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Discussion Starter #1
I have a 2017 sti and considering a carbon fiber driveshaft. Anyone install and have positive reviews or any issues? If so what brand?
 

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I have a PST carbon fiber DS on my 17 STI. It went in easy with my brothers help. About an hour to do. A favorite and well worth it upgrade IMO. The car just drives and performs better.

The other consideration was Drive Shaft Shop. Didn't go that way because you have to drill out the holes on the rear coupler for larger bolts. Some people run the stock smaller size bolts, but that wasn’t for me and I didn’t want to have to put in the effort to get them properly drilled straight.

Both make good quality products.
 

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One of the few mods you can do that has no downside. That said its a small difference for a significant amount of money. I would buy another Drive shaft shopp part - and I like they fact they they bother to tell you that for higher power upgrading the bolts is a good idea :) Drilling a few holes is one of the easier things you can do in a mod . . . sure most of us will never get that high though more and more of us are. But worrying about four drilled holes? Not me.
 

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I did DSS, didn't drill out holes, just centered the shaft and bolted it down...amazing upgrade in driveability overall!!!
 

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I have a 2015 STi and also went with the PST carbon fiber DS for the main reason not to drill out the holes. Been on the car now for 3 years and ZERO issues. Easy install, will loose a little transmission gear oil but just lift the rear end up more than the front and should help in the loss of fluid. Great upgrade in daily driving with smoother acc. and shifting and a lot less sloppy play when in 1st gear in stop and go traffic. I agree with mheyman in "small difference for a significant amount of money" but worth it at the same time, at least for me. Been to the drag strip a few times and many track days and it held up well with no issues. Free up those unsprung horsepower's:lol::lol:
 

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Discussion Starter #6
Thanks guys, I appreciate the advise. Looks like ill be getting one come spring time. So its between the PST and "The Driveshaft shop" driveshaft. I see the driveshaft shop DS is rated at 850hp and 180 mph, anyone know the rating of the PST? Is the only difference drilling the holes?
 

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So here's my take on them. First let me say that GD's have way less clearance then later models.

OK, so I bought a PST CF driveshaft from RSD a couple years ago. It was to cure a problem I was having. On hard launches at the track the driveshaft was really bouncing around. Enough that it was contacting the body of the car. I determined the problem was the 1/2" or so of play in the carrier bearing assembly. It was really moving around in there.

When I fitted the CF driveshaft it was super tight. I'd say less than a millimeter of clearance. It was pretty much kissing the body structure. After talking to RSD and PST they offered to make me a custom shaft. Honestly I have no idea how to accurately measure for that. On the forums "clearancing" (is that a word?) was mentioned. Basically taking a steel pipe and a big hammer and banging on it until the body bends out of the way. Yea... that's not for me. I returned the driveshaft, but still had a problem. I needed to stop the OEM shaft from banging around. I came across a 2-part urethane that comes in different durometer ratings called Liquid Engine Mount. The details are in my build thread on page 9.

Basically I mixed it up and filled the void in the rubber bushing that surrounds the carrier bearing. It worked better than I expected. Not only did it stop the driveshaft from moving around, but now the car takes off very smoothly without any bucking in lower gears. It made it much easier to launch at autocross and time attacks and even from a stop light. In the end I'm glad the CF shaft didn't fit. I got the effect I wanted at $40 instead of $1000. At this point the only advantage a CF shaft has is reduced weight which could translate to quicker response. I did not drive my car with the CF shaft installed I could not make a comparison. I will say I'm very happy with the way things turned out and have no desire to go to a CF shaft at this point.
 

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OK, so I bought a PST CF driveshaft from RSD a couple years ago. . . . It was to cure a problem I was having. On hard launches at the track the driveshaft was really bouncing around. Enough that it was contacting the body of the car. I determined the problem was the 1/2" or so of play in the carrier bearing assembly. It was really moving around in there.

When I fitted the CF driveshaft it was super tight. I'd say less than a millimeter of clearance. It was pretty much kissing the body structure.
You might be the only person that's had a real issue, but your experience is one of several reasons I lean DSS :) Mine had around an inch of clearance. Are DSS shafts that much smaller in diameter?

Now rereading it, I wonder if there is something with your body. You've had two shafts that hit it. Yeah I realize that when you froze the stock one you solved the issue.
 

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I actually will need to be replacing my OEM on my '06 in the near future as well. The u-joint at the diff is starting to bind up. I'm considering the PST due to some of the stuff I've heard about DSS (bolt sizing, some customer service). I know its going to be close but I'm hoping I don't have to "clearance" the tunnel like Suby Sal mentioned... I'm not totally against it tho. We shall see, I'm not sure how soon I'll get to this one.
 

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I ran a PST in my 05 STi. Had balance issues. Would be 100% unnoticeable on the street, but at a 1/2 mile event it cause severe vibration at +140. Enough that it deflected a good 1/4" and made contact with the shield on the front of the rear diff. PST told me to rotate it 90°. It got worse so we kept rotating it until we got the least amount of vibration, which was marginally better at best. They would not take it back claiming the balance was good to +200mph.

