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Discussion Starter #1
I just installed my PST Carbon Fiber Driveshaft with some helpful tips from @dublezero. Thanks again dude.

I have a couple of questions based on the install.

1. Is the front spline, of the CF Driveshaft, that goes into the tranny, NOT suppose to go in all the way? Mine seems to be in halfway. Is this normal? Feels like the driveshaft is too "short"



2. The 4 stock bolts that connect the driveshaft to the rear diff: did the flat part of the heads not sit right up against the u-joint like the stock shaft? I had to wedge a large flathead screwdriver in the gap in order to tighten the nuts, to keep the bolt from spinning.



@dublezero confirmed that his install was like mine. If others, with the PST CF driveshaft, can chime in and confirm (or not) that theirs is the same way, that would put my mind at ease.


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Top pic. There needs top be gap. The splines slide in and out when your rear suspension and/or transmission moves. That does look large, but halfway is probably about right.

Bottom pic. Can the bolts fit in from the other direction? The heads are shorter than the nuts.
Wait, they are not touching anything, right? Then OK.

ADDED 8/29/19: STI rears don't move and the trans only moves a bit. My bad.
The u-joint and sliding does allow for that trans movement though. Also while all DSs slide there, my DSS does not end up looking like that.
 

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Discussion Starter #3 (Edited)
Top pic. There needs top be gap. The splines slide in and out when your rear suspension and/or transmission moves. That does look large, but halfway is probably about right.



Bottom pic. Can the bolts fit in from the other direction? The heads are shorter than the nuts.

Wait, they are not touching anything, right? Then OK.


Cool.

I figured the shaft needs some telescoping action due to movement differences between the front and rear. I re-checked the stock shaft and I didn't notice the spline not being in 100% of the way because it has a protective cover welded on to the front joint.

The flat part of the bolt heads do not make contact whatsoever with the wall of the u-joint. In other words, the bolt head spins freely if I attempt to tighten the nut on the other side.


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Discussion Starter #5
So how does the car drive now ? Initial impression please


I've only taken her out on a mild drive to ensure nothing is binding and the bolts remained torqued.

I'm going on a more spirited drive soon and I'll post up my impressions.


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FYI about the OEM bolts - I had the same situation with my DSS CF driveshaft. The u-joint is just a different design and I did the same as you did (wedge a screwdriver to hold the bolt head in place).
 

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The spline looks much further "off" than my 2015 STi. It was seated in the rear of the transmission pretty close to full. Are there any markings or indicators on the shaft itself like a model number? Maybe its possible you have the wrong model year? I don't think the shaft has changed since the 04, but I could be wrong.
 

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I have a CF driveshaft on my 15 sti from DSS and it has about the same gap. I wouldn't be worried too much.

The drive-ability is much better. I have a QM twin, which is one of the worst clutches for street driving you can buy, and the car would buck and stall in low gear low speed, say a parking lot. The CF driveshaft doesn't do any of that.
 

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Discussion Starter #10
The spline looks much further "off" than my 2015 STi. It was seated in the rear of the transmission pretty close to full. Are there any markings or indicators on the shaft itself like a model number? Maybe its possible you have the wrong model year? I don't think the shaft has changed since the 04, but I could be wrong.


I've been driving with this shaft for about 5000kms. No issues. I think I'm good. Others have chimed in saying they have the same gap.


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I installed the PST on my '16. With those bolts, you can still fit a open wrench on them to hold them while you tighten. I don't recall my gap being that big, but there def was a gap.

I read somewhere that there is a balancing paint mark on the rear diff flange and the PST, but I didn't see anything, and don't feel any weird vibrations.
 

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Discussion Starter #12
I installed the PST on my '16. With those bolts, you can still fit a open wrench on them to hold them while you tighten. I don't recall my gap being that big, but there def was a gap.



I read somewhere that there is a balancing paint mark on the rear diff flange and the PST, but I didn't see anything, and don't feel any weird vibrations.


I don't know what type of open ended wrenches you have, but there was no way I was getting one in there.


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I don't know what type of open ended wrenches you have, but there was no way I was getting one in there.

"good tools" - seriously. Been a while and I think I used a screw driver too, but I'd be surprised I didn't have tools that would fit today. did mine on ramps. Once fully under, I don't come back out if I have something that will work.
 

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Discussion Starter #14
"good tools" - seriously. Been a while and I think I used a screw driver too, but I'd be surprised I didn't have tools that would fit today. did mine on ramps. Once fully under, I don't come back out if I have something that will work.


Sorry misunderstood. You're right you can use an open ended wrench on the nuts. But the bolt heads do need a flathead wedge. The heads are circular with a flat part that mates with OEM shaft u-joint.


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Discussion Starter #16
Check it out bruh:


Damn. Never thought of trying.

Does that hold the bolt with only one side flat?

But with that wrench shown in the pic, you would not be able to get that in the space between the u-joint and the bolt head.


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Did I just blow your mind? ;)

This works. Align the flat part of the bolt head perpendicular to the shaft, so your wrench is sticking straight out. Rotate shaft to next bolt so there's room.
 

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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.

Thanks,
-Nigel
 

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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.

Thanks,
-Nigel
What brand? Most of the balance issues are well behind us with this product or so I've seen.
 
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