[lenul]

Hello,

Yesterday It was the dyno session for my Giulia with its new 2L engine, but nothing happened as planned... In the fifth gear the at 5300 rpm the propshaft split in two... the slide come out of its housing...

So now, the big question is : what happened ?

All components were new, everything was well put together, balanced..
So I don't understand.... I do not have the beginning of an idea...

Have you an idea about that ?

PS : when the propshaft split in two we had 225 N.m and 170 hp at 5300 rpm

 

[mechtild]

I knew a 116 gtv racer.
He had issues with drive shafts and propshafts.
He told me when the transaxle was hit by the torque it moved so much that the pull force on the drive shafts and the propshaft caused them to break.
Maybe your rear axle was to vivid and pulled it to a point where the nut couldn't hold anymore

 

[GTA Alfa]

Lucky no one got hurt.

 

[sh0rtlife]

drive shaft safety loops save lives.....your tunnel survived pretty good

obvious answer is torque pulled things aprt, so something flexed way more than it should have....however a solid question i do have is how much of the slider was exposed when you started this.....i ask as i had a dodge truck that would do this on the front axle on hard launch all the time and it was due to suspension fex, so i learned that the correct slide ratio is that when the suspension is bottomed out the slider should also be almost bottomed out, and as full flex/rise you should still have atleast 2 inches inside the slider..and ive found this to genuinely be true on ANY slider rig thats applying a good amount of torque and flex

 

[PSk]

Frightening!

Pete

 

[spiderserie4]

was that an original alfa rear prop section/splined joint or one of the new sections you can buy now from the various suppliers?

 

[Alfajay]

So now, the big question is : what happened ?

The thin wall tubing of the driveshaft just buckled under the torque. You subjected it to a load larger than it was designed to carry.

You can induce a similar buckling if you take an aluminum soft drink or beer can and twist it with your two hands.

 

[Legin]

I would say that has failed in bending not torsion. No visible evidence I can see of twist. Is there any possibility it was damaged ie kinked in the middle / dented, banana shaped. The inertia loads due to whip would increase dramatically with rpm. What gear were you running at 5300 rpm ?

 

[nealric]

The thin wall tubing of the driveshaft just buckled under the torque. You subjected it to a load larger than it was designed to carry.

You can induce a similar buckling if you take an aluminum soft drink or beer can and twist it with your two hands.

Plenty of people have run more power than that through an Alfa driveshaft. I think something else beyond too much power is going on.

 

[Alfajay]

I think something else beyond too much power is going on.

Well, at a minimum, there was too much power for that driveshaft!

any possibility it was damaged ie kinked in the middle / dented, banana shaped

Sure, something like Legin suggests could have initiated the failure. Put a little dent in your beer can before twisting it, and it will crumple a lot easier than an undamaged one.

 

[PSk]

What's the rear axle setup?

1. Lowered?
2. Rubber or poly bushes in trailing arms?
3. Cracked trailing arms?
4. Trunnion end bushes, new or old?
5. Trunnion pivot bush, new or old?
6. Trailing arm connection to the floor solid or rusty?

7. Engine and gearbox mounts new/solid as the other option is the engine moving forward

Pete

 

[Gordon Raymond]

Where did you source that driveshaft? I'm curious having seen similar failures of other components from one supplier....

 

[PSk]

Plenty of people have run WAY more power than that through an Alfa driveshaft. I think something else beyond too much power is going on.

Something was defective somewhere. Maybe the driveshaft or ... ?

Pete

 

[1978alfa]

Bad u-joint?

 

[yvesmontreal]

Was it a 2000 driveshaft? Unlikely as you have a Giulia sedan and no car with this wheelbase was sold with anything larger than a 1600. Alfa enlarged the bolts (8 to 9 mm) for the 2000, perhaps the tube was thicker as well.

 

[GTV-074]

That was my thought… as it’s had a 2L engine change, did it have a berlina tail shaft fitted?

they are longer, perhaps it’s run out of expansion/sliding space.

whatever it ends up being, certainly would have focused your attention at the time!

Paul.

 

[Sergio105]

He ripped off the rigid gasoline pipe... wow! Moment of fear...
Never seen such damage.
I remember in a race here in Italy, in the GTAm of a friend literally exploded the flywheel (badly modified...) with the pieces that entered the ****pit through the transmission tunnel chipping the windshield from the inside (I let you imagine...). Despite this damage joint and transmission shaft, although damaged, they remained in place and when it exploded the whole engine was in full, around 6500/7000 rpm. For this reason I attribute your damage to a structural failure of the transmission shaft (some cracks not seen in the old welds?).
My 2 cents...

 

[lenul]

Thank you for all your answers!

There were no injuries but it could have ended badly if it had been on the road....

The test was done in fifth gear and it broke at 5300 rpm, so I think the problem is not the torque, plus there are no torsion marks on the shaft.

The propshaft is from OKP it's a new one with 9mm bolts, it has a smaller diameter than the original but I checked it is the same length.

The propshaft didn't really break, it split in two at the level of the slide.

I called the dealer who told me that they had already mounted this shaft on a car with more than 200 horsepower without any problem.

The only thing that was not perfect was that there was a slight vibration at high speed but nothing alarming.

What's the rear axle setup?

1. Lowered?
2. Rubber or poly bushes in trailing arms?
3. Cracked trailing arms?
4. Trunnion end bushes, new or old?
5. Trunnion pivot bush, new or old?
6. Trailing arm connection to the floor solid or rusty?

7. Engine and gearbox mounts new/solid as the other option is the engine moving forward

Pete

1. Yes, approximately like that

2. Heavy duty rubber for trailing arms
3. I don't feel like
4. 5. Absolutely new
6. Solid no rust on this car


Do you think that if the rubber of the shaft support had broken it could have had this kind of effect ? (even if it is new)

 

[yvesmontreal]

Can you show a photo of the split area...

 

[lenul]

Nothing suspicious…