Sorry to bust your bubble boys. Old school engine swapping is done with engine and diff parallel. Let the driveshaft U-joints do all the angles.

A line drawn out of the diff yoke should parallel a line drawn out the trans tailshaft. Lines never cross.

Look at any Monster truck and u will see the tremendous angles made by the u-joints but the trans tailshaft and diff axis lines remain in parