R65 Front Brake Bleeding Help Needed

[jsbrusso]

Hi gang,
I have a 1980 stock R65 with a single disc ATE brake in the front. The ATE caliper looks nearly identical to a Brembo although it's silver instead of black. I discovered one of the two pistons leaking, so I purchased a complete rebuild kit and pistons from Boxer2valve. I replaced the two pistons after carefully cleaning the bores, and installed new seals and dust covers. The rebuild went great, no issues. Installed new brake pads and started the bleeding process. Prior to bleeding, I intentionally allowed all the old fluid to drain out the open flexible brake line that went to the caliper ( maybe a mistake?)
I started using the traditional pump the handle and crack the bleeder screw method dozens of times and got some air out, but the handle would always go through half it's travel before firming up. Then, I allowed it to gravity bleed through many refills of the master cylinder, same result.
So then, I purchased a vacuum bleeder though Harbor Freight that uses compressed air to create a vacuum ( It's a nice unit for $35 imho). It worked great at pulling fluid through at a slow enough rate that I could easily keep up with refilling the mc. The device has a latch on the trigger that allows you to keep the device on continually without having to continually hold it. My compressor was set at 120psi that results in moderate suction from the device.
So....after about 32oz of fluid going through the system, still no improvement. Handle goes halfway before firming up.
Weird observation: When initially pulling the brake handle, fluid will squirt straight up through one of the two holes at bottom of the mc (smaller diameter one I think) and WAY out of the mc (Think water fountain) if I pulled too rapidly. Made that mistake several times, fortunately didn't get on tank or fender, just some around base of mc that I cleaned off immediately.
For those not familiar with the R65, the routing of lines goes like this (in descending direction) Master Cylinder, short flexible line, short metal tube, Brass union block behind headlight, flexible line to caliper.
Alright Airhead Collective, can anyone help me figure out how to bleed this thing? Any input greatly appreciated!
Thanks, John Brusso (Mufflerbearing)

 

[20774]

John -

I'm not familiar with this version of ATE brakes...or Brembos for that matter. But where's the bleed nipple for the brakes? Is it as high as it can get? I know that on some rear brakes on RT/RS bikes you have to remove the caliper and rotate it to get the nipple at the top.

One trick you could try is to find something to tie up the hand lever and pull the lever back to about half stroke. Then leave it in that position overnight and let any air migrate out.

 

[stevenrankin]

Possible air bubble

So, I am not at all familiar with the front brakes on a 1980 R65 however, I have myself driven myself crazy trying to bleed a BMW brake system.

In my case, it is the rear brakes of my 78 R100RS. I know, it is not the same as yours but, I had the same problem only with a foot lever rather than hand lever.

In my case I was told the system as it is mounted on the bike allows air to be trapped in the caliper which under normal bleeding procedures cannot be purged. A bubble forms which is trapped due to the orientation of the bleeder position. In order to properly bleed the caliper, it has to be removed from the mount, inverted, a spacer has to be inserted between the pads. Once this is done, the air bubble will escape.

It drove me crazy trying to get a good pedal before someone told me about the air bubble problem and the solution.

So, look carefully for places that air can get trapped. Look carefully at the position of the bleeder screw, is it such that it allows all the air to escape?

Also, if the caliper needed rebuilt, are you sure the master cylinder does not need a rebuild as well? If it is not leaking, I kind of think not, just a thought. St.

 

[gregfeeler]

As I read the description of your problem it sounds like the symptom is the brake lever moving half way before firming up. Although that could still be an air bubble, it could also be deteriorated seals in the master cylinder. I had a similar problem on the front brake of a K75 caused by worn/old master cylinder seals. I disassembled the master cylinder, cleaned the bore with emery cloth, and reassembled with new seals and everything firmed up correctly. In my experience it's not uncommon for master cylinder piston seals to fail during a brake bleeding when they move into areas of the cylinder bore past their typical travel range as you are pumping fluid through the system.

