Author Topic: Shuddering Front Brake  (Read 2135 times)

Offline Brucie64

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Shuddering Front Brake
« on: 14.09. 2009 11:24 »
Anyone any idea why my front brake should shudder violently, during normal riding (without brake) everythings ticky-taboo but apply the almost non existent front brake and it's like being on a rollercoaster!
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Bruce
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Offline MikeN

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Re: Shuddering Front Brake
« Reply #1 on: 14.09. 2009 12:02 »
  If it shudders when you apply the brake then you may have a brake drum that is worn out of round or loose steering head bearings or worn fork bushes.
  if the drum is out of round it will have to be bored true on a lathe. You will then require oversize brake linings machined to suit.
Mike
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Offline rocket man

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Re: Shuddering Front Brake
« Reply #2 on: 14.09. 2009 21:03 »
i had the same problem with my brakes after they had been rebuilt
with new spokes and rims it must have distorted the drums
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Offline muskrat

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Re: Shuddering Front Brake
« Reply #3 on: 14.09. 2009 22:14 »
Same here. I backed off all the nipples 1/2 turn which helped. I then backed them off another full turn and re-tightened using a spring scale on the spanner.Good as gold. If you can remedy this way before too many break applications you may save the drum.
Cheers
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Offline A10Boy

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Re: Shuddering Front Brake
« Reply #4 on: 14.09. 2009 22:31 »
Which drum is it ?
The full width cast iron ones are notorious for heat distortion, if its suddenly happened after a re-spoke then as has been said its been pulled oval by the wheel builders.

The way to check is raise the front wheel off the ground and spin the wheel and apply the brake lightly until it just starts to bind, you will feel if its gone oval.

Oil contamination will make it judder to.
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Offline trevinoz

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Re: Shuddering Front Brake
« Reply #5 on: 15.09. 2009 07:43 »
I always machine the drum concentric to the axle after a rebuild. I then get linings made to suit.
Trev.
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Offline Brucie64

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Re: Shuddering Front Brake
« Reply #6 on: 15.09. 2009 10:16 »
Hi Guys,

Thanks for the info, I am not sure long the brake has been shuddering for as it's done it as long as I have owned the bike (6 months). The wheels don't look as though they have been recently built as they have  very small specks of corrosion on the rims and the bike had been off the road for some 5 years as far as I can tell.

As a first stab in the dark I will prop up the front wheel sometime this week and see if it is running true, then probably start to dismantle the brake depending upon what I find. I am also not sure what size or type the brake is so I have enclosed a photo for reference.
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Bruce
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Online orabanda

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Re: Shuddering Front Brake
« Reply #7 on: 15.09. 2009 10:58 »
I take the same approach as Trev. Machine up a dummy axle (mandrel), set it up in lathe to run true, then fit drum onto axle, lock up with nut (friction lock), then machine true.

This is best done as an assembled wheel, as the spokes will sometimes pull the drum surface out of true (some designs distort less than others!). I can't fit a complete wheel in my lathe, so machine the drum before spoking. This has still givens a good result for my brakes.

So, once hub drum is true, then have oversize linings bonded (AND RIVETED) onto shoes, set up the backing plate up the same way, and machine away!

Use appropriate breathing apparatus AND vacuum cleaner to control / remove fibres during the machining. I like 0.010" clearance between drum and shoes. Also put 0.010" shim packer behind the flat portion of each shoe.

Brucie, what is also important is that the backing plate / shoe assembly is centralisedwhen assembled in relation to the wheel hub. You might get some improvement if you try this now.

Loosen axle a little, and torque arm, hold brake on, and pump forks several times. Whilst holding brake on, have assistant lock up axle, etc. Road test; you might get an improvement.

Richard
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Offline beezalex

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Re: Shuddering Front Brake
« Reply #8 on: 15.09. 2009 16:24 »
Check for wheel balance as well.  I had a bad shudder that would only appear during heavy braking at speed.  It was caused by wheel imbalance.
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Alex

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Re: Shuddering Front Brake
« Reply #9 on: 15.09. 2009 17:29 »
Had my front hub skimmed at a local engineering firm ( they do truck wheels too), did'nt cost much either, £12 UK although this is probably 8 or 9 years ago, if there is such a firm in your area might be worth asking if they can do it.

All the best - Bill
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All the best - Bill
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Offline Brucie64

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Re: Shuddering Front Brake
« Reply #10 on: 20.09. 2009 08:44 »
After raising and spinning the front wheel I noticed that the wheel is slightly (in my humble opinion) not concentric. I managed to rig up a measuring device (straight bar sat on a beer crate) which just touched the wheel rim. I then span the wheel and noticed that the rim wavered closer to then further away from the measuring bar by up to around 5mm. Could this degree of error be the primary cause of my brake judder?

If so, then is there a novice guide to adjusting the wheel spokes to correct this issue or is it generally deemed a job only to be undertaken by an expert wheel builder?
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Bruce
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Re: Shuddering Front Brake
« Reply #11 on: 20.09. 2009 09:24 »
Have a go it's very satisfying.
Remember always slacken one side before tightening the other. ( where it out of true )
Not too sure about this but I think you are allowed 1mm out of true, so you have to shift it 3mm, try slackening half a turn then tighten other side half a turn then remeasure.

All the best - Bill
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All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline beezalex

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Re: Shuddering Front Brake
« Reply #12 on: 20.09. 2009 14:18 »
Yes, you will notice 5 mm on the road.  1-1.5 mm is acceptable.

You will be surprised by how easy it is to adjust the spokes.  You will need a spoke wrench and a spring scale (unless you have a spoke torque wrench).  If the runout is side-to-side, loosen spokes on the same side as the direction of maximum deflection and tighten spokes on the side of the direction of minimum deflection.  The wheel should start to move to minimize deflection.  Once you've got things in the right place, use your torque wrench or hook your spring scale hooked to the end of your spoke wrench to get about 35 in-lbs of torque.  To get this with the spring scale, simply multiply the length of the spoke wrench in inches by the amount of force (in lbs) indicated on the spring scale.  It just takes a little bit of patience, I'm sure you'll catch on quickly.
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Alex

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Offline Brucie64

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Re: Shuddering Front Brake
« Reply #13 on: 20.09. 2009 16:06 »
Many Thanks for the top tips on how to adjust the wheel circumference by tightening or loosening the spokes, However which way is to tighten and which way is to loosen on a spoke? (is it the same as a normal nut & bolt i.e. anticlockwise to loosen?).

I take it you should loosen a few of the spokes closest as possible to the tight section and tighten the opposite spokes accordingly?
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Re: Shuddering Front Brake
« Reply #14 on: 20.09. 2009 17:37 »
Yes - tighten is to shorten spoke length, spokes being righthand thread as per normal bolt.

All the best - Bill
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All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco