Master Cylinder change - do you have to completely bleed the system after?

[Gubro30]

If you keep the hose with the banjo fitting up, can you simply unbolt the old, bolt up the new, fill the reservoir and squeeze the brake lever until no more air bubbles? Thanks!

[frankenduck]

Yes.

[Gubro30]

Thanks!

[frankenduck]

Turn the handlebars so that the hole in the bottom of the reservoir is the high point.

[Scott_]

Maybe another question or 2 would be:
Why are you replacing the master cylinder,
When was the last time the brake fluid was flushed and replaced....

[Gubro30]

The brake fluid was replaced about 100miles / a week ago, but it's still leaking.

Tried cleaning it, no luck and since it's also leaking from under the reservoir, plus the reservoir itself looking cooked by 26yrs of UV, I grabbed a new complete unit from Beemer boneyard.

Any hints on bleeding? I've worked on cars and downhill mountain bikes (very similar to MCs) but never encountered dual discs setup before.

Thanks!

[frankenduck]

ABS or non-ABS?

Hint: It helps us help you if you put the year and model of your bike in your signature. (Profile->Modify Profile->Forum Profile)

[Gubro30]

Thanks duck I'll modify my profile right away

1986 K75C, non-abs. For front brake.

[Gubro30]

Oh and do stainless-steel braided lines really make a difference in braking? IE Is it worth the cost? http://www.ebay.ca/itm/Goodridge-BMW-K75C-Full-Front-86-88-Front-Braided-Brake-Lines-Hoses-/280850931445?pt=UK_Motorcycle_Parts&hash=item4164051ef5#ht_2028wt_1199

[frankenduck]

The brake fluid was replaced about 100miles / a week ago, but it's still leaking.

Tried cleaning it, no luck and since it's also leaking from under the reservoir, plus the reservoir itself looking cooked by 26yrs of UV, I grabbed a new complete unit from Beemer boneyard.

Any hints on bleeding? I've worked on cars and downhill mountain bikes (very similar to MCs) but never encountered dual discs setup before.

Thanks!

It is pretty straightforward on non-ABS bikes. Pretty much like a car.  (ABS bikes have a "hump" in the brake line from the modulator to the calipers where air can get trapped.)

[Gubro30]

So I proceed like this I guess:

Open the bleeder on the caliper, while its open, pull the brake lever to the bar.

While the lever is back, close the bleeder.

repeat, and repeat as needed, doing both calipers.

Check the RES often, and dont let it go empty.

Oh yeh, also, ONLY do this while the caliper is on the bike, WITH the brake pads IN place.
Basically do this until you are getting ONLY clean brake fluid. no air, or odd colored fluid.



Do I need to "fill" the master cylinder prior to do this?

[frankenduck]

Yep, pretty much just like a car.

But don't overfill it when putting it back on at the end of the procedure.  Some of the rubber gasket dips into the brake fluid taking up some of the volume of the reservoir.

I can't remember if it happens on 2V bikes too but at least on 4V bikes you need to pull the brake lever in VERY slowly or brake fluid will spurt out of the master cylinder reservoir if the cap isn't on.