Rear disk brake causing wheel to torque sideways when braking

[JNizza92]

hey guys, I just got my XS650 back on the road last night, but I am having a major problem...

I have a disk rear brake setup (mag wheels) and everytime I push the rear brake it feels like the whole rear tire gets pulled sideways, almost like the axle is not aligned correctly, everything on the axle looks to be aligned correctly, I am not missing any spacers and the adjusters are both tight and at the same notches.

Has anyone had this problem before? or even heard of it happening for that matter, and how should I go about fixing it... It was a little bit terrifying when I pushed the rear brake lever and the bike started to wobble...

Thanks,
Jordan

 

[blackbetty]

Replaced rear wheel bearings?

How about the swing arm pivot/bearings?

 

[retiredgentleman]

That does sound strange indeed, and dangerous!

Is the back axle castleated nut tight? Is there any play in the swing arm pivot shaft?

 

[Visegrippe]

i was having a similar problem last summer, it seems that there's nothing keeping the wheel forward but the chain. i tightened the axle up and it got better, but not perfect.

i rebuilt the whole assembly over the winter, so we'll have to see once the snow clears up.

 

[Royboy]

Something is moving under braking torque. If the axle is tight then it's about gotta be the swingarm. Find it before you ride it, way dangerous.

roy

 

[650Skull]

Adding to what is above.

If you have original axle adjusters and the axle is not tightened up the wheel can slide back not forward. If your swing arm bushings were that bad it would be easy to detect by moving the swing arm from side to side.

You had the spacer from the disk side missing. Did you get the right one or did the replacement have the right dimensions?

Are your disk bolts tightened up properly or maybe you have some foreign bodies between the disk and rim?

Are your shocks mounted and working properly?

 

[1974jh5]

Definitely lift the bike, then try to wiggle the swingarm etc and look for movement. particularly check the wheel bearings, the axle and the swingarm bushings.

In the 'damn that was simple' department, be sure the tires are properly inflated. A very low or flat tire will cause some WEIRD feeling stuff to happen. If it has a stiff sidewall but very low tire pressure it may look OK at rest but deflect, deform and do all kinds of stupid stuff under load.

 

[JNizza92]

rear axle castle nut is tight, I have brand new bronze bushings in the swingarm so I do not think it is that, rear wheels bearings are brand new, I have the correct spacers (I found the one I needed off of an XS1100), shocks seems to be fine, no issues there...

I will have to tear it down and rebuild it over the weekend, double check everything

 

[jamesgs4]

what did you torque the rear castle nut to?

 

[JNizza92]

I do not have a torque wrench, I did it till it was tight then backed it off 1/8 turn, that is typically what I do on all of my dirtbikes and such

 

[5twins]

Check the axle length, with the conversion you've done maybe you're running out of threads on the axle before it's really as tight as it should be. Maybe just adding a washer under the nut will help. Pics of how the whole set-up looks would really help here.

 

[hmusket]

One thing l thought of when you mentioned you replaced the rear bearings, is if you reinstalled the bearing spacer. lts part 4 in the attachment. This is a topic that comes up everry so often, the case of the missing inner spacer.

 

[pregrid]

hey guys, I just got my XS650 back on the road last night, but I am having a major problem...

-I have a disk rear brake setup (mag wheels) and everytime I push the rear brake it feels like the whole rear tire gets pulled sideways-
- when I pushed the rear brake lever and the bike started to wobble...

Thanks,
Jordan

Hmmm, two different descriptions of the problem. If the rear gets pulled sideways you want to address some of the above items. If the bike wobbles you may have a warped rear rotor. So clarify if you would please. Does the rear seem to shift once for every brake application ot does it wobble/vibrate?

 

[JNizza92]

The rear shifts one for every brake application, it is not a wobble.

I do have part 4 installed, it was a pain to get in there correctly haha

I will check my axle length, but I am fairly confident that it is the correct one and that it is not bottoming out the threads.

 

[Visegrippe]

I was just going over the geometry in my head there, and i'm wondering if a worn brake stay bar will cause this behaviour... it seems that at nominal length the reaction force of the stay would cause the brake caliper assembly to rotate "backwards" (reaction is above or in line with the pads), pushing the axle forward. when the slots are elongated with wear, the caliper assembly will be further forward, and the pivot point will be lower(below the pads), the caliper will rotate forwards, pushing the axle back instead.
i've got about 1/4" elongation in each hole on the stay bar plus wear on the bolts, how much is there on yours?

 

[JNizza92]

I will investigate the stay bar when I get home from work, but the brake caliper is not sitting in the correct space on the wheel, when I did the conversion I had to use the one from the drum rear setup because the one that came with the disk rear end was touching my shock, so maybe I need to focus on getting the caliper in the correct location on the wheel? it should be almost directly on top of the rotor, correct?

 

[XSLeo]

You mentioned using spacers from an XS1100. I don't think they are right. The XS1100 is a shaft drive. The spacers are different with a chain drive.
When I was doing the drum to disc conversion on my 75 I tried shaft drive spacers from an XS750, shaft drive. They were to thin, two wouldn't work, too thick. I ended up grinding one down till it would fit with another one.
If the wheel is aligned right and the axle is tigtened properly the wheel can't shift in the swing arm.
You mentioned putting in new bronze bushings in the swing arm. If the pivot bolt isn't properly tightened the swing arm can shift in the frame.
I can only reccomend using a torque wrench to tighten pivot bolt. My Factory books list different specs for different years. In my 70-74 book I don't find a spec. The 74 to 77 book where they list the torque specs says 36.2 to 58 ft/lbs. where threy describe the swing arm remove and replace they spec 862-955 in/lbs converted to ft/lbs is 71.8 to 79.5 ft/lbs. In the 78 and later books they call for 47 ft/lbs.
When working on my 81 and 75 I found the lighter torque values let the swing arm move side to side to much.
To work the way they are designed the swing arm and bushings pivot around the pivot tube as the pivot tube is held tightly in the frame. At the lighter values the pivot tube isn't held by the frame. This allows the pivot tube to rotate around the bolt. There is too much clearance between the tube and bolt and allow the swing arm to move side to side.
Now as you increase the torque this squeezes the frame against the ends of the pivot tube. In my experience it takes about 55-60 ft/lbs to get the frame to hold the pivot tube tightly. On both the 75 and the 81 the pivot tubne was a snug slip fit in the swing arm bushings. Well greased the pivot tube was snug enough I couldn't turn the tube in the bushings by hand. They slid in and out with a firm push. No tools needed. When I installed the swingarm in the frame and torqued to 47 ft/lbs the swing arm had excess side play and when lifted to a level position and released it fell down. I realized the frame was not holding the pivot tube. I addded ten ft/lbs of torque. This removed some of the side play. And the swing arm would fall slowly. I added ten more ft/lbs. This removed almost all of the side play and the swing arm would hold position. The swing arm stayed level but moved with very little effort. I did play with the torque value to find the best torque. It was between 65 and 70 ft/lbs.
I say all this because the shifting you are feeling may be from this. I would remove the wheel and unhook the shocks so just the swing arm is on the bike. No extra weight. Now at the torque level you have can you feel any side play. Will the swing arm drop quickly under it's own weight? Add some torque, 5 or 10 ft/lbs at a time to find the place where the swing arm falls slowly or barely holds it's weight, as in holds but you can move it with no effort. This means the frame is clamping the pivot tube and making the bushings rotate around the pivot tube. Yours may need a torque value more or less than mine.
This may fix the sensation of the wheel moving during braking, or not but it will elimanate it from the problem.
Leo