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I've had DOT 5 in my 67 for about 15 years with no issues at all. As an avid autocrosser, I've made thousands of hard near-stops on course. I've also tracked the car at Laguna Seca and Reno-Fernley with no issues. DOT 5 is the ideal brake fluid for our old cars or any non-ABS car.
I discovered in recent years that there is confusion between DOT 5 and DOT 5.1 fluid. DOT 5 is silicone and DOT 5.1 is ethylene glycol, so they are completely different. The 5.1 eats paint and is simply an updated version of normal DOT 3 or 4, as I understand it, with a higher boiling point.
Jim, DOT 5 is susceptible to aeration and becomes highly compressible when this occurs. It's a nightmare trying to bleed it when it has the microscopic bubbles in it. That is why it's not used in antilock applications. When I was at HDMC, we had to switch back from DOT 5 to DOT4 when antilock launched.
Because DOT 5 is not hygroscopic I suspect you will find the reason it's not recommended in racing is the extreme brake temperatures and concern of the non-absorbed water boiling off sooner than you would see a failure with DOT3/4 as that water is absorbed by the fluid.
Jim, DOT 5 is susceptible to aeration and becomes highly compressible when this occurs. It's a nightmare trying to bleed it when it has the microscopic bubbles in it. That is why it's not used in antilock applications. When I was at HDMC, we had to switch back from DOT 5 to DOT4 when antilock launched.
Because DOT 5 is not hygroscopic I suspect you will find the reason it's not recommended in racing is the extreme brake temperatures and concern of the non-absorbed water boiling off sooner than you would see a failure with DOT3/4 as that water is absorbed by the fluid.
I'm intimately familiar with the properties of DOT5, having converted all of my old cars to it, and having used it in two track cars. I understand why it can not be used in ABS systems.
As far as racing applications, like mine, I've never seen a research-based recommendation to not use DOT5. Instead, the reluctance to use it seems to be no more scientific than, "Well, we've never done it that way...."
This alleged issue with water getting into a DOT5 system and causing problems makes no sense. Do people leave their cars out in the rain with the caps off the master cylinders??
The extreme temperatures in racing are the exact reason DOT5 should be the brake fluid of choice since both its wet and dry boiling points are the highest of any of the available choices.
And to that point, the brake system in my vintage racer is filled with DOT5 and has never, ever, not once experienced any kind of issue, no matter how hard or how frequently I stand on the brakes. I'm not the only vintage racer who uses DOT5, but I probably am the most vocal. I don't mind speaking up whenever I detect hearsay-based reasons to avoid DOT5.
I'm intimately familiar with the properties of DOT5, having converted all of my old cars to it, and having used it in two track cars. I understand why it can not be used in ABS systems.
As far as racing applications, like mine, I've never seen a research-based recommendation to not use DOT5. Instead, the reluctance to use it seems to be no more scientific than, "Well, we've never done it that way...."
This alleged issue with water getting into a DOT5 system and causing problems makes no sense. Do people leave their cars out in the rain with the caps off the master cylinders??
The extreme temperatures in racing are the exact reason DOT5 should be the brake fluid of choice since both its wet and dry boiling points are the highest of any of the available choices.
And to that point, the brake system in my vintage racer is filled with DOT5 and has never, ever, not once experienced any kind of issue, no matter how hard or how frequently I stand on the brakes. I'm not the only vintage racer who uses DOT5, but I probably am the most vocal. I don't mind speaking up whenever I detect hearsay-based reasons to avoid DOT5.
I guess I misunderstood your post. Anyway that is interesting because Wilwood has it posted that they do not recommend it for racing.
I had read some older literature that stated it could be a moisture problem, I do not remember exactly who said what, but the current Wilwood recommendation against DOT5 in racing is the aeration issue. Personally I prefer DOT5 and did a lot of research with engineers regarding replacing DOT3/4 with it. After what I learned, I wouldn't do it with ABS, but certain other applications I wouldn't have a problem converting over.
I guess I misunderstood your post. Anyway that is interesting because Wilwood has it posted that they do not recommend it for racing.
I had read some older Wilwood brake fluid recommendations in the past as well as other manufacturer literature that stated it could be a moisture problem, I do not remember exactly who said what, but the current Wilwood recommendation against DOT5 in racing is the aeration issue.
Lone Star also has warnings not to use DOT 5. Supposedly, they changed the formula several years back that causes it to degrade the rubber seals.
Years ago I ran it in my 69 with no problems. Except, it was harder to bleed the system. ( manual bleeding )
Lone Star also has warnings not to use DOT 5. Supposedly, they changed the formula several years back that causes it to degrade the rubber seals.
Years ago I ran it in my 69 with no problems. Except, it was harder to bleed the system. ( manual bleeding )
Yeah, and their warning cites some EPA regulation which has nothing to do with DOT5.
There is an old saying in the military, “If the terrain doesn’t match the map, go with the terrain.”
