I just installed a new Inland Empire aluminum drive shaft in my 91 Z. Since I'm running a new decently powerful 383, and switched to 3.73 rear gears, I figured a drive shaft loop made sense. Based on my research, the front is really the critical one, since that can pogo a car, or damage the car worst, or the driver... If the rear fails, the shaft just generally falls out.

So, I got the cheap universal kit from Summit since it came with all the steel and hardware for cheaper than I could buy it otherwise. I've got a decent variety of fabrication tools so I figured I would give it a try on my own. I wanted it to remain somewhat modular, so it could be removed without having to remove the drive shaft. I also didn't want to have to tear out my interior, so I decided to mount it to my also new BMR torque arm relocation brace/trans crossmember.

Here is the current status of where I'm at. I'm getting close to getting it to fit up. Still have a couple additional welds and maybe some minor bending to do to get it to fit right. Its tight in there with a tubular torque arm, and a 3" drive shaft... I also plan to add a couple more triangular gussets to make sure it is ridged enough and doesn't vibrate. I'm curious to hear thoughts on my design, and if anyone has any suggestions from their own experience doing something similar.

 

yup, looks like itll work
dont over think it

hope you never need it

 

Looks nice.

My only thought is that the loop is cantilevered out there a bit. Adding a gusset (as you mentioned) or shark fin down it's back and between the fasteners might stiffen that up a bit. Not sure how much room is left in that area. Bad drawing attached.

 

I agree, I was thinking something similar. I have to see what kind of material I have left sitting around for the gusset and rib (shark fin).

 

Couple hours more progress tonight. Finished welding a few spots, and added a rib and a gusset. Man, this custom fab stuff takes a lot of time... It looks a bit rough now, but once everything fits, I'll clean it up and re-paint it all.




This is where I'll weld the second gusset, once I make sure the angles work and it all fits right.

 

Looks nice!

 

Couple hopefully final alterations and improvements. I put welds in a couple places to eliminate some of the fasteners. Also put a quick coat of paint on it.

 

Problem now is I found when trying to torque down the trans crossmember, that my two drivers side nuts are stripped out! It was slightly outside my comfort zone, but I just started cutting... cut a new piece out of some thicker stock in the same shape, marked the holes, drilled them, and welded some fresh flange nuts on. I then attempted to weld that plate back in... I'm going to grind it all back down and try welding it again. I got some pointers today from someone I work with who is a very well trained and experienced welder.

I'll say it SUCKS doing all this on my back under the car on jack stands. I don't even really have it up high enough, since I wasn't expecting g this much extra work... I need a lift.

 

Nice repair.

I only recently became aware of this weakness in the trans crossmember attachment scheme. I have to take my car into the body sop to have a seatbelt anchor replaced. I'm tempted to have him do this work pre-emptively while it's there.

 

Looks nice, however Mythbusters already tested the "launch the car from a broken front u-joint" myth.
They said BUSTED - can't happen. Season 3, Episode 14 Drive Shaft Pole Vault

 

A lot of racing organizations require front ones, so I'm sure there is something to it... better safe than sorry.

Additional note, I drilled holes into the three spot welds I saw, thinking something would come loose and I could easily work it out the larger hole further forward, but nothing did... Any of you doing this, just cut a clean rectangle, of a logical size, then make your new plate a little longer so it overlaps the existing support, this should make it stronger, and less reliant on the quality of your welds.

 

its not the pole vault we all dreamed up, it’s the driveshaft spinning at a high RPMs turning itself into a blender next to your body.. just google some pics of the after math, and you’ll understand why safety loops are very needed.
​​yessir, the devastation is wild..

 

I have one on my TA too for the same reason.

 

So this project certainly became a bit more involved than I expected, but I'm nearly done now!

I finished what I believe will be a perminant repair of the stripped frame nuts that the trans crossmember bolts to. Once it was all done I hit it with a quick coat of black spray paint.

PSA: I was grinding down the welds, that need to be at least relatively flush where the crossmember mounts, which my makita 18v grinder and a 4.5" grinding wheel, and it was taking FOR EVER! For giggles I tried switching over to my corded Dewalt with a 5" wheel, and OMG it went SO MUCH FASTER!




After the paint dried I mounted everything up. It fits about how I had planned. The crossmember/ torque arm relocation bracket is all torqued down using new grade 10.9 flange bolts from Menards to the specified 40 ft-lbs, no issues with the new frame nuts. I think I may go back and cut 2 threads off the bolts for the loop, so they sit flush with the nuts, just to give a little extra clearance. Then I'll go back and apply blue loctite and tighten everything down. Hopefully tonight...

One additional thing to point out. The factory crossmember bolts I've been reusing all these years, are actually somewhat undersized compared to my new bolts, and also are not perfectly round. For some reason the threaded portion is somewhat triangular, further reducing thread engagement. I wonder if I replaced those bolts years ago, if the frame nuts would have ever stripped out... May be a good proactive step for people to take in general with those bolts.

 

Finished everything up last night, but haven't had a chance to test drive yet. Everything is quite close, but it's pretty rigid, hopefully nothing touches or vibrates. Hopefully my wife gives me a few min to take a spin at some point today...

Happy mothers day to all the moms out there!

Since I am relocating the torque arm slightly, I tweaked the pinion angle with my adjustable torque arm. The trans and differential pinion were pretty close to parallel, but I adjusted it for the pinion to be one degree below parallel so under heavy throttle it should clime up to parallel. For poly bushing suspension, they say 2-3 deg down, but I've got roto joints, so for those and my stiff beefy tubular torque arm, I'm going with 1 degree.


Pinion

Slip yolk

 

looks good man! good successful project