Imagine my horror - cracking Magura fork

No. I was planning to sell the older Thor - before I scraped the stanchion.

Thinking about what might have caused the crack, given that the brake calliper is cast out of the same magnesium alloy would you not expect that to crack before the more substantial mount? I'm no engineer, but there's a lot less material/strength in the calliper. Would this not point to a flaw in the fork casting?

Eeek.
Be interested to see how you get on - please update us when you hear back.

wynne":2ojjk87y said:

Thinking about what might have caused the crack, given that the brake calliper is cast out of the same magnesium alloy would you not expect that to crack before the more substantial mount? I'm no engineer, but there's a lot less material/strength in the calliper. Would this not point to a flaw in the fork casting?

Click to expand...

I would tend to agree - when the sliders are cast there will be a cored hole cast into them, which is later drilled to size/tapped for the caliper mounting. It's done this way as it's stronger than casting them solid and drilling out completely. As the molten metal has flowed around these cores it has failed to properly meld with itself at the flow front and so you get what is called a "weld line", a weak point which has afterwards started to open up.
Usually caused by the mould or cores being at too low a temperature, injection being too slow, air entrapment or insufficient back pressure.

I am convinced that these cracks are not caused by any overtorque.
Looks more like stress corrosion cracking or cracks caused by material imperfections.

shouldn t there be some spacers between the mount and the forks ?

cchris2lou":n2npovk9 said:

shouldn t there be some spacers between the mount and the forks ?

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not necessarily - Formula R1,RX, Shimano, AVID XX, magura post mount callipers do not use them - the only model I know that use CPS (Caliper Positioning System = cupped washer) is Avids.

OK, got a reply from Winstanleys, from whom I bought the fork. Not great news - basically saying that I overtightened the brake bolts.
They say they have spoken with Magura UK about this and they have confirmed that this is their view.

Just wondering whether to say sod it and swap the sliders over from the other fork and be done with it? Or should I take it further? Any thoughts?

Full initial reply from Winstanleys:

Hi Richard,



Thank you for your patience while we look into the issue with the cracks on the disc mounts of your Magura Thor forks.



Having looked closer at the photos, the cracks in the magnesium lowers have been caused by over tightening of the calliper bolts which is unfortunately not covered by your warranty with us and would not be replaced free of charge.



Replacement lowers (minus stickers) are available from the suppliers at £130.56, with the forks also needing a service to swap the lowers at £93, with the forks needing to be returned to the UK suppliers of Magura for the lowers to be fitted. With the added total postage costs of £15 to add to that.



If you have any other questions before you decide how you would like to proceed, I would be happy to answer them for you.



Best Regards

Alex,



Returns & Warranty,

Winstanleys Bikes



e:returns@winstanleysbikes.co.uk

w:www.winstanleysbikes.co.uk

w:www.winstanleysbmx.com

t:01942 707646

I would certaintly escalate this [as the system admin at my school says], This doesn't seem like a overtighted bolt.

hmmmm, sounds like manufacturer/dealer trying to wheedle out - how can they prove it was the case, or indeed how can youo prove it was not? Not sure what more you can do but this repsonse i n not surprising and I bet most manufacturer's would say similar to avoid having to pay.

I'm sorry but I think Winstanley's and Magura are talking out of their arses, if the bolt hole was properly molded/tapped and you have used the correct length bolt then you can drive that in until you can't drive it any more, the only way they would split was if you were trying to force it open with a larger diameter bolt, over torquing it would not cause this problem. The mounts have split in the middle which looks as though it's a defect rather than something you have done, tell Winstanley's your going to get onto your Credit Card company informing them of this issue and let them sort it out. Contact your Card company and inform them of the situation and tell them to do a Chargeback, they'll then write to the supplier who has to defend themselves and the Credit Card company will inform you about the info passed back and forth. They may even appoint someone to independently inspect them. Forgot to add as it's a NOS Fork sold by Winstanley's chances are it no longer has a warranty with Magura, but as you've bought it as new the supplier has to provide you with a warranty, looks like Winstanley's may be trying to weedle out of this one.

Regards

Liam