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Rip Driveshaft


WallerZ

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So, here is the latest picture of my car.

 

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"What a strange and dangerous place to park for a photo?!" I hear you say? Well...it was not by choice.....

 

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Ah. Well. I'm sure that used to be attached to something.....

 

Far from ideal. Inside lane on the A444 and M6 roundabout in the dark, with speeding cars, tired truckers and general muppets on the road. Needless to say, hazards were on and I was 10m up the road warning road users of my predicament!

 

Thankfully, Gaz lives round the corner and was able to come rescue me with a tow rope, again. Big thanks to Gaz!

Here are some more photos of the issue....

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So there we have it, a snapped driveshaft....anyone done that in their Zero before?!

I have already made my own conclusions on the matter however I have requested some further information from GBS (long shot I know) with regards to the process that goes into manufacturing these. As you can clearly see, this is two different shafts friction welded together (which is common for shafts) however having spoken with a driveshaft specialist, they find it hard to see if it has been friction welded properly and suggested it was a single shaft that has a step. As I know the MX5 shafts are not stepped and there are 2 diameters depending on the car, plus GBS having the shafts to "modify" under cloak and dagger, it was disregarded and refocused on the friction weld. Common shaft failures from friction welds occur 3-4mm away from the weld in the weakened HAZ (Heat Affected Zone) from the welding process. To see one fail so cleanly on the weld raised concerns over the original weld, hence the required information from GBS. Initial viewing by eye says the outside failed (potentially due to the weld quality) which caused the centre to fatigue due to the reduced diameter and torsional movement of the shaft. As such, this polished the outside faces and left the centre to break. I'm hoping to squeeze in some time with the Metallurgy expert at work to confirm under a microscope the likely series of events and during that time I hope to at least open some discussion with GBS...other than their usual "out of warranty" statement when things go wrong....I'll keep you posted on those fronts....

It will not however keep me down. Plans are already in motion to get the car back up and running, avoiding the GBS option and a recurrence of this failure (I like to make my own problems!). Watch this space!

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Do GBS actually make them? Don't they just take them off a donor (if you didn't do that yourself?) and hand them over? That's what they did for my Ford driveshafts, which don't have a step in them.

 

I'd be pretty concerned if something as important as the drive shaft was welded together in the middle, or is that common? Doesn't seem right for something that has to resist a twisting force...

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Do GBS actually make them? Don't they just take them off a donor (if you didn't do that yourself?) and hand them over? That's what they did for my Ford driveshafts, which don't have a step in them.

 

I'd be pretty concerned if something as important as the drive shaft was welded together in the middle, or is that common? Doesn't seem right for something that has to resist a twisting force...

They will take your donor ones in, refurb and modify them (no details every given on what modify means) then handed back with a hefty bill and away you go. Its common for shafts to be friction welded like this, and I have on good authority, that it is usually more than suitable for our needs.

 

 

 

If it was a solid rod with step-down in diameter all the twisting force would tend to be concentrated at the point of step. If solid would have faired better with a tapered reduction in diameter. IMO.

Yep, it is a solid bar with continuous diameter in standard form. As such this change probably had a role to play in this failure. Having a vague understanding of the way GBS work, I believe they would have sent a batch of shafts off to a supplier to modify,(I do not believe they possess this ability in house - or certainly didn't when I visited during my kit purchase/build) who will have produced finished products from the batch they were given, hence the different diameters and therefore a step. Make of that what you will.....

Edited by WallerZ
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I had new shafts made for my Mazda build, rated to 600 hp. Never liked the idea of friction weld of driveline parts. Especially for your V6, it would be the way to go. Supposedly the inner hubs are not removable/replaceable but this is not true and can get you YouTube links for 'how-to' if needed. Speaking of the clip-in type, not sure of the bolt on hubs. Car is not on the road yet so no actual road experience.

 

When that let loose must have caused quite a racket. Any damage to the chassis? Glad your still at it. ^_^

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I can now confirm Nelmo that in the MX5, the diff is slightly offset due to the PPF (Power Plant Frame) which is taken up in the diff with different stub axles in the diff. This allows the driveshafts to be common on the MX5. GBS however have mounted the diff centrally to aid balance and allow space in the trans tunnel (how many of us would be concerned with a prop flange offset when building lol?!) Hence the modified shafts. As Richard confirms, it would appear the Ford set up was central already so no modification required.

Marlin, I have it from 2 shaft specialists that it is the common choice for shaft modification and with my set up, I should not have seen the weld fail like that. I have been quoted a price for a set of new custom, single bar shafts which sadly are waaaay overrated for my needs or even future needs. I'm sure the chassis would go before they did! :rofl:
It did indeed. It was one hell of a bang! Felt it through the car. Luckily it quickly found its place on the lower wishbone and sat there rotating happily lol. No obvious damage at all thankfully.

In other news, I have spoken with GBS and they are going to swap for a replacement so they can also investigate why this has failed. This is news to them so hopefully an isolated incident. My money is on the modified shaft being stepped, adding a further stress point to the weld which has subsequently let go. Hopefully the new shaft is all the same diameter :good:

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Isolated incident ? How many mx5 zeros are there on the rd ? At a guess not many. Further more would you trust one of there shafts again? I wouldn't, i.d be getting it made by a professional company, for peace of mind if nothing else....

Well I've definitely not seen another lol. Unfortunately there isn't a register of Mazda Zeros with how many miles each has done however as one of the first built and used as a daily for 9 months, I'd put it up there...

 

To be honest though, logic is saying the difference in shaft diameters, hence a step, has created a stress hot spot which has finally given up. Equally the weld should have held or meant the shaft broke before the weld, so again, failure could have come from the process. Eitherway, I have a containment in place to ensure I don't lose more summer (or whats left), I need to test it but it has been approved as an acceptable alternative to friction welding. Hopefully I make the West Mids meet tonight with it haha. I may throw the replacement in whenever it arrives, I may not. A custom shaft elsewhere is an avenue I am exploring though as I doubt GBS have a guarantee on what these shafts can take.

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GBS are very good when dealing with these situations, I would trust them.

As its something that shouldn't have failed I shall try a replacement presuming the failure was due to the step in the shaft (which shouldn't have been there) and all being well, the replacement works perfect. Sure its not ideal but it happens and so far GBS have done exactly what I'd hope they would rather than what I feared they would do.....

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