scootrs disc pulling wheel out of line?

[cezeta]

i fitted a scoot rs disc over christmas with a remote master cylinder. it may be unrelated to the scoot rs disc but made more obvious by it but on heavy braking the wheel leans to the left and if you keep the brake on and rock the wheel forwards and back while straddling the bike then the wheel can bee seen pulling to the left going forward and pulling to the right rolling back.

they are mb springs with sx200 links and west coast lambretta needle roller bearings in the links.

the wheel has no play if i manually try to flex it.

Any pointers?

[shocky]

thats normal IMO the last few i have done have been like that ,all looked straight and even between the fork legs (after some modification )

[cezeta]

eeek! thats crap then. does that happen on all lammy brakes?

im riding with no front mudguard at the moment so i am noticing these things. i had the same on a vega and managed to cure it during a fork rebuild but could not put my finger on what part cured it as everything was new.

scooters are s**t

[shocky]

it depends on by how much a slight pulling is normal if it goes way over id say one of the spings is soft or perhaps is long in some way this could be the cup inside the leg at fault , i always check the alighnment without dampers fitted as these should not be used to mask a problem or if adjustable be used on a hard setting to act as an anti dive .Another possible cause could be one of the fork links is tight in the fork leg this is a common problem these need to be checked with out the springs or rods fitted ball ache i know and some fettling of the bushes maybe required even if the bushes are the top of the range ones,

[frank sanderson]

All std lambrettas by design have the brake be it either drum or disc as close to the centre line beetween the trailing links as possible this is so that what is happening on your scooter wont occur. Even though std brakes may not work that well they put as close as possible an equal ammount of pressure on both links and springs at the same time. The further away from the centre line the disc is more pressure is put on one link than the other. Like wise the stronger and bigger the disc and calliper the more pressure is put on one link than the other .Regardless of what set up you have in your forks this will still occur. Do not make the mistake of stiffening your set up so that the suspension is so stiff if does not absorb undulations in the road surface . ideal supension should be soft enough to absorb bumps but not be compressed to rapidly by the brake as once it is compressed under braking it cant act as suspension.

[cezeta]

so it looks like its just the design oddity. is there a quick fix frank?

[RICSPEED]

the fact that the caliper bracket it fixed to the link doesn't help matters either ,when braking the right link compresses and the left is forced to follow

[Rich_T]

You have a mis match in the front suspension. Either odd springs, odd links, double stops in one side and not the other or a stop that has not seated correctly. Take the links out and compare them carefully, some have the axel slot higher than others (some times if the bike has been crashed the link gets distorted). When odd links are used it results in one of the fork springs being preloaded more than the other when the axel is tightened up.

It has nothing to do with the centre line of the disc or drum. As a point of fact all original Lambretta breaks (and for that matter most other bikes) the braking effort is transfered to the back plate (the RH link on a Lambretta). The use of your new disc brake has high lighted this problem because it is applying some decent force, the error has probably been there for ages.

The fact that the wheel leans to the left under breaking indicates that either something is too firm on the LH link or too soft on the RH link. Check the parts next to each other and check the free length of the springs too, then closely inspect and search for additional stops inside the forks (at the very least measure the depth to the stop to confirm symmetry).

You do need to to something about this because every time the assembly distorts in this way under braking you are stressing the front axel and that could be messy.

[cezeta]

right......im fitting a px front end, should look fine on a series 1

[storkfoot]

Cezeta, I had this with a ScootRS set up, SR progressive springs, Escort dampers. I didn't even notice until I realised the front tyre was wearing more on one side.

It was nothing to do with the brake, it was the links. Looking at everything with the scoot on the stand and it was all central and looked good. Apply the brake and it pulled badly to one side.

As Rich T says, it was the links. Whilst to the naked eye they looked straight, they had actually gone out of plane when they had damper mounts welded. The learning point was never to use Indian fork links when welding mounts.