The Stovebolt Site Forums The Shop Area Engine Shop Which modern modern brake fluid to use

The Chevy manual for a 52 truck (stock suburban w 261) mentions using Chevy branded oils and fluids throughout the book. What shoudl one use when looking for brake fluid (or even trans) when shopping at pep boys, auto zone etc? DOT 4, 5, other? Thank you

Drew that depends on if your a 'by the book' kinda person or not

If your rig still runs the original or even 'replaced at some time in the distant past' lines what you do not want is the new synthetic type... even if it says CHEVY on the bottle.

I am not familiar with brake fluids in general. Can i get a non-synthetic type from a local auto parts store? Do non synthetics have diffferent classification like 4 or 5?

As the fluid in the truck came with the truck, is there a way for me to tell what it is? I just need to top upt he fluid that is there now. I assume glycol is non-synthetic and and silicone is synthetic, correct?

The standard glycerine/alcohol based fluid which would be a direct replacement for the original equipment fluid would be DOT 3. DOT 4 is a similar type fluid with a higher boiling point. It is interchangeable with DOT 3 and just has a higher temperature rating for heavy-duty use in disc brake systems where operating temps can be above the boiling point of DOT 3. DOT 5 is a silicone-based fluid that should not be mixed with the others, or used in a system that has had 3 or 4 installed before.

Alcohol-based fluids like DOT 3 and 4 are "hygroscopic"- - -they can absorb moisture from the air. Fluid containers need to be sealed or the moisture the fluid absorbs can lower the boiling point dramatically. Silicone-based fluid does not absorb moisture, but it has some other oddball characteristics that don't make it a good choice for older brake systems.
Jerry

To add a bit to what Jerry has stated; Glycol based brake fluid is available in both regular and synthetic, with most of the synthetic being DOT 4. There is also a DOT 5.1 that is glycol based, it has a similar boiling point as the silicone based DOT 5.
Just from my own experience, stick with the glycol based fluid. Silicone based fluids can cause issues with incompatible rubber parts.

Where is the non-synthetic/regular terminology for brake fluids coming from? All the DOT 3,4,5.1 fluids I'm aware of are based on glycol ethers. All glycol ethers are synthetic materials.

I have a friend who rebuilt his 64 nova break system and put in Dot 5. He ran that for 150,000 and never had another break cylinder or master cylinder service. Dot 5 is not hydroscopic (absorbs water). I am going to use dot 5 in my 46 system that is a total rebuild. DOT 3 fluid absorbs water and this is what causes the rust and corrosion in the systems. I know you cannot use DOT 5 in modern cars due to seal issues.

If you're going to use silicone DOT 5, you want to make 100% sure that the rubber is compatible. Otherwise, you may end up with seal failure. Also, while true that DOT 5 does not absorb water, it also floats on top of it. Any moisture that gets in the system will condense at the lowest point, usually as a "slug" in the lines. This will lead to soft/spongy pedal fell when the brakes are hot.

It's starting to show up on the bottles. I haven't really looked into what difference (if any) there really is, other than claims of "better corrosion protection" and "longer rubber part life". Might just be an advertizing ploy, slap the term "synthetic" on it and raise the price. As mentioned, I've only seen it on DOT 4 and 5.1.

I totally rebuilt my brake system in July 2010... Used Dot 5 Silicone brake fluid so far no problems... Made sure all rubber parts were compatible with silicone brake fluid... Used NAPA for all the wheel cylinders, master cylinder from Golden State...

This thread has some good posts with links and other information ... Brake Fluid ...

Hi folks,

I searched and did not find any definitive positions on "DOT3 Synthetic" vs DOT3 "regular". Any thoughts on this?

My truck's system went soft over the last couple of months. When I checked the master, it was all but empty. I refilled with what I had (DOT3 Synthetic) and am watching for fluid loss.

So two questions:
1) Any issue with "DOT3 Synthetic" (the bottle claims compatibility with any DOT3 fluid)
2) Any thoughts on "disappearing" brake fluid - no leaks or seeps discovered.

Thanks,

Bill

Both my trucks are DOT 3 "regular" or were until I was in need of fluid and I found that DOT 3 Synthetic had taken over the auto parts store shelf and they weren't stocking regular any more. So, with a frown, I used the new DOT 3 Synthetic to top off my '37. It is a daily driver and that was over a year ago. I have not noticed any problems.

As far as disappearing fluid, you might want to pull your drums to see if there are any wheel cylinder leaks.

also note re the disappearing fluid, these vented MC's lose fluid from evaporation, it's a good idea to check level regular to avoid low levels allowing air into the lines, don't wait 'til pedal feel warns you

Bill

If you read the Truck Shop Manual, you will see that the presence of some brake fluid under the rubber boots is acceptable. That would be another source of leakage over time.
Compared to modern master cylinders, the ones on these old trucks have a tiny reservoir in them. Therefore, with what Bill says above, it is extremely important to check your fluid level.
Carl

"Synthetic" is nothing but advertising hype, pay no attention to it. Back in the 80's I worked in a development group for a large company which manufactured and held some of the original patents for "moisture resistant" DOT 4 Fluids. At that time ALL DOT 3,4 & 5.1 brake fluids on the market were synthetic. I doubt the technology has changed a lot since then. If the fluid is labeled DOT 3 or DOT 4 each batch has to pass a compatibility test (at lest it did then).

