Dot 3 to Dot 5 Brake fluid
Cruiser
Joined: Jul 2017
Posts: 172
Likes: 28
From: :
If it helps I have been through similar. I brought a drag specialties master cylinder which had dot4 only on it. But I had been usuing dot5 before the master cylinder swap. After a few questions back and forth, the drag specialties guy said yes there unit would be ok. Heavy duty seals.
I'd guess dot5 wouldn't be as harsh as other fluids. Mine hasn't been installed yet but I have had the ok to do so.
The hard part was getting the question across that I'm not mixing fluid, I'm starting from new.
I'd guess dot5 wouldn't be as harsh as other fluids. Mine hasn't been installed yet but I have had the ok to do so.
The hard part was getting the question across that I'm not mixing fluid, I'm starting from new.
Road Master
Joined: Jul 2010
Posts: 798
Likes: 168
From: Tryon, NC Cape Vincent NY
If it helps I have been through similar. I brought a drag specialties master cylinder which had dot4 only on it. But I had been usuing dot5 before the master cylinder swap. After a few questions back and forth, the drag specialties guy said yes there unit would be ok. Heavy duty seals.
I'd guess dot5 wouldn't be as harsh as other fluids. Mine hasn't been installed yet but I have had the ok to do so.
The hard part was getting the question across that I'm not mixing fluid, I'm starting from new.
I'd guess dot5 wouldn't be as harsh as other fluids. Mine hasn't been installed yet but I have had the ok to do so.
The hard part was getting the question across that I'm not mixing fluid, I'm starting from new.
Ken
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
dot 5 and dot 3 will not mix, like oil and vinegar. although best to thoroughly cleaning system with alcohol, not necessarily have to, all depends upon what is left over. the big issue with mixing is that any moisture will form in the inter-phase zone between the two and will become acidic and corrosion will set in.
can dot 5 be used in an ABS, sure if it is designed for it. the big issue here is viscosity. we know that ABS will cycle the brakes extremely rapidly and dot 5 flow rate is less than glycol based.
can you use the master to bleed, sure, been that way from conception. in all actuality the fluid does and will flow past the cup lip on retraction since there will be a diff'l pressure and the lip will relax, look at the piston assy and how the fluid returns to the master.
the norm is to lube the components with the fluid you are going to use.
can dot 5 be used in an ABS, sure if it is designed for it. the big issue here is viscosity. we know that ABS will cycle the brakes extremely rapidly and dot 5 flow rate is less than glycol based.
can you use the master to bleed, sure, been that way from conception. in all actuality the fluid does and will flow past the cup lip on retraction since there will be a diff'l pressure and the lip will relax, look at the piston assy and how the fluid returns to the master.
the norm is to lube the components with the fluid you are going to use.
Last edited by bustert; Feb 4, 2018 at 09:07 AM.
Seasoned HDF Member
Joined: Mar 2010
Posts: 38,586
Likes: 6,435
From: Honah Lee
One thing since we are seeing some bad info and misunderstood is on the older TCs. Least mine before the bimbo systems. Harley is one of the few who call out for a caliper piston grease for lubrication. It's on the rebuild kit from the mother ship or a PDF on line version is available if you look for it at harley.com associated with there parts. Using just breakfluid for a lubrication will get you sticking pistons in short order. See it all the time. Also pushing the piston back at a pad change before cleaning it will cause them to stick or later see uneven pad wear in about half the milage as the first set of pads.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,071
Likes: 1,006
well the market is full of greases for every purpose and every mfg has diff opinions. i think subaru mentions grease for the front but excludes the rear. for sure, the grease MUST be compatible.
so are we talking the piston or the seal??? there is a big diff! also, is this item going into storage?? another big diff.
one thing for sure, the seal must have a lube for assy as a dry approach can have issues. also of interest is whether the piston is plain steel, composite,aluminum or coated. one thing for sure is if it is lubed with what it is going to be using, the issues are reduced to nil.
most old books say only to lube the seal (not just mc) since the back side is exposed to fluid anyway and the front side if contaminates enter the boot will stick to the lube. chrysler went to a composite puck which turned out to have issues, my 1977 warlock truck was rife with them so i went to a steel puck and issue resolved. after the caliper works awhile, the lube gets pushed aside so greasing the daylights out of them is counter productive.
now i have read where the BOOT gets a special grease and its purpose is to maintain the elasticity since the boot acts like a bellows.
so are we talking the piston or the seal??? there is a big diff! also, is this item going into storage?? another big diff.
one thing for sure, the seal must have a lube for assy as a dry approach can have issues. also of interest is whether the piston is plain steel, composite,aluminum or coated. one thing for sure is if it is lubed with what it is going to be using, the issues are reduced to nil.
most old books say only to lube the seal (not just mc) since the back side is exposed to fluid anyway and the front side if contaminates enter the boot will stick to the lube. chrysler went to a composite puck which turned out to have issues, my 1977 warlock truck was rife with them so i went to a steel puck and issue resolved. after the caliper works awhile, the lube gets pushed aside so greasing the daylights out of them is counter productive.
now i have read where the BOOT gets a special grease and its purpose is to maintain the elasticity since the boot acts like a bellows.
Cruiser
Joined: Jul 2017
Posts: 172
Likes: 28
From: :
They didn't say how they are assembled. I did my old one with a mechanic friend, we used a little grease, rubber grease I'm sure it was.
Stage III
Joined: Sep 2019
Posts: 3
Likes: 0
From: GA
Dot 3 system with dot 5 master cylinder
I have a 1966 pan shovel trike that has a bad master cylinder, I ordered a new wagner masters cylinder from bikers choice it came in and say use dot 5 fluid only but I have read so much crap about dot 5 and would rather not have to build wheel cylinder again. Question is can dot 3 or 4 be used in a master cylinder marked dot 5 only? Whats different about it if you can't?
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
I have a 1966 pan shovel trike that has a bad master cylinder, I ordered a new wagner masters cylinder from bikers choice it came in and say use dot 5 fluid only but I have read so much crap about dot 5 and would rather not have to build wheel cylinder again. Question is can dot 3 or 4 be used in a master cylinder marked dot 5 only? Whats different about it if you can't?
It is quite likely the rubber used for the seals is designed to be compatible with DOT5. You could simply use DOT4 (DOT3 is a poor alternative), or get a set of new DOT4 seals to replace those in your new cylinder.
By the way, DOT5 doesn't absorb water, one reason it is preferred over the others. DOT3 absorbs a lot of water, DOT4 absorbs less but still too much, DOT5.1 (which is NOT silicon-based!) absorbs least.
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