Rear Brake

[NigelGF Profile]

Hi, I recently bought a AJS Tempest Scrambler having had several motorcycle over the years but now that I have reached 71 years old I need something nice and light and this motorcycle is great, but have a slight problem with the Rear Brake,the rear brake pedal moves a long way down before it activates the back brake, I have adjusted the brake rod slightly which moves the brake pedal slightly lower but it still goes down a long way before the back brake will work, any help on this would be greatly appreciated .

[spookefoote1956 Profile]

Hello Nigel. If I'm right that bike is disc front and rear? Or is it drum back?

Put the bike on the centre stand, adjust the rod (if that's what it is) whilst turning the back wheel. When it starts to grab back it off a bit and you should be ok. However still let me know if it's disc or drum. If possible upload a piccy as that will help.

Cheers, Chris

[Mick D Profile]

Hi

It sounds like the rear system either needs bleeding or the addition of more fluid followed by bleeding, - have a good look at the whole combined system to ensure it's not leaking fluid.

Regards Mick

[SPRIDDLER Profile]

Hi Nigel. That's very interesting as I have the same issue with my 'Mutchless' (My Chinese Herald 250 Classic. Engine based upon the 250cc Suzuki GN 250).
When operating the rear brake the pedal travel 'slack' is excessive and my toes are damn near pointing at the ground before the pads contact the disc. It seems as though the pads are retracting too far back into the caliper.

2016-05-21 Mutchless resized 009 (640x480).jpg

This is a G.A. of the slave cylinder location....

2019-09-18 Mutchless rear brake 004 (480x640).jpg

In the photo below you will see that the threaded adjuster 'A' is fully extended so no further adjustment is possible. I had considered making a longer threaded adjuster but it appears to be an integral part of the piston inside the cylinder even though the locknuts at its rubber boot end suggest otherwise. I am intending to experiment by making a deeper (longer) clevis 'C' which connects the pedal arm to the threaded adjuster in order to take up the slack.

Mutchless rear brake slave cylinder (640x480).jpg

The dealer from whom I bought it 3 years ago suggested the following causes, none of which apply to my brake........
Low Hydraulic fluid level.
Hydraulics need to be bled.
Brake pads worn.
Disc distorted (pushing the pads back further into the caliper).
Brake pedal arm bent.
Wear in clevis pin.

[g80csp11 Profile]

Neville , I assume both bikes have combined braking where there is a bias to stop the rear brake locking up
if you apply the front brake and then the rear brake does the foot brake go so far down ?

[SPRIDDLER Profile]

Neville , I assume both bikes have combined braking ........

No, mine's two independent systems but I believe the Ajay's are combined.

[Mick D Profile]

Hi

The 'mechanism' that retracts the pads from the disc is usually the design of the calliper to piston seal(s), when the brake pressure is released the pads should withdraw from the disc by a few thou, (say two to three typically).
Without moving your bike apply the rear brake firmly for a few seconds then release it and measure the pad to disc clearances with feeler gauges, then spin the rear wheel a couple of times and re-measure the clearances.

If the first set of measurements are significantly larger than three thou or significantly different from side to side, (if the calliper is a twin piston one), the calliper seals are suspect.

If the second set of results are significantly larger than the first it suggests the disc is warped or not mounted on the same plane as the calliper.

Regards Mick

[NigelGF Profile]

Yes, my AJS has combined braking, so I will check what has been mentioned regarding the front brake.

[39speedtwin Profile]

Having been out today with my Tempest Scrambler on a 55 mile run round the lanes, I decided to try the rear brake, same problem as Nigel, when coasting in neutral it hardly slows the bike down.
Normally I always use the front brake, use both in an emergency.
When I got home I checked the brake, with the pedal hard down I can move the wheel, looking at the rear brake disc it appears that only half the pad is touching the disc, also when pushing the pedal with my hand there is resistance then movement as if a valve is opening in the cylinder.
Bled the brake no air present and no difference. Front brake is fine.
Having read Peters post I will check tomorrow with the front brake applied.
Otherwise I will be calling Andover on Monday as the bike was new in December and has only covered 299.5 kms.

[39speedtwin Profile]

Checked Peters suggestion, there was no difference with the front brake applied.
I pumped the rear hard several times, this realigned the pads in the calliper.
See picture of disc showing pads touching half.
Wheel cannot be turned now with hard hand pressure on the pedal, will check when next out for a ride, probably Wednesday.