Question about drive shafts
- Thread starter Alin
- Start date
The U-joint and hanger bearing in the middle can go bad, i.e. have a lot of play in it. In the most extreme cases, it can break and then reeeeaallly bad things happen as I'm sure you can imagine. :lol: But otherwise, if the older drive shaft is in good shape then I don't think a new OEM shaft would be any better per se.
If you are thinking about replacing the driveshaft, seriously consider an aftermarket one-piece. I know they are expensive, but I think it's worth it. Aluminum shafts can often handle more power and higher speeds than a carbon fiber shaft, but I highly doubt you'd get close to the horsepower and speed limits (850whp/180mph) of a CF shaft. Also, many aluminum shafts are so much larger in diameter that the driveshaft tunnel needs to be modified (beaten to death with a hand sledge) in order to fit without rubbing. So for me, the only reasonable option is a one-piece CF shaft if you choose to replace the OEM unit.
Jordan @Defined Performance probably still carries the Driveshaft Shop one-piece Carbon Fiber units. That's where I got mine.
If you are thinking about replacing the driveshaft, seriously consider an aftermarket one-piece. I know they are expensive, but I think it's worth it. Aluminum shafts can often handle more power and higher speeds than a carbon fiber shaft, but I highly doubt you'd get close to the horsepower and speed limits (850whp/180mph) of a CF shaft. Also, many aluminum shafts are so much larger in diameter that the driveshaft tunnel needs to be modified (beaten to death with a hand sledge) in order to fit without rubbing. So for me, the only reasonable option is a one-piece CF shaft if you choose to replace the OEM unit.
Jordan @Defined Performance probably still carries the Driveshaft Shop one-piece Carbon Fiber units. That's where I got mine.
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Carbon drive shaft and ligjt weight subframe are on my cars wish list. I just hope I get them before they become discontinued and super hard to find.
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Grinder34
Track Monkey
CF driveshaft is definitely cool. To bring a bit of rigor to the discussion, it does have one drawback: it raises the CG of the car. Probably not by much, but its another data point for you.
Which lightweight subframe? I ditched mine altogether since the stock one is super heavy and adds virtually 0 rigidity.
Unlike a driveshaft, you should be able to fab one yourself with a bit of welding experience. Same thing applies, though, it raises your car's CG.
Grinder34
Track Monkey
Probably not enough to matter? I thought there was more weight savings, but it says it's half the weight at ~12 lbs. So 12 lbs off the bottom is kinda negligible compared to ~3,000 lbs.
I think the U-brace is another 25lbs? So 37 lbs total. ~1/100th the car weight removed, right at the bottom. Not sure it would add up enough to make a difference, but the CG will move up. The driveshaft will move the CG forward, the U-brace, move it backwards, so lets call it offsetting.
Do you think the subframe adds any safety aspect though. I know it dosen't help with the rigidity of the car but always figured replacing it would be a better safer option compared too removing it.
The reason I want a carbon fiber drive shaft is really more for the lighter rotating mass to allow for faster revs.
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Grinder34
Track Monkey
IIRC, there is a safety aspect. Something about directing the engine in a crash. I believe (with 0 evidence, just logic) that any aftermarket subframe will totally eliminate the "safety" aspect as they have closed in what was left open by the engineers. Sure, it'll add rigidity, but I just cant see it having the same "benefit" in impact testing.
As for faster revs... Since the driveshaft is rather compact radially, without much mass (low moment of inertia) you're really not using that much force to accelerate it. All the spinny things add up, such as 4x wheels, 4x rotors, flywheel, clutch, crankshaft, pistons, etc... But I bet the moment of inertia of ONE wheel is about the same as that of the whole driveshaft.
What do you really mean rev faster? Like rev faster in neutral...the driveshaft's not spinning when the clutch is engaged. Faster to redline in first? Most of the work is accelerating the weight of the car, vs spinning the driveshaft and wheels.
You really will rev faster (in gear of course, going down the road) and reach redline faster with a CF driveshaft. I can personally attest to that. In fact, I had to move my shift point alarm down 1k rpms to avoid slamming the rev limiter after installing it. Especially in 1st and 2nd gear, you're at 7,000 rpms so fast, your head will spin.
Another nice thing about CF shafts is that they flex ever so slightly. This is helpful when you are making a lot of power and drag racing the car hard. Some people that are making a ton of power and were breaking axles on a hard launch have stopped breaking axles after installing a CF shaft with no other modification or changes to the way they were launching the car.
Another nice thing about CF shafts is that they flex ever so slightly. This is helpful when you are making a lot of power and drag racing the car hard. Some people that are making a ton of power and were breaking axles on a hard launch have stopped breaking axles after installing a CF shaft with no other modification or changes to the way they were launching the car.
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Grinder34
Track Monkey
Is there a proven decrease in 0-60 time, or say 5-60 time (to eliminate the launch variable)? I'd expect it to go down, but by thousandths of a second...
[MENTION=652]Grinder34[/MENTION] the personal feedback I've had from two true d's with c.f. drive shafts pretty much said the driving characteristics are completely changed. Quicker revs thru out the gears, faster acceleration out of the twisties and better response when rev matching shifts.
The personal feedback of the friends is why I want and will eventually our base one since they said it's one of the mods that made the largest impact on driving characteristics.
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The personal feedback of the friends is why I want and will eventually our base one since they said it's one of the mods that made the largest impact on driving characteristics.
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Proven? Not that I'm aware of, although I'd imagine that someone has performed a scientific test and recorded data.
From what my butt-dyno tells me, there is definitely improved acceleration, although I would bet that it's only in tenths or hundredths of seconds.
Alin
Diehard Car Enthusiast!
How much modification is needed to the tunnel? If I can get this for $250, would it be worth it?
04-07 STI Aluminum driveshaft
https://forums.nasioc.com/forums/showthread.php?t=2853848
04-07 STI Aluminum driveshaft
https://forums.nasioc.com/forums/showthread.php?t=2853848
Not sure. I've seen a couple videos of people making the large aluminum ones fit. I don't remember specifically what all needs done, but I do remember a ridiculous amount of pounding with a hand sledge. It made me cringe, to be honest. I'm sure you can find a video on YouTube or a DIY somewhere.
Another thing to consider is C.F. drive shafts shatter in a bad wreck compared to a one piece aluminum drive shaft.
If you ever seen photos of a drive shaft that came up thru the floor plan you'll know why this is a good safety feature.
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If you ever seen photos of a drive shaft that came up thru the floor plan you'll know why this is a good safety feature.
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