School me on driveshafts

So, at BRS this year, I was again struck by my Curse of BRS. 3rd DNF in a row, and to make matters worse, it's a 1200 mile tow to just get there. Ugh.

Anyway, one of my failure points this time round was my propeller shaft (or driveshaft for the rest of the world). For my sexy combination of parts, the OEM driveshaft that I need can't be found anymore as it hasn't been in production in 10 years, and wasn't on this continent. There are alternatives that are the right length, but have different joints, etc.

So, my question is as follows:

If building a custom driveshaft, would it be preferred to have the OEM 2-piece style or go with a single-piece unit for rally purposes? Material? Steel? Al? CF? (My guess is CF is a HORRIBLE idea for rally).

I've seen the Driveshaft shop whip out single-piece Al units all day long for Subarus and are more than willing to make OEM-like 2-piece beefed up units that are serviceable.

What do you folks think?

I would go with a single piece steel driveline. The rear diff doesn't move (compared to a live axle) so not much room needed for yoke movement. AL drivelines need to be pretty big in diameter from what I see in production stuff. KISS seems like a good approach to me. We used to have a wrecking yard that had a small machine shop and an old guy in a corner. He did amazing work and could build a Sube/Mazda driveline with replaceable joints for about 40% of what the driveline shops wanted. Never had a vibration issue either. Sadly he retired now we're back to $500 replacements. Couldn't hurt to do some asking around .

Longer needs to be larger in diameter for harmonics reasons. That's the reason for the aluminum driveshaft in the first place, a 5" diameter steel shaft is gonna be a heavy SOB. It's also generally why the OEMs will have two- or three-piece driveshafts, less harmonics issues.

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

I had a driveline shop make me a 1 piece for the 240SX, I provided the yolks, cost $100, it's been in service since late 2006, done 30+ rallies, no problems. It's not big diameter, maybe 3.5", no vibration, and no noticeable harmonics issues. Like Gene says KISS...

-Martin.

Eric,

What prop shaft did you have in the car?

How did it break?

Assuming that you are running the 6 spd with an r180, they should be a dime a dozen! There are piles around, lots of guys on Nasioc replacing their stocker for a Alloy or Carbon unit. Really any impreza that came with a 6 spd and R180....

I'm curious, because this part usually is not a weak point on the cars. Assuming you are ofcourse running the 6 spd shaft with R180 diff (and if you aren't, you should be!)

Also FWIW, talk to Mike about the alloy shafts...I personally contemplated it for a while, and he pretty much talked me out of it.

---

Chris

So, my car was originally a 4EAT. I did a 6mt swap w/ an R160 in the rear in it somewhere around 2006, and have been running that transmission forever. The shaft I used at that time was my 4-speed auto propshaft.

Now, after destroying my R160 diff at RallyWV and subsequently found chunks in my transmission, I replaced the trans, but have an R180 (w/ an R160 flange that can be easily changed out). I've done a LOT of searching on this subject.

https://docs.google.com/spreadsheet/ccc?key=0AlHHrwRakue6dDRoNEJhWnRBRnBTYkMyUHR5QWpzNnc&usp=drive_web#gid=0

While all 6mt STi propshafts are the same length, they do not have the same section lenghts due to a mix of transmission cradle, bushings, and other odds and ends. What I am trying to avoid is putting too much load on the center bearing by using a shaft that's 5mm too long/short.

You can modify the center mount if needed. Lengthen the carrier ears, move the floor fasteners. I'd still single piece with replaceable ujoints.

Trying to monster any prop shaft is just silly!!

Run the R180 with the R180 flange, and run a bone stock JDM or USDM STi Propshaft. Probably available for payment in Beer.

There is MORE than enough slack between the transmisison output shaft and center bearing hanger in the front yoke. +- 5MM won't make no difference and there is barely any movement there anyways.

---

Chris

So, for the exact shaft to match the setup I have:
Front length, rear length, total length

2002 JDM STi - 584,708,1292 <-ideal shaft
2004+ USDM STi - 574,706,1280


12mm is a fair amount. I was running a 2002 4EAT turbo shaft (579,713,1292).

It's still a slip spline in the end of the trans like every other Subaru right?

Most slip splines can travel a couple inches. 12mm is probably within how much it normally moves around anyway as the drivetrain skootches around under loads and the car flexes and twists.

Hell, just hit something really hard to shove the front subframe back a half inch. Problem solved...

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 10/21/2013 07:43PM by Pete.

Seems like is you're rallying a subaru and have/need special/rare parts you're doing something wrong. I thought you worked for Google nor Apple.

---

Grant Hughes

!2mm is nothing to worry about. There is plenty of plunge to makeup for it.