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Discussion Starter #1
Hi Guys and Gals

Well I took the 30 year sleeper car out for a quick 20 miles drive. Its those ongoing brakes again. I found that I have to : on a gentle stop throw the tranny into neutral to relieve the torque off the drive train to reduce the momentum and by that action get a better stop. I had even a timed signal traffic light stop me rather suddenly and I used the E brake. The cable obviously getting more pull on the rears than my foot.

So I wondered if its the just a viscosity issue on the DOT 5 Silicone I use . A change from the DOT 3 thats not giving me safe pressure.? If I could only measure the pressure coming out of the 50 year old Beer car single master on my four drums.


I have replaced all shoes and parts with new. Bleed the lines three times now. ,. I wonder what DOT number are you running on your car>?

It's probably time to upgrade but Id like to find the trouble before doing so.
 

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All 4 of my classics are running DOT 3 brake fluid but then I didn't make any changes other than replacing stock parts.
 

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We've all got opinions but to me the only cars that should have DOT 5 fluid are race cars that get meticulous maintenance and are exposed to extremely high brake temperatures. The rest of us should be using DOT 3. Back in my younger days I worked on a mid 70's corvette at a Chevy dealership that the owner seemed to have constant complaints about braking. It turned out that the car had been swapped to DOT 5 fluid at some point but somewhere along the line the master cylinder had been topped off with DOT 3 (because basically nobody uses DOT 5). The combination of DOT 3&5 made for some nasty brake fluid.

A flush of the system and a refill of DOT 3 and we never had the car in the shop for brake issues again.
 

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Been using DOT 5 for years. Never a problem, but I also do all of my own work, so there no mistakes made.
 

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67 coupe, 69 Sportsroof, 86 hatchback
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Sounds like you've got air in the lines or other problems not the fluid. To nail down exactly what in your case sounds like might take some brake pressure gauge testing. You can have situations where you've bled the brakes X amount of times and still have air in the system somewhere. (I hate those.) In such cases you have to start looking at alternative bleeding methods.

As far as viscosity goes, years ago I ran into a guy running rubbing alcohol in his brake system. Because he was off the rails loony basically, but it worked.
 

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DOT5? Did you thoroughly FLUSH your brake hydraulic system before changing to DOT5? DOT5 silicone-based fluid is incompatible with DOT3/4/5.1 glycol-based fluid. Did you flush your brake hydraulic system regularly? DOT5 is not hygroscopic which means that any moisture in the system will condense and collect in the lowest point, typically the wheel cylinders or caliper piston bores causing rust and seizure of the pistons. DOT5 is also easily aerated frequently resulting in a pedal that becomes spongy after repeated application (ever wonder why you see racers pumping the brake pedal right before a corner?). FWIW, a small difference in viscosity won't change the amount of pressure as a minimum volume of fluid is passed through the various orifices. As the fluid is incompressible it's just like you had a solid, mechanical connection.
 

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Im using DOT 34, I guess its at least 6X better than DOT 5 right?

I wish I could find a transcript of this, he might make good points but I dont understand.
 

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Im using DOT 34, I guess its at least 6X better than DOT 5 right?

I wish I could find a transcript of this, he might make good points but I dont understand.
I've heard that there are no chemical reactions that will occur is if you mix Dot 5 with other fluids. The fluids will separate and not much else will happen. Silicone is an extremely stable molecule. If there is a chemical reaction that can occur, a chemist should be able to make an equation showing what reacts with what. As far as that video goes, Wayne, who messed around with brakes for 40 years with Uncle Ron and Joe and has a "background" in a science he can hardly pronounce, I can't find any credibility in anything he says. It looks like those swelled rubber parts were soaked in transmission fluid.
 

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Discussion Starter #10 (Edited)
Sounds like you've got air in the lines or other problems not the fluid. To nail down exactly what in your case sounds like might take some brake pressure gauge testing. You can have situations where you've bled the brakes X amount of times and still have air in the system somewhere. (I hate those.) In such cases you have to start looking at alternative bleeding methods.

