Wobbly Front Wheel under braking

[manalog]

Hi,
I have converted my Pinnacle Lithium 6 using an 8Fun Kit. This bike has Hydraulic disc with 180mm rotor and the wheel wobble under braking. I can see the fork vibrating backward and forward. I have checked the wheel for trueness and it seems fine. I have also checked the rotor bolts and the caliper bolts.
Im getting a little worried that the fork might fail. The Fork is a Cromo with no suspension. I have never experience this before conversion. The original bike had a 160mm rotor but I had to replace to 180mm to accomodate the motor using a 180mm adaptor post. Any ideas what might cause this?

Many Thanks,
Gerry

 

[KirstinS]

Hmm, try

1) check to see if new rotor is warped or has any chips in it

2) stand over bike and with the front brake on, rock it back and forth - any play mean the headset needs tightening

 

[Deleted member 4366]

Check your steering head bearings too.

 

[flecc]

It may be the added motor weight provoking that fore and aft flexing. The original eZee Torq had a front motor and "rigid" forks that flexed forward and backwards to an alarming degree on the road, especially on poor surfaces, but when I converted mine to a rear motor, the fork flexing was very greatly reduced.

That Torq's forks were fine, but of course I can't vouch for yours being strong enough.

 

[KirstinS]

Has it always done this since conversion ? Or a new thing after plenty electric miles ?

Is it progressive in line with braking? I mean gentle braking = gentle judder and heavy braking = heavy judder

 

[manalog]

Hmm, try

1) check to see if new rotor is warped or has any chips in it

2) stand over bike and with the front brake on, rock it back and forth - any play mean the headset needs tightening

Hi Kirstin,
The rotor seems fine and there is no play in the Headset. This is a brand new bike and since conversion I have always have this issue but a bit more worrying now with my Booster pack
The fork moves backwards and forward under braking as if the caliper is grabbing the rotor on and off, its a shame I cant install the original rotor as the rotor Im using is not Avid but a generic 180mm I can't even remember the name but it seems good quality.
Cheers,
Gerry

 

[manalog]

Check your steering head bearings too.

Hi D8veh,
This is a brand new bike but I'll check just in case they put in a dodgy headset but there is no play when I did the backward and forward test.

 

[manalog]

It may be the added motor weight provoking that fore and aft flexing. The original eZee Torq had a front motor and "rigid" forks that flexed forward and backwards to an alarming degree on the road, especially on poor surfaces, but when I converted mine to a rear motor, the fork flexing was very greatly reduced.

That Torq's forks were fine, but of course I can't vouch for yours being strong enough.

Hi Flecc,
I'm considering buying a rear hub because of the weight at front plus the increase torque on the fork. I will do some testing atthe weekend. Installt he original wheel with the 180mm rotor and see if Istill get this issue. Can loose spokes cause this?
G

 

[flecc]

Loose spokes with a disc brake can have an effect, braking the hub without stable transfer of the braking force to the tyre tread. So it's worth correcting those first before trying the original wheel.

 

[Scimitar]

Hi Kirstin,
The rotor seems fine and there is no play in the Headset. This is a brand new bike and since conversion I have always have this issue but a bit more worrying now with my Booster pack
The fork moves backwards and forward under braking as if the caliper is grabbing the rotor on and off, its a shame I cant install the original rotor as the rotor Im using is not Avid but a generic 180mm I can't even remember the name but it seems good quality.
Cheers,
Gerry

I wouldn't be surprised if the disc is contaminated. Try scrubbing it with Fairy Liquid (other kind to your hand liquids are available) and hot water. It might need more than that - and check the pads for any sign of oil/grease contamination.

 

[Deleted member 4366]

You've probably got some sort of resonance . Tightening the spokes could well make a difference. They're often not tight enough on kits anyway. Another thing you could try is a different brake-pad material.

 

[Gdread]

You've probably got some sort of resonance . Tightening the spokes could well make a difference. They're often not tight enough on kits anyway. Another thing you could try is a different brake-pad material.

Good point about the pads, if its a new rotor but existing pads that may be an issue. Also, my kit came with plastic washers and rotor screws, the plastic washers are not meant to be reused with the rotor.

 

[manalog]

Good point about the pads, if its a new rotor but existing pads that may be an issue. Also, my kit came with plastic washers and rotor screws, the plastic washers are not meant to be reused with the rotor.

This is a good point, I wonder if I have rotor/pads mismatch. I used the bike for approx 50 miles before conversion . I wii tighten the spokes first before going for new pads.
Cheers,
Gerry

 

[Gdread]

I think it's already been said but spokes, spokes and spokes often the problem for all sorts of problems and noises

 

[manalog]

I think it's already been said but spokes, spokes and spokes often the problem for all sorts of problems and noises

I have checked the spokes last night ant they are a bit loose but I don't want to tighten them in case I mess it up completely. I might take it to my LBS on Saturday.
Cheers,
Gerry

 

[trex]

You could try to reduce the tyre pressure on the front wheel, let the tyre absorb a bit more vibration from the motor and thus the tyre will shift the resonance frequery to lower and reduce resonance. If the vibrations occur only when braking then the brake pads may not have bedded well to your disc. The only cure then is either change rotor or pads.