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Discussion Starter · #1 ·
I would make a poll but I don't know how to and I don't think that many people would have responded anyway.

Here's my dilemma, I have a pst carbon fiber drive shaft, three weeks ago the epoxy that holds the flange that connects to the differential to the CF shaft failed and i was left stranded. I sent the DS in to PST and they bored it out, gave me a new flange, epoxied it and sent it back to me after torque testing it to 1000ft/lbs.

I reinstall it Wednesday and come Sunday I decide to go out for some canyon runs, long story short after a brief rest stop the DS lets go again. This time it’s the slip yolk to DS epoxy that failed. I was stranded out in the mountains with no reception for 3 hours before I was able to contact a tow truck and get back.

I talked to PST today and they offered to either fix it again or, I can send them mine and pay for shipping both ways and they will make me an aluminum one, but they will probably use the lower grade aluminum. The drive shaft is 2 years old but it only has maybe 10k miles on it, if that.

I’m not sure what to do because the aluminum one weighs a couple of pounds more according to them and new they range from $230-$430, whereas I had paid $900 for mine when I bought it. I don’t want to run into the same problems but I don’t want an inferior product either.

I’d also like to repeat that they torque tested it to 1000lb/ft and they said it passed; my cobra makes 315lb/ft at the wheels.

Any suggestions?
 

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Any high heat areas nearby possibly causing the epoxy to fail? Are they doing any kind of analysis to figure out why they are having failures?
 

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I would think after 2 failures your mind would be made up. I think I would go with the aluminum and be done with it. just my 2 cents. I would be interested to know if anyone else has run into these issues. And I would like to know how many people actually run this same d/s on the street all the time. That way it would rule out everyday use vs just strip or road coarse only.
 

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I would have the yoke fixed on the Carbon Fiber DS. No way would I accept an aluminum DS as a replacement.
 

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simple, have the one your bought fixed, and ebay the f-er, get a new aluminum one, and pocket the difference.
 

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Discussion Starter · #6 ·
elyrain- the problem is the difference isn't much. They told me my new aluminum one would be a 450-550 dollar drive shaft, and i heard that the carbon fiber one i have now is worth about the same price. Mine has steel yolks/flanges while the new one will have aluminum.

Venomous Cobra- Its nothing really different then what you would see on the underside of a IRS SN-95 chassis car. I do have the FR500 exhaust which has another X right by the differential but its actually on the other side of the diff.

I know after two times my mind should be made up but accepting something that is advertised as lower quality is kinda hard to swallow.
 

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Discussion Starter · #8 ·
I have a 99 Cobra with most boltons, and suspension. It has alot of modifications that contribute to open track racing but none of that should have any impact on the driveshaft failing. The first time when the flange went and they asked if there was any excessive heat around it i though maybe the second x crossover from the FR500 catback might have caused some damage, eventhough i highly doubt it, but this time with the slip yoke connection going bad it makes no sense what so ever.
 

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This scares me. I have had a PST for a year now and no problems yet on a DD. The only problem with selling it on ebay/forums is if the buyer buys it, installs it and a week later it fails again than its going to be hell on the seller. I went from an aluminum one to the PST and its right at 12% lighter. Not sure if any of this helps. I would ask for a brand new one from PST.
 

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We use PST carbon fiber driveshafts in all of our 2000HP applications and have never had a failure.

Our concerns would be:

Nearby heat source
Chemicals leaking onto the shaft
Incorrect shaft length (yolk bottoming in transmission during max suspension travel)

Good Luck, hope you figure it out!

MMR
 

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So with the steel ones being heavier, would the weight of them cause a breaking point?
Could you switch to aluminum yokes?
I thought about this last night as well- Carbon shafts are possibly more for track cars, brief running time. Unlike the aluminum would be better for street.
Even more so- the steel yokes and street driving would allow the carbon to weaken via the weaves stretching. then a bump in the road just enough angle for the yokes to seperate the rest of the heat soaked areas.
Me- buy an aluminum shaft, have the cf repaired. Install the aluminum one for street driving, Save the cf for the track days.
 

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Discussion Starter · #12 ·
MMR - I've already addressed the heat source, its a 99 cobra, i don't have a torch lit at all times directed to the shaft or the ends what heat source could there be. I already said i have the extra x crossover due to the FR500 exhaust but its not even on the driveshaft side of the differential.

I have had an oil leak before from my canton oil pan but there was no evidence what so ever of saturation on the driveshaft. Realistically how would the oil even soak into the shaft when its spinning, i don't think its possible.