With our 2019 STi I went with DSS.

Now while I did not have them side-by-side, I can shed some light on obvious differences. DSS uses billet aluminum ends, not cast steel. DSS weight is lighter. PST holes where it meets the diff do not need to be enlarged. For now, we kept the stock bolts with our DSS as we are only stage II power levels and I don't want to modify the OEM diff unless we have to. The car has not been driven above a full 4th gear pull (around 110mph I think) but so far balance seems good.

On the larger bolts... When the time comes, I may just drill out the holes in the rear diff. It's not a huge deal as doing that won't hurt anything going back to stock. The bolt heads take the brunt of the load not the bolt shaft. Considering looking into hardened shoulder bolts, but that would require that the heads are modified, but it looks like the DSS supplied bolts are just ground anyway so that may be fine.
 

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You might be the only person that's had a real issue, but your experience is one of several reasons I lean DSS :) Mine had around an inch of clearance. Are DSS shafts that much smaller in diameter?

Now rereading it, I wonder if there is something with your body. You've had two shafts that hit it. Yeah I realize that when you froze the stock one you solved the issue.
Well a buddy of mine that was a Subaru tech and now has his own shop said the chassis on the GD STI's could vary as much as 3/4". So yes maybe my car has tighter clearances than most. It also has a small build up of undercoat/sound deadening right above the shaft. So that could play a role too. I have found other threads with people that had the same clearance issue though. That's where the hammer and pipe idea came from. I have no idea on the dimensional differences between DSS and PST.

Killer B brings up a another good point. I forgot about the semi-frequent balance issues that I read about when I was shopping for a CF driveshaft. A con of a one-piece shaft. It makes sense though. In a car like the STI with a fairly high top speed and a long driveshaft a two-piece driveshaft is less likely to vibrate. As driveshafts get longer two-piece unit usually have a higher critical speed than one-piece units.

The biggest drawback in the two-piece design is the play in the carrier bearing bushing. In my car at least it caused all that bucking in 1st and 2nd gear. Though that could also be since every other bushing in the car was replaced it focused it there. Anyway I think if someone produced a carrier bearing with a solid bushing or maybe even a poly insert it would take a real chunk out of the one-piece driveshaft market. You'd get 90% or better of the same affect for like 1/50th of the price. Before I found the liquid poly I was actually trying to source an large O-ring that would fill the void for a quick easy fix.

In the end it was just easier to fill the bushing with poly even though it's more work (turning my shop into a 77ºF oven for a week was the most inconvenient part of it). I think the result is worth it. You can pick your durometer rating and that stuff is specifically designed to bond to existing rubber. I've beat the heck out of it over the last couple seasons. Driving the car hard enough to wear out the dampers, rear diff and bust two half-shafts. Still that stuff is welded into that carrier bushing. I couldn't be happier with the way it has worked, but I digress.
 

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I have found other threads with people that had the same clearance issue though. That's where the hammer and pipe idea came from.
We've been through this before. Clearancing was a given with older AL single piece shafts. Never been a thing with CF. It's why they became popular and why people are willing to spend twice as much on them.



Killer B brings up a another good point. I forgot about the semi-frequent PST balance issues that I read about when I was shopping for a CF driveshaft.
Fixed that for others . .

The biggest drawback in the two-piece design is the play in the carrier bearing bushing.
Agreed, but they also have an "extra" U-Joint and a higher angle on the rear half and the extra carrier bearing . . . High end cars come with CF drive shaft these days and they are getting more common. STI's really ought to too.

Added: that "high" angle on the rear half is the larger part of what causes the center bearing to move. If it were straight the would be almost no force trying to move it.
 

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We've been through this before. Clearancing was a given with older AL single piece shafts. Never been a thing with CF. It's why they became popular and why people are willing to spend twice as much on them.
It was a thing with CF driveshafts too. The difference is with aluminum shafts they always have to be clearanced and with CF shafts it's only occasionally. The thread I found a few years ago pertained to a CF driveshaft. I would not have bothered looking at a thread using an aluminum shaft.

This is a pic of the PST driveshaft installed. For the record nothing is out of place on my car. I measured it against another GD STI. Also I chose the PST over the DSS because at the time it seemed like people were having problems with the DSS shaft. I think the bonding between the u joint and shaft was coming undone. Bad glue or something. Plus I didn't want to have to drill out holes in my yoke.






Fixed that for others . .
Yea I've heard about balance issues on DSS CF driveshafts too.



Agreed, but they also have an "extra" U-Joint and a higher angle on the rear half and the extra carrier bearing . . . High end cars come with CF drive shaft these days and they are getting more common. STI's really ought to too.

