Honda CBR 1000RR Forums banner
1 - 11 of 11 Posts

·
Classifieds Moderator
Joined
·
638 Posts
Discussion Starter · #1 · (Edited)
It's not often that I do a write up with this much excitement, but I want to share the results of an afternoon's experiment with vacuum filling a brake system. To summarize, the result is the best brake feel I've ever experienced with minimal lever travel that suddenly hits a "wall." Best part is that the process is instant!

I was inspired by a recent Ohlins shock service I did, which involved hooking up the shock to a vacuum that sucked all the air out and while the inside of the shock was under vacuum oil is injected so that there are no air bubbles in the shock. It's nearly impossible to hand bleed an Ohlins TTX shock due to all the tiny crevices inside for air bubbles to hide. That is the reason Ohlins rear shocks and gas charged front forks need to be vacuum filled.

Why not try the same with the front brake? I planned to machine a M10x1.0 adapter for the master cylinder to use as a fill port, but I came up with a simple way that any person can do with a vacuum pump and some Silly Putty.

My front brake system is RCS19 master cylinder connected via 2 separate Galfer SBK lines via double banjo to a pair of GP4-RR calipers. Vacuum bleed setup is shown below. A vacuum pump is mandatory. You cannot use a air compressor brake bleeder because it cannot draw a proper vacuum. Bleeder wrench (11mm for Brembo, 8mm for OEM) is highly recommended.
263497


With all pistons pushed in (fresh rebuild), I fill the reservoir and bleed from each caliper with a vacuum until fluid shows up (do not squeeze brake lever). Point here is to get some fluid in the lines so our tiny reservoir doesn't run dry. Tighten up the caliper bleed bolts and disconnect the vacuum hose.
263498


Turn the vacuum off. Now we focus on the master cylinder. Unscrew the master cylinder bleed bolt 1/2 turn and seal around the threads with some Silly Putty. This is necessary because there is a small amount of air leakage around the threads. Teflon tape won't work because it cannot seal straight threads under any significant pressure differential.
263499


Take a paper towel and wrap it around the hose from reservoir to master cylinder. Then clamp it down with a pair of plastic pliers (I did not have locking ones that would've made it easier).
263500


Turn the vacuum on and you will see a ton of bubbles come up the hose hooked to the master cylinder bleed bolt. The entire braking system is now placed under a vacuum. Wait until there are no air bubbles in the fluid running into the clear tubing. This takes about 2-3 minutes to fully stabilize.
263501


Fully close the master cylinder bleeder then release the pliers from the reservoir hose. Fluid level in the reservoir will quickly drop (about 1/2) as the fluid replaces all the air that was sucked out by the vacuum. At this point, the pistons are still all the way in. Fill up the reservoir and pump the brake lever (flick the lever on release) until the brake pads touch the rotor.
263502


That's it! If you want a really thorough job, you can repeat the process but the pistons will get sucked back in and you will have to pump them back out. I try to describe the feel in the diagram below. There are so many crevices in calipers, lines, fittings, etc. that add up to a small space where air can hide. You can bleed all day, run bottles of fluid, rebleed after riding, etc. to try and get that air out but it's not easy because there are blind spaces where air has no way to go up. That air acts as a cushion between the brake fluid and master cylinder piston so feel is diminished. It's like putting a foam pad on a table and pressing on it. Eventually it gets hard and you hit the table but there's a mushy bit and it's in that part where brake modulation occurs because long before you hit the table the front wheel will locked up.
263503


Brake lever travel before it stiffens up is only 5/8 inch (16mm) measured at the TIP of a LONG lever. This is true even braking with the front wheel spinning on a stand. Granted I am testing this on Brembo brakes but I would be very curious how well this works on OEM brakes. At the very least, it's a massive time saver because it takes 5 minutes to perfectly bleed a system and requires a bare minimum amount of brake fluid.
263504


One very interesting observation is that the "zip-tie" trick for stiffening up a mushy lever has NO DIFFERENCE on my vacuum filled system. For those of us who have tried it, the zip-tie on the brake lever makes the brake lever TEMPORARILY stiffer. But that is exactly how my brakes feel ALL THE TIME now.

Based on this observation, I believe (I may be wrong) that the zip-tie on the brake lever puts the brake fluid and small amount of air in the system under pressure such that the air dissolves in the fluid over several hours. That may be why the brakes feel so good after taking off that zip-tie but quickly revert as the dissolved air comes back out as bubbles.

Also, any residual air in calipers will expand as the calipers heat up. This may explain the mushy sensation that occurs when brakes are used hard on the track. A vacuum filled brake system may alleviate this issue.
 

·
Registered
2019 CBR1000RR SP
Joined
·
23 Posts
Blade
Thanks for providing this procedure


I am going to acquire a vacuum
Pump to implement this after I install my new hoses and RCS19

Look forward to similar results that you obtained
Thanks again!
 