I always buy a name brand. At that time we faced stiff competition from off branded products which were made from inferior ingredients but still passed the DOT tests. For example all our fluids were formulated with distilled glycols where some of the off branded fluids used what distillers term bottoms glycol ethers.

all I know is when I used to work in Alaska, before we switched to silicone fluid in all the equipment. We had to refurbish all the brake cylinders every year, after we switched to the silicone, the problem went away entirely.

Forgive me guys if I missed something in these two pages of
replies, but.....here's my story cuz I just don't see where the
big deal is about brake fluid.

Back on a hot day in August of 2006 I bought 'Old Blue' from
a guy sweetie face worked with. Me and the mutt, who was only
a year old at the time, rode into work with her that morning
to settle up and get the keys. It was a 40 mile trip and the
PO assured us he'd been driving the truck to work from a few
blocks away on occasion. First stop a half mile down the road
was to fill up for the trip home. I decided to take the
tollway west to avoid driving through a dozen heavily
populated towns. We hit the highway and even with my foot all
the way down could barely get it over 40mph, and it felt like
the brakes were dragging us down. got about five miles down
the road and I couldn't even keep it above 25mph and pulled
off to the side. Smoke was coming off all four wheels and when
I tried to rock the truck back and forth I could see the brakes
were seized all the way round. Put the leash on the mutt and
we started the walk to the toll booth which was a few miles down
the road. As I said it was a hot day, bout 100° by now and the
pavement was just too hot for her paws so I had to carry her for
a couple of miles, 30lbs. she was she was.
Drippin' wet I made it to the phone and called a tollway wrecker
to pick us up.
A couple hours later we were pulling into the yard and I had
him dump it in front of the garage and shelled out a pocket full coin.
Before I drove it another mile I spent the rest of the summer
doing a complete brake system and suspension rebuild. New
wheel and master kits from JC or Chevy Duty, don't recall now
which one, all new lines, all new fittings, tees, etc., took
a light pass on the drums, inspected and repacked the brgs.
front and rear, (full floater 3/4-ton) new seals.
Fluid of choice was what I'd been using in everything, midget
and Pitts airplane included, for the past 40 plus years, DOT3.
http://www.pbase.com/dennygraham/image/159348260/large
It's been what, eight years now since I've rebuilt the stock
system, and 16,000 miles. I've never added fluid to it, have
a rock hard pedal 1 1/2" from the top, have adjusted the
shoes several times because of normal wear. Drive her on the
tollways and freeways (right lane) at 55 mph often, have had
to make panic stops, have never had a brake problem such as
fade or pull. Can lock them up if I'm to hard on the touch.
So.....the point of all of this is....I just don't see any of those
problems with my totally stock 1950 Huck style brakes, that
I'm always hearing people complain about.
Unless I were going road racing with my AD, I also don't see the need
for disc brakes or exotic silicone brake fluids. This truck is driven in the
hot weather of summer and the cold extremes of northern Illinois winters,
no brake problems yet, just keeping it simple works for me as it did when
this truck was new in 1950.

DG

I was having trouble with my master cylinder about 10 years ago so I rebuilt my entire brake system with new. The only reason I used Dot 5 was because it doesn't eat paint like Dot 3 does. I have not had any problems with its performance. All my daily drivers are using Dot 3. No problems, except that brake lines rust out due to our dirt road and the calcium chloride for dust control.

Rick

Thanks all.

I'll keep an eye on the system for leaks and check the MC more often.

Bill

Funny you bring up racing, Denny. It turns out that silicone brake fluid is not recommended for racing use. Seems when it gets hot, it leads to a mushy brake pedal and severe loss of braking force due to it holding too much air in suspension in the fluid. That's an unfortunate problem with silicone fluid.

Your correct Bill, I try but I can't always cover all the
bases, think I post way to much explanation and detail most
of the time anyway in an effort give a complete statement.

Should have just simply left off the comment about the
silicone fluid and said, "Unless I were going road racing
with my AD, I also don't see the need for disc brakes."
The main advantage of disc brakes on a passenger car is low
maintenance and ease of replacement when the time comes.

On the silicone brake fluid I would post this which I quote:
"Compressibility of silicone fluid is very unstable
throughout the temperature range encountered in normal usage.
As the temperature increases, the pedal travel necessary to
compress the fluid changes, resulting in unpredictable pedal
height."
This being one of the reasons that I don't need it in my
vintage truck. I might add that my truck is well over due
for a DOT3 oil change. Polyglycol fluids down side is that
they are quite hygroscopic and can even suck up moisture in
a closed system over time so a change every few years is a
good idea.

dg

Hi All,

I'm "hijacking" this thread a little bit.

Since writing my post in March, I've pulled the front clip, removed the engine, and powerwashed the exposed frame. Following that, I noticed a greasy spot on the passenger side near one of the brake line junction blocks. I thought the spot may have been washed down from elsewhere and cleaned it with a solvent. The stain reappeared, but now was recognizable as brake fluid. (one of the many benefits of this hobby is learning to identify various petroleum based stains as to their origin). So the correct course of action is to replace these 68-ish year old lines.

Now my question:
Multiple sources suggest either 1/4" or 3/16" lines, 1/4" seems to be preferred for a 1947 3100 (my truck). What is the O.D. of a 1/4" brake line so that I am certain I order the correct item?

Thanks in advance for the help.

Bill