Dot 4 or Dot 5??

[kobi67]

Getting ready to add fluid to my body off resto. Leaning to Dot 5 fluid. Other than not hurting the paint, what is the advantage of Dot 5? Thanks, Kurt

 

[stepinwolf]

The only advantage of using the DOT 5, is if you are using it in a very high demanding situation, such as a race car. It's boiling point is much higher, hence the need for this type of performance in a brake fluid. I do not recommend you put it in your car only because of the paint issue. :nono

It does not mix with previous fluids, and you will need to have the master cylinder, and all the calipers, ( even if they are all brand new ) completely dis-assembled, and washed out along with ALL the brake lines. Many lean towards it's use mainly because it does not absorb water, but moisture in the system, then gives you a spongy pedal after a while. Take a close look at your master cylinder cover, and you will see that even the manufacturers do not recommend it's use.

If you want a slightly better performing fluid you can safely use the DOT 4 , rather then the regular DOT 3 because of the higher boiling point. Other then that, they are identical.

Stepinwolf

 

[I'mAVettehead]

I agree with Bob, DOT 4.

 

[John Mcgraw]

Kurt,
I use DOT 5 simply because it does not attack paint. Dot 3 and DOT 4 will remove any paint it gets on. The DOT 5 is a little harder to bleed, and it can't be used on cars with ABS, but it is good brake fluid that performs well.
On older Corvettes, it has an additional advantage. Modern cars have a rubber diaphram that keeps the brake fluid away from the atmospheric air, but older Corvettes do not. They have master cylinders that are simply vented to the atmosphere. DOT 3 and DOT 4 glycol based fluids are very hydroscopic and will absorb moisture out of the air, and this moisture will eventually condense out and settle out to the low part of the system.
With a MC that has a barrier diaphram this is not a big issue since the ammount of moisture that is avaialble is limited, but on the old vented systems, new moist air is allways being introduced. This is the reason the it is reccomended that you change the brake fluid on a regularly scheduled basis, moisture settling out in the system will eventually corrode the bores of the wheel and master cylinders. Since Dot 5 is not hydroscopic, this is a non-issue.
The protection of my paint is more than sufficient justification for me to endure the slower bleeding procedure and higher initial cost. If it was retro- fitting a system that has Glycol in it now, then You may want to really consider if you are willing to perform the complete flushing necessary to make the change, but with your complete new, clean system, it is a no-brainer from my perspective. Go with the DOT 5 and never again worry if a stray drop of brake fluid landed somewhwere on your body or frame and did not get washed off.

Regards, John McGraw

 

[critchie]

I agree with John for the reasons he stated. I've got DOT 5 (silicone) in my '62. Works great. Did not have a problem bleeding the system. I wouldn't change my whole system over to do DOT 5. But I was starting with everything brand new.

It seems to be good practice to flush the fluid every 2 years. Some of today's OEMs recommend that. I do most of the work on my car. My mechanical abilities are such that I know that someday I'd spill DOT 3 or 4 on my paint. Guaranteed. My last name isn't Murphy, but I'm very familiar with his law.

 

[stepinwolf]

Here is another opinion

The comments I made in a previous post were the results of my personal, albit limited experience. The following picture shows the results, and recommendations from a technical article that appeared in the September issue, of Super Chevy magazine. I was obliged to reduce it's size, so if anyone is interested in receiving a fax of a clear copy of the page ( I'v got free long distance ) just e-me at the following robert.pelland@cgocable.ca and I will get the copy of the complete article out to you. Sorry for the poor quality of the illustration.

Stepinwolf

 

[Kid_Again]

I take Steppinwolf's points. Interesting.

I think it is a HUGE mistake to not clear out the entrapped water in a DOT3 system before going to DOT5. The General has always had the right idea. If you go back to the shop manuals printed in the 60's, you'll see that the manufacturer recommended blowing out the brake fluid system with pure alcohol (also known as absolute ethanol...the stuff with the tax stamps on it because it's a few steps removed from pure vodka).

You can go to a pharmacy and ask for 95% ethanol instead and use less than a pint to entirely blow out your system. There will be NO water left in the system and you don't have to worry about rust, sponginess due to the water/DOT5 mixture. When absolute ethanol is left open for a few minutes, it sucks up water from the air and turns into 95/5. Even 95/5 will suck water out of a stone and will not harm the rubber components.

The more things change, the more they stay the same.

 

[kobi67]

Based on all the info provided, I think I will do the dot 5. The safety issues with the paint out way any soft pedal issues that may result. Thanks for the feedback.. Kurt

 

[stepinwolf]

To each his own

From my previous posts, I guess everyone knows which side I stand on, regarding my choice in brake fluids.

