DOT5 Brake Fluid

[Careless]

So I'm getting around the point to install the brake components that are missing and to put a fluid in that does not discolour as much as regular DOT3 or 4, in hopes that it won't  yellow the new plastic reservoirs mainly.

Has anyone had issues with early 240Z brake components utilizing DOT5 brake fluid? 

I like the fact that DOT5 won't peel paint it it spills or drips, it has a higher boiling point (a bonus, really), and it won't absorb water like DOT4 would, so it would generally last longer and stay clearer (though it also won't let paint adhere if I get it on anything that is un-coated, which may be a problem if I am... careless)

My main concern is having to flush the system if it starts to weep due to incompatibility. 

Any issues with the stock 240Z stuff on this matter?

 

Edited June 28, 2016 by Careless

[Chickenman]

DOT 5.0 or DOT 5.1? There is a big difference. DOT 5.0 is a silicone fluid. It does not absorb water and does not damage paint. Thus it is good for Antique vehicles and certain Military applications. However... it has very poor compressability. Silicone fluids don't absorb water, but they do create air bubbles when compressed and then released. That makes them unsuitable for any form of competition and most forms of highway driving, particularily in Mountainous Terrain. They also cannot be used on vehicles with ABS. DOT 5.0 must also be thoroughly flushed and can NOT be mixed with any DOT3, DOT 4 or DOT 5.1 fluids. Generally not recommended these days for anything but Antique vehicles stored in Museums. Bottom line: It's a good storage fluid...it's not a good brake fluid.

DOT 5.1 are a polyalkylene glycol ether and borate ester combination with higher boiling points than DOT 4 and a lower viscosity to make it more compatible with ABS systems. Many Auto manufacturers now recommend DOT 5.1 fluids. It can be safely mixed with DOT3 and DOT 4.  DOT 5.1 can NOT be mixed with DOT 5.0

Here's a good explanation of the various types of DOT brake fluids.

http://www.advancepetro.com/differentbrakefluid.htm

http://www.gomog.com/allmorgan/brakefluids.html

Edit: I use WilWood 570 race fluid ( DOT 3 ) in most of my vehicles. As do many of our local Datsun 510 members. No issues. Castrol LMA is also a good DOT 3/4 fluid

 

Edited June 28, 2016 by Chickenman

[Chickenman]

A warning from CarboTech and AP Racing on using DOT 5.0 ( Silicone ) fluids:

http://www.ctbrakes.com/brake-fluid.asp

 

Quote

SILICONE BRAKE FLUIDS – A WORD OF CAUTION

Carbotech Performance Brakes & AP RACING NEITHER MARKETS SUCH FLUIDS NOR RECOMMENDS THEIR USE WITH OUR OWN OR ANY OTHER BRAKING SYSTEM

Virtually all of the problems with Silicone Brake Fluids relate to:

• Long/spongy pedal
• Sudden loss of brakes
• Hanging on of brakes

They reflect certain properties of silicone fluids identified by us over many years and recently ratified in SAE publications, namely:

• High ambient viscosity
• High air absorption
• High compressibility
• Low lubricity
• Immiscibility with water

Research has shown that the relationships between problems reported and properties identified
may be expressed as follows:

Long /Spongy Pedal

1. Compressibility, up to three times that of glycol based fluids
2. High viscosity, twice that of glycol based fluids, leading to slow rates of fill and retention of free air entrapped during filling, and hence bleeding difficulties.

Sudden loss of brakes

1. Air absorption. Gasification of absorbed air at relatively low temperature produces vapor lock effect.
2. Immiscibility (failure to mix) with water. Whilst the presence of dissolved water will reduce the boiling point of glycol based fluids any free water entrapped in silicone-filled systems will boil and produce vapor lock at much lower temperatures (100°C or thereabouts)

Hanging on of brakes

1. Low lubricity. In disc brake systems the sole mechanism for normalization of system pressure upon release of pedal pressure is a designed-in tendency of seals to recover to their ‘at rest’ attitude. Low lubricity works against this tendency.
2. High viscosity exacerbates the effect of (a) above. It should not be assumed, therefore, that the high price of silicone fluids implies higher performance in hard driving or even normal road use.

AP Racing glycol based fluids do not contain the adverse properties described above. The
recently introduced Formula DOT 5.1 which exceeds the performance criteria of DOT 5 (Silicone),
is suitable for all conditions likely to be encountered in modern driving conditions.

