WIll this cause my halfshafts to break?

SilverBullitt

Registered User
I think I may have located the problem....on the differential...the cover for the pumpkin...it has a black bracket attatched to it to connect the rear of the pumpkin to the car...the bracket is two peice with solid rubber in between connecting the 2 pieces...I think it is reffered as the back differential brace...if the rubber has broken and just about deteriorated, would this cause the right shaft to break under slight load such as accelerating lightly from a stop...I have broke 2 new halfshafts on the right side and the cover is not broken on the pumpkin, the differential turns freely and makes no noise...the hub has been replaced with new bearings...could this bracket be the cause? I am replacing it and all of the IRS bushings....thanks
Chris
 
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SilverBullitt said:
I think I may have located the problem....on the differential...the cover for the pumpkin...it has a black bracket attatched to it to connect the rear of the pumpkin to the car...the bracket is two peice with solid rubber in between connecting the 2 pieces...I think it is reffered as the back differential brace...if the rubber has broken and just about deteriorated, would this cause the right shaft to break under slight load such as accelerating lightly from a stop...I have broke 2 new halfshafts on the right side and the cover is not broken on the pumpkin, the differential turns freely and makes no noise...the hub has been replaced with new bearings...could this bracket be the cause? I am replacing it and all of the IRS bushings....thanks
Chris

I don't think so. What did you do to break the axles each time?
 
XR7 Dave said:
I don't think so. What did you do to break the axles each time?

Nothing...they just started breaking...the right side one...I keep replacing it and under very light acceleration, it breaks...I have replaced the hub and it still breaks...no signs of the diff being broken...something is twisting and torquing and cause the halfshaft on the right to break at the cv joint near the diff...but the drivers side wont break...any ideas?
 
I'd suspect a bad bearing in the diff is causing vibration which is fatiguing the metal. I've seen some really bad bushings but they didn't cause broken axles and I don't think the whole diff could oscillate fast enough to fatigue the metal anyway.

I vote bearings in the diff itself.
 
XR7 Dave said:
I'd suspect a bad bearing in the diff is causing vibration which is fatiguing the metal. I've seen some really bad bushings but they didn't cause broken axles and I don't think the whole diff could oscillate fast enough to fatigue the metal anyway.

I vote bearings in the diff itself.

Well, I tested the halfshafts with the rear wheels off the ground and the car running at 90mph in 4th gear and the halfshafts did not vibrate or nothing...I could not see anything wrong...yet accelerating to 35mph at 1psi on the boost breaks it....does that still sound like the bearing could cause that?
 
Were the wheels at ride height when you tested them? If the car was held up by the frame, it wouldint be a good test.
 
Tickler said:
Were the wheels at ride height when you tested them? If the car was held up by the frame, it wouldint be a good test.


It was up on jack stands only to see if it would break the shafts when I tested it that way...when on the ground, there is something shifting around causing it to break at the cv joint nearest to the diff...it is breaking the boot and causing it to break the shaft almost instantly...I get a loud bang and thats it...
 
SilverBullitt said:
Well, I tested the halfshafts with the rear wheels off the ground and the car running at 90mph in 4th gear and the halfshafts did not vibrate or nothing...I could not see anything wrong...yet accelerating to 35mph at 1psi on the boost breaks it....does that still sound like the bearing could cause that?

Maybe someone else could give you a better explanation or possible cause, but I'm still thinking bearings. I broke 2 axles myself and I believe the cause was bad wheel bearings. I broke mine out by the hubs.

A bearing may spin nice and smooth but when you put a load on it may chatter. The same thing happens to supercharger snout bearings. They may spin absolutely smooth when turned by hand but chatter badly under acceleration (load).
 
I read in a chiltons about marking the position on lower control arm when removing before swapping half shafts,if you don't repostion them in the same location they were originally bolted in it could cause the joint toward the hub to bind up. Maybe I am wrong but this could be a cause of the problem. I'll look up the exact section when I have time tommorow .
 
First thing you need to do is find a machinist and do a failure analysis of the broken shafts. They'll be able to see if it's a issue with shock loading, fatigue failure, or possibly a bad batch of shafts.

Where it breaks on the shaft would be interesting to see. If it's breaking on the part of the shaft that's splined into the side gears, it's almost certainly an issue of the output shaft bearing failing or excess movement of the side gears in the differential assembly. Excess motion in either of these areas when under load will place extreme stress on the shaft as it wouldn't be properly supported anylonger.

The CV joint should be able to deal with any motion between the differential housing and the wheel hub. To break at that point it would have to be two things fixed within the diff housing working against the shaft.

I would consider pulling the entire diff pumpkin and having a driveline shop check it for tollerances and possibly replace the bearings.
 
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