Dot 5, Silicone
Thread Starter
Instructor
Joined: Apr 2006
Posts: 201
Likes: 3
Dot 5, Silicone
Well slowly making progress. After assembling the brake system with all new components, including lines and master cyl. I started bleeding the system. I decided to use Dot 5 silicone brake fluid in case things got messy I wouldn't have to worry about the paint on the chassy and elsewhere.
I have never used Dot 5, silicone before, and wouldn't you know it I am having touble getting a hard pedal. I have run about 4 bottles of fluid thru the system using the pump the pedal method with a helper. I have a steady stream of fluid at all wheels with no air bubbles at all. And there are no leaks. I should have a firm pedal by now but I don't. Something is amiss. So my question is, does this DOT 5 silicone brake fluid act differently than what I am use to?
Thanks Dave.
I have never used Dot 5, silicone before, and wouldn't you know it I am having touble getting a hard pedal. I have run about 4 bottles of fluid thru the system using the pump the pedal method with a helper. I have a steady stream of fluid at all wheels with no air bubbles at all. And there are no leaks. I should have a firm pedal by now but I don't. Something is amiss. So my question is, does this DOT 5 silicone brake fluid act differently than what I am use to?
Thanks Dave.
Burning Brakes
Joined: Jan 2005
Posts: 768
Likes: 0
From: Leavenworth Washington
Mine didn't. DOT 5 likes to hold air but it works the same. Personal opinion is I like it - you just have to be patient, bleed it, let it sit a day and bleed it again. However it sounds to me like the air is in the master and not the lines. You bench bleed the system? Makes a huge difference.
G
G
Le Mans Master
Joined: Dec 2007
Posts: 8,000
Likes: 659
From: Puget Sound
Mine didn't. DOT 5 likes to hold air but it works the same. Personal opinion is I like it - you just have to be patient, bleed it, let it sit a day and bleed it again. However it sounds to me like the air is in the master and not the lines. You bench bleed the system? Makes a huge difference.
G
G
I use DOT 5 in every car I restore. Never had a single problem with it. Don't shake the bottle, bench bleed the M/C and pour it gently. Jim
Le Mans Master
Joined: Nov 2000
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From: Going too fast over the hill. Iowa
Race Director
Joined: Feb 2007
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From: northern california
C2 of Year Finalist (track prepared) 2019
Bleeding the master cylinder might help, many recommend it, but I've never found it to be necessary.
The big thing is to just go slowly. Glacially slowly. Pour slowly and use a clean screwdriver as a pouring guide. Pump slowly. Don't agitate the brake fluid. Don't let it get air bubbles.
Go slowly (oh, I said that already).
Jim
Burning Brakes
Joined: Feb 2008
Posts: 916
Likes: 2
From: prescott arizona
Well slowly making progress. After assembling the brake system with all new components, including lines and master cyl. I started bleeding the system. I decided to use Dot 5 silicone brake fluid in case things got messy I wouldn't have to worry about the paint on the chassy and elsewhere.
I have never used Dot 5, silicone before, and wouldn't you know it I am having touble getting a hard pedal. I have run about 4 bottles of fluid thru the system using the pump the pedal method with a helper. I have a steady stream of fluid at all wheels with no air bubbles at all. And there are no leaks. I should have a firm pedal by now but I don't. Something is amiss. So my question is, does this DOT 5 silicone brake fluid act differently than what I am use to?
Thanks Dave.
I have never used Dot 5, silicone before, and wouldn't you know it I am having touble getting a hard pedal. I have run about 4 bottles of fluid thru the system using the pump the pedal method with a helper. I have a steady stream of fluid at all wheels with no air bubbles at all. And there are no leaks. I should have a firm pedal by now but I don't. Something is amiss. So my question is, does this DOT 5 silicone brake fluid act differently than what I am use to?
Thanks Dave.
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Team Owner
Joined: Mar 2003
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From: Greenville, Indiana
I've never had to bench bleed a single reservoir master cylinder. Usually always had to on a dual, or maybe I just did it. I'd certainly do it in your case.
Some disc brake Corvettes are just hard to get the air out, some aren't. I've never found the dot 5 vs dot 3-4 made any difference in bleeding difficulty. A quart of fluid should be more than enough to do the job.
Make sure your bleeder screws on the calipers are all facing up. Are they?
Some disc brake Corvettes are just hard to get the air out, some aren't. I've never found the dot 5 vs dot 3-4 made any difference in bleeding difficulty. A quart of fluid should be more than enough to do the job.
Make sure your bleeder screws on the calipers are all facing up. Are they?
