How to remove seized brake disc retaining screws?

[bill888]

My 57 Jazz which is only used as a runabout doesn't do much miles.  Coming up to 16k in 12.5 years.   When I had new UniRoyal tyres fitted before Christmas, ATS reported the front pads may need attention.  When I checked the pads, the factory fitted inner facing pads were down to 4mm and the outer facing pads were 6mm.  ie. uneven pad wear on each wheel.  Discs looked in good shape apart from slight lip on the circumference.  Rear brake pads were 6mm, and discs were fine.   

I was pondering whether to change the front discs at the same time as the pads myself.

Anyway, I bought a Vessel 980 Impacta P3 x150 screwdriver from Amazon UK, and went round all 8 screws (2 per hub).  https://www.amazon.co.uk/Vessel-125943-P3x150-Impacta-Screwdriver/dp/B003BGTTSE

3 could be undone without using impact function. The remaining 5 are stubbornly seized even when the Vessel is struck with a 4lb club hammer.  WD40 didn't make any difference.

Any advice on how to remove the seized screws?

I studied a few youtube videos and suspect I'll end up having to drill them out.  Any advice on what bits to use?

Otherwise, plan 'B' is to just change the pads and check the sliding pins are okay and forget changing the discs.

ps. the JIS P3 screw bit on end of the Vessel fitted the screws perfectly.  No cam out or damage to the screw heads.  Sadly, not able to undo them.

 

[culzean]

Counter-intuitively I found that reversing the impact driver and actually trying to TIGHTEN the screw before trying to slacken it off often works.  Otherwise drilling out is the answer.  You can buy Left handed drill bits that are actually trying to unscrew the fastener as you drill it out,  and often when you get to a certain depth the screw will wind itself out.

One last tip, WD40 is not a penetrating oil, plusgas and others are.  We know that WD40 is sold like cure-all snake oil,  but it is for Water Dispersal and leaves a sticky film behind that is not a lubricant and in fact is great for attracting dirt.   WD40 is actually Water Dispersant formula 40 and was designed for electrical systems to get rid of damp.

I have actually reassembled brakes without the countersunk screws,  when you think about it the disc also has 4 x M12 studs to stop it rotating and clamping it in place.   Otherwise put copper grease on the thread and under the head of screw,  countersink screws have a nasty habit of the head binding metal to metal, it is not always the thread that is the problem.

You will also notice 2 x M8 threaded holes in the disc - sometimes discs are reluctant to come off even with screws out,  you can screw a couple of M8 bolts into the holes to 'jack' the disc away from mounting face.  And don't use petroleum based grease ( eg copper grease ) anywhere near the rubber gaiters or seals it will cause them to swell and break,  For many years now I have used this for slide pins  https://www.amazon.co.uk/TRW-PFG110-Grease/dp/B00H8ZX4F8    and have never had a caliper seize. 

[sparky Paul]

What usually works for me is a few good whacks on the face of the screw with a 2lb hammer and a large pin punch, say 8 or 10mm, before any attempt to unscrew. As Culzean says, a bit of tighten-untighten action, back and forth can sometimes help. You have to be a bit tentative, as these screws can soften over time, with the heating/cooling of the brakes.

If that fails, best thing is some heat to crack the rust bond between the screw and the hub. Even a few minutes with one of those high temperature butane torches beloved of chefs can work wonders.

If the discs measure okay for thickness, i.e. above the minimum, and are not badly scored or corroded, I wouldn't change them.

[bill888]

Thanks for all the advice so far.   

For curiosity, I did put a 8mm bolt into one of the screw holes of one of the rear discs but I don't think there is any metal to push against.  Later I checked the front hub and can see how the 8mm bolt can push against the hub.

Sadly, the Vessel screwdriver only offers impact action for unscrewing only.  In hindsight, I perhaps should have purchased a regular impact driver and JIS screw bits.

