I've experienced exactly one u-joint failure in my lifetime.  My buddy's '95 Lighting kept making this noise on take off and I told him likely it was a bad u-joint.  Of course I didn't know what I was talking about, until a month or two later he tried to pull out onto the highway and the rear u-joint let go.  Trashed the aluminum driveshaft too.

I think if you inspect the u-joints regularly the odds of one failing is pretty slim.  Safety loops are for racing, where cars running fast with 5,000 RPM clutch dump launches or coming off the line on a trans brake shock load the drivetrain to a degree never seen on the street.  I have seen u-joints fail at the strip and its is not pretty (catapults the car if its the front, etc.).  IIRC NHRA mandates a loop for cars running 13.99 or quicker, must be within 6" of the front u-joint, and must be a minimum of 1/4" thick x 2" wide or 7/8" x 0.065" wall tubing.  Mounting criteria is not specific.  I've run faster than that at the strip without one and never broken one, and the tech inspectors are pretty lax at my local track. 
 

Last edited by TKOPerformance (4/06/2024 6:01 AM)

I have one in my Lightning, but it's only because I was going to run it at the track with sticky tires every so often. On the street with street tires I really do not think it's necessary.

 

I wonder if the plate used for the convertible floor pans can be used as a safety loop?   I already added a heavy piece of bar stock to the front of it.

Although I also believe a driveshaft loop is likely unnecessary for a street car, if one installs one make sure that it is a 'loop' around the driveshaft.  You don't want that driveshaft coming up through the floor board. 

I had a F100 short bed that that had a driveshaft issues when I was about 19-20. This was a 6 cylinder truck with a Borg Warner T-18 granny first 4 speed. I had tore up 2 three speeds and this was a good upgrade. The drive shaft had U-bolts on both ends. There were issues with the pinion because the rear U-joint got replaced on several occasions when I heard it making noise. The truck sounded like a bucket of bolts rattling down the road at any given moment when everything was normal-ish. I was probable going 60 MPH on Beltway 8 heading for home one afternoon when the noise in the truck suddenly changed, then the drive shaft came loose at the transmission. It was making loops under the truck hitting the floor board and bouncing off the concrete. No catapults, thankfully. It was not a pleasant experience. I think this was more of a U-bolt failing that held the driveshaft than the U-joint itself. It was at a point in life where the Borg and Beck rebuilt clutches I was buying would go out every 93 -95 days..... just long enough to be out of warranty. I can't say I gave enough attention to detail at that point to make sure the U-bolts were tightened evenly!! I could change the clutch by myself in 3 hours taking 45 minutes for a parts run. 

Since then, I've tried to pay more attention to the sounds and way the car acts. If a U-joint is going out, there will be telltale signs. 

The danger isn't if the rear u-joint fails.  Its if the front fails, which can catapult the car (seen this happen at the strip).

6sally6 wrote:

I was showing my boney-white-fanny a few years back and tore the rear u-joint out...going from 1st to 2nd in an expedited manner. (BOY what a racket that thing made!)
I knew instantly what happened when the engine revved UP big time and all the noise the shaft made framm'in on the road.
I 'neutralized' the trans and coasted about 1/2 mile to a parking lot.
When I welded in the new exhaust pipes from the headers back to the muffler/tailpipes....I tack welded a small piece of round stock between the pipes underneath the driveshaft
NOT a driveshaft loop by any means butt... just 'something' to hopefully keep the shaft from bouncing off the road if the u-joint ever does it's 'thang' again !
6sal6

Yikes! This makes me nervous

MS wrote:

Put good ujoints in it and find something else to worry about.

Copy that
 

MS wrote:

Put good u joints in it and find something else to worry about.

 
X-2 !
6s6