Brake Problems

[pathfinder]

Ok here's the story, all new rubber parts in the calipers front and rear including all new pistons, rebuild kit in the rear M/C, Randy's S/S lines all around, Dot 5 fluid, speed bleeders, turned rotors almost down to min thickness of 6.5mm. On the front m/c all parts seem good. It is a Yamaha m/c that came off of a newer model for twin discs, say's 5/8" as of yet I have not been able to ID it for new parts but they look good. Been using it for about 10 years with no problems. I'm taking to dealer tomorrow to try to ID.

Using Myti-Vac at 17psi pull all air out of sytem, using smaller than Myti-Vac standard clear tubing but still using wire around the bleeder to make sure sealed off so as not to allow air into tube. No detectable leakage at any banjos, caliper pistons or bleeders.

I have no handle or pedal resistance. They will both go all the way in. Spin tire pull front handle stops tire but with handle still depressed I can spin the tire with very little resistance. Same way on the rear. What I'm saying is, there is no way these brakes will stop this bike and a rider from even 20 mph and I never go that slow.

When I take the m/c's apart the rubbers do not seem to be unseated.

What my question is in rebuilding the front and rear m/c there is a thin flat washer, does it go on the plunger on top of the boss with the 4 holes, then the second rubber piece on top of that. On the Yamaha parts fish this washer is shown on the front m/c but not the rear.

I have the Clymer, Haynes and factory manuals but all are unclear as to the order that the kit is installed. I have had these brakes and m/c apart many times in the past with no trouble getting everything to work properly. Now when I try to do it right with all new parts, I can't get them to work worth a damn.

Sorry about the long post but I have been messing with these brakes on and off for over a month.

I know I'm missing something but I can't figure out what.

[Pat Kelly]

I've been an automotive front-end and brake mechanic for 20 years. My XS's give me fits when it comes time to bleed the brakes.
The method I've used on the XS is dangerouse and wouldn't work in your case. I just ride the bike with the brake not working and it eventually pumps up.
I think the road vibration works air out from a pocket that convintional bleeding methods won't get. It's been the same with my E (3 times) and my wifes XS750 (twice). The XSception is replacing the rear hose on the E, that went well.
Next time I'm gong to try bleeding with the front calipers not mounted, a piece of wood between the pads (thickness of the rotor), and holding the caliper higher than the master cylinder. This may get the air out.
Good luck...

[randy]

Elevating the caliper works, but vacuum bleeding AND elevating does a faster and better job. Vigorous lever pumping can cause bubbles to form and then stopping to refill the reservoir can let those bubbles creep up the line. Hence the 'endless bleed"

[Ken Talbot]

I think you're on the right track, Pathfinder, but there are a couple of little critical items to watch for.


Using the parts for a front master cylinder as an example:
- the thin metal washer sits between the plunger and one of the rubber cups
- the flared end of both rubber cups is towards the pressure side
- the two rubber cups are actually quite different and are not interchangeable

The rubber cup that actually builds and holds the pressure is slightly thnner than the other one, it has a more pronounced square shape on the cup side, and it has six very small dimples around the edge that sits against the washer. You can just see a couple of the dimples in the photo.

[rneal55555]

I tried to bleed my front brake off and on for about a week a couple of winters ago. I looked all over for a mighty vac bleeder and couldn't find one. I finally got the idea to use the vacuum oil change rig I have for my boat. It pulled fluid through the system so fast I had to get help to keep the reservoir full. Did the let then right caliper and I had decent brakes. They were a little soft but as Pat said after about a half hour test ride they firmed right up.

I'm not sure but I think it moves the fluid fast enough that it carries most of the bubbles with it.

[randy]

Right. That's the trick, getting the fluid moving fast. And it's almost impossible with the lever.

I use a home-made rig of a vacuum bottle ( large pickle jar ). I charge up the bottle to 15 - 20 inches using the engine and then hook it up to the bleeder.

Jar has a dial vacuum guage on the lid so I can monitor the charge and large (gallon) jar acts as a reservior for spent fluid. Maybe i'll post a photo today if i get around to it. It has come in very handy for all of my vehicles.

[sksxs1100]

large pickle jar is a cool idea..... i think i will have to try that one
a picture would be nice too

[pathfinder]

Stops Now

I figured it out all 3 brake bleed screws where they seat in the calipers had been bugered up. Took an old bleed screw ground off all threads so that it would slip in all the way to the bottom, used valve lapping compound to lap the seat. Put it all back together, bleds for about 5 minutes front and rear and I GOT BRAKES.

Ken, thanks for the pic I had it together right but its nice to know for sure.

Thanks to all.

[randy]

Here's a photo of my bleeder. you have to like pickles to build this!

On the left of the cap is a common vacuum check valve, on the right is an old bleeder nipple. Center is the vacuum guage. everything that goes through the cap is silly-coned for a good seal.

I charge it up to 15-20 inches and the check valve keeps the vacuum in, then bleed away. You're looking at the residue from a few cars and a few bikes.