Brake Fluid ?
 

Is non synthetic Dot 3 brake fluid correct for a 40 pickup ?

Thank u, Dave

Re: Brake Fluid ?
 

Dot 3 is OK but it does absorb moisture more than the synthetic Dot 5. None are perfect and they all deteriorate to some extent so use what you feel comfortable with. Check with the source of new rubber parts to find out what they recommend for fluid. Basically, if you start with a particular fluid, you should stay with it. Rubber parts don't like fluid spec changes.

Re: Brake Fluid ?
 

Dave, The sad truth is that DOT 3 and 4 do absorb water causing rust , requiring bleeding the entire system every 2 years. I have found this is not to be a problem using DOT 5 in my 40 car.

Re: Brake Fluid ?
 

Dave,

Be aware that in many cases, switching to DOT 5 requires you to replace all components in the brake system including master cylinder, wheel cylinders and all brake lines. The DOT 5 does not handle the contamination/residue in a brake system that was previously DOT 3....

Re: Brake Fluid ?
 

From personal experience it is better to use dot 4 in stead of dot 3. I ran a durability test on some clutch slave cylinders and they failed prematurely that was using dot 3 fluid. I reran on dot 4 fluid and they passed the test no problem.

Mart.

Re: Brake Fluid ?
 

I have some insight as to the life expectancy of DOT3/DOT4 brake fluid. I have always been concerned about this, so about 6 years ago, I bought an electronic device that can be used to determine the moisture content of the Glycol based fluids. At that time, I used it to test all of my vehicles, and found that the moisture content did indeed increase with age, which also indicated to me that the device did indeed work as expected. I had put new brakes in my '67 Corvette two years previously, and when tested, it showed less than 1% moisture content, which is well within the specified limits. My 1951 Ford had about 2% in the fluid that I had installed about 10 years earlier when I went through the system. Both of these were deemed acceptable, though the '51 was close to the edge. I also tested the fluid on our 1984 Fiero, which we bought new and still has the original brake fluid; it tested at 4%. (This car has 30,000 very easy miles from new and has essentially just sat in the corner of my shop for the last 25 years.) From this I extrapolated that Glycol based fluid has a minimum life of at least 10 years and will remain effective for much longer than that, as witnessed by the Fiero, whose brakes were still working like they should. How many 20 to 30 year old vehicles are out there with their original factory fluid? A whole bunch, I would expect.

As a result, I flushed the system on the Ford and installed new fluid, which tested at well under 1%. (Sadly, the Fiero was stuck behind a bunch of other stuff, so I didn't get around to flushing it. I plan on getting to it in the next week or so.) I test the systems ever year or so. and they are all still withing specifications. Thus, the member flushing his system every two years is probably wasting some time and money, but to each his own. I would much rather KNOW the condition of the system rather than guessing at it.

A couple of things. The information I have given here are for well cared for cars that get minimal mileage, are garaged when not in use, and are not used in wet weather. I don't know if it would apply to a daily driver. I tested my 1999 F150 and it was good, but I had done some brake work a couple of years ago. Also, when I flushed the systems, I installed "Speed-Bleeders" on the vehicles, which makes bleeding (and therefore flushing) and easy one-person job.

As a side note, I put DOT5 in my '68 Corvette when I did the brakes about 15 years ago, and they still work fine, as expected. However, given the difficulty I had in bleeding the system, the cost of the fluid, and the advent of speed bleeder, I have gone back to using DOT4 and flushing the system when necessary.

Re: Brake Fluid ?
 

Mart,

I also use DOT4 fluid rather than DOT3. That being said, I have always read that the difference between the two was the ability of DOT4 to tolerate higher heat, and other than that, they were functionally the same. While heat tolerance would be a factor with brakes, I don't see how it would come into play on a clutch system. Do you have any insight as to why the DOT3 failed? How did it fail?

Just curious.

Tubman

Re: Brake Fluid ?
 

Can't remember. It was over 30 years ago. The rubbers wore. It may have been that the dot 3 was an inferior brand. The oe fitment was dot 4. As the fluid was also used in brakes it made sense to use it in the clutch too. For the difference in price, I just get dot 4.

Mart.

Re: Brake Fluid ?
 

Only because my vehicle had be stored for an extended period with dot-3 I opted to go DOT-5 when I was in the process of replacing pretty much everything just so I wouldn't need to go through that hassle/expense again down the road.

Re: Brake Fluid ?
 

Can DOT 3 & 4 be mixed ? Thanks in advance !

Re: Brake Fluid ?
 

Yes they can be mixed.

Re: Brake Fluid ?
 

Hey Tubman,
When you say 'difficulty bleeding system'....was it because of system design/hard to get to ...why difficult. Was it something to do with Dot 5 use, itself ?
I've read/heard that Dot 5 should NOT be stirred/shaken. Something about bubbles.
Never understood that, as bubbles should quickly exit master cylinder...no ?

Re: Brake Fluid ?
 

Been using dot-5 for years in our two 38s...no problems

Re: Brake Fluid ?
 

It just didn't want to bleed. I almost got a divorce from the number of times I said, "Hey Honey, can you come out to the garage again?". I was aware of the care that has to be taken with this fluid, and followed the instructions to a "T". The fluid I had said to heat the fluid on a stove to almost boiling to drive out the air which I did. I was extremely careful during the whole process, and we finally got the system bled, but it was challenge. I have heard the C2-C3 Corvettes are notoriously hard to bleed, and since I've done it a couple of times, I believe it.

This is all about personal choice; some people like it; some don't.

I refuse to be drawn into yo a DOT5 vs Glycol discussion. I know what my experiences have been and I have made my choice. If you find something better, congratulations.

Re: Brake Fluid ?
 

Hm, never heard/saw anywhere about heating on stove ?
Know what you mean about mixing wife and brake bleeding. I know that I'd be in double trouble...if caught with brake fluid cooking in her kitchen :) !!

Re: Brake Fluid ?
 

Wives and brake bleeding can be fraught with difficulties. Like explaining that while, thankful for the help, actually pressing the brake pedal and not the clutch pedal up and down might be more productive.

Mart.

Re: Brake Fluid ?
 

Are you charging up a new system or filling an old? If the fluid is purple it is DOT 5. If it is not most likely DOT 3

Re: Brake Fluid ?
 

mart im sitting laughing here, ive had that very conversation too!

Re: Brake Fluid ?
 

Technically, glycol based DOT 3, 4 and 5.1, along with silicone based DOT 5 are all "synthetic". :)