 

[jonathanrussell]

In general, I use DOT 4 in my z cars. I am refreshing an original orange paint 72 low miles car and really want to use DOT 5 (paint paranoia) but likely will use DOT 4. About 10 years ago, I rebuilt the brake system in my dad's original paint black pearl 78 280z. I used DOT 5 in the rebuild. The good- dad's car went through a period of 8 years where it wasn't driven once. When we started it up, it started right up and the brakes were not rusted, frozen, etc which is typical if DOT 3/4 doesn't get flushed every year or two. I did flush in fresh DOT 5 at that time. The bad- the pedal is a bit spongy (but not terrible). I would say that the brake pedal engages about an inch or so lower than a normal 280z with DOT 3/4 fluid and has a bit of sponge at full contact...in my experience. Also, I think the brakes are a bit grabby. Now, either dad or I drive the car at least once every month and I am considering switching to DOT 4 to solve the spongy brake. When I do this I will likely replace the Master Cylinder, open up all the lines and attempt to drain as much fluid as possible out, and then flush in multiple liters of DOT 4. I might remove / rebuild / clean out calipers and cylinders but haven't decided yet. 

So, in my experience DOT 5 has its place but if you care about having a solid brake pedal and want to do any spirited driving with confidence, I would suggest DOT 4. Still, I hate the fact that paint damage can occur. And, I am not talking about spilling a bit when I flush or refill; I am in control and careful then. What I worry about is a failing Master Cylinder seal. It is one of the reasons why I only use Nissan Master Cylinders (at least to date I have been able to locate) AND flush DOT 4 once per year.

[Mike W]

I went through this same dilemma about a year ago when I upgraded my brakes with the big brake kit from Arizona Z Car.  I did a lot of research on this and talked to a lot of people whose opinions I trust, but in the end I opted to give the DOT 5 a try.  Here was my situation:

1. I do not track or autocross my car, but it does see a fair amount of spirited driving on the roads throughout Texas

2. The car is shown frequently, and so the corrosive nature of DOT 3/4 was a huge concern especially in the engine bay

3. All of the major components of the brake system were being replaced including a larger master cylinder and the proportioning valve, so most of the unions throughout the system had to be loosened and removed.  As a result of this, there was at least some possibility that I would encounter a loose / leaking fitting on startup and run the risk of damaging my paint if I used DOT 3/4.  Given that the car had recently been repainted, including the engine bay, I was extremely nervous about this possibility

4. Much of the material I had read about DOT 5 suggested that it was less compressable than DOT 3/4 resulting in a spongy pedal feel.  Many articles also pointed out that it was difficult to remove all of the air from the system which would aggravate further the spongy pedal feel

My installation procedure went as follows:

1. Since all of the major components were new, I was not all that concerned about the possibility of mixing the new DOT 5 fluid with remnants of any DOT 3/4 that might have still been in the system.  Regardless, I did use compressed air to blow out my lines in order to remove any remaining DOT 3/4 that might have been in my lines

2. I used a pressure based Power Bleeder initially with just air to try and detect if any leaks were in my system.  This did detect a couple of joints that had not been tightened sufficiently and so I had the chance to resolve those issues before a drop of fluid went into the system

3. Once that had been completed I filled the reservoirs with DOT 5 and began the bleeding process.  Sure enough a number of leaks were observed especially around the new proportioning valve where I had to use adapters to go from metric to NPT and as it turns out these unions were just not tight enough.  Fortunately, with the DOT 5 there were no detrimental effects to the paint

4. Once I cured all of the leaking unions, I completed the bleeding process and then let the car sit overnight

5. On the following day, I bled the entire system again and sure enough a little more air was detected in the system as things had settled out

Finally time for the road test. 

Now bear in mind that my entire braking system had been upgraded from stock so it was not just a change of fluid from DOT 3/4 to DOT 5 so I  was expecting things to feel different. 

To sum it up, I just could not believe the improvement in braking capability.  Clearly much of this was due to the upgraded system, but I did not experience any sponginess in the pedal and in fact it never felt better.  In all of the driving I have done over the last year I have not noticed any degradation in the braking power of the car or in the feel of the pedal.  In the end I couldn't be happier. 

Even if the DOT 5 had resulted in some of the negatives associated with this fluid I would have likely replaced it with DOT 3/4, but at least with the DOT 5 I was been able to leak test the system without any detrimental effects to the paint.  In the end, the DOT 5 has performed so well in my particular situation, I have decided to stick with it.  I even went as far as changing out the fluid in my clutch system as well.

 

Here's a few links that I used to help me decide the path to take:

http://www.classiczcars.com/topic/49490-dot-5-fluid-in-my-240z-keep-or-flush/?hl=%2Bbrake+%2Bfluid

 

http://forums.mtbr.com/brake-time/silicone-based-dot5-busting-myth-832808.html

 

http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm

 

I suspect that this topic will always fuel a raging debate, but from my perspective if it is used in the proper application and you have a concern about detrimental effects to the looks of your car, DOT 5 can be a perfectly fine solution.

 

Hope this helps.

 

Mike.

