Jag rear end front to back alignment

[roadrod2000]

I have been working on my Unique 289 FIA and discovered that the rear axle (a Jag unit) was tilted slightly to the right. I have corrected that alignment issue (not easy because it meant relocating the mounting plate that is welded to the frame above the axle) and now I am trying to find information on the alignment of the axle front to back.
I am trying to determine if the rear axle (which hangs from a top mount) needs to be tilted forward or backward from a "level to ride Height" position and thus changing the direction of travel of the rear suspension from straight up and down to slightly forward or backward. Thanks in advance for the help
Rod

[mickmate]

Hey Rod, Dougs CCX was a question for us when we did the drivetrain alignment. I seem to remember the diff was tilted back about 4.5 - 5 degrees. As you've said that effectively gives the rear a caster angle. Are you using a radius rod or control arm of any kind off the lower arms (dogbones)? If you can add it to the top of your hubs or have provision for it a Watts linkage is the way to go.

[strictlypersonl]

Set the vertical angle of the pinion flange perpendicular to the angle of the transmission output shaft. Everything else follows.

[roadrod2000]

Thanks for the quick reply, that is exactly what I am looking for. The car has radius rods that come from the very back and center of the frame forward to the control arms, there is also a brace that comes forward from the same area as the radius rods and attaches to the Jag center section. Just to clarify, when you say tilted back I'm guessing that you mean (since the center section hangs from the top) I need to swing the axle forward and thus create a positive caster (probably not the right word since caster has to do with steering)
Do you think that I should fix the center section at 4.5 to 5 degrees or allow for adjustment for different set-ups?

[roadrod2000]

Originally Posted by strictlypersonl

Set the vertical angle of the pinion flange perpendicular to the angle of the transmission output shaft. Everything else follows.

This also makes sense. If this is not followed will it cause vibration?

[mickmate]

Yes Bob is saying make the angles the same on the back of the tranny as the front of the diff. Check out a driveline angles drawing to clarify http://www.streetrodderweb.com/tech/.../photo_02.html. They should be the same but not too much or too little of an angle. Most people recommend 2-3 deg. The rods description is sounding like a Watts if it's going forward and back.

[roadrod2000]

Thanks for the info guys, the link and related article explain it well. I'll double check the pinion angle and make sure that it is right.

[767Jockey]

What does Unique say? How do they set theirs up from the factory?

[roadrod2000]

Originally Posted by 767Jockey

What does Unique say? How do they set theirs up from the factory?

I posted this same question on the Unique owners forum and didn't get a reply. I sure they come from Unique Properly set up, but I have had to re-build, reverse, and/or re-engineer alot of modifications done by the previous owner. When I relocated the center section to correct the right to left problem I realized that I also needed to know the proper front to back alignment.

[767Jockey]

Originally Posted by roadrod2000

I posted this same question on the Unique owners forum and didn't get a reply. I sure they come from Unique Properly set up, but I have had to re-build, reverse, and/or re-engineer alot of modifications done by the previous owner. When I relocated the center section to correct the right to left problem I realized that I also needed to know the proper front to back alignment.

I don't own a Unique so I have no first hand experience with them, but I have always heard that the Weavers are excellent folks to deal with. Why not give them a call and run the problem past them? They've been around for ages, they have probably seen your problem before, maybe more than once. Good luck.