Help! Front Brake Judder

Barnsleyrob

Pedelecer
Jul 20, 2020
148
23
I noticed on a ride today that my front forks are juddering under braking. The bike has been performing ok as far as I recall up to now but if it support myself on a bench and pull the front brake it seems to grab and judder.

I’m around 13 stone and have hydraulic brakes. I tried tightening the tube cap up to 6nm (didn‘t want to go higher and it was only 1/4 turn anyway) and that didn’t make much difference So I don’t know whether it’s the steering tube or just a spot on the disk that’s got muck on it.

any ideas please.
 

GSV3MiaC

Pedelecer
Jun 6, 2020
195
127
If the steering tube you should be able to notice the 'wobble' if you put the front brake on and try pushing the bike back and forward. My money is on the brake though.. Did you try cleaning the disk, checking it for warp, burr, or trapped junk in the vents, and inspecting the brake mountings themselves?
 

Barnsleyrob

Pedelecer
Jul 20, 2020
148
23
With my weight off the bike, it’s all fine. It’s only when I drop my full weight on and then rock it back and forth. The callipers, disks and mounts are all tightened to the right torque.

I can live with it as the bike stops just fine although I can’t lock up the front wheel (tested on a safe bit of the road) so I guess it could be contamination.

Is 6nm too high for the top cap ? The steering is free.
 

Barnsleyrob

Pedelecer
Jul 20, 2020
148
23
How do I do that ? I want to change the stem anyway so don’t mind getting my hands dirty.
The bike has done 100 miles from new and I only noticed the problem this week. Of course the temps have been higher so maybe that showed up some issues.
 

Richard Newton

Finding my (electric) wheels
May 24, 2021
10
1
my main concern is whether tightening the top cap could cause long term damage.
I suggest you go back to the brake and inspect the pads. Judder sounds very much like the pads are contaminated with an oily substance. The brake may also squeal a bit when applied. If you have tested the head for play as your previous contact has suggested it is unlikely to be loose. If you do decide to change the pads make sure your discs are clean and if they are contaminated then check for hydraulic leak at the disc pad end. If you find even the smallest leak I would go to a bike dealer you know and have the hydraulic line looked at just in case. Over tightening the line nut may not fracture immediately but could fail at a later more in convenient time like when you need to stop in a hurry.
Hope this helps.
RichardN
 

awol

Esteemed Pedelecer
Sep 4, 2013
1,211
374
my main concern is whether tightening the top cap could cause long term damage.
Tightening the steerer topcap on it's own won't have done anything if the 2x stem bolts were still tight so won't have caused any damage.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
3,943
Basildon
How do I do that ? I want to change the stem anyway so don’t mind getting my hands dirty.
The bike has done 100 miles from new and I only noticed the problem this week. Of course the temps have been higher so maybe that showed up some issues.
I can't help you unless you show what type of steering head and stem that you have.
 
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GSV3MiaC

Pedelecer
Jun 6, 2020
195
127
And if the bike has front suspension, that could well behave differently under load (i.e. with your weight on, or stopping).
 

Barnsleyrob

Pedelecer
Jul 20, 2020
148
23
Thanks for the suggestions guys. My fork is fixed without suspension and I’m strongly favouring a light contamination of the disks as I use the Mucoff shine product to make it easier to keep the bike clean. I use a shower cap on the disks but I guess it’s not infallible.

Anyway the real question is whether 6nm is likely to cause damage.

No idea what tube or bearings I have and an external photo probably wont help. I’d sooner not strip the bike back to bare components.
 

Barnsleyrob

Pedelecer
Jul 20, 2020
148
23
This seems to be an interesting topic in that Google searches, including other forums, have no answer as to what the top cap torque settings should be. Plenty of answers saying what it should be (15nm seems to be way too high) so maybe a topic for more research.
 

Raboa

Esteemed Pedelecer
Aug 12, 2014
475
159
49
Your brakes might need burped / bleed.


Rotate/move the hand lever assembly until the reservoir cap is facing up and at level.

Take off the reservoir cap.

Slowly squeeze the lever repeatedly, until no more air bubbles come off.

Refill the reservoir with brake fluid.

Put the cap back on and return the lever assembly to his normal position.

There are tons of videos in YouTube if you want more details.
 

GLJoe

Esteemed Pedelecer
May 21, 2017
738
327
UK
I tried tightening the tube cap up to 6nm...
You need to explain exactly (preferably with photos) what it is you're doing.

My suspicion is that you're adjusting the headset bearing tension incorrectly, and thinking its similar to the old Quill stem method.
With modern bikes, the 'tube cap' is not really used to adjust the tension (as in you don't set it to a given torque setting), hence the reason you can't find any figures out there.
 

vfr400

Esteemed Pedelecer
Jun 12, 2011
9,822
3,943
Basildon
You can turn the cap screw to any torque you want. You can even strip the thread. It makes absolutely no difference if the stem is still clamped
 

Nealh

Esteemed Pedelecer
Aug 7, 2014
15,074
5,854
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West Sx RH
After checking out brakes, personally I would drop the forks out and thoroughly check out the lower and upper bearings for rust and wear, semi -sealed bearings can become rusty as do loose bearings.
Quite simply remove the handle bars from the stem, undo the top head bolt and then loosen the two stem bolts all should be approx. 5nm and hand tightened. If need be wallop the head tube with a rubber mallet if needed or hammer and woodblock.

Re brakes have you removed the pads and celaned them of any any road contamination or glazing ?
Are they worn or are the discs worn too thin, can you feel a ridge on the disc braking area to the inner disc ?
Washing up liquid works well, apply some to the surface and gently rub together for 20 odd secs and wash off. May need two or three washes.