·
Classifieds Moderator
Joined
·
638 Posts
Discussion Starter · #3 ·
What is stunning is that with traditional bleeding procedure on the exact same setup (RCS19 + GP4-RR + SS lines) I put over a liter of fluid through the system bleeding from the calipers and master cylinder. Then went out for riding and repeated bleeding several times and the best I ever got was 22mm of lever travel before the lever hardens up.

For the first time ever, the brake light switch on my RCS19 does not even come on until you apply moderate brake pressure because the brakes engage so soon! I attempted this almost as a joke because I was too lazy to bleed the brake system the normal way.

I am extremely curious how this works out on the SP Brembo calipers and OEM Tokico calipers. Since I haven't tried this on stock calipers I don't know for sure if the insanely short 16mm lever engagement distance is only attainable on race calipers that lack dust seals.
 

·
Registered
Joined
·
171 Posts
So when do you want to try this out on a bike with the POS ABS unit on it? About to bypass the ABS once again on my newest Honda as it is never consistent lever pressure (not confidence inspiring what so ever)...
 

·
Classifieds Moderator
Joined
·
638 Posts
Discussion Starter · #5 ·
So when do you want to try this out on a bike with the POS ABS unit on it? About to bypass the ABS once again on my newest Honda as it is never consistent lever pressure (not confidence inspiring what so ever)...
That is the reason I removed the entire (20+ lb) ABS system from my '09. It would work fine but sometimes the lever travel suddenly gets close to the grip so I had to leave the lever further out than I would want. I think that's more to do with the system itself rather than air because on 2009-2016 the ABS is different from 2017+.

IMO if you want consistent lever exactly same travel and feel EVERY SINGLE TIME no matter if you go 5mph or 150mph then ditch the ABS because it's another source of variability.
 

·
Registered
2007 CBR1000RR
Joined
·
25 Posts
I am going to switch to a RCS 19 on my 07 Blade after I install my Speigler steel brake lines. Until then, I am running to harbor freight and getting a vacuum pump so I can try this. I will let you know if it makes any difference on a totally stock system, I expect it will.
 

·
Premium Member
Joined
·
1,489 Posts
Someone should do one on YouTube.
I’m thinking: instead of pinching the reservoir line, plug the reservoir hole with something too big and non-porous, so fluid cannot get sucked down too much. It may require a plug with a stem and pair of pliers.
How much vacuum did you use? Any reason this wouldn’t work with a hand vacuum?
 

·
Classifieds Moderator
Joined
·
638 Posts
Discussion Starter · #8 ·
Someone should do one on YouTube.
I’m thinking: instead of pinching the reservoir line, plug the reservoir hole with something too big and non-porous, so fluid cannot get sucked down too much. It may require a plug with a stem and pair of pliers.
How much vacuum did you use? Any reason this wouldn’t work with a hand vacuum?
It will not work with a hand vacuum. The quality of bleed is only as good as the vacuum you pull because the idea is to get all the air out first then replace that space with brake fluid. If you use a hand vacuum it may only pull 95% vacuum at best and leave 5% air that will not be a good bleed. Must draw a full vacuum of -14.7psi or -760mmHg on the gauge.
 

·
Premium Member
Joined
·
1,489 Posts
There are hand bleeders that will go up to 30psi. I'm reading that there are cautions that going above 20psi could rupture seals but to be effective, the vacuum needs to be 15-20psi.
 

·
Classifieds Moderator
Joined
·
638 Posts
Discussion Starter · #10 · (Edited)
There are hand bleeders that will go up to 30psi. I'm reading that there are cautions that going above 20psi could rupture seals but to be effective, the vacuum needs to be 15-20psi.
The "-30" on the dial is not in psi it's inches of mercury which is equal to -14.7psi (confusing because left side of dial is in inHg right side is in psi).You are not going to rupture a brake caliper seal with -14.7psi in fact it's impossible to draw a vacuum under -14.7psi under atmospheric conditions. The seals in the braking system are designed to handle hundreds of times more pressure so should be safe.

Those 15-20psi recommendations are for pressure bleeding automotive brake systems by forcing fluid in at the master cylinder reservoir. In that case you don't want to use too much pressure because the reservoir/hose are not designed to handle that much pressure. That is NOT what we are doing here so those pressure recommendations do not apply.
263511


Also bear in mind that when using a brake bleeder in the traditional way the vacuum pulled on the gauge is the pressure in the hose leading to the bleeder NOT the pressure in the brake fluid circuit because that circuit is open at the master cylinder reservoir (which is why we need to pinch the hose to actually put the brake fluid circuit under vacuum) and equal to atmospheric pressure.
 

·
Stand your ground
Joined
·
1,184 Posts
Thank you for this write up. As always very well explained.
 
1 - 11 of 11 Posts
Top