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Snapped Drive Shaft - new wall thickness suggestions.

eclipsh

Proven Member
1,607
55
Jun 16, 2005
Durango, Colorado
So I was driving home last night and had a small explosion happen under my car. Turns out my drive shaft snapped. I was under full throttle and going about 70-80 MPH when it happened. I've got some pictures of the carnage.

From the driver's side:

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Passenger's side:

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This is from the back. Notice the rear section of drive shaft jumped up over the exhaust and wedged itself in:

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Here's the broken off end of the rear section:

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I was trying to pull the front drive shaft off and noticed the transfer case wiggling so I put the camera up in and took a shot:

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I ended up having to pry the shaft out with a wrench. It had managed to stick on pretty well which meant I didn't have to hunt any parts down along the road.

Here is the section that broke off:

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I've got another t-case housing I can use to repair that. Part of the reason it broke was that it had rubbed against the exhaust a bit at one point and scratched this area up a bit. That made it the weakest point in the shaft. The wall thickness on the pipe seems a little thin though. This is a two piece shaft (now three, haha) so the section that broke is pretty long. I'm wondering if any of you wise folks have a knowledgeable suggestion on wall thicknesses to run. My mods list is current. For now I'm only pushing 13 psi above sea level atmosphere but I'll be bumping it to 20 or so in the near future. From what I hear with the 2.4 at 9:1 compression that should be good for 350-400 ft. lbs. of torque. I'm not sure how much shaft I need to handle that given the 53" length.
 

turboglenn

Proven Member
6,378
111
Nov 5, 2007
RIpley, West_Virginia
unless you have balncing equipment, are good at TIG welding and have a jig to make sure the run-out is within tolerances, you'd be better off gettign the aluminum one (forget which one my frined has) but it's LIGHT and he has made over 730HP and launches by sidestepping the clutch at 8+K RP's and it's held up fine (he broke the stocker just like you a long time ago)
 

eclipsh

Proven Member
1,607
55
Jun 16, 2005
Durango, Colorado
This wasn't stock, my car was FWD and never came AWD in North America. The shaft that broke was a custom unit build by a drive shaft shop. I'll have them make and balance the new one too I just want some knowledgeable suggestions on how thick the walls should be so I can get be a bit more informed when I go talk to them tomorrow. As you can see in the photo below space is tight. I've opened it up bit more by pushing the exhaust further to the driver's side but there will never be much room so a bigger diameter aluminum shaft isn't going to work.

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eclipsh

Proven Member
1,607
55
Jun 16, 2005
Durango, Colorado
It was a two piece. It is the one in my avatar <------. It is in my 94 Galant which has a slightly longer wheel base than the 2g DSMs and doesn't have a wide enough tunnel to allow for a mid-tunnel joint/mount, hence the 53" long section.
 

needsy

Proven Member
94
0
Sep 21, 2008
NW, Iowa
I'm thinking that is something the driveshaft shop should know. I can't imagine they don't have a table that correlates shaft thickness and diameter to torque capacity. I would give them a call and ask.
 

Slippi84

Proven Member
4,454
20
Jun 8, 2005
Cinnaminson, New_Jersey
No amount of thickness will hold up to it banging up against your exhaust. Look into what the DSS 2pc kits are made of thickness wise or even better my ACPT 1 piece.
 

eclipsh

Proven Member
1,607
55
Jun 16, 2005
Durango, Colorado
Thanks for the replies everyone. The exhaust wasn't banging up against it when it broke, it had been pushed far enough over that it shouldn't have been an issue. The exhaust flange had rubbed against the driveshaft at one point though and weakened it at that spot. It didn't look deep but I didn't know the walls were only 1/16" thick.

Regardless, I found this nifty driveshaft critical speed calculator over on a Supra site. The broken shaft is 2.5" diameter and about 1/16" thick walls. Using the roughly 3.55 ratio rear end and my 245/40/17 tires it says it should be able to handle 135 mph and 727 ft lbs of torque. If I drop the wall thickness to 1/32 it can still handle 377 ft lbs. It puts the half-critical speed dead center in my highway cruising 60-70 mph zone though which I guess is a bad thing. So I'm going to talk to them about doing a 3" shaft with 1/16" walls. It will be overkill at 1060 ft lbs and capable of 160 mph speeds but that'll be a good safety margin. It also puts the half-critical speed at 80mph which I'll only see for any real length of time if I'm heading out to LA.
 
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