79F Rear Brake problem

[Snow]

Hi all.
Let me first ask a question:
Will a rear disc from an XJ fit my 79F rear?

Here's today's "This sucks" bitching by Snow

So I am almost home, turn on my road and notice that I seem to be leaning a little bit foward like when braking....also my engine seems to be struggling a little bit. So I pull in the clutch to see if something is dragging and immediately start slowing down even faster! At this point I should have just pulled over and not been an idiot and gone the extra 1/8th mile to my house....but you know me.
So I pull into my driveway and notice that she is really struggling so I stop short of my normal space and kill the motor. Then I smell the stench of unhappiness...smoke arises from my rear caliper...realization of what I have just done to my poor Maya sets in.

I am waiting for the SO to get home with my car so I can pull my tools out and see the extent of my stupidness but I am pretty sure I have just wasted my rotor.

Other question, is it likely that I will need to rebuild the rear caliper also?

[oldfart]

rear brake

There was a reason why the brake seized up.So,it would be prudent to disassemble the unit and refurbish.Also the cause could have been the piston actuating rod,the lock nut on the adjuster could have worked loose and allowed the rod to engage the brake.(needs to have a degree of freeplay)As for the interchangeability of the rotors between xj and xs I cannot say....Will

[Snow]

There seems to be plenty of play between the rod and the the piston (I guess that's what its called), prolly about 4 mm at first guess.
Looks like I will be ordering a rebuild kit ASAP (as soon as my paycheck is direct deposited tonight).

Well, at least I have been planning on working on the rear brakes - I've got brake pads, a new(er) rear master cylinder from ebay, and full SS brakelines from Mr. Rawson on the way soon. Now all I need is a newer disc and a rebuild kit :/

[Jerry]

You need to read this *excellent* article:

http://www.xs11.com/forum/showthread.php?s=&threadid=14

Chances are crud in your brake system plugged the 'spooge hole', a little pressure relief passage in the master cylinder. A block in this passage keeps pressure in the brake lines instead of letting fluid return to the M/C.

Open the bleed nipple on the caliper, and if fluid comes out under pressure and the brakes then release, a cleaning is in order.

[Snow]

I just loosened the bleeder and presto, the caliper realesed. So, what might have happened is the rear MC needed to be cleaned (I purged the front one at least twice since I got the bike, but don't actually recall doing the rear), got "spooged" all up, locked the caliper, and fried a disc? Am I way off base with this theory?

[sixtysix]

yep sounds right to me!!

[Ken Talbot]

it's spooge all right - guaranteed....

[Snow]

Thanks to the wonders of technology and the awesome people here at XS11.com, I have ordered a rebuild kit from partsnmore.com and managed to get a winning bid on a nice looking used rear disc on ebay tonight.
BTW, great price on the rebuild kit, $14!!!

Thanks for replying so quickly with all of the extremely helpful info guys

[uk1.1s]

Brake rotor check

Could be an idea to check out the rotor before you spend on a replacement.

I guess you assume that you've warped the disc with all that heat (which is a definite possibility!)

Before you get one to replace it - could be an idea to check if it is warped first as XS's have much more mass than current hi-tech brakes and are not 'full floating. This equals a good rate of thermal dissipation / inertia - so the hefty lump may not have warped (fingers crossed).

[Snow]

Just visually inspecting and feeling the disc, I can tell that there is something extremely wrong with it - I'll try to borrow a digicam to show you guys just how bad it looks.
I can actually feel a large dip going from teh outer edge in about 1 or 2mm at the most and there are deep feeling grooves all the way in.