Is batwing placement determined by pinion angle?

[JeffP1167]

As part of my c4 suspension into c3 frame swap the rear suspension will enter the picture. Is correct placement of the batwing mounts determined by pinion angle? What determines how high or low to mount the batwing? In a installation article I read 2-3 degrees is a preferred setting.

I assume the placement of the control arms on my c3 frame would be more in the area of the stock c3 trailing arms. What determine the angle of mounting the control arm bracket?

I will be using the factory rear transverse spring so by using all the stock stuff does this eliminate some of the guess work on fore and aft position of the control arm bracket or is wheel base the deciding factor?

After the front suspension is grafted into place and the frame is still on a jig is it best to mount the motor and transmission to set the rear end up & when you get the 2-3 degrees of pinion angle how do you determine the best angle for the transmission mount?

I believe the 82 has a steel driveshaft (but not sure) but either way will the C4 driveshaft from the c4 be the better choice due to possible u-joint differences?

Also what are the square looking blocks by the batwing mounting bushing?

 

[427Swede]

You should have the same angle on the out going transmission shaft but oppsite the pinion shaft. If pinion is up 3° the yoke on the transmission must be down 3°. Generally a maximum of 0,5° difference can be accepted. The more difference, the more un-synchronised will the u-joints be. That means driveline vibrations. Not good.

You have to work with both the transmission/engine and rear axle at the same time and try to achieve the best compromise.
Also consider the angle of the drive shafts, they also needs to be in correct position. I have no deeper knowledge of that subject so I leave that to others.
Keep up the good work you are doing!

 

[BBShark]

Forward control rods in a C4 intersect the CG of the car like this:

 

[clutchdust]

If given the opportunity, wouldn't it make more sense for that CG to be lower? I mean for what Jeff is doing, he's going to be fabricating quite a bit anyway. So if the lower control link was more parallel and the upper link was the one at more of an angle, it should put the CG point closer to the footwell.
Of course, I see that upon compression that would effectively rotate the CG underground. What would that do to handling? Good? Bad?

 

[JeffP1167]

Forward control rods in a C4 intersect the CG of the car like this:

But is it possible to do this on a c3? Being all this is going into my 82 I would think weight distribution, higher center of gravity. That a c4 placement would not give the results they designed it for like that on my 82.

I'm sure though if I get a very close placement no matter what I will feel a massive difference in handling.

 

[BBShark]

But is it possible to do this on a c3? Being all this is going into my 82 I would think weight distribution, higher center of gravity. That a c4 placement would not give the results they designed it for like that on my 82.

I'm sure though if I get a very close placement no matter what I will feel a massive difference in handling.

I wasn't saying that you should replicate the C4 position on your C3. Just showing you why they put them where they did.

 

[Ralphy]

I would think you have to start at the halfshafts. First you would need to determine what your ride height will be. At this point the halfshafts should be parallel (static). Now you need to determine at what degree the third member needs to be to match angles. Curious, is there a difference between the differentials center lines, halfshaft to pinion?