This is why I always listen to the voices of experience like Jim vs. literature often written by lawyers. They have driven the terrain of silicon based brake fluids and zinc enriched oils. I may read literature that maps out the risk, but I default to those who have real world experience with the terrain.
Yeah, and their warning cites some EPA regulation which has nothing to do with DOT5.
I believe I know as much as any hobby dude regarding old car brakes and the use of DOT 5. The only legend I've heard about DOT 5 that turned out to be true is the very slight compressibility over that of glycol based (DOT 3&4) AND that instructions for slow, easy bleeding without dancing on the pedal need to be followed.
The formula has not changed on the NAPA brand fluid I use
The brakes won't go away at high elevations
There is no problem racing with the stuff, I have 6 friends who do.
The pedal feel and travel MIGHT change depending upon the master, wheel cylinders and pedal geometry. DOT 5 in my 65 Corvette presented no change in feel or travel whatsoever, but there was noticeable but not objectional difference in feel with two early 60's Chrysler products.
With 9 cars, 3 are on DOT 5 today. The rest will be converted as I do major brake work on them. For cars that sit far more than they are used, DOT 5 is the only way to go, especially when rare and hard to find hydraulic parts are involved.
It wouldn't be sold and guys like Jim Lockwood wouldn't be using it for years if it was problematic. If we listened to everyone with something "they heard" we wouldn't be eating eggs. And I like my eggs.
I'm not disputing anyone's experience here, just relating mine. I used to use DOT 5 in an my AH Sprite for all of the reasons above. Never have any problem with functionality when the car was driven on a regular basis. However after the car was parked for ~15 years it did degrade the seals to the point all fluid leaked out of the master cylinder. The rubber in those Lockheed brakes may be different than in US made parts. Just be careful and keep an eye out for leaks.
I'm not disputing anyone's experience here, just relating mine. I used to use DOT 5 in an my AH Sprite for all of the reasons above. Never have any problem with functionality when the car was driven on a regular basis. However after the car was parked for ~15 years it did degrade the seals to the point all fluid leaked out of the master cylinder. The rubber in those Lockheed brakes may be different than in US made parts. Just be careful and keep an eye out for leaks.
How can you be certain it was the DOT5 fluid which degraded the seals and not just the passage of time?
How can you be certain it was the DOT5 fluid which degraded the seals and not just the passage of time?
I'm not certain, just suspect. I haven't taken the MC apart yet. It could also be corrosion due to free water in the DOT 5. I am not trying to say there is anything wrong with silicone brake fluid, just that like all things automotive, it doesn't last forever and still requires regular maintenance.
On the Moss article I think I have seen it but my memory fades. Sadly I have neglected the Sprite for far too many years.
I'm not disputing anyone's experience here, just relating mine. I used to use DOT 5 in an my AH Sprite for all of the reasons above. Never have any problem with functionality when the car was driven on a regular basis. However after the car was parked for ~15 years it did degrade the seals to the point all fluid leaked out of the master cylinder. The rubber in those Lockheed brakes may be different than in US made parts. Just be careful and keep an eye out for leaks.
I remember back in the day we could not put dot 3 brake fluid in any British system. It had to be Girling fliud or the rubber would fail.
This Tech Nerd column in the Dec. 2021 issue of Corvette Magazine clarifies the DOT 5 issue. Looks like DOT 5 brake fluid hasn’t changed in any meaningful way, but that the brake seals have. What I take from this column is that until just a few years ago all Corvette caliper lip or o-ring seals were made with EPDM rubber that was compatible with DOT 5. The lip seals in my 67’s Lonestar calipers have been bathed in DOT 5 for around 15 years with not a single problem. However, it seems that in recent years some caliper seals have been made with EPDM that is not compatible with DOT 5 for whatever reason.
We know that ZIP, Lonestar, Mid America, Dr. Rebuild, SSBC, Paragon and many others used to source long-lasting EPDM seals compatible with DOT 5, because so many of us have had them for decades. It seems a shame that we owners are deprived of the benefits of DOT 5 fluid and long-lasting EPDM seals and can do nothing about it as individuals. Some owners claim to have bought rebuilt calipers and used DOT 5 in recent years with no problems, so perhaps some of the seals out there are made out of durable EPDM. Using DOT 5 is therefore a crapshoot for us owners. What we all need is for the parts vendors to take the lead and find (or commission) the quality EPDM seals that they used to sell us, and begin selling them to us again. They can even call them “premium seals” and charge extra for them. For us owners it would be a great thing to have one less maintenance headache, have more reliable brakes, and not worry about brake fluid ruining our paint. This would be a win-win situation for the vendors and owners.
Wouldn’t it be great if the vendors got together, or one of them took the lead, on this seals issue to make vintage Corvette ownership an even greater experience that it already is? After all, the more we’re on the road with great brakes, the more supplies we’ll need to keep going (and stopping).