Racer
Joined: Jul 2009
Posts: 339
Likes: 1
From: Covington Louisiana
St. Jude Donor '10
When replaced my calipers I drained the entire brake system. I removed the master cylinder and bench bled it first. Very slowly. then I gravity bled the system opening up one caliper at a time, starting with the furthest from the M/C. Then the next furthest and so on. When it was done I let it sit a couple of days (I was in no hurry) and did it again. When I felt it was clear of air I used the conventional method of having someone slowly pump and hold the pedal. More air came out. Then I tested the pedal and it was fine. I had just heard too many horror stories about air in DOT 5 to even try putting pressure on the master until I felt I did all I could without pumping on it.
One more note. After running a few hundred miles over a few months this winter I checked my brake fluid level just to see if it was okay, but it was about an inch lower than I had left it. Of course I checked for leaks from the back of the M/C all the way down to each fitting and caliper and had none. I have been told that it is very possible that trapped air in the fluid had made its way up to the top. But again, I never had any soft pedal issues.
One more note. After running a few hundred miles over a few months this winter I checked my brake fluid level just to see if it was okay, but it was about an inch lower than I had left it. Of course I checked for leaks from the back of the M/C all the way down to each fitting and caliper and had none. I have been told that it is very possible that trapped air in the fluid had made its way up to the top. But again, I never had any soft pedal issues.
Pro
Joined: Feb 2003
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From: Carlisle Pa.
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All good advice above. One additional thing that I have found in the Northeast. In the winter time if the fluid and shop are cold it adds an additional degree of difficulty to the bleeding. I'm note sure why, but silicone fluid always bleed better for me in the warm weather. I use silicone fluid in all of my Corvettes except the race cars and my C5 with ABS.
Regards,
Dave Gray
Carlisle, Pa.
Regards,
Dave Gray
Carlisle, Pa.
Thread Starter
Instructor
Joined: Apr 2006
Posts: 201
Likes: 3
Dot 5 Sillicone Brake Fluid.
Thanks for all the good advice. I guess I should have said from the onset that the car in question is a '56. Not my c-3. Hence the post to this forum. No disc or calipers here. Has only one resourvour and all parts are new. There are diffinately no leaks. Have checked it repeatedly. Master cyl. not leaking either.
I believe I will crack the fitting at the master cylinder and bleed. And good advice to let it settle awhile then bleed slowly.
Thanks, Dave.
I believe I will crack the fitting at the master cylinder and bleed. And good advice to let it settle awhile then bleed slowly.
Thanks, Dave.
Team Owner
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From: Greenville, Indiana
Safety Car
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From: Georgetown TX
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Mike, I believe you hit the nail on the head! Agree with Mike.
Instructor
Joined: Mar 2006
Posts: 227
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From: South East, USA
Picking up on this old thread, someone advised that Dot5 is a must in a very hot/humid climate (such as Houston) as Dot3 and 4 absorb water and Dot5 is hydrophobic and does not and so dot5 keeps water out (?) and prevents corrosion
it does appear that Dot5 is hydrophobic, so no confirmation needed there - but what happens to the moisture then, if it is not absorbed in the fluid? - does it just sit in the lines and cylinder? - wouldn't that cause just as much corrosion? - have others used dot5 for this reason and does it help eliminate or minimize corrosion in the system?
thanks!
it does appear that Dot5 is hydrophobic, so no confirmation needed there - but what happens to the moisture then, if it is not absorbed in the fluid? - does it just sit in the lines and cylinder? - wouldn't that cause just as much corrosion? - have others used dot5 for this reason and does it help eliminate or minimize corrosion in the system?
thanks!
Instructor
Joined: Mar 2006
Posts: 227
Likes: 0
From: South East, USA
thanks
if i want to switch from 3/4 to 5, i am supposed to "flush the system thoroughly" - what, exactly does that mean?
is it sufficient to pull new fluid through the bleeders on each caliper? how much/long? - a full reservoir worth? (single pot, '66 brake system) - more?
is there any other part of the system that is not flushed this way and only would get flushed by using the brake pedal (or bench bleeding the m/c)?
if i want to switch from 3/4 to 5, i am supposed to "flush the system thoroughly" - what, exactly does that mean?
is it sufficient to pull new fluid through the bleeders on each caliper? how much/long? - a full reservoir worth? (single pot, '66 brake system) - more?
is there any other part of the system that is not flushed this way and only would get flushed by using the brake pedal (or bench bleeding the m/c)?
Race Director
Joined: Feb 2007
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From: northern california
C2 of Year Finalist (track prepared) 2019
Better to flush with alcohol and compressed air,... maybe a couple of times.
Jim