Front breaks suddenly not working

[DavesXS]

Dunno if any one can help here.

I did my 2nd gear, paint job, jet carbs, clutch and springs, handle bars, instruments, every thing works great


Except my F&^$%*(&ing front breaks

I did nothing with them. The piston in the mastercylender doesn't seem to make pressure. I try to bleed and I get just a trickle. The handle is super soft, and adjustment screw is all the way in. I managed to trickle out half of whats in the reservior. So there can't be air still in the lines(if there was any)

Any clues?

[fredintoon]

Hi Dave,
Yamaha dual front disk brakes are a right swine to bleed. Try this:- Remove both calipers and shove pieces of 1/4" thick plywood between the pads to stop them over-closing. Hang the calipers up higher than the master cylinder. Bleed'n'bleed'n'bleed until all the air is gone. (Using a mityvac helps here). Reassemble.

[AlanB]

Re: Front breaks suddenly not working

Hi Dave,

Originally posted by DavesXS
adjustment screw is all the way in.
Any clues?

If you mean the adjuster in the hand lever; it needs some free play to the end of the piston in the master. If you have the adjuster too far in, the piston won't clear the spooge hole, no fresh fluid can get in, and the line can't bleed.

Make sure there is a gap between the end of the piston and the tip of the adjuster screw and try again.

AlanB

[DavesXS]

Ok, I backed the screw just off the plunger. No dice. No need to pull calipers, and shove 2x4 in to prevent calipers from closing. They don't move. The lines have no pressure, and the handle has no resistance what so ever.
With the reservoir cover off, working the break, I can see tiny little bubbles coming from the bottom.

fluid is getting into the line, and bleeds out, but no pressure, no resistance.

[DavesXS]

Would a master cylender from other bikes work. Like xs650, xs750, xs850, or the same year range?

I found this...

http://cgi.ebay.com/ebaymotors/80-YA...spagenameZWD1V

[John]

Yes as long asa the bore of the cylinder is 5/8 or 11/16 of an inch. The bore size is usually found on the bottom of the M/C assy. You will be able to see it by looking at the under side of the M/C.

[DavesXS]

Thanks John,

Mine is 11/16. I messaged they guy and asked him to check. So either 5/8 or 11/16 will work right? Since its only 1/16th differance?

[Rasputin]

I got a rebuild Kit from georgefix on ebay for about 24 bucks. It works great. I had a little problem getting mine to pump at first after the rebuild so I took a needle from my ink cartridge refill and pulled a little air out of the cylinder. When I inserted the needle into the larger hole I pulled back on the needle and watched a bunch of air go into the needle. Then I used very short quick strokes on the handle and it all primed up nicely.

[TopCatGr58]

Hey Dave,

I can't remember if this is the OEM front MC for the bike?

Did you read the tech tips about the spooge hole? Did you take the lines off of the MC during the work?

Some folks found that even with a NEW MC, they first had to bench bleed the MC alone without the lines attached. Just put their thumb/finger over the brake line hole and did the PUMPING ACTION until they felt pressure pushing their finger away. Then connected the lines, and bleed, etc.!

Did you have to clean out the MC much..lotsa of gunk???

Possibly a damaged piston cup allowing fluid to leak past??
T.C.

[DavesXS]

Originally posted by TopCatGr58
Hey Dave,

I can't remember if this is the OEM front MC for the bike?

Did you read the tech tips about the spooge hole? Did you take the lines off of the MC during the work?

Some folks found that even with a NEW MC, they first had to bench bleed the MC alone without the lines attached. Just put their thumb/finger over the brake line hole and did the PUMPING ACTION until they felt pressure pushing their finger away. Then connected the lines, and bleed, etc.!

Did you have to clean out the MC much..lotsa of gunk???

Possibly a damaged piston cup allowing fluid to leak past??
T.C.

Thanks TC,

I didn't take it apart until everything was back together, and it was mounted on the handle bars. And that was to check fluid level after finding it not working, and bleeding a few min. I had it tied to the frame where the tank goes to keep it out of the way.
Makes sense if I have to prime it. It could have lost its prime if set the wrong way too long?
I didn't get that needle thing in the above post. I'll check the tech tips section.
I won't buy anything until I get the prime thing right.

[trbig]

If, when you squeeze and release the brake handle with the reservoir lid off, you don't squirt brake fluid up into the air, then your return (Spooge hole) is plugged.


Tod

[skids]

Oh boy... you had better cover the tank and faring with plastic if you are going to try that!

[DavesXS]

I tried ev erything. The spooge holes are clear, it has very weak pressure when I place my finger over the hole. I primed it, put it back in and bleeded the mess out of it. Still only trickles out. It should shoot a stream when pumped up several times, and held down.

I found this guy. I messaged him to see if he has one that would be compatable. I told him the bore, only thing is the threads the bolt that hold the line goes into.

http://cgi.ebay.com/ebaymotors/FRONT...3286.m14.l1318

[JACKHAMMER01]

Dave, if you choose to purchase a new MC, here is the one I bought for mine.

Master Cylinder Assembly
Master Cylinder Assembly - 16mm bore. - Recommended for late dual disc Front
brakes on 1977-84 XS650’s or single front disc brake (1972-76 650’s). Yamaha
OEM type. Complete with brake lever, brake light switch, banjo bolt and washers.


Part #08-0265 $79.00 USD EA.


http://www.mikesxs.net/mikesxs-chass...ategory_id=1.2

This one bled easy, Yamaha mirrors fit exactly, and it will stop you on a dime. Mike's also does not charge shipping.

[newc4]

My SF has a non-stock Yamaha MC. With the front brakes, I found that if you don't crank the handle all the way to the stop the sytem will begin to pressure up. Took me 3 hours and my son checking the internet to figure this out.

Darrell