They're 3/8-24 threads. I wrapped the threads on each with a 5" piece of teflon tape.

They still leak a little air when bleeding. In my recent experience, actual air in the lines comes out as big bubbles the same diameter as the clear tube; bleed screw leakage is a tiny stream of perrier-fizz sized bubbles. Once you've got the big bubbles out, you're good.
Click to expand...

Steve I am now at bleeding stage after installing rear left brake cylinder and new reservoir. Have run some new dot 3 to clear out dark fluid. I wonder if I need new left rear shoes? When I turn hub 360 degrees it drags in one same spot every time. Shoes are like new but at least 4K miles or way more on them but look newish. Maybe this is part of my original problem of this wheel locking up. Old wheel cylinder really looked dirty and seemed a little stuck. New now. I replaced all as before. Took photo.

I cleaned shoes with brake cleaner. Maybe I should do it again or just try to order new shoes? Thanks Marty
 
In my somewhat limited experience you cannot 'clean' brake shoes of BF, and I've tried; the material is surprisingly absorbent.

As for dragging at one spot, that isn't likely due to contamination, or an 'out-of-round' shoe (that would cause dragging 360 degrees). It's more likely an alignment issue with the shoes; have you checked that the shoes are 90deg to the backplate (there are steady posts that can be adjusted)? Less likely, but not impossible, is some out-of-roundness in the drum.
 
Thanks Bob it looks like your steady post idea did the trick. I used the method in 100 BN2 manual to do it but wonder if that is accurate or not. Manual said to loosened steady post then lock shoes to hub. Next I turned stead post in until I felt it and also heard it move. Wheel rotates smooth now so that must be good enough.

Now I will get back to bleeding brakes. I read that if you can pump to get steady pedal then block pedal in place for 24 hours and air bleeds out on it's own through reservoir. Dreaming I know but why not try it, lol?

Well Bob I spoke too soon. They now grab again but in a little wider drag area now than before. After I apply emergence brake or the brake pedal drum is harder to turn after I release both. Then will get normal after I turn hub a few times around but with this one wheel still with drag area. It is starting to sound like they never fully rerelease until I turn wheel, right? I did notice that heal and toe of shoes have sharp taper that I thought was normal but very rough surface. Maybe not normal. Will try to send photo later. Thanks Marty
 
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Good deal; glad to help. As for the 'block pedal in place for 24 hours' technique, it makes no sense to me, based on my (limited) knowledge of physics. Air is lighter than BF, obviously, so in a can, for example, air would float to the surface (or the fluid would settle to the bottom, if you prefer). But, there are many turns in a brake system and, in some places the air would have to travel up, then down, or vice versa (or both), to get past some of the turns. It seems to me, putting pressure on a bubble would force it to travel opposite to the direction you want it to; or, more likely, the bubble will be compressed smaller (note pressure bleeding pushes bubbles out the bleeders at the wheels). If there's any benefit to this, it's likely that just letting the BF settle for a day would be the cause. But I'm open to any rational explanation how this works (it's alleged that silicone brake fluid can somehow absorb air, so it's possible letting it sit for a day would allow some air to percolate up).
 
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