Is Dot 5 ruining my brake cylinders?

[tom'sB2B]

I noticed today that I have two brake leaks at the wheels. I pulled the front hub off and found that my cylinder is leaking. It looks fairly new. I also have a leak on one of my back wheels. I haven't pulled the hub yet but I'm suspecting that it is the cylinder and I just replace it last year. When I redid the brakes and lines last year, I used Dot5.

Was that a mistake? What should I use instead? What should I do?

thanks

Tom

[TodFitch]

I've had DOT5 in my Plymouth for about 13 or 14 years now with no leaks. I did have the hydraulic stop light switch go out last year. That has been the only issue I've had with the hydraulic system.

I did have new hoses, new brake lines and either new or rebuilt cylinders all round. I've heard of people having issues if they simply flushed when they changed fluid types.

[MBF]

You can't mix DOT3 and DOT5 fluids. The mixture will destroy rubber parts. When switching from one to the other, Wagner suggested a complete flush and replacement of all rubber parts. This is according to a RAYMOND factory service bulletin published a few years ago. I'm not sure if that is causing your problem, but if you have run DOT3 in the past in that system, it may be something to look at. Mike

[wayfarer]

Yeah, DOT 5 is an animal all to its own and doesn't play well with others...

Considering the cost, there is little reason to use it unless you are driving a Formula 1 car and generating obscene amounts of heat. You can mix 3 & 4, but again the 4 is costly.

You might want to disassemble one of the leakers and see if the rubber has been damaged. On everything but a serious hot-rod I recommend using Dot 3when building/rebuilding the brake system.

.

[TodFitch]

Yeah, DOT 5 is an animal all to its own and doesn't play well with others...

Considering the cost, there is little reason to use it unless you are driving a Formula 1 car and generating obscene amounts of heat. You can mix 3 & 4, but again the 4 is costly.

You might want to disassemble one of the leakers and see if the rubber has been damaged. On everything but a serious hot-rod I recommend using Dot 3when building/rebuilding the brake system.

.

Hmmm. The couple of people I know that are into racing claim that DOT5 gets spongy when the brakes get really hot so they use DOT3 or DOT4 (depending on the person). They also flush and re-bleed their brakes after every weekend race to take care of any heat degradation in their brake fluid.

It was my understanding that DOT5 was actually best for vehicles that may be parked for long periods of time as its major advantage in service is that it is not hygroscopic.

For me another advantage is that it does not dissolve paint.

[Guest P15-D24]

It was my understanding that DOT5 was actually best for vehicles that may be parked for long periods of time as its major advantage in service is that it is not hygroscopic.

For me another advantage is that it does not dissolve paint.

I have been using Dot 5 for over 25 years and never had an issue. With Dot 3 I was doing rebuilds every couple years because they would start to rust/leak after they sat. You just have to make sure you do the job right the first time and you will not have problems.

[Fernando Mendes]

What I have heard:"DOT3 and DOT5 both contain SILICONE.DOT4 contains PETROLEUM":)

[Fernando Mendes]

Silicone brings condensation and rust.

[Merle Coggins]

Actually Fernando, DOT 3 and 4 are Glycol based fluids. The main difference between them is that DOT 4 has a higher boiling point. DOT 5 is Silicone based.

Merle

[grey beard]

I also use dot 5 in my Pilothouse, and have had no issues. Dot 5 fluid, if used in a squeaky-new system - all wheel cylinders, lines and master cylinder - will last a lifetime and likely never need further replacement of hydraulic cojponents. It is used by high-end car makers and seldom ever causes any problems whatsoever EXCEPT whenit is inadvertently mixed with the glycol type 3 or 4 fluids. If you use dot 5, I suggest you have a sign made to place on the firewall - DOT 5 ONLY. jmho

[JBNeal]

I've been using DOT 5 since '98 when I completely overhauled the brakes, new lines included. The '48 sits for long stretches, and the pedal is still firm, and the fluid is still purple. I saw what the original DOT 3 did once it was saturated with moisture: pitted wheel cylinders, corroded lines, and a leaky master cylinder.

[41/53dodges]

in this case, how would one flush the system to replace the fluids? run some kind of cleaner through that will evaporate when you're done?

[JBNeal]

to change over from DOT 3 to DOT 5, all of the DOT 3 has to be removed, so a brake system disassembly, cleaning & overhaul would be the best time to make the switch. Rubber components may absorb some of the DOT 3, and that's where the biggest cleaning problem would be. Long runs of metal brake line would have to be flushed thoroughly, and this would probably best be done with the lines in a vertical position, removed from the vehicle. Since I had replaced the metal & rubber lines and all cylinders on the '48 & '49, I went with DOT 5 since none of the components had been in contact with DOT 3.

IMO, if one has a working brake system on DOT 3, changing to DOT 5 could be a real headache; it's easiest to start from scratch when switching to DOT 5.

[Big_John]

It is used by high-end car makers

Aside from Harley Davidson, what car makers spec Dot 5?

I could understand Dot 5.1 (glycol based) in some high end sports cars, but not Dot 5.