However I can't help but be surprised, if not puzzled, to see Corvette owners spend thousands of dollars on high performance tires, rotors, calipers, pads, even braided lines, in order to try and get the very best performing braking system, and then would be willing to settle for, or compromise the cars performance, with a fluid that might not give you the best performance, for the sake of the paint issue. :ugh

Let's face it, we are not filling up the master cylinder, or playing with the fluid, every time we put gas in the car. The regular fluid ( Dot 3 or 4 ) has been in use since hydraulic brakes were first installed in vehicles in the beginning of the last century, and I have yet to have anyone come up to me and say that they needed a re-paint because of a fluid spill.

I am quite aware that when misused it will remove paint, but realistically, ask yourself how many people do you know who actually needed to have their car painted because of a spill. ?

Anyway I would like to wish you all, good luck with your choices

Stepinwolf

 

[I'mAVettehead]

I couldn't agree more.

From my previous posts, I guess everyone knows which side I stand on, regarding my choice in brake fluids.

However I can't help but be surprised, if not puzzled, to see Corvette owners spend thousands of dollars on high performance tires, rotors, calipers, pads, even braided lines, in order to try and get the very best performing braking system, and then would be willing to settle for, or compromise the cars performance, with a fluid that might not give you the best performance, for the sake of the paint issue. :ugh

Let's face it, we are not filling up the master cylinder, or playing with the fluid, every time we put gas in the car. The regular fluid ( Dot 3 or 4 ) has been in use since hydraulic brakes were first installed in vehicles in the beginning of the last century, and I have yet to have anyone come up to me and say that they needed a re-paint because of a fluid spill.

I am quite aware that when misused it will remove paint, but realistically, ask yourself how many people do you know who actually needed to have their car painted because of a spill. ?

Anyway I would like to wish you all, good luck with your choices

Stepinwolf

 

[John Mcgraw]

Well guys, You may have never known anyone who has damaged their paint with glycol brake fluid, but I have known many people who have, including myself. I have used DOT 5 for many, many miles of driving in all my classic cars, and have never encountered any of the problems that are constantly alluded to with regard to a soft pedal. It is a little more fussy about bleeding, but aside from that, I can not tell any difference between it and glycol fluid. If you have a hard pedal after bleeding, you will have a hard pedal in use. Can the pedal go soft on C2 cars? You bet they can, but they do the same thing on DOT 3 fluid. The problem is rotor runout and the pistons pump air into the system, but this is not an issue with any particular type of brake fluid.
I would not go to the trouble of putting silicone fluid in a car that already had DOT 3 in it, due to the labor, but on a clean new system, the choice is real clear for me. I suppose as soon as I have the dreaded "soft pedal" that everyone says happens with DOT 5, I will probably stop using it, but after 9 cars that have used it with no problems, I don't expect that this will be anytime soon. As for putting your car at risk, I would submit that you are putting your car at higher risk by using DOT 3 and not changing your fluid on a regular basis. It is an absolute fact that DOT 3 fluid is hydroscopic, and WILL absorb moisture from the air, and WILL corrode the bores of your master cylinder and wheel cylinders if not changed on a regularly scheduled basis. Does anyone know of anyone who has not had the calipers sleeved on their midyear? I will bet that they are few and far between, because people do not change their fluid like they are supposed to. With DOT 5 fluid, there is no reason that these bores will not last forever, these bores do not wear out they corrode away! Of course, this is unlike to cause a car to wreck, but neither is any of the supposed problems with DOT 5. This constant inference by people who do not agree on an issue, that people are somehow putting their car or their life at risk is silly.

Regards, John McGraw

 

[stepinwolf]

John,

I have too much respect for you, to continue to debate the issue, but in all fairness, I am just stating the facts as I have experienced them myself. However, opinions are just that, and that is why it is so great to have a Forum such as this one in order to be able to express them. We cannot all love the same woman, nor the same car, so there has to be diversity for everyone.

Personally I have installed, and used both fluids in many of my vehicles, and I have reached the conclusion that as far as I'm concerned, I will be content to use the basic fluid, even if it must be replaced every few years.

In as much as corrosion or rust is concerned, my impression is that there are very few people restoring Corvettes today, that have not had the master cylinder sleeved ( SS ) and also the calipers rebuilt, or replaced with stainless sleeved units. This alone in my opinion, would by far justify the use of regular brake fluid.

You have my best regards

Bob
a.k.a. Stepinwolf

BTW John, I have asked my Auto Parts people to contact the manfacturers and inquire about using the Dot 5 in any of their components, and was informed by all, that even if the parts had not had any previous brake fluid in them, they are already put together with assembly fluid that would be incompatable with the Dot 5, and in order to use them with Dot 5, they would need to be dis-assembled and cleaned out once again before introducing any silicon fluid in them. For what ever it's worth,,,

 

[BarryK]

ok, sorry to slightly sidetrack this thread but a simple question. Assuming my '65 probably has regular DOT 3 or DOT 4 brake fluid, how often should that be changed?
i've had the car almost 2 years (will be 2 years in March). I have no clue what amount of time the fluid was in the car prior to my purchasing it so to be safe I'd figure the fluid is probably at least 3 years old. The pedal feels fine and she stops well. How do I determine if I should change the fluid or if it's good for a while longer?

