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GR STi - PST Carbon Fiber Driveshaft Review

INSTALLATION TIPS

No instructions came with the item which would have helped with some post-installation concerns I had. However, the install is pretty straight forward.

You can solo this install with a set of jackstands, but having a car lift and a buddy would help out big time. I did it solo with jackstands.

You need to remove the mid-pipe heat shield, driveshaft brace (located near the middle of the shaft) and the 4 bolts connecting the shaft to the rear diff. As an option, you can remove the mid-pipe, it would make removing/installing the driveshafts easier, but not necessary.

Remove in the following order if you are doing it solo: heat shield, 4 rear diff bolts and then the support bracket. Keeping the support bracket on till the end will give you insurance that the driveshaft won’t come falling on your exhaust system, or worse, your face. This is where a second set of hands would help.

When dealing with the 4 bolts that connect the shaft to the rear diff, space is tight. I wasn’t able to use a standard socket and an open ended wrench wasn’t long enough to get the leverage needed to break the rusted bolts free. In the end, I was successful with a combination of a crows foot wrench on my 24” breaker bar. Work on 2 bolts, spin shaft to get access to remaining bolts and remove those. Use the handbrake to keep the shaft from spinning too much while you are breaking the nuts.

When installing the PST front spline into the front transmission, slightly rotate the shaft while pushing the spline in to find the right alignment. Do NOT insert the the spline in all the way. Just enough for you to connect the rear u-joint to the rear diff.

The bolts that hold the shaft and the diff together have a circular head with a flat part (see pic). That flat part is meant sit right up against the u-joint of the stock shaft, this contact prevents the bolt from spinning when tightening or loosening the nut on the other end. The PST shaft’s u-joint is smaller than the stock so the flat portion of the bolt head does NOT seat up against the u-joint (see pic). This means the bolt will spin while you try and tighten the nut down to 22.9 ft.lbs of torque. To remedy this, I stuck a large flat head screw diver in the space while tightening the nut to proper torque specs.





You do not need to use the stock driveshaft brace.

When it is all installed, you will notice that the front spline does not completely fit into the front tranny and that half of it is exposed. This is where an included set of install instructions would have came in handy. After confirming with a couple of other members on the board, this is normal. It allows the shaft some telescoping action between the front and rear axles. It looks like the shaft is too “short” (see pic), but it makes sense that it needs to be able to slide in and out based on independent movement between the front and rear axles. I didn’t notice this exposed spline with the stock driveshaft because the stocker has a thin steel tube protecting this exposed part making it hidden at quick glance.




PREFORMANCE

In a nutshell: SMOOTH.

Gone are the jerky launches if your were not perfect with your clutch release. It is probably because the nature of the carbon fibre material allows more twisting action than still or aluminum material counterparts. This twisting action not only gives you smoother launches, but also helps save other transmission-connected components from high horsepower/torque setups. BTW this shaft is rated at a ridiculous 2700 ft.lbs. (I read that somewhere, can’t find link to back it up tho).

She revs faster. I also noticed that my engine has an easier time to get up to speed from a stop. It feels like it takes less effort, which makes sense since you shaved off about half the weight of the stock driveshaft (~28 lbs vs ~14 lbs). Is it a neck snapping difference? No. Don’t expect to be thrown back into your seat from the improved acceleration after this mod. Having said that, you will probably get used to the new and improved acceleration very soon and forget that you even done this mod.

On the opposite end of acceleration, deceleration from downshifting has changed. I find the car doesn't slow down as fast as it did with the stock driveshaft. Not a huge difference, but noticeable.

There is no change in NVH. At least for me.

CONCLUSION

Is this mod for you? Well for most, considering the price, no.

But if you are at a point in your mod path where you are happy with your power/torque and looking to free up some of the horses wasted on turning heavy drivetrain components, then yes. Maybe you are looking to go for big power soon and are prepping the rest of the supporting cast to handle it. Then yes, again. If you are looking to reduce weight in your car, then starting with the drivetrain components is a good idea as it benefits the overall weight of the car as well as creating a more efficient drivetrain. Two birds. One expensive stone.

If you haven't done your standard air intake, exhaust, custom tune set of mods, stay away from this one for the time being. Your money is better spent on those things first and you will see a more drastic difference in your car's behavior.

Currently I'm am concentrating my next set of mods on reducing weight from the drivetrain. About a week ago I installed a set of GFB underdriven pulleys. Now I've done the driveshaft. Next up I'm looking at wheels and a street-friendly flywheel. All this in preparation for my next jump in power.


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Overall good (and reasonable!) review :)

One thing - I'm not convinced there is enough twisting going occurring in any normal start to feel it. I'm pretty sure the difference you feel if from eliminating play in the OEM center U-joint carrier, andI expect that people with older cars with more wear notice more of a difference.