I installed a complete brand new brake system on my 1956 Bel Air. The setup was a front disk brake it with stock rear wheel cylinders. Every single part of the system was new, brake lines, both hard and soft, front calipers, rear wheel cylinders, proportioning valve, everything new.
I poured in DOT 5 fluid very slowly and carefully, so as not to generate air bubbles, etc.
I then literally spent the better part of a month trying to get a solid brake pedal, without success. I tried everything I could think of, I solicited input from other more knowledgeable people, nothing worked. During this process I replaced the brake master cylinder twice, the brake proportioning valve once, both rear wheel cylinders once each, all to absolutely no results. I bled the brakes using a variety of methods, all of which are well known. NADA.
The shop that installed the Holley Sniper system on the car told me that they have had a great deal of issues with DOT 5 fluid. They do a LOT of high end cars, mostly serious horsepower cars, so they need serious brakes. Many customers would bring their cars in already full of DOT 5 and wanting the shop to firm up the pedal.
The now pretty much standard answer is, we can do that is you allow us to change over to DOT 3 fluid. Some customers said OK, and a complete flush and swap was made. Some customers insisted on keeping the DOT 5 and the shop would put a serious effort into it, sometimes a bit more successful than the customer, other times not. The shop is getting $85 a hour for this effort, so where do you / the customer draw the line.
Once I heard this story, I told the shop not to worry about dealing with the brakes, I would flush everything and change over to DOT 3 myself.
I went the extra miles and replaced every component except the brake lines, which got flushed with denatured alcohol.
I filled the system with DOT 3 fluid, did the standard brake bleed, and i now have a SOLID brake pedal.
I do not understand what happened, or why, since my 64 Corvette coupe has DOT 5 in it. But the DOT 5 in the 64 was put in the car in 2015.
One other thing that I have noticed is that I could not seem to locate a "brand name" DOT 5 fluid anymore. I used to get my DOT 5 (not 5.1) fluid in the Prestone bright yellow bottle. I cannot find that anymore.
Also, since the 1956 Bel Air is going to be as much of a daily driver as I can make it, DOT 3 seemed like the way to go.
Something has happened with DOT 5; I just do not know what the something is.
I installed a complete brand new brake system on my 1956 Bel Air. The setup was a front disk brake it with stock rear wheel cylinders. Every single part of the system was new, brake lines, both hard and soft, front calipers, rear wheel cylinders, proportioning valve, everything new.
I poured in DOT 5 fluid very slowly and carefully, so as not to generate air bubbles, etc.
I then literally spent the better part of a month trying to get a solid brake pedal, without success. I tried everything I could think of, I solicited input from other more knowledgeable people, nothing worked. During this process I replaced the brake master cylinder twice, the brake proportioning valve once, both rear wheel cylinders once each, all to absolutely no results. I bled the brakes using a variety of methods, all of which are well known. NADA.
The shop that installed the Holley Sniper system on the car told me that they have had a great deal of issues with DOT 5 fluid. They do a LOT of high end cars, mostly serious horsepower cars, so they need serious brakes. Many customers would bring their cars in already full of DOT 5 and wanting the shop to firm up the pedal.
The now pretty much standard answer is, we can do that is you allow us to change over to DOT 3 fluid. Some customers said OK, and a complete flush and swap was made. Some customers insisted on keeping the DOT 5 and the shop would put a serious effort into it, sometimes a bit more successful than the customer, other times not. The shop is getting $85 a hour for this effort, so where do you / the customer draw the line.
Once I heard this story, I told the shop not to worry about dealing with the brakes, I would flush everything and change over to DOT 3 myself.
I went the extra miles and replaced every component except the brake lines, which got flushed with denatured alcohol.
I filled the system with DOT 3 fluid, did the standard brake bleed, and i now have a SOLID brake pedal.
I do not understand what happened, or why, since my 64 Corvette coupe has DOT 5 in it. But the DOT 5 in the 64 was put in the car in 2015.
One other thing that I have noticed is that I could not seem to locate a "brand name" DOT 5 fluid anymore. I used to get my DOT 5 (not 5.1) fluid in the Prestone bright yellow bottle. I cannot find that anymore.
Also, since the 1956 Bel Air is going to be as much of a daily driver as I can make it, DOT 3 seemed like the way to go.
Something has happened with DOT 5; I just do not know what the something is.
Brake systems have many variables, pedal lever geometry, master cylinder bore, wheel cylinder/caliper piston bore diameter, length of pipes and fluid medium. The expert articles featured above all agree that DOT 5 has some compressibility that can make a pedal less firm than that of DOT 3. I have had similar experiences as yours with 5 in one particular car (a 60 Chrysler) but no issues on two others that includes my 65 Corvette. The problem is either you still had air - recognizing that 5 can be hard to bleed - depending upon line design. If not that than some pedal geometry and/or cylinder/piston bore diameter/stroke is insufficient when confronted with the slight compressibility of 5.
03-10-2019, 09:53 PM
