Replacing Rear brake disc

[dilboy]

Hi all[/size]First I need a new rear brake discs on the advice of my mot Any recommendations,up to £80 is my limit How easy is it to do yourself


Cheers

[Fazerider]

Hi all
First I need a new rear brake discs on the advice of my mot Any recommendations,up to £80 is my limit How easy is it to do yourself
Cheers

I've had 2nd hand ones and a new OEM in the past… the real difficulty is removal of the old one.
The screws corrode and the threadlock cures until it's up to full superglue strength. They are almost impossible to extract without them shearing. I've found that welding a bar to the head dumps enough heat in and gives the leverage needed to undo them, but the screws are obviously not reusable after that. So budget for some replacement screws and maybe some mechanics time if you don't have the equipment yourself.

[Disorderlypunk]

if the wheel isnt off yet hit the bolts with some plus gas every day for a few days while your waiting for the new disc

if you aint got a welder but have a blowtorch get some heat on those bolts then hit them with some plus gas /wd40 / thin oil and let them cool
and give them a good whack with a hammer to shock them (every little helps)

there is also the candle wax trick but hardly anyone has candles anymore
then its time to get out the shortest socket you have and a breaker bar - those fuckers are tighter than a ducks arse but not as waterproof

[darrsi]

if the wheel isnt off yet hit the bolts with some plus gas every day for a few days while your waiting for the new disc

if you aint got a welder but have a blowtorch get some heat on those bolts then hit them with some plus gas /wd40 / thin oil and let them cool
and give them a good whack with a hammer to shock them (every little helps)

there is also the candle wax trick but hardly anyone has candles anymore
then its time to get out the shortest socket you have and a breaker bar - those fuckers are tighter than a ducks arse but not as waterproof

I wouldn't really do this if the bike's still being used, otherwise it's all gonna get rather dangerous with oil on the disc and pads!

[darrsi]

I've gotta change my rear disc and tyre at the weekend, I'm not looking forward to it at all to be honest, as the last time resulted in a new wheel when the only bolt that hinted at budging snapped in half, flush with the wheel hub.  :'(

I have a feeling that it may have been the original disc though so there would've been plenty of thread lock on the bolts.

[celticdog]

I've not long replaced mine it's not a foccin pleasant job, lots of heat required and lots of swearing. I ended up snapping one and had to have it drilled out with a carbide tool.
You'll need to keep heat on the wheel at the bottom of the thread bosses to melt the threadlock before the bolts will budge. Re-chasing the threads with a tap also helps as you can easily destroy the threadforms when removing the old bolts. Don't forget to use threadlock when fitting the new bolts.

[Fazerider]

[quote author=Disorderlypunk link=topic=23511.msg271425#msg271425 date=1511183124]


if the wheel isnt off yet hit the bolts with some plus gas every day for a few days while your waiting for the new disc


if you aint got a welder but have a blowtorch get some heat on those bolts then hit them with some plus gas /wd40 / thin oil and let them cool
and give them a good whack with a hammer to shock them (every little helps)


there is also the candle wax trick but hardly anyone has candles anymore
then its time to get out the shortest socket you have and a breaker bar - those fuckers are tighter than a ducks arse but not as waterproof

I wouldn't really do this if the bike's still being used, otherwise it's all gonna get rather dangerous with oil on the disc and pads!
[/quote]
The best place to squirt the Plusgas is to aim inside the hub where the open ends of the threaded holes are so it should be possible to keep it off the disc and pads. Spraying the heads of the screws won't get it where it's needed so it won't have much effect (other than on your braking, as you suggest).


I too need to get a disc off, Fortunately it's my spare wheel, but it's an original disc. I made one attempt earlier this year: liberal application of penetrating oil for weeks, warming the whole wheel over a gas ring until it was at 90º and then I attacked with the impact driver. Other than destroying the allen heads it achieved nothing.  :'(


I'll use the welder method next time.
My preference is to use Copaslip rather than threadlock on reassembly!

[Disorderlypunk]

im not sure there is any threadlock in there (could be) the main problem we face is galvanic corrosion and it is a bastard.
its the same problem removing the bolts from the front mudguard which i ended up retapping larger after drilling them out


there are all sorts of tricks out there for stuck bolts from this corrosion but the problem is you cant really get to the threads to implement them
remember once it starts coming out to screw it back in a little every so often (seriously- it unbinds the crap from the threads)

[mogster]

Hi all just thought i would mention that one of the foccer members managed to use a dremell or simalar
with a bendy attachment and a small wire brush to clean the offending area. takes a couple of hours but
well worth the time. against a new wheel sorry cant find the link hope this helps  mogs.

