Author Topic: Bleeding the brakes on my 77 750k....just the facts please!!!!  (Read 2311 times)

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shuswap_rider

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The brake fluid was cloudy so i drained and flushed the system.........now iI have put new fluid in and am having troubles bleeding the system.I have been in the archives...but to tell you the truth all they were doing was arguing over the best way......and I read for 20 miniuts........and i still didnt figure out the best way.....Help i have no front brakes!!!! ???
Thanx
Mark

Offline TwoTired

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #1 on: July 05, 2005, 12:08:25 AM »
Section on brake bleeding in here:
http://sohc4.us/node/50
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Six

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #2 on: July 05, 2005, 10:09:28 AM »
I'll be a witness - Did it exactly as the link states and it worked like a charm!.   Took me about one hour to get 95% of the air out.  Most of that time it felt like NOTHING was happening, but that's OK.  Most of the air came out the top with the lever partly pulled after I noticed some bubbles coming through.  Had the son doing some pumping at the lever and when he built up some resistance,(between 3-10 pumps) I would release the nipple (with a clear hose to a catch-can) and let some old fluid and bubbles out the bottom too! Left it overnight (With the cap-on!) and the lever pulled tight against the grip - Must have released some more air through the vent hole because the fluid was a bit lower in the morning. - Topped off, and it's good to go!   Time consuming, but satisfying to know everything is OK!

Six- Minneapolis.

Offline MikeDeB

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #3 on: July 05, 2005, 01:49:42 PM »
The brake fluid was cloudy so i drained and flushed the system.........now iI have put new fluid in and am having troubles bleeding the system.I have been in the archives...but to tell you the truth all they were doing was arguing over the best way......and I read for 20 miniuts........and i still didnt figure out the best way.....Help i have no front brakes!!!! ???
Thanx
Mark

Yep, there are a bazillion different ways to bleed the brakes; and people will argue over it.  I just did the front brakes on my K5 a couple of weeks ago and had a solid lever in less than an hour.  The lever has remainded solid since then and has not required any additional bleeding.

First you must prime the system like it says in the article.  I cheat and use a Mity-Vac to prime mine but once I have fluid coming out of the bleeder screw I close it off.  I then use the method I learned many years ago when I was an auto mechanic.  Fill the resevior to about 2/3rds and replace the cap.  Stroke the lever fast, all the way to the handlebar.  Do this about 15 or 20 strokes and even if you don't feel resistance, crack the bleeder screw.  Remember to never let up on the lever while the bleeder screw is open (you'll let air back into the system).

Keep this up and in short order you will feel resistance building up.  Check the fluid level in the resevior after every 3rd or 4th cycle.  Initially it will go down quickly.  After the resistance builds up in the lever you'll only have to stoke it 4 to 6 times to get a solid lever and you won't have to add as much fluid to the resevior each time you check it.

The reason you never slow stroke the lever is that between strokes air bubbles have a chance to return to their original size thereby defeating the purpose of stroking the lever.  When you stroke the lever fast the master cylinder is acting like a pump and compressing the air bubbles smaller and smaller with every stroke.  Air compresses, fluid does not.  When you see those bubbles coming out of the bleeder screw, they were much smaller before you cracked the bleeder screw open.  Also, when the master cylinder is acting like a pump it tends to move the air downstream and cracking the bleeder screw accentuates this.

I used this same method when I changed out the clutch slave cylinder on my Ducati Monster and had an air free hydraulic clutch in less than 3 hours (Ducati hydraulic clutch systems are notoriously difficult to bleed when starting with an empty system).

Hope this helps.  Just my .02 and YMMV.   :)
Mike (Old SOHC/4 #2641)
Holt, MI
71 CB750K1
72 CB750K2
72 CB100K2
97 Ducati 900 SS/SP w/FCRs
98 Ducati 750 Monster w/FCRs
80 SR500

"Growing older is inevitable, growing up is an option."

Offline TwoTired

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #4 on: July 05, 2005, 05:25:29 PM »
The reason you never slow stroke the lever is that between strokes air bubbles have a chance to return to their original size thereby defeating the purpose of stroking the lever.  When you stroke the lever fast the master cylinder is acting like a pump and compressing the air bubbles smaller and smaller with every stroke.  Air compresses, fluid does not.  When you see those bubbles coming out of the bleeder screw, they were much smaller before you cracked the bleeder screw open.  Also, when the master cylinder is acting like a pump it tends to move the air downstream and cracking the bleeder screw accentuates this.

It's funny you should prefer this.  I always found that the tiny bubbles (almost like foam) moved the slowest inside the system, found places to hide and hang up, and generally took much longer to reach the master cylinder hole (or bleed nipple) and escape.  High pressure and fast stroking will indeed make the bubbles very small.  And, it makes larger ones into a whole lot more smaller ones.  It seems like high flow and volume of fluid will get these small bubbles out.  But, then there is more waste of new, good, fluid tossed asside, too.