 

[jsbrusso]

Thanks guys for all the input and suggestions. My gut feeling is that there is still air in the system, although the theory about the master cylinder moving through a greater range during the bleeding process seems possible too. I think I should be able to remove the caliper and place it above the master cylinder. I will give that a try next to see if I can remove any more air. I'll report back once I have tried this.
John

 

[20774]

Unless I'm missing something, I don't see what you gain by raising the caliper above the master cylinder. You want the blade nipple to be the highest point on the caliper.

Is the brake hose original rubber? If so it could be ballooning on you when you pull the handle acting like there's air in the line.

 

[ccolwell]

The first thing I would try is to crack the brake lie at the master cylinder and gently pull in the lever until some fluid comes out, then tighten with the lever in. I have seen air trapped there and not be bled out by the usual means. Obviously this is dangerous to your finish so loosen the connection to finger tight, cover everything and do this slowly with a rag wrapped underneath it. You want to be able to see when the fluid escapes and you don't need to see much to know that any air there already was pressed out. If that doesn't work, I would rebuild the MC.

 

[jsbrusso]

Hi guys, thanks for the suggestions. I did try 20774 (Kurt's) suggestion of tying the handle about half way and letting it sit overnight. Additionally I thumped all the lines and bumped the handlebars firmly against the mechanical stops in an effort to shake air bubbles loose. It seemed to help a little, I'm now at about 30% of lever travel instead of 50 %.
I'll try the suggestion of loosening the fitting by the mc and pumping the handle to get any air out in that area. To address one of the earlier questions, the bleed nipple is at (or very near) the top of the caliper, so guessing no air at the caliper.
Thanks guys, really appreciate the suggestions. I will report back any improvements.
John

 

[98lee]

There are MANY bikes that need to have the bars turned all the way to the left. Due to the angle of the bore of the master when the bars are straight ahead, there ends up being an air pocket just above where the hose exits. The R65 might be one of those bikes.

Try rebleeding with the bars turned all the way to the left with the HF vacuum bleeder.

 

[ccolwell]

I'll try the suggestion of loosening the fitting by the mc and pumping the handle to get any air out in that area.
John

Don't pump. Loosen and gently squeeze until a little fluid comes out.

 

[jsbrusso]

Thanks 98lee (BTW I also have a K100-love my Brick!) and Ccolwell. Great suggestions. I'll keep trying and report back. Thanks guys.
John

 

[stevenrankin]

Air pockets

Ah yes, the bloody air pocket! Scourge of mechanics everywhere source of many a wondrous miracle vacuum tool. Maker of the insane and frustrated. I too have battled this scourge.

Sorry, got carried away, no ideas other than what has been posted already. Cheers, St.

 

[jsbrusso]

Thanks for chiming in Steve, at least I know I'm not the only one who's experienced this. Well, took another stab at it last night with the vacuum bleeder and still no better, but while I was looking in the direction of the caliper while bleeding it appeared that one piston was pushing and maybe(?) the other wasn't. So my theory now is that maybe one piston has air behind it. When I get time I'll remove the caliper and try moving it around in different positions to see if I can get more air out of the system.

Thanks again for everyone's input, really appreciate the suggestions. I'll report back as soon as I have an opportunity to work on it again.
John

 

[jsbrusso]

BTW, 98lee I did try your suggestion of moving the bars all the way to the left (I can see exactly what you were talking about) but didn't help in my case. I tried numerous times tapping the lines, moving the bars to the mechanical stops, thumping the brake lever allowing it to rebound, traditional bleeding, vacuum bleeding. Ugghhh.

 

[pglaves]

Remove the caliper and manually move the pistons to the fully retracted positions. Then block them in this position. I use two pieces of tapered wood (shingles) for this purpose. Then re-bleed the system.

 

[jsbrusso]

Thanks Plglaves,
I've seemingly tried everything else, I'll give that a try.
I did remove the brake pads yesterday and confirmed that both pistons are moving when I pull on the brake lever. I used a C-clamp to return both pistons to their retracted position before putting pads back in.

 

[jsbrusso]

Thanks PGlaves,
I'll give that a try too. There is a recess area on the underside of each piston, so I question whether that will get any air out if that's where it's hiding, but worth a shot.
John

 

[jsbrusso]

Thanks for that PGlaves
For the last year, I've just lived with it but going to try again, starting with your suggestion. I'll report back if I have any success.