As far as viscosity goes, years ago I ran into a guy running rubbing alcohol in his brake system. Because he was off the rails loony basically, but it worked.

Thank you GypsyR

I have been looking at the brake testing kit. Looks easy peasy except for the price. But if it keeps me from a fender bender,






!


Hard to believe its air in the lines. But if I had the gauge. .......

Is it logical to assume that air in the system will reduce the gauge reading when tested?
 

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Discussion Starter #11 (Edited)
DOT5? Did you thoroughly FLUSH your brake hydraulic system before changing to DOT5? DOT5 silicone-based fluid is incompatible with DOT3/4/5.1 glycol-based fluid. Did you flush your brake hydraulic system regularly? DOT5 is not hygroscopic which means that any moisture in the system will condense and collect in the lowest point, typically the wheel cylinders or caliper piston bores causing rust and seizure of the pistons. DOT5 is also easily aerated frequently resulting in a pedal that becomes spongy after repeated application (ever wonder why you see racers pumping the brake pedal right before a corner?). FWIW, a small difference in viscosity won't change the amount of pressure as a minimum volume of fluid is passed through the various orifices. As the fluid is in compressible it's just like you had a solid, mechanical connection.

Thanks Bart.

I did flush with denatured alcohol. I did replace front brake cylinders and one hose. I suspect the Master. the bottom of the master bowl was slightly rusted from sitting , but it cleaned right up. The lines run clear! Is there a trick I can preform. Can I disconnect the rear brake lines and Cap them. Then drive test to see if my foot tells me there is any difference?

Probably easier to buy the gauge.


BY THE WAY>>> anybody know what pressures I should be getting on a old single master cylinder. OR the wheel cylinders front/rear?






!
 

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DOT 5 will not absorb water so the fluid will stay cleaner longer, but water can pool at the bottom of master, lines, calipers. If enough water gets into the system, and the calipers get hot enough, you could have boiling water vapor in the calipers which can cause spongy brakes. Higher pressure increases water boiling temperature though. A lot of things would have to simultaneously happen for this to happen so it's unlikely this is your problem...enough water in the calipers and hot calipers and low fluid pressure.

DOT 5 is harder to bleed also so maybe a new bleed would be in order or a flush.

I have DOT 5 in my car and no problems after 5 years.

800-900 psi line pressure should be enough to lock up your brakes. I went through this exercise 5years ago. Got a brake line pressure gauge also. Pressure when I really stomped on it went as high as 1700 psi. I found out that my Porterfield brake pads had gotten old and hard and glazed badly or combination thereof and new semi-metallic brake pads solved the problem. I also went from a 1" to a 7/8" master cylinder.
 
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Discussion Starter #13
DOT 5 will not absorb water so the fluid will stay cleaner longer, but water can pool at the bottom of master, lines, calipers. If enough water gets into the system, and the calipers get hot enough, you could have boiling water vapor in the calipers which can cause spongy brakes. Higher pressure increases water boiling temperature though. A lot of things would have to simultaneously happen for this to happen so it's unlikely this is your problem...enough water in the calipers and hot calipers and low fluid pressure.

DOT 5 is harder to bleed also so maybe a new bleed would be in order or a flush.

I have DOT 5 in my car and no problems after 5 years.

800-900 psi line pressure should be enough to lock up your brakes. I went through this exercise 5years ago. Got a brake line pressure gauge also. Pressure when I really stomped on it went as high as 1700 psi. I found out that my Porterfield brake pads had gotten old and hard and glazed badly or combination thereof and new semi-metallic brake pads solved the problem. I also went from a 1" to a 7/8" master cylinder.
Thank you Tracy !