Added: that "high" angle on the rear half is the larger part of what causes the center bearing to move. If it were straight the would be almost no force trying to move it.
I think the angle causes the driveshaft to move in the same direction under torque. I saw a spot on the bushing that had been hammered repeatedly enough to leave a small indentation. I think if the driveshaft had no angle it would still try to push to the outside due to the freedom the u-joints allow, but just not always hit the same place. Don't forget there will still be deflection in other parts of the system and even the slightest angle will push the shaft to the outside. And yes it would have been nice to have a one-piece carbon driveshaft from the factory. Even my last truck and my current truck have aluminum shafts.
 

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PST driveshaft is nice because it makes it that much easier to get the car going.

But my PST starts to vibrates somewhere near 140mph, then it gets real nasty 140mph+.

I already clocked it 3 times, so I guess that's as good as I can get it to.
 

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I would definitely like to go for a CF driveshaft myself one day but like others have said, the small difference compared to the cost. Based on reviews i think that it would be worth it if you are someone who is in alot of traffic or stop and go situations often. Anything really to help any generation sti feel smoother and less sloppy is big plus in my book. Even though this would be a great upgrade for myself and others, i think i will only go this route if i am in need of replacing my OEM driveshaft. Kind of on the premis of "if it aint broke, dont fix"
 

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It was a thing with CF driveshafts too. The difference is with aluminum shafts they always have to be clearanced and with CF shafts it's only occasionally. The thread I found a few years ago pertained to a CF driveshaft. I would not have bothered looking at a thread using an aluminum shaft.

Yea I've heard about balance issues on DSS CF driveshafts too.
but you have no links . . i can say first page of a google search finds a PST balance issue, and not a DSS issue. BTW: they are most on Mustangs. Guess they could get them right right either . . . like I said we've (you and I) done this before. Not going to do the work again. Killer -b's description ought to weigh on a choice, not to mention his experience. Perhaps you were luck you didn't use your's! You didn't even get to discover a balance issue!


I think the angle causes the driveshaft to move in the same direction under torque. . . . I think if the driveshaft had no angle
The fact that the increased angle produces more uneven rotation and more force in a disadvantageous directions is something that can be calculated via engineering and math, not something to write "I think" about. It is what it is.

Not a bad place to start: General Universal Joint Characteristics and Applications from SDP/SI
 

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but you have no links . . i can say first page of a google search finds a PST balance issue, and not a DSS issue. BTW: they are most on Mustangs. Guess they could get them right right either . . . like I said we've (you and I) done this before. Not going to do the work again. Killer -b's description ought to weigh on a choice, not to mention his experience. Perhaps you were luck you didn't use your's! You didn't even get to discover a balance issue!
Yea same here. I don't know where these links are anymore. This was years ago. I see no point in wasting my time to find them when I've already solved this problem for myself years ago. You're speaking in absolutes. DSS driveshafts have there issues too, but no apparently the balance issues are not as prolific as the PST shafts. Regardless I'm glad I avoided the whole thing. I was just trying to offer the OP an alternative by telling my story. After that he can do what he thinks best.




The fact that the increased angle produces more uneven rotation and more force in a disadvantageous directions is something that can be calculated via engineering and math, not something to write "I think" about. It is what it is.

Not a bad place to start: General Universal Joint Characteristics and Applications from SDP/SI
OK first of all without any angle there is no need for a universal joint. It's purpose in life is to transfer power along a non-linear channel. Yes as the angle increases efficiency decreases as side loading on the universal bearings increase. However there is an operational range. And the difference in angle between the one-piece and two-piece driveshaft on an STI is not significant. Not to mention an STI with an OEM driveshaft has no vibration issue regardless of speed. In fact the reason for multi piece driveshafts is to reduce vibration at higher speeds. It's the bending or deflection of the shaft that causes the vibration. The longer shaft the more easily that will occur. Of course core material and material strength are huge factors here. The reason why CF works so well is it's very light and very strong. This helps it resist deflection over other materials like aluminum which are a bit heavier and don't have the same tensile strength. Aluminum having no memory is another problem. In other words it doesn't "spring" back when deformed. Steel works very well in this application as it has high tensile strength and memory (plus it's cheap), but unfortunately is very heavy compared to the other materials listed here. A steel shaft can't reach the critical speeds of lighter materials because it's mass causes deflection sooner than the others. So the shaft itself has to be shorter which requires carrier bearings. AS with many things in life it's a compromise. In the end you pick what works best for you. And with that I have nothing more to say.
 

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I was just trying to offer the OP an alternative by telling my story. After that he can do what he thinks best.
Note that I have never criticized you solution . . . more power to you!


fact the reason for multi piece driveshafts is to reduce vibration at higher speeds.
Not really. It allows a a less strong and hence smaller diameter shaft for the same shaft speed. There is some question by our community as to whether it plays a safety role as well.


It's the bending or deflection of the shaft that causes the vibration.
Is vibrating tolerable?
If it's vibrating how long will it hold up?
Then at higher shaft speed it would lt self destruct.


The longer shaft the more easily that will occur . . .
you got it :)

You mentioned spring with steel being better than AL, but its' another thing CF does even better, lots better. Benefits the whole drive train.

and with that I have nothing more to say.
K then . . .
 
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