Hurricane IRS and Driveshaft Problem

[Spuddyboy]

Hi All,

I am building a Hurricane Motorsports kit.

I am at the point of measuring and ordering my driveshaft. I have discovered a problem and would welcome your thoughts.

My differential is not square to the frame, it is twisted to the passenger side. This is different than the "offset" the pinion has in the case to the passenger side. The centerline of the pinion actually points towords the passenger side.

My engine/transmission centerline is parallell to the frame.

I discovered this by measuring the set up pictured.

I was 5/8" closer on the passenger side than the drivers side.

In discussions with the people at Denny's Driveshafts, I need to have the relative angles between the pinion and the transmission tailshaft as close as possible. If one is more than the other, a destructive vibration can occur. I will probably have to re-fabricate the back bracket holding the differential to the IRS frame, and move the back of the diff slightly to the passenger side to bring the pinion back square and parrallel to the frame. This might knock my axle shafts off from being perpendicular to the diff. I see dominoes falling here. The Denny's guy also mentioned that I need to be aware of the "plunge" in the CV joints of the axle. Moving the diff might limit the amount of plunge available in the joint. I ran a string between the two axle nuts across the top of the entire IRS, and the axles appear to be straight and perpendicular to the diff housing at this point. I plan on measuring the axles and suspension mounting points to determine if they are square or offset in relation to the frame. This might suggest that the whole assembly is off, not just the differential.

Denny's also recommended avoiding compound angles (angles in two planes). This is a second problem. The pinion actually points up approx 4 degrees. The tailshaft points down approx 4 degrees. The tailshaft is slightly lower than the pinion. This sets up a decent angle in the up-down plane. Since the pinion is already offset to the passenger side about an inch from the centerline in the side to side plane, that creates an angle in that plane too. I will probably have to shim the transmission mount up, and adjust that bracket mentioned above for the diff to bring these closer to the same height and parallel. That would remove the angles in the up-down plane.

I would welcome others thoughts, suggestions and findings.

Regards,

Evan Smith
Hurricane HM1103

[mickmate]

Does the flange rotate straight? Can you loosen your diff mounts and get it to straighten slightly? Have you done some frame measurements to check whether that piece of the frame is out? The diff should have been fixtured for welding. The 4 deg angle sounds pretty good being parallel like that. You want the angle to allow needles in u-joints to roll without having excessive angles.

[Spuddyboy]

Hi Mickmate,

Thanks for the reply.

The flange does rotate straight. The nose of the pinion points 4 degrees up and 3.8 degrees to the passenger side.

I did check the frame for overall square and plumb a while back, but did not check to see if the IRS sub-frame is square to the main frame.

That's next I guess.

I removed the back bracket from the Diff and can rotate and lift the unit to square. I am considering fabbing up a new rear bracket, as long as the axle positions check out.


Regards,

Evan

[mickmate]

Sounds like you're on the right track, hang in there it's all worth it!