rear brake temporary (!?) failure

[naughtyG]

well it's happened a couple of times now, so I'm wondering if this is a common failure: after 20-25 miles of highway riding, I hit my rear brake and nothing happened. Pedal went all the way down as if there was no fluid left.
When I got home I checked it, and it was working again ?!?

So I went ahead and bled the rear caliper and renewed all of the fluid. It seemed to bleed just fine, building up resistance on the pedal ok. It did feel a little spongy still, but as I could block the rear wheel while riding with the brake, I thought it was ok.

Then last night I got on the highway home. After 60 miles I stopped for gas, and again the rear brake failed completely - pedal all the way down with no braking. After refuelling, I checked it again and it had once again recovered..

So, any advice here - glazed rotor? Shite pads? Dead caliper or master cylinder?
:ummm:

 

[John R]

NaughtyG, I have the brake post about the shims and spring replacements. My rear brake started doing the same thing about three weeks ago and then the front brake started squelling. I assumed it was due to pad wear and that's why I started to work on replacing all of the pads with EBC. I would be on the highway for 30 minutes or so, get off at an exit ramp and the rear brake pedal goes all the way to the pavement. I get off the bike, clean my shorts, try the rear brake again and it works just fine.

 

[Jayhawk]

Maybe I'm just dumb, but I don't see how this problem can be anything other than something hydraulic. Bad cylinder, air in the line, something.

 

[maleko89]

Maybe the pistons are sticking?

 

[4gasem]

My 2006 does the same thing sometimes. I was really hard on the back the other day and let off and went back for it and nothing...:confused2:

Haven't bothered looking at it. It had new fluid last year so I may replace again. Maybe moisture built up. (doubt it):damn angry:

 

[richwrench]

I was just looking at my '96 with stock exhaust & I noticed that my rear brake hose is routed less than 1" from the exhaust. I've never had an issue with my 'Max yet , but theoretically ( i can't spell ) if your brake hose got hot enough the fluid could boil & cause a loss of braking as you said. That would dis-appear after it cooled off - I've seen that a number of times on Verizon trucks when a brake caliper seizes & the fluid overheats. I suppose a sticking piston in a caliper could do the same thing as an over-heated hose , as was already posted. For the sake over arguement you could re-route/insulate the brake hose just to prove that's not the cause. If nothing else, it's free & it certainly won't hurt anything to try - just my opinion...

 

[dannymax]

Just a thought, but could a bad o-ring cause this kind of intermittent problem? Rolling over allowing blow-by occasionally? :ummm:

Scarier'n hell, to say the least!!

 

[naughtyG]

Well a good inspection today revealed the problem: a sticking piston in the caliper. This is pretty bad actually - the outer piston is stuck all the way in, so the inner piston has been doing al the work, pushing the disk so far that its mounting screws have got against the caliper itself!
Also noticed that my rear disk is under 7mm thick, so now I'm in the market for:
- a rear brake rotor
- the rotor mounting bolts
- new pads (wanna get a whole set - both fronts and the rear)
- possibly a rear caliper, unless I manage to make this one work again :-/

All the above to fit a 1986 model - if anyone can help please PM me!

Thanks

 

[naughtyG]

So I took off the rear caliper and wheel today, and found out what my problem was: whoever had the wheel off last forgot to put the collar that goes behind the caliper bracket back in!! :bang head:
My rear wheel was actually loose! Once I got the caliper off, I could move the wheel sideways by almost half an inch. I'm amazed I'm not dead yet, doing up to 130mph like this :damn angry:

The rotor is dead - I got another one on the way from eBay for $75. Also got new EBC HH pads and the missing collar on their way from Gary McCoy. Both pistons are coming out ok when I push on the brake pedal, so I'll clean those up and it should be all good. Mad one - the outer piston wasn't even sticking in the caliper, it just didn't come out because the whole rear brake assembly was being pushed out of alignment by the other piston because of the missing collar!

 

[maleko89]

Are you talking about that washer that fits between caliper bracket and swing arm?

 

[naughtyG]

nope - I'm talking about the collar that goes between the caliper bracket and the wheel (bearing). On the rear caliper microfiche, ref #7, part #90387-200J2-00

That was MISSING (!!!)

 

[maleko89]

Day-am! Lucky!

 

[ssnsltd]

nope - I'm talking about the collar that goes between the caliper bracket and the wheel (bearing). On the rear caliper microfiche, ref #7, part #90387-200J2-00

That was MISSING (!!!)

you will likely find the caliper bracket is bent now as well. IOT torque the axle it has to pull the whole assembly through the tire now instead of putting the pressure on the collar and bearing race.

 

[naughtyG]

Ok I got the collar, new EBC HH pads and a decent rotor off ebay. Put it all back together, and braking in the rear pads. It's definitely working better now, the caliper bracket was eaten a little by the rotor bolts but wasn't bent so is ok.
The bike seems more stable in a straight line now, but going over bumps or leaning at higher speeds (90mph+) still gets major scary wobbles. Next upgrade will be tires, when I can afford them. Until then I just have to go slow :-(

 

[rebar]

I think I may have a issue with how my rear wheel/ caliper were reinstalled. It looks like washer #23 was installed on the left side next to #20 washer plate.

#23 is supposed to be on the right. Correct?:confused2:

Anyone have a pic? The microfiche has me confused.

http://www.mondakmotorsports.com/fiche_section_detail.asp

 

[maleko89]

#23 should be on the right side in between the brake stay and the swing arm.

 

[naughtyG]

You can download both the Owner's manual and Yamaha Service manual from www.vmaxoutlaw.com