As for the wrong length, anythings possible, i ordered one for 99 cobra and this is what i got. Given now i have a 3650 instead of a t45, and maybe the lengths are different, but besides that i don't see the slip yolk bottoming out anywhere.

When i bought the 3650 i was told its the exact same length as the t-45 so i don't think thats the problem, the first time it failed on me i was driving 15mph on sunset blvd, the second time i was just starting out in first, rolling into it. Basically there wasn't much of any suspension travel at those times.

Also they don't want to give me back my carbon fiber driveshaft.

I don't want to bash or belittle PST, i'm not saying this is common of all their driveshafts as they have held up perfectly for MMR but i just don't understand why mine keeps taking a dump.
 

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I'd make them repair the one that failed. You paid for it. It shouldn't have failed, and it's on them for whatever is wrong with it. If they really want to solve the problem they'd eat the cost and give you a new one if they really think it's something wrong with the shaft itself.
 

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MMR - I've already addressed the heat source, its a 99 cobra, i don't have a torch lit at all times directed to the shaft or the ends what heat source could there be. I already said i have the extra x crossover due to the FR500 exhaust but its not even on the driveshaft side of the differential.

I have had an oil leak before from my canton oil pan but there was no evidence what so ever of saturation on the driveshaft. Realistically how would the oil even soak into the shaft when its spinning, i don't think its possible.

As for the wrong length, anythings possible, i ordered one for 99 cobra and this is what i got. Given now i have a 3650 instead of a t45, and maybe the lengths are different, but besides that i don't see the slip yolk bottoming out anywhere.

When i bought the 3650 i was told its the exact same length as the t-45 so i don't think thats the problem, the first time it failed on me i was driving 15mph on sunset blvd, the second time i was just starting out in first, rolling into it. Basically there wasn't much of any suspension travel at those times.

Also they don't want to give me back my carbon fiber driveshaft.

I don't want to bash or belittle PST, i'm not saying this is common of all their driveshafts as they have held up perfectly for MMR but i just don't understand why mine keeps taking a dump.
Gotcha.. If you look under the car at the yolk do you see any of the shaft/yolk showing or is is butted against the seal?

MMR
 

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Discussion Starter · #15 ·
Gotcha.. If you look under the car at the yolk do you see any of the shaft/yolk showing or is is butted against the seal?

MMR
I sent the shaft out yesterday so i'm not 100% sure, but from what i remember there was a section about 3/4'' sticking out of the tail shaft.

Maybe it was wrong from the beginning and it finally failed, because i had noticed that the slip yolk had a grove instead of 2 splines, as if to align it onto the output shaft but there is no such thing on the trans.
 

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Hmm, maybe hard to tell now, with the history of the shaft I am sure PST will double check everything on their end, when you get it back maybe take a pic so that we can make sure that is not the problem. Good luck with it, please let us know how we can help!

MMR
 

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Discussion Starter · #17 ·
Hmm, maybe hard to tell now, with the history of the shaft I am sure PST will double check everything on their end, when you get it back maybe take a pic so that we can make sure that is not the problem. Good luck with it, please let us know how we can help!

MMR
They did double check everything when i got it back last wednesday for the flange side breaking. They said they repaired that end, waited a day and torque tested the drive shaft. I installed it on wednesday and my first drive out on sunday it failed.

And i most probably won't ever get my CF shaft back.

Does anyone have a measurement from the output shaft of the trans to the flange on the differential? They told me to give them that measurement so they can build a new one as they didn't want to go off the old one for some reason.

I'm to lazy to put it back up on jack stands.

Thanks for all the input guys
 

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.

Does anyone have a measurement from the output shaft of the trans to the flange on the differential? They told me to give them that measurement so they can build a new one as they didn't want to go off the old one for some reason.

I'm to lazy to put it back up on jack stands.
If I were you I'd go measure and give them your exact measurement. Giving them a measurement from another car isn't a good idea considering the problems you've had.

Odds are they're all the same, but for peace of mind sake, I'd measure it.
 

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With a 99 Cobra there is no suspension movement to affect the drive shaft. It's an IRS and the differential doesn't move so it can't be the drive shaft bottoming out in the tranny due to suspension movement.
 

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With a 99 Cobra there is no suspension movement to affect the drive shaft. It's an IRS and the differential doesn't move so it can't be the drive shaft bottoming out in the tranny due to suspension movement.
Not true, you are assuming that a engine that is rubber mounted and a IRS center section that is rubber mounted along with a unibody construction has no movement??? If the yolk was bottomed out this would break the driveshaft every time. Yes, this is a small amount of movement but if the yolk is bottomed out it doesnt take much.
 
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