(If you could feel the twist in a normal start, imagine how much twisting would have to occur during a launch in a car that produces 600+ awhp - I think it would look like a rubber band :) )
 

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Oh man...

I was worried about this upgrade for a number of reason (harshness, install difficulty, drivability), but your post helped me greatly pull the trigger and I'm so glad I did! I know many people downplay, or say this isn't worth the money, etc... but I can tell you from my experience; one of the best mods I have ever done on a car. If I had 1 word to describe this upgrade... BUTTER.

The IAG AOS install the following day, on the other hand... :crying:


Great post, great upgrade, 9/10 would bang!:tup:
 

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Oh man...



I was worried about this upgrade for a number of reason (harshness, install difficulty, drivability), but your post helped me greatly pull the trigger and I'm so glad I did! I know many people downplay, or say this isn't worth the money, etc... but I can tell you from my experience; one of the best mods I have ever done on a car. If I had 1 word to describe this upgrade... BUTTER.



The IAG AOS install the following day, on the other hand... :crying:





Great post, great upgrade, 9/10 would bang!:tup:


I'm glad I could help you out with your shaft.

Sorry, this particular car part lends itself to well with sexual innuendos. It practically writes itself.

In all seriousness, did you solo the install? How did you keep the bolt heads from spinning on you? And lastly, how much of the front spline was exposed after everything was tightened down?


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Oh man...



I was worried about this upgrade for a number of reason (harshness, install difficulty, drivability), but your post helped me greatly pull the trigger and I'm so glad I did! I know many people downplay, or say this isn't worth the money, etc... but I can tell you from my experience; one of the best mods I have ever done on a car. If I had 1 word to describe this upgrade... BUTTER.



The IAG AOS install the following day, on the other hand... :crying:





Great post, great upgrade, 9/10 would bang!:tup:


I know the feels on the AOS too. But it's not as bad as the turbo inlet. That was a bitch.


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Nice write up!

I ran a light weight crank pulley on an n/a Saabaru & a LWFW on my 05 LGT in cars past. Lol

I imagine this has a, more drastic, but similar feel to the change in load on the engine. I had fun with both. I didn't do the flywheel in my STi when I did my clutch. Not sure this is a mod for me but I may look into it down the road as this car becomes more of a track toy.
 

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Nice write up!

I ran a light weight crank pulley on an n/a Saabaru & a LWFW on my 05 LGT in cars past. Lol

I imagine this has a, more drastic, but similar feel to the change in load on the engine. I had fun with both. I didn't do the flywheel in my STi when I did my clutch. Not sure this is a mod for me but I may look into it down the road as this car becomes more of a track toy.
I'm on a mission to lighten up my drivetrain as much as possible. So far I have GFB pulley kit,
ACT Streetlite Flywheel, Competition Clutch (lighter than stock), and PST CF driveshaft.

All I need are 2-piece rotors and the lightest 18" wheels and I will be able to spin my entire drive train with my thumb and index finger. lol.
 

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Sounds ideal! No issues with the LWFW and CP? By pulley kit I assume you mean that and replacement alternator pulley?


No issues yet. I heard about the misfire issue.

Pulley kit included the crank, alternator, and power steering. All under driven and requiring a smaller belt (which it came with).

Girodisc front and rear on the horizon.

I don't want to, but the lightest wheels in 18s, looks like the RPF1s. Nothing against them. Just not my style.


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I agree! I have this shaft with my volks and in my case, It was night and day for me. I could break lose easily in 1st and 2nd feels like it's on the edge in corners. This was done on a stage 1 sti. With the OEM it didn't feel as eager to kick out. I went from Stock STI wheel with conti DWS to RE30 and PSS. Traction shouldn't be an issue here haha.
 

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Shouldn't downshifting work better as well?
After all, you're decelerating less mass after the tranny.
Did you add a carbon fibre crankshaft too, or lose a few points in compression somewhere along the way?
 

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When you're down shifting you use engine braking to slow the mass of the car and the rotational mass of the entire drive train.
With a CF shaft, you're reducing the rotational mass of the drive train.

Ergo, engine braking should be improved exactly the same way that acceleration of the drive train is improved.
 

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Looking to pick this up for my 05' STi... Figure why not.

Looking to see how it still is for your vehicle? How has it held up?

I saw the process they use to balance the shafts but it still worries me about putting it on the car and or having it not be balanced (is that possible, and if so what do you do?).

I don't drive the STi a lot but honestly this looks like a fun little mod that's pretty easy to install... just seeing for an update. Everyone is quick to say they love it but then years down the road really tell it for me.

I've read several reviews now on people saying they've gone through two of the PST cf drive shafts because they were not balanced right or caused the car to sound/feel like an airplane. Wobble..etc.

Did you have to bang on the tranny tunnel to make it fit? I keep seeing that here and there as well..

Thanks,
-Nigel
 
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