 

[critchie]

ok, sorry to slightly sidetrack this thread but a simple question. Assuming my '65 probably has regular DOT 3 or DOT 4 brake fluid, how often should that be changed?

Modern German cars specify that the brake fluid be flushed every 2 years. I believe they've had this recommendation for a long time. Chevrolet didn't have a service recommendation for changing brake fluid on '65s. So, I guess that means that you never had to flush it. I wonder what their recommendation is for their 2006 products? Don't believe any American OEM recommended flushing brake fluid in the 1960s (or 1970s, or ...).

What's good engineering practice? Don't know. But we tend to over-maintain these cars. One more thing to add to the list.

 

[BarryK]

so, that means what? i'm never supposes to change the fluid??
I find that hard to imagine.

 

[stepinwolf]

ok, sorry to slightly sidetrack this thread but a simple question. Assuming my '65 probably has regular DOT 3 or DOT 4 brake fluid, how often should that be changed?
i've had the car almost 2 years (will be 2 years in March). I have no clue what amount of time the fluid was in the car prior to my purchasing it so to be safe I'd figure the fluid is probably at least 3 years old. The pedal feels fine and she stops well. How do I determine if I should change the fluid or if it's good for a while longer?

Barry,

Here's my recommendation on the subject, undoubtedly there will be others.

My present Corvette see's very little use, and is stored in a heated garage all year long. As such, it does not go through the heat/cold cycle that might be a cause for condensation in the system, however the M/C still lets in outside air that could be a cause for humidity entering the system. Most of the manufacturers recommend that the fluid be replaced when ever any darkening, or discoloration is observed, but I play it on the safe side and try to do so every couple of years.

I have devised a simple , safe way to bleed a system at initial start/up, and use the same system to replace the oil. This procedure does not necessitate and bleeding, or pumping of the system, and can be done by oneself in our home garage. After laying out protective covers, I disconnect the fitting at the master cylinder, and hook it up to a container with new brake fluid that attaches to the hood a few feet higher then the M/C.

Then a small transparent plastic tube is connected to each bleeder, and inserted into a clear glass bottle at all four wheels. Once all the tubes have been installed, I simply open up the bleeders ( only one at a time starting at the farthest position ) and watch the fluid pour into the glass jar until the fluid flows clear. After this is completed, I replace the oil in the M/C, and then re-install the brake fittings. When done correctly, there is no need to bleed the system, as no air has been introduced into the lines, and I have a very high, firm brake pedal.

Now, this is what has WORKED FOR ME but there might be others who have different opinions, or procedures so keep following this thread.

regards
Bob,

BTW Barry, you are not high jacking this thread, just contributing, and by doing so, it is likely to take off, so keep a close watch.

 

[BarryK]

so, every two or three years than? Mine also gets limited use per year but in the wainter my garage is not heated so most likely the fluid is picking up more moisture than yours.

I guess it's time to learn brake fluid change next........
This winter has become quite an education for me on this car!

 

[JohnZ]

A flush-and-bleed every three or four years is more than adequate, and is good practice to follow. Most domestic manufacturers don't even address this as a maintenance item in their owner's manuals, and there are millions and millions of cars running around out there with DOT3 fluid that's ten or twenty years old (and looks like grape jelly) :ugh . Most of them never see fresh brake fluid or a bleed until they have a brake job or brake system overhaul done, and that's scary (to me, anyway).

I flush/bleed my garage-kept toys about every three years, have never had a problem. The pressure bleeder makes it a ten-minute job. I use Castrol GT-LMA (low moisture absorbent) DOT4 fluid.

 

[BarryK]

thanks John

i guess I'm good for another year than.

maybe next winter I'll try to tackle the brake fluid.

 

[PTighe]

After I put new brake lines in my '67, I flushed the whole system out with a gallon of denatured alcohol. Just gravity bled it over a couple days, so it got a lot of "hang time" in the calipers and MC.

Then I put a new quart of DOT 5 in a large, clean coffee can and put it on the stove at medium/low heat. After a while you can see the entrapped air bubbles rise to the surface. You have to get this air out before you put it into the brake system. Continue heating...not boiling, until you don't see any more bubbles and the silicone is slightly steaming.

Then shut the stove off and let the silicone cool to room temperature. Put the plastic lid on. Do NOT agitate the can, because you will mix air back in again. When you're ready, slowly pour the silicone into the MC and gravity bleed or what ever you do. PT