'74 Commando rear brakes feel unsafe.

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998cc

998cc

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I am working a the bugs out of the Commando and while riding today, I noticed the rear brake actually applies when traveling over short rises in the road surface. It's a bit alarming and does not feel safe. Also, when slightly riding the brake, the pedal pushes back as the road surface varies.

The seller said he had "replaced the hub, brakes and rubber shock absorbers". I can't observe the wheel while riding.

Any thoughts?
Thanks.
998cc
 
Your rear brake cable may also be too tight, give it some more slack.
As the bike goes over a bump the rear suspension first contracts and then elongates.
This action may cause the cable to tighten as the shocks react.
You should be able to push the brake pedal down about at least a half an inch before there is braking effect. You can check all this by putting the bike on the center stand and spin the back while while
testing when the wheel slows down as the brake pedal is depressed.
 
998cc said:
I am working a the bugs out of the Commando and while riding today, I noticed the rear brake actually applies when traveling over short rises in the road surface. It's a bit alarming and does not feel safe. Also, when slightly riding the brake, the pedal pushes back as the road surface varies.
Click to expand...


As 1973x75 said, the cable is very likely routed incorrectly under the Z-plate where it fouls the underside of the plate and applies the brake as the suspension compresses.

The cable must go over the Z-plate and I would urge owners (except of 850 Mk3s) to check the rear brake cable is routed correctly over the plate as the cable routed under the plate is common mistake often seen on Commandos.

'74 Commando rear brakes feel unsafe.
 
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L.A.B.,
I checked the install. Yes the cable is routed under the "Z" plate, so that has to be it.

Thank you!

Regards,
998cc
 
Following up with this thread: Today, I removed the rear brake cable to reroute it over the Z brace and found a bent inner. Fixed that, washed out and re-lubed the cable. The result is the braking problem is gone, and the brake pedal now more positively returns to the stop which fixed the problem with the brake light intermittently staying on.

After the fix, I took the bike on its first real ride on some very rural country backroads, and it handles just like my old '71 Commando which is just how I hoped it would. Still have a few bugs such as leaking gas cap (new Ceandess cap ordered).

Oil leaks: I have now seen a few drops of oil from the transmission but nothing at all from the engine and primary.

Thanks again gentlemen for your insight into the brake problem! Planning a short 60-odd mile ride this Saturday morning.:)
~998cc
 
Good to hear that the problem is solved, it is not mentioned here, but it also help when you apply the rear brake when tightening the LH rear wheel spindle nut, this centers the brake drum in relation to the brake shoes.
 
Agreed; a dropped pedal could create a hazardous situation at speed. Does anyone produce a spring for this purpose similar to the return spring at the hub? A clean installation would be preferable.
Thanks!
~998cc
 
The safety spring is a bit of a Chinese puzzle to get it on in correct orientation...but be persistent and it will go on correctly.
 
My bike came with a section of inner tube wrapped several times around rear brake pedal and foot peg .... left it like that for quite some time before buying the “proper” spring .... actually liked the look and action of the inner tube safety bodge better ... looked kinda like I knew what I was up to , eh .....
 
L.A.B. said:
As 1973x75 said, the cable is very likely routed incorrectly under the Z-plate where it fouls the underside of the plate and applies the brake as the suspension compresses.

The cable must go over the Z-plate and I would urge owners (except of 850 Mk3s) to check the rear brake cable is routed correctly over the plate as the cable routed under the plate is common mistake often seen on Commandos.

'74 Commando rear brakes feel unsafe.
Click to expand...

My cable is over the Z-plate, but passes between the exhaust hanger plates...under the upper rubber isolastic (headsteady type) bushing and other the lower/rear isolastic bushing. Is that OK or should the cable pass completely to the inside of the z-plate/exhaust brackets?
 
Tornado said:
My cable is over the Z-plate, but passes between the exhaust hanger plates...under the upper rubber isolastic (headsteady type) bushing and other the lower/rear isolastic bushing. Is that OK or should the cable pass completely to the inside of the z-plate/exhaust brackets?
Click to expand...

'Factory' photos always seem to show the cable running behind both plates, however, the INOA Tech. Digest includes a copy of a June '75 service release which states:

"The only correct route for the rear brake cable is between the inner muffler bracket and the outer passenger footpeg bracket, above the alloy footpeg plate and below the passenger footpeg hangar spacer..."

...which [Edit] does match your description of: "..under the upper rubber isolastic (headsteady type) bushing and other the lower/rear isolastic bushing." [Edit] for the peashooter exhaust system.
 
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Interesting. I looked another bike yesterday...'72 750. It had the cable between the right of the inner plate and swingarm, not through the isolastic bushings at all. This path seems to allow cable to move vertically with swingarm motion. Having between the plates, through the bushing seems to create some pinching of the cable sleeve on the exposed threaded end of one mounting bolt. The sleeve has been mashed up a bit there.
I'll need to review the "correct " path while looking at the bike...not sure I understand it as written.
 
Tornado said:
I'll need to review the "correct " path while looking at the bike...not sure I understand it as written.
Click to expand...

I have edited in my previous post.

For the peashooter exhaust system the cable would be routed as described in the service release and pass between the two rubber mounts.
 
L.A.B. said:
I have edited in my previous post.

For the peashooter exhaust system the cable would be routed as described in the service release and pass between the two rubber mounts.
Click to expand...
Here is how mine routes...
IMG_20181018_093111407.jpg
you can see how it impinges on the bolt threads and mangled the plastic casing.
It also creates a slight displacement to the left of a direct run to the swingarm boss where the casing end
abuts against.
I have not noticed any rear brake activation when hitting bumps, so maybe this is all fine.
 
And, now I've looked at my bike, I'd clarify the the above service bulletin statement "above the alloy footpeg plate" actually means the Z-plate...in the more common parlance :-)
 
Tornado said:
Here is how mine routes...you can see how it impinges on the bolt threads and mangled the plastic casing.
Click to expand...

It looks as if shortening that stud would probably help reduce the damage to the plastic sheathing? And/or fit a short length of hose (fuel pipe?) over the cable to protect it (this can be done simply by slitting the hose lengthwise and fitting it over the cable)?

Tornado said:
It also creates a slight displacement to the left of a direct run to the swingarm boss where the casing end abuts against. I have not noticed any rear brake activation when hitting bumps, so maybe this is all fine.
Click to expand...


You could try it with the cable routed between the inner plate and the swingarm which is how the factory apparently did it for several years?

Late edit:

However, I believe the INOA cable routing information is intended for low-level or black cap/bean can silencers where the cable only has to pass through the passenger footrest bracket plate section and not between the mounting bracket rubbers where the sheathing could be damaged by the silencer mounting studs as the previous photo shows.
 
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