Recommended Brake Fluid MK II Front Brake?
- Thread starter Dan1950
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Not wishing to thread hijack, but why is silicon a 'not'?.
I'm not debating or disagreeing, just asking, as I seem to remember it was hailed as the bees knees in the classic car community many years back, as it neither absorbed water NOR damaged paintwork.. Have times or specs moved on??
I'm not debating or disagreeing, just asking, as I seem to remember it was hailed as the bees knees in the classic car community many years back, as it neither absorbed water NOR damaged paintwork.. Have times or specs moved on??
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DOT 3, 4, and 5.1 are poly-glycol based fluids, DOT 5 is silicone based. These fluids require different sealing materials, and very few materials are optimized and compatible with both. Even the materials that are optimized should not be used with an alternate fluid once they have been exposed to their counterpart.
My preference is DOT 4 in my bike, but I do not see a reason that DOT 3 would not work fine - my front brake does not ever get hot enough to boil the fluid.
My preference is DOT 4 in my bike, but I do not see a reason that DOT 3 would not work fine - my front brake does not ever get hot enough to boil the fluid.
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The fact that it doesn't absorb water makes it desirable since my bike will spend months in winter storage albeit in a heated garage.
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As does most everyone else's bike.
As long as the cap seal on your master cylinder is in good condition, and you are not using a neoprene based brake hose, there is very little chance your fluid will absorb much water.
If you do go Silicone - you will need to change all of the seals in your master cylinder and caliper to compatible materials - unsure of availability for Lockheed-Norton design parts.
cliffa
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As far as I'm aware AP ( formerly Lockheed) do not recommend it for our systems). I guess it must affect the seals ?
As you say It does have a lot of advantages though, [ EDIT]however I believe it is still hydroscopic but instead of the water content but any ingress of water through condensation, power washing, rain etc. instead of being evenly absorbed throughout the system, will pool in the lowest spot. Not ideal if you have iron calipers or plain steel pistons in your classic oldtimer, so that needs to be changed regularly too.
As you say It does have a lot of advantages though, [ EDIT]
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Hi Cliffa
Again, it was purely out of interest I asked, rather than disagree with other's recommendations...
But: This from the makers:
'DOT 5 silicone brake fluid is a very high specification fluid based on polydimethylsiloxanes (silicones) and offers many advantages over conventional glycol based fluids. Silicone fluid does not absorb water from the surrounding atmosphere while in service and therefore offers greatly extended service life whilst improving corrosion resistance of the main components of the braking system.
Recommended for use in the hydraulic brake and clutch systems of all cars, commercial vehicles and motorcycles for which non-petroleum based fluid is specified. Particularly recommended for classic cars or vehicles that are garaged for much of their life but must be usable at short notice.
This fluid must only ever be mixed with DOT 5 fluid which has the same silicone base. Never mix DOT 5 with regular glycol based fluids.'
So perhaps more homework if anyone wants to go that route?
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Water will get in, instead of being absorbed with Dot5 the water will pool at the bottom in the caliper and affect whatever it touches.
Deets55
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I'll take a stab at this.
First, if you already have a system filled w/ DOT 3, 4, or 5.1 it will require a complete cleaning because of compatibilty issuses.
Second, a lot of the classic car guys use it because of the paintwork issue, but complain of a soft or mushy pedal. So it looks like a trade off issue here. Never used it so I can't give any first hand info.
I also think I read somewhere Harley is getting away from the Dot 5, was factory on a lot of their bikes.
To answer Dan,
I use Motul 5.1. Because why buy any Dot 3 or 4 at probaly half the price if I can spend more for something I don't really need (scarcasm here).
Stuff should get changed every couple of years anyway, if not sooner. Especially for ABS/Traction control bikes. Those control modules are stupid expensive are rarely serviciable.
So basically, IMO, anything will work. Just treat it as a comsumable, like oil. 15 minute job if the system is in good shape.
Pete
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And cause corrosion issues...
Craig
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Out of habit always bleed all bikes hyd. systs. yearly …. my bikes live in heated/cooled shed …. I use DOT 4 in all now …. When I used CNW (Honda) m/c SS line and rebuilt caliper , the instructions suggested I use 5 .1 (I think) , so I did no issues , a good regular . routine of maintenance/service will always save time and $ in long run …..
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I'll be doing the front brake system rebuild before the tank and side covers will be installed.
I'll probably go with DOT 4. I am interested in maximum braking for emergency situations but will not be using the brakes repeatedly for hard braking. Maximum boiling point specs are not really relevant in my situation.
cliffa
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Believe me I know all about that. I had an immaculate MG-B ( you can see it in the background of my icon photo). The brake and clutch master both leaked over the winter and melted all the paint below them. I had to remove the whole kit and caboodle to repaint the area. It took me about 3 hours to just get the small self tapping bolts that hold the pedal box back in. I seriously considered DOT 5 but read about the water pooling and went for DOT 4 (Castrol).
Interestingly I just read that 4 absorbs less moisture than 5.1. so all round I think 4 is the best for normal use.
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DOT 5 is "compressible" compared to the other DOT s. DO NOT use it unless the brake system was specifically designed for it - (saying so in a table/placard/owners manual). The braking performance will suffer with dot 5 in a NON DOT 5 system and there are DOT 4 fluids now that have an equally high or higher boiling point than 5. The moisture thing is a non-issue for any sort of normal use. Heck, people buy cars and sell them years later without ever changing brake fluid and no issues... 
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