This car has been stored for many many years ! But well cared for. Thank you also for your experience notes on the PSI and DOT 5 Support.. My brakes are not spongy or fade-y but Down there in the travel and need a hard push for little reward.

and thanks for the confirm on the bore size on the Master. I thought bigger bore is not better when making a conversion to Power booster dual MC.

My buddy e-mailed his experience which I hope is not mine.

..........."Laurence, this is why in my previous email I asked if you changed the brake lines. The mix of DOT-3 and DOT-5 can cause jelling inside the brake lines, which is what I suspected was happening with your system. To my knowledge there's no way to flush them, but maybe someone on the forum has been able to do this successfully. Short of that replacing the lines (solid & flex lines) is in order. You'll also want to flush the master cylinder as well before adding fluid after you change the lines. I had to replace my lines after having the car stored for several years. "............

So I now wonder what tool I can use to test the 'Jelling' theory. Brake Pressure tool I guess.
29 feet of roto rooter auger.
 

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You can test for a mixture of DOT3/DOT5 by flushing the system and collecting the old fluid in a glass jar. Glycol based DOT3 and Silicone based DOT5 do not have the same specific gravity, so once it sits for a while it'll separate and you'll see it in the jar in a manner similar to water and oil. Doing a pressure check isnt going to tell you if someone mixed fluids.
 

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Discussion Starter #15
You can test for a mixture of DOT3/DOT5 by flushing the system and collecting the old fluid in a glass jar. Glycol based DOT3 and Silicone based DOT5 do not have the same specific gravity, so once it sits for a while it'll separate and you'll see it in the jar in a manner similar to water and oil. Doing a pressure check isnt going to tell you if someone mixed fluids.

Thanks Lighting.

I have already done this and found the DOT 5 is running clear. I would have been the evil doer. The car went into storage for one year with new front cylinders. The I watch ed in denial as wet gloss speared on the inner tires. I put it back on insurance a pulled it out and found mushy brakes ! I then looked at the my policy and three years had passed not one!


I them replace d the cylinders. So I strongly suspect the master has be corrupted by the DOT 5 . The DOT 5 has been installed since 1998 .................I need that P guage. !
 

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Dot 5 is not immune to poor maintenance. You still have to flush and bleed it periodically. Just like Dot 3/4. You still need to make sure all brakes components are still functioning properly with good seals. Rubber seals in brake systems still age no matter what brake fluid you use.

That Dot 5 is not hygroscopic is immaterial since you need to do this maintenance for all brakes systems anyway.

I have used Dot 5 for decades in both non-abs equipped cars and vintage motorcycles. It works very well for both storage and for road use.

The super huge advantage of Dot 5 is that it will not ruin paint.
 

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Discussion Starter #17
Dot 5 is not immune to poor maintenance. You still have to flush and bleed it periodically. Just like Dot 3/4. You still need to make sure all brakes components are still functioning properly with good seals. Rubber seals in brake systems still age no matter what brake fluid you use.

That Dot 5 is not hygroscopic is immaterial since you need to do this maintenance for all brakes systems anyway.

I have used Dot 5 for decades in both non-abs equipped cars and vintage motorcycles. It works very well for both storage and for road use.

The super huge advantage of Dot 5 is that it will not ruin paint.

Thanks Paul ! I will go back to another bleed and try again! Yup thats kinda why I changed to DOT 5 ..the paint advantage.
 
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I’d like to who’s spilling/spraying brake fluid all over your paint that necessitates changing to DOT 5 to begin with.

I bleed my brakes 4-6 times a year and after doing that for 16 years, I have yet to get any on the paint.


Mark
 

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I’d like to who’s spilling/spraying brake fluid all over your paint that necessitates changing to DOT 5 to begin with.

I bleed my brakes 4-6 times a year and after doing that for 16 years, I have yet to get any on the paint.

Mark
Obviously not you
 

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Im 51 years old, college educated in the automotive field and dont recall ever speaking with someone who damaged paint with brake fluid.
 
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