I spent some time looking over my chassis rebuild last night checking for loose bolts etc and noticed the differential is offset in the frame a small amount to the right (passenger side). See pics in my last"Rookie" posting.

If anyone can confirm this to be correct, please let me know the logic behind it and what the offset dimension should be.

Thanks
Ian

 

ttt
looking at mine when i had the body off I thought i noticed the same thing but i think it was just the angle i was looking at it. Only way for it to be wrong is if someone retapped the holes in the crossmember or the car was hit and you would see bent framerails.

Look at it from the rear. The front portion of the differential is tricky to the eye. Take some measurements from the left and right frame edge to the diff.

 

I know that my engine is offset to the passenger side of the car, and I'm not sure if this is a big block thing or not. I didn't notice my differential being offset, but I haven't measured it.

 

The engine and driveshaft are offset. The diff. itself is centered.

 

To answer your question, the offset IS correct. Chevrolet engineers had the engine offset 1" to the right incorporated in the 1963 Vette and it continued through 1982.

 

Not only is it offset but it is also crooked. If you could put a square on the pinion yoke you would find it points off towards the passengers front tire.

 

I've noticed the same thing. The offset measures out at about 1" so I can understand this being a factory set-up possibly for torque reasons with the big block, but there is very little clearance in the bolt holes that would cause the pinion to point right. I'm not happy with the alignment of the rear sway bar, so I think I'll disconnect the rear spring and try to line things up a little better.

 

I slotted 3 of my 4 mounting holes and rotated the rearend towards the drivers seat to better align the drive train. I made a gage that goes on the front of the pinion and to the center drilling in the back of the output shaft on the transmission.

 

the diff is centered, the pinion and the engine/trans are offset. The diff is NOT supposed to be crooked, the pinion/input axis should point straight ahead parallel to the car's center line, same for the engine & trans. Offset but parallel to the centerline. The only part that should be crooked is the drivehsaft, pointing inboard and down.

I spent a lot of time and put in a lot of effort to get it all lined up eprfectly (with the ZF6 speed and the C4 Dana 44) and I used laser levels to align the whole deal.
This topic comes up every now and then and you should most definitely NOT angle the engine/trans and diff to point at each other from a birdseye view. The opposing angles rule that you use from a side view also applies to the birdseye view and the only way to get this right is to have everything parallel with the center line.

Take a look at this pic, this is how it must be done (the cneterlines are excaggereted as is the offset, otherwise it's not visible in the model). The pic is a view from UNDER the car so the offset is to the pass side, even if at first glance it appears otherwise. I did this because the underside of the model is less cluttered and this makes it easier to see. Notice the driveshaft angle, at each yoke end you have similar but opposing angles. The engine is offset by about 1 (in my car, exactly 2.5cm) the pinion offset is around .85".

The diff offset is there for an obvious reason, both halfshafts have to be the same length and the rest of the suspension corner also, so this means the case has to be centered but with the ring & pinion setup like it is the pinion is a little off center.

 

The motor and the transmission are offset 1 inch to the passenger side. The diff is centered with the pinion yoke offset about 1/2 inch to the passenger side.

 

I even measured it on my car, the pass side engine mount is shorter by 5cm that's almost 2" meaning that there's a 1" offset. When i measured the pinion it came to .85" offset.

 

You guys can do what you want about a birds eye alignment but mine is right on. I spent considerable time getting this birds eye alignment straight. I don't believe you need both up and down and side to side to be off. Universals need a slight bit of angle to allow the needles to roll, if you have perfect alignment the needles would not move and thus pound into the caps. The slight movement keeps them from pounding but you do not need both up and down and side to side movement.
I had a vibration at high speed and once I corrected the alignment it runs perfectly smooth at any speed. I often cruise in the 120 mph range and it is dead smooth. The shifter doesn't vibrate.
A race car builder told me about aligning the drivetrain and I went by him and it worked for me.

Marck I have a running car, no theory but an actual test car that I can take out and find out if theory or not is right.

 

All the engineering books tell you to algn w/ the centerline and only angle the driveshaft. Universals need a misalignment yes, in the way I align it, it has misalignment in 2 planes, yours just in 1. You angle the trans to aim at the diff and vice versa, so in birdseye view you have absolutely no angle, you are contradicting your own advice ??

That race car builder probably used a 0 offset drivetrain or one that has the same offset as the pinion offset, a common practice.

Running car or not, can't argue with solid engineering. Just because it works for your car that's no reason to tell others to do it the same way when sound engineering principles and rules tell you to do it differently.

 

http://www.clubfte.com/users/jniolon...nephasing.html

read that

 

As mentioned above, the most important thing is that the centrelines of both the diff and the engine/tranny are parallel , from above/below and from the side.

Universal joints aren't true "constant velocity" joints, meaning that if you turn one end of a "bent" UJ at a constant speed, the other end will slow down and speed up (like a sine wave)...obviously this doesn't happen if the UJ is totally aligned.

But if you have another UJ on the other end of the same shaft, at an identical angle, this same effect cancels out the oscilations. So in effect you have an oscillating input coming out as a constant speed output.
That's why UJ's should always be used in pairs, and both be angled at the same degree from the centreline of the shaft connecting them. It's hard to describe in words alone, but with the propshaft set up right, you should have:

front uj: constant rpm from tranny o/p shaft is converted to oscillating rpm in prop shaft
rear uj: oscillating rpm of prop shaft is exactly cancelled and "converted" back to constant rpm in pinion yoke.

but this only happens if the angles are right.

If they're not, you end up with vibrations, and premature UJ and drivetrain failure.

 

TT, think your last post and mine just crossed in cyberspace there, I believe your link probably says much the same as what I've just said - they've got the benefit of piccies though!

 

another thing, if you angle the differential to have the pinion point to the pass side, this also moves the suspension corners, with a stock type trailing arm setup this means that for a set toe the left halfshaft is angled differently from the right (fore and aft), as are the camber rods. if you then add the 6 link rods and weld the mounts to the crossmember and use the same length welded mounts then the 6 link rods are not in the same birdseye plane as the other components. More reason not to angle the diff.

 

Yeah, I basically also said the same thing in my 1st post above. We totally agree
This whole discussion has visited the forums before, on the alignment of a keisler conversion and then there was a discussion also and since some people don't believe what I said or the mdoel pics I searched the net and found that site, it describes the whole thing neatly and with pics...can't beat that

Having a car that drives or not has little to do with it IMO and frankly I find that a little below the belt.

 

From what I've read so far, it looks like I need to take some serious measurements and continue the research before making any adjustments. At this point in the rebuild, I do not have the motor or the transmission in the chassis. This sounds like it needs to happen before a baseline can be taken. Hopefully the set-up I currently have was not effected by the frame repairs done. We were very carefull with this alignment before and after replacing the #3 mount frame rails (+/- 1/16").

 

[QUOTE=norvalwilhelm;1558453372]You guys can do what you want about a birds eye alignment but mine is right on. QUOTE]

Except by moving the pinion to the left your right side yoke/halfshaft is now pointing forward of the axle centerline and your left side yoke/halfshaft is pointing behind the centerline....it sure sounds like your diff is in there crooked...and the race car builder....probably using a 9" or a quickchange but not an independent rear axle??
...redvetracr

PS: after reading the Chevy Power book (information supplied by GM engineers) I would think if the diff/pinion needed to be moved sideways they would have told us to do it.....Like you said Norval "your going to do what you want"...Me...I`m listening to GM engineers and I HAVE a running/race winning car to prove them right.....