I'm really not trying to arguing here.  If it works for you and you're happy with your method, then that's great.  It just seems so counter to my experience, it gave me a little chuckle.

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline chippyfive50

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #5 on: July 05, 2005, 07:00:49 PM »
I pump from the bottom up with a small hand pump I got @ the auto parts store. I drain  the system, the stick the "draw" side of the pump into the brake fluid bottle and attach a hose from the "feed" side to the bleeder nipple. I put the master resivior cap on 1 turn (so the air can escape) then pump slowly, 1 pump @ a time until the level in the res is good, tighten the nipple, done and done, 15min.
the bottom up method floats all the air out. It has worked like a dream every time I have done it.

regards...
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78' 550
72' 750K2(sold to "Craig")
74' 750K4 #2306334--E2303422
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Offline Dennis

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #6 on: July 06, 2005, 06:29:39 AM »
Chippy,
I also like to bleed from the bottom up, but have been using animal syringes which are difficult to find unless you have some contacts who routinely use them.
So what kind of pump is this?
Can you provide a manufacturer and model number? A picture?
Thanks

Offline MikeDeB

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #7 on: July 06, 2005, 02:07:35 PM »

It's funny you should prefer this.  I always found that the tiny bubbles (almost like foam) moved the slowest inside the system, found places to hide and hang up, and generally took much longer to reach the master cylinder hole (or bleed nipple) and escape.  High pressure and fast stroking will indeed make the bubbles very small.  And, it makes larger ones into a whole lot more smaller ones.  It seems like high flow and volume of fluid will get these small bubbles out.  But, then there is more waste of new, good, fluid tossed asside, too.

I'm really not trying to arguing here.  If it works for you and you're happy with your method, then that's great.  It just seems so counter to my experience, it gave me a little chuckle.

Cheers,



Like I said in my earlier post, a solid lever in less than an hour with no rebleeding.  Same with the Ducati hydraulic clutch in less than 3 hours (a notorious PITA when starting from scratch).  A couple of weeks ago we installed a Magura master cylinder on my buddies K3 and had a very firm lever in about 20 minutes using the same method (still holding with no rebleeding).

When you fast stroke the lever you build up high pressures so when you crack the bleeder screw you do get high flow and volume.  And it does get all the bubbles out (path of least resistance).  Keep in mind, larger bubbles don't break up into smaller bubbles, they compress.  And, I have never had air hang up in the system using this method.  Since brake fluid has virtually no surface tension (unlike water) I don't see how air bubbles can cling to anything in the system.

Sure, you waste some brake fluid but at $2.59 a bottle for Valvoline brake fluid it is very cheap insurance.  And, when I did my K5 recently I still have 2/3rds of a bottle left so now I have to do my K2 so I don't waste so much fluid in the long run.  Long term storage of an opened container of brake fluid is not a good idea.  Brake fluid is very hydroscopic (read serious water magnet).  Which means that an opened container of brake fluid should be disposed of after about 6 to 12 months.  Bottom line, don't be cheap when it comes to brake fluid and the maintenance of a major safety system.

The method I use I learned over 30 years ago when I was an auto mechanic.  I learned it from experienced mechanics and was the preferred method when a power bleeder wasn't available (as in our shop).  It has worked extremely well ever since and is so simple.

I guess it just boils down to what your goal is when doing this sort of maintenance.  Mine is I want a hydraulic system that is solid, free of air and performs as good as or better than the engineers that designed it had intended.  And if that meant springing for all new seals, a piston and using a whole bottle of $2.59 brake fluid then so be it.  Brakes are the most important safety system on the bike; you gotta be able to slow down and stop.

Just my .02 and again YMMV.

Cheers
Mike (Old SOHC/4 #2641)
Holt, MI
71 CB750K1
72 CB750K2
72 CB100K2
97 Ducati 900 SS/SP w/FCRs
98 Ducati 750 Monster w/FCRs
80 SR500

"Growing older is inevitable, growing up is an option."

Offline chippyfive50

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Re: Bleeding the brakes on my 77 750k....just the facts please!!!!
« Reply #8 on: July 07, 2005, 07:52:01 PM »
Found the package to the brake  pump, I got it @ my local autoparts store. unfortunately the brand name is incomplete. the spec says
 1 OZ. per pump.
SOHC Member#4000
71' 500K0 #1021237--E1108327
78' 550
72' 750K2(sold to "Craig")
74' 750K4 #2306334--E2303422
73' CL175
http://gallery.sohc4.net/main.php?g2_itemId=14013