[sparky Paul]

For curiosity, I did put a 8mm bolt into one of the screw holes.  But exactly how deep should they go?   The bolt I used had 22mm length thread and didn't seem to touch the rear wheel hub when fully screwed in - I didn't investigate further as I didn't have any longer M8 bolts.

The disc securing screws only fix the disc to the hub face, and so are only short. The original screws are M6x14, so 14mm long, and you can get away with shorter ones. Any longer, and you risk fouling something.

I've got a good impact driver, but it's a bit too heavy duty to use for removing disc screws.

[bill888]

Update:

I looked at it again after an hour. The WD40 had no effect as confirmed by culzean.

I then tried a variation of Sparky Paul's suggestion which I'd seen on Youtube. 
https://youtu.be/YxQk7Pz_vfc
Update: see Sparky Paul's safety advice further down.  I wear specs, otherwise wear goggles to be safe.

I placed the ball of a large hammer against the screw and struck the other end with the 4lb club hammer a few times.  It did slightly deform the crosshead of the screw, but I then used club hammer with my Vessel screwdrdiver to reform the 'cross head' and successfully loosen all the previously seized retaining screws a few millimetres before they became difficult to turn.  I didn't try to take the screws completely out because I haven't yet bought any new brake discs - if they are even required at this time.

Thank you to all.

[culzean]

This isn't a bad impact driver,  Halfords tools are pretty good quality.
https://www.halfords.com/tools/hand-tools/screwdrivers-and-hex-keys/halfords-advanced--impact-driver-and-bits-178172.html

[sparky Paul]

I then tried a variation of Sparky Paul's suggestion which I'd seen on Youtube. 
https://youtu.be/YxQk7Pz_vfc

If anyone decides to look at that, I don't advise copying the bloke in the video. Hammers have hardened faces, and hitting one with another can cause them to chip - and the slivers of metal that shoot off can do some real eye damage.

[MicktheMonster]

I've managed in the past with the vessel impacta, on one occasion I even gave up with it, tried drilling them out, snapping drill bits, going back to the impact driver and succeeding, I did have to use ridiculous force but it always came off in the end.
The impact driver should have tighten and loosen if it's the same one I have, put it on the screw and put pressure on it, turning it clockwise to tighten, anti-clockwise to loosen and keep the pressure on as you strike it with the hammer.I
I found tighten/loosen helped free them, the key seemed to be brute force though.

[bill888]

The impacta I have looks like a regular screwdriver.  See pic below.

I thought it only 'unscrews' but I could be wrong.  Any instructions on the back of the pack are in japanese!

[Jocko]

Going by the diagram on the handle that is only designed to unscrew.

[culzean]

The impacta I have looks like a regular screwdriver.  See pic below.

I thought it only 'unscrews' but I could be wrong.  Any instructions on the back of the pack are in japanese!

For £15 get a proper impact driver like the Halfords one, I have had a 'Laser' impact driver ( which looks remarkably like the Halfords one ) for many years, because it takes 1/2" drive bits you can fit all sorts to it...including hexagon Allen bits and hex sockets.

[sparky Paul]

Those Impacta screwdrivers use the same principle as an impact driver - the clever bit is hidden inside the handle.

They only work anti-clockwise, as you would expect.

[madasafish]

I have an impact driver but for stuck screws nothing beats a small chisel with a sharpish end and a 2lb hammer.
 Engage the chisel with the screw hole  and with part of the chisel end on the flat surface on the screw outside . Hammer chisel gently in direction of undoing screw trying to cut into flat surface of screw.
When achieved, hammer chisel hard as a lever to unscrew screw..

Works well.

Judicious blow lamp and penetrating oil helps as well to break rust

[MicktheMonster]

That is the same driver I have, apologies, I was under the impression it tightened as well, but as you say, the instructions are in Japanese.
It has worked for me on 3 sets of discs so far, every time it was a struggle and I can't stress enough how hard you need to hit it, and keep on hitting it.