 

[Hardway]

Mike's concern about his paint possibly being damaged by brake fluid is completely warranted as the paint job on his car is absolutely stunning.  I will add my experience to this conversation.  I only drive my car to shows, get togethers, and to work on occasion.  The brake system on my '71 240z is 100% stock with pretty much all new components at the time of the rebuild by the previous owner.  He filled the system with DOT 5 and when I took delivery of the car the pedal was a big spongy and the parking brake did not grab until it was fully pulled in to the Up position.  Once I home I adjusted the rear shoes as they were out of spec, tightened the brake cable adjustment, and went through two rounds of bleeding with help from my wife.  The end result is a brake pedal that stops the car confidently every time but it does have a little more travel than I would like before they really bite.  This might be remedied with another round of bleeding and I might need to look at adjusting the pedal a little as well.  All in all, given the benefits DOT 5 provides I don't think you can go wrong with it as long as you understand its limitations.

[grannyknot]

I have used Dot 5 in all my bikes for 15 yrs, never had a problem and I can stop on a dime.

I used Dot 5 in a stock braking set up on a 74 Triumph TR6, never felt the spongy pedal that you read about. Works fine for me. Just don't ever spill it on paint that you intend to sand down and paint again, it doesn't matter what you clean it with you will always get fish eyes in the new paint.

[Careless]

I think I'll be giving DOT5 a try in this system mainly due to old hardlines and fittings being re-plated and reused. Much of you guys running DOT5 fluid are using it for the same reason as my main concern, which is the paint and discolouration/longevity thing- and it seems many would agree that's what DOT5 is good for.

Glad to hear it is compatible with 240z braking components. I've heard some stories about older domestic stuff not enjoying DOT5, but was never sure.

 

I'll most likely be doing a full brake bleed with some cleaning agent first, though.

Edited June 29, 2016 by Careless

[Zed Head]

I don't think that the fluid is causing the yellowing.  The reservoir material is probably nylon, which tends to yellow over time.  So if that's the main reason, it won't really help.  On the paint protection issue, maybe so, but silicones can cause other problems, like screwing up the application of paint.  Fisheyes and adhesion problems.  And if your car has been repainted with a two component system, like a typical urethane, you may not need that protection.  The paint is crosslinked.

But, apparently, different chemistries can be used to achieve the DOT5 spec. The spec. is a physical property spec. not a chemistry spec.  Kind of like GL-4 and GL-5 in gear oils.  So DOT 5 may not be what you think it is.  

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

http://ebcbrakes.com/product/brake-fluids/

So, if you want the paint protection, just make sure that the fluid is silicone based.  Read the fine print.

Random thoughts.  I used to work at a paint company.

[Careless]

yellowing of the fluid definitely causes discoloration on whatever material the reservoir is made of- all of the nissan reservoirs i've seen have a defined line as to where the fluid sat at rest for most of its life. I thought it may be due to the fluid amplifying any kind of UV rays that may travel through the container at or below the fluid line- but we don't drive with our hoods open or off (most of the time, anyways. lol) so I don't think it's purely the plastic itself.

whether or not DOT5 will reduce the discoloration over time i am not sure of, but all things i'm reading on various other resto and hotrod forums say that it does keep it noticeably cleaner- so that's something to think about. i guess its something ill have to test for myself, as long as the braking system on the 240Z can handle it. looks like it will be ok.

as far as the fluid damaging the paint... my dearly beloved soon to be worked on personal project, my 1988 300ZX Turbo that has been covered in cosmoline in every corner and crevasse is a total loss now due to a leaky pair of masters that drained themselves when the car was in storage. i'm not sure when it happened, but the car all the way down the frame rail is junk now :-(

This is the freshly-cleaned side, the oil / cosmoline preserved it so well, and was a bitch to clean off without any heating of the substance.

 

not bad for an 88. you can see remnants of the oil behind the strut tower. it was much thicker than that.

here it is after cleaning the driver side. err..... what's left of it.

wish i would have seen it dripping before i locked it away for half a decade.

 

it's almost comical, really. snow must have built up in the corner of the "barn" or shed it was under since it was against the wall. that driver side, front to back, is rotted to hell. the pass side better than "pretty good". almost as if it were from two different cars.

needless to say, the brake fluid + my negligence, multiplied by my lack of funds to pay attention to this car really did a number on it.

I think i'll try silicon based DOT5 for now. 

Edited July 1, 2016 by Careless

[grannyknot]

I have only ever used Prestone Dot 5, it's purple, other Dot 5 brake fluid might be a different colour. It has never stained any of the M/C reservoirs but sure stained the the hell out of the white plastic pressure vessel on the vacuum pump I use to bleed brakes. Probably won't be a problem for you but thought I would mention it.

[Careless]

1 hour ago, grannyknot said:

I have only ever used Prestone Dot 5, it's purple, other Dot 5 brake fluid might be a different colour. It has never stained any of the M/C reservoirs but sure stained the the hell out of the white plastic pressure vessel on the vacuum pump I use to bleed brakes. Probably won't be a problem for you but thought I would mention it.

The ATE SuperBlu I ran in my 87 Z did the same thing. Looks like blueberry juice. Was tempted to drink it once. Purple sounds tasty too. $50 bucks says it's grape flavour! 

Edited July 1, 2016 by Careless