Topic: Dot 5

[jwurbel]

In a moment of insanity during my CB 750 resto, I decided to change to Dot 5.  Reasoning at the time was to avoid paint damage on my NOS tank etc.  I was replacing brake lines, seals, puck, and a complete rebuild of the master cylinder, so the option seemed feasible.

No matter what I do, I can’t get the air completely out.  I have used speed bleeders and alternately a MiteVac.  I have sprayed soapy water on all fittings to see if I could spot an air leak. I found nothing.

The lever, due to the captured air, will be hard on one stroke and go soft on the next.

Not sure what I am missing, but converting back to Dot 3 is beginning to look like an option.  Not looking forward to that if it can be avoided.

Any thoughts?

[Shtonecb500]

you probably need to bleed the master..you shouldn't have an issue with mixing fluids since stuff is cleaned rebuilt/new.

[MRieck]

That sounds like DOT 5. I tried it about 40 years ago....ended up replacing all lines and rebuilding masters/calipers and went to DOT 4.
It's a lot easier protecting the tank during brake bleeding.

[MauiK3]

I don't think 5 is supposed to be mixed with anything else.
Flush everything out well.
When you finally refill, pull the lever back a little and let it sit over night allowing the air to slowly move up, it's always worked for me.
I use DOT 3 and 4

[jwurbel]

Not sure on the “master cylinder bleed” procedure. 

Can you elaborate? 

Bike I’d 1972 K2.

Thanks

[newday777]

Not sure on the “master cylinder bleed” procedure. 

Can you elaborate? 

Bike I’d 1972 K2.

Thanks

Use the banjo bolt at the master cylinder as 1st bleed point then down the line from there.
Remove the tank and cover everything else with sheet of plastic for protection from brake fluid spills and drips.

[MRieck]

Not sure on the “master cylinder bleed” procedure. 

Can you elaborate? 

Bike I’d 1972 K2.

Thanks

Use the banjo bolt at the master cylinder as 1st bleed point then down the line from there.
Remove the tank and cover everything else with sheet of plastic for protection from brake fluid spills and drips.

Right....just common sense stuff.

[CycleRanger]

Not sure on the “master cylinder bleed” procedure. 

Can you elaborate? 

Bike I’d 1972 K2.

Thanks

here's what Honda recommends.

[Don R]

  I used silicone in my 40 chevy street rod, the M/C is under the floor, it always had a soft pedal until the car warmed up. Just idling a few minutes would fix it. Crazy.
  I changed it to conventional fluid and have had no trouble since, over 20 years. 

[Bailgang]

Dot 3 or 4 brake fluid isn't what you would call a fast acting paint stripper. Yes it can strip paint but it takes time for it to do so if you neglect to wipe it up. I've spilled brake fluid on my tanks before but I quickly wiped it up and cleaned the area and the paint is fine, I simply don't give it time to mess with the paint.

[bwaller]

Like Mike, I tried DOT 5 and I found it "too dry" and pistons just didn't retract well. This with all new parts.

Not sure how some do well with it, but it seems some do!

[Tracksnblades1]

I tried Dot 5 years ago too.
Had to bleed the front brake several times over several days to get a firm handle.
Remember constantly having to lightly tap the front brake line to encourage all the small air bubbles entrained to move.
The local Honda Guy (Honda man is taken) used a vibrator to speed the process up, but he only used dot 3.
I would be more concerned if you didn’t get all the dot 3 glycol based out of the system before using the silicone based Dot5.
I don’t think they mix well and heard the system needs to be completely flushed prior to changing from a glycol based to a silicone based or vice versa. I think all the Dot brake fluids will mix and are glycol based except Dot 5 which is silicone based.

[70CB750]

For spilled brake fluid I keep a windex bottle handy a just use the spray to wash any spilled brake fluid away.

[newday777]

For spilled brake fluid I keep a windex bottle handy a just use the spray to wash any spilled brake fluid away.

Spray bottle of water works too.

