SlotForum banner rear wheel grub screws too tight

2759 Views 34 Replies 21 Participants Last post by  Martyn_
I've just bought a new Audi R8C (CA12C) which has had its rear wheel grub screws over-tightened in the factory. I've ruined three new allen keys trying to loosen the screws, only have two undamaged allen keys left and don't want to ruin those. I need to loosen the grub screws to reposition the rear wheels, which have been fixed too far inboard at manufacture.

I've tried alternately gently heating and cooling the axle and wheel assembly, which succeeded in loosening one screw, but the other is still jammed tight. Any ideas how to undo it?
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Thanks for all your suggestions, gentlemen. Problem now solved.

Repeated heating/cooling cycles didn't work, nor did penetrating oil.
I don't own a hardened allen wrench (nor do I feel that one should be necessary. The provided wrench should last long enough for at least one use and/or the screws should be properly tightened at the point of manufacture)
Returning the car was an option I considered and dismissed, because 1) I fixed the problem, and 2) I bought if from the eBay seller theslotoutlet, whose customer service when it comes to returns is poor (I know. I've returned three cars to them in the past and have always been left out of pocket)

The fix was to remove the wheel insert and, using a drift, hammer the axle out of the wheel.

I can't help wondering why don't produce their axles with small flats on each end, which would increase the efficiency of a grub screw tenfold, with the added bonus that the screws could be tightened to a lower torque. It would result in fewer damaged allen wrenches and screws, more reliable location and it probably wouldn't cost a fortune either. How about it,
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QUOTE (snurfen @ 17 Sep 2012, 16:51) <{POST_SNAPBACK}>And I'd probably not be using that eBay seller if I'd been left out of pocket by them on three occasions!
Glad to see all sorted now, have you tried grinding a flat on the axle yet?
It's the same old eBay story and my own fault for chasing bargains: bargain hunter suffers a bad experience and resolves not to use the seller again, but their continuing low prices break my resolve and I buy from them again.

I know the risks of buying from this seller and take them into account when bidding on the auctions. (Note to anyone still interested in buying a new Audi R8C for £29.99: bid at the opening bid on theslotoutlet's auctions and bid no higher. Most times you'll be given a second chance offer at your opening bid, which also then counts as a buy-it-now purchase, not an auction purchase, which gives you greater consumer protection and, in theory, you should not have to pay the cost of returns, as you do with auctions. It's theslotoutlet's refusal to reimburse return p/p that has left me out of pocket.)

I haven't tried grinding a flat yet. I'll try it later and let you know how it works.
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QUOTE ( @ 18 Sep 2012, 08:59) <{POST_SNAPBACK}>A bigger grub screw is two to three times as heavy, thus creates much more vibration when spun at high rev. It is a noticeable difference.
I agree, and the balance issue is yet another reason to consider manufacturing your axles with flats on each end. I'm making an assumption (always a dangerous thing and I could be wrong) that the grub screw weighs more than the amount of alloy removed when the screw hole is cut, thus rendering the wheel/screw combination unbalanced. Adding an axle flat will; 1) move the grub screw marginally closer to the centre of rotation, reducing vibration (although possibly almost imperceptibly), 2) The localised loss of axle weight caused by grinding a flat goes someway to offsetting the added weight of the grub screw, again reducing vibration. My maths isn't good enough to calculate the forces involved at high revs, but the improvements should be easy to prove for someone who knows the equations, and 3) you could advertise your axle assemblies as "dynamically balanced", which would, I'm sure, be a hit with many buyers.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>Heating up light alloy and metals will cause the material to expand faster than the bolt and thus crush the bolt in tighter and even ruin the internal thread.
Response 1: Bingo. That's the reason for using a heat/cool/heat/cool cycle; the different rates of expansion can sometimes free the bolt.
Response 2: What? The alloy expands faster than the steel so will crush the steel? How does that logic work? If you're in any doubt and have access to a photo editing program (or a magnifying glass), photograph a wheel and enlarge the picture slightly to replicate the effect of heat expansion. The grub screw hole gets bigger, not smaller.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>You have also probably already stripped out the hex bolt hole.
Nope. Not everyone is a ham-fisted ape. Even if I was, the tool isn't hard enough to damage warm chocolate, let alone a grub screw.

QUOTE (Screwneck @ 18 Sep 2012, 06:07) <{POST_SNAPBACK}>use WD40 penetrating spray or 3-in-1 oil. A tiny drop in the bolt hole is all you need.
That didn't work.
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I'm astonished that this thread has reached a third page. What started as a simple request for ideas for loosening factory overtightened grub screws has clearly hit a chord with many users who have expressed varying degrees of dissatisfaction and frustration with's grub screws and tools.

Personally this is the one and only time I've had a problem with them. I'm satisfied that it was a fault of the factory and not an inherent design or quality flaw, but the volume of responses does suggest that not everyone is entirely happy.

QUOTE (Screwneck @ 19 Sep 2012, 06:42) <{POST_SNAPBACK}>2. Thanks Dopamine. You obviously know what you're doing and you must be 100% correct on all counts, so carry on regardless of what you clearly see is rubbish advice! But if you are right on all counts, how come you can't get the bolts to move?
You're welcome Screwneck. It won't come as any surprise to you that I consider most of your pearls of wisdom and "advice" to be utter BS and thoroughly misleading for those new to the hobby.

As stated, the screws were overtightened in the factory. I could easily have moved them by hitting them with a hammer, using dynamite, cutting a slot for a screwdriver (a sensible suggestion but a last resort) and many other methods that caused irreparable damage, but I chose not to. Instead someone suggested knocking the axle out of the hub. That worked perfectly and the car is now happily purring around my track, still using the original grub screw and hub, with no damage done.
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