Stuttering, juddering forks.

[pablodubyah]

Just got back from a ride and I noticed during heavy braking my forks were juddering at the very bottom.
They are marzocchi atom 80`s and the brakes are xt V`s.
Headset seems tight enough, brake bolts are tightened too.
Very noticable on the road under heavy braking.

Any ideas?
Thanks in advance.

 

[We_are_Stevo]

From the bottom up;

Is the wheel true?

Is there any play in the wheel bearings?

Is there any play in the fork bushes?

Is the braking surface on the rim smooth and within it's limit?

Are the brake pads okay; toe in set up correctly?

Is there any play in the brake pivots; bosses?

Have you REALLY checked your headset adjustment - slacken off pinch bolts, tighten cap, re-tighten pinch bolts?

If the answer to all the above is 'Yes' then I dunno... :?

...apart from flexing in the forks :?:

 

[pablodubyah]

I will try all of those.
Thanks Stevo, you`re a gentleman.

 

[We_are_Stevo]

One tries...

 

[marc two tone]

judder

got the same prob with rigid forks. I have ajdusted the canti blocks and made sure they are towed right. Also made sure all is secure but, the rim is a couple of mm's out of true so, thats going into lbs soon. My blocks are 55 mm , being short they can add to juddering as there is less surface area to absorb braking force. Good luck mate.

 

[suburbanreuben]

Loose headset adjustment is often accompanied by an unhealthy dose of tank slap at speed.

 

[mikee]

on rigid forks , flex in the fork legs can cause this when using canti's
the flex causes the brake cable to effectivly change length
this is more noticeable with a headset or stem mounted hanger

 

[velomaniac]

Mikee's point further emphasises the often sited point made by todays yoof that old bikes are cr**.

I love old bikes me, full of 'character', a term that can be freely translated by us all.

Curiously enough I'm having the same fork judder but I just need to retoe my blocks

 

[marc two tone]

judder

a common problem with cantis.

v brakes bully the rim into stopping but cantis get pushed around a bit. and have inherent play on the bosses no matter what you do.

 

[Anthony]

pablodubyah doesn't have either a rigid fork or cantis.

If the juddering is from the brakes, it can often be caused by grease/dirt on the rim. Clean the braking surface very thoroughly with degreaser.

But you say it feels as though it's from the bottom of the fork. Have you checked how tight the skewer is? Does the fork need a service?

The juddering is caused by the brakes engaging then disengaging then engaging again. That's why it is often caused by grease on the rim - variations in the braking surface. Compounding this, if your XT Vs are M739, they could well have excess play in the parallel-push linkages. If your rim is slightly concave, when you try to bring the pads together, the concavity pushes them sideways, rather than inwards. This again can cause intermittent disengagement, coming through as juddering. It could be that replacing your XT M739 with LX M600 would solve it. Simpler, but less to go wrong.