[MauiK3]

I angle the handle bars so the master cylinder is the highest point with the lever pointing as much up as possible. I then slowly move the lever back and forth, not all the way. Bubbles will steadily come out of the holes for a long time.
I have also used a rubber band to bring the lever in about an inch or so ( I forget how much exactly) and leave it over night. Come back and slowly exercise to release bubbles that remain.
I just did this on my K3 750 with a dry, new master cylinder. Bled out fine. Nice firm lever now.

[Don R]

 I saw a video taken in the Yoshimura race shop with a full brake system on a bench fixture and the lever was tied back. Good enough for them, good enough for me. I just do mine on the bike.

[ofreen]

I always used to have trouble getting all the air out of the front brake lines on the '75 750F  A bubble gets trapped somewhere, even when using a vacuum bleeder.  So with a dry system, I start with the vacuum bleeder, follow up with a few squeezes the old fashioned way and that usually get a few more bubbles out.  But the lever will still be soft, so I remove the caliper from from the rotor and pump the piston out a ways (don't go too far unless you want to start over )  Then I push the piston back in.  This seems to dislodge the bubble wherever it is, pushing it up to the m/c.  This works every time for me. 

Also, I put a thick towel over the tank whenever I working anywhere around it.  That has saved me a lot of grief over the years.

[rotortiller]

I angle the handle bars so the master cylinder is the highest point with the lever pointing as much up as possible. I then slowly move the lever back and forth, not all the way. Bubbles will steadily come out of the holes for a long time.

Best bit of advice on this topic given. I bleed mine forcing fluid up from the caliper using a syringe with tubing connection to the bleeder screw. Quick, accurate, and painless finished off with the quoted text. Also flushes the system lines of old fluid.

[RAFster122s]

I recall reading that to switch to DOT5 in cars they recommended an alcohol flush of the system and ideally change any hoses in the system as well as rubber components such as caliper seals. Gotta be committed to the change. DOT5.1 , is that the number, gives the higher boiling point and other good properties of DOT5.0 without some of the particular side effects. If I remember correctly...

[C317414]

Dot 3 or 4 brake fluid isn't what you would call a fast acting paint stripper. Yes it can strip paint but it takes time for it to do so if you neglect to wipe it up. I've spilled brake fluid on my tanks before but I quickly wiped it up and cleaned the area and the paint is fine, I simply don't give it time to mess with the paint.

It actually depends on the quality of the paint.  I remember when the master cylinder on my 74 Ducati 450 Desmo leaked a drop of brake fluid on the bike's front fender.  It took off the OEM paint almost instantly.

[TwoTired]

Remember when the US army converted to DOT 5?  It was able to meet worldwide temperature extremes so vehicles could be shipped anywhere, as well as reduce maintenance.  It lived up to the former.  But, the maintenance benefit never occurred.  Sediment still gathers in the low points of the hydraulic system and water still gets in via rubber membranes and seals throughout, which does not get absorbed in the silicone fluid like it does with glycol.   When 5.1 came around meeting the temp extreme demands.  The US Army tried to convert back to the glycol based fluid which removes water with routine fluid changes.  They found it wasn't possible to flush all the Silicone dot 5 from the system, and required replacing the whole hydraulic system to enable a total and complete conversion.  Too expensive.  You can flush Glycol from the system with solvents.  But, there is no solvent that effects, dissolves, or dilutes the silicone.  It has to be mechanically removed from any surface it contacts and some will always remain behind to contaminate the glycol in the system.  Making for some undesirable behavior.

DOT 5 is a one way conversion.  I don't recommend it, despite the marketing hype or glowing testimonials. But, perhaps if you are sloppy and careless around painted surfaces, it might save you a repaint, and you can then spend that time fixing brake issues.  :-)

[ekpent]

Silicone as is found in some furniture polish etc. was always a pain in the arse when I had my furniture refinishing biz. Very hard to get rid of it so additives like "fish eye killer" went into my lacquer mix/spray gun.  Anybody who has tried to paint a tank or other items knows the feeling when it orange peels or goes bad.