[darrsi]

im not sure there is any threadlock in there (could be) the main problem we face is galvanic corrosion and it is a bastard.
its the same problem removing the bolts from the front mudguard which i ended up retapping larger after drilling them out


there are all sorts of tricks out there for stuck bolts from this corrosion but the problem is you cant really get to the threads to implement them
remember once it starts coming out to screw it back in a little every so often (seriously- it unbinds the crap from the threads)

There will definitely be threadlock if it's the original disc and bolts.
The last disc i put on i think i just used a dot of threadlock, but i have an impact driver and some spare bolts at the ready this time.
And i"ll be changing the disc before taking the wheel to my mechanic to get the tyre changed, so worst scenario he"ll get lumbered with it, at my expense though of course.

[tommyardin]

The original bolts that hold the disc on are too long, they poke about 10 mm or so into the centre of the alloy hub, there the buggers sit gathering rust, shit and and all sorts or other electrolysis type corrosion (Steel Bolts in cast alloy not good) the ends of these bolts become engorged with this corrosion and as you force them out of the alloy hub they will bring a lot of the threads with the or even worse shear off.
I used a Dremel with a flexi drive about a foot long and with a small wire brush I managed to clean a lot of the crap off the threads, you can not reach it all but if you get 70% off it will stand you in good stead. lots and lots of Plus Gas release agent for a couple of day before you start (WD40 will not do it, it lubes a thread once its turning but will not help release it) give each of the dome headed bolts a good sharp crack with a hammer and drift (Remember the hub is Alloy) and if necessary a blow lamp on each bolt before you try undoing it.
As someone said earlier try rocking the bolt back and forward once its moving and gradually ease them out.
The stupid bolts that are holding the disc are made of cheddar cheese so make sure your allen key is in good nick or even a new one. cos once it slips your down to a hammer a small chisel to drift the bolt round.
I replace all my disc bolts with shallow headed stainless steel hex head bolts that were about 10mm shorter, I copper slipped the new bolts before they went in, don't use loctite no one has ever had one of those bolts come undone, in fact one one can usually undo the foccing things when they really try.
The bolts need to be shallow headed to allow them to pass through the outer edge of the caliper. 

[darrsi]

You're not wrong about the cheese like bolts, i've found a few similar bolts or even small screws as well that are just stupidly feeble, bearing in mind they do a serious job.
I'll let you know how i get on at the weekend, i'm quietly hopeful but you just never know?

[Disorderlypunk]

i only mentioned wd40 (the devils semen) because unfortunately that seems to be the only lubrication some people tend to know about
wd40 your ignition barrel  - NO NO NO (use carb cleaner then a graphite spray - never an oil) (try carb/brake cleaner first as a test next time)
wd40 your tight bolts - NO use a proper penetration spray
wd40 your wifes arse - NO NO NO be nice and use Another type of penetration lube


wd40 is great for some jobs dont get me wrong and i always have some but it is rarely the correct thing to use
we have a can in our rally cars tool box but rarely use it back at the garage is its primary roll is water displacement
can it penetrate YES - is it the best HELL NO

[celticdog]

I would never use slip on these bolts. The act of removing the bolts will damage the threads hence the need for a thread tap. I'ts very unlikely you will be able to re-tighten the bolts back up to torque without stripping the threads. The threadlock is used for a reason- to prevent loosening due to vibration. It is however your own personal decision.

[tommyardin]

i only mentioned wd40 (the devils semen) because unfortunately that seems to be the only lubrication some people tend to know about
wd40 your ignition barrel  - NO NO NO (use carb cleaner then a graphite spray - never an oil) (try carb/brake cleaner first as a test next time)
wd40 your tight bolts - NO use a proper penetration spray
wd40 your wifes arse - NO NO NO be nice and use Another type of penetration lube


wd40 is great for some jobs dfont get me wrong and i always have some but it is rarely the correct thing to use
we have a can in our rally cars tool box but rarely use it back at the garage is its primary roll is water displacement
can it penetrate YES - is it the best HELL NO

Yes yes yes for that job I find that little red straw is just perfect.

[Arfa]

Yeah, attempted this myself a couple of months ago. Completely rounded three of the bolts. Gave up in end, garage I took it to, gave a very long intake of breath too.... Got a new wheel for £25 - cheaper than labour mucking around with old seized disc and wheel. Personally - I'd just take it to a garage to begin with...

As for choice of disc, Brembo rear discs are about £80 - got mine from Demon Tweeks.

[unfazed]

Heat is your Friend when trying to undo the Disc bolts :thumbup

[dilboy]

Cheers for all the advice

[darrsi]

I measured the width of my disc earlier and it's still a bit over 4.5mm, the outer lip was 5.4mm so i think it was wider than average.


But looking at weather reports of "feeling like -4 deg" in the morning i've decided just to get the tyre changed tomorrow instead and leave the disc for a more pleasant day.


I need the tyre sorted this weekend as i'm off work, so the disc can wait for now as my mechanic's doing me a favour fitting me in, rather than it being a proper appointment.

[darrsi]

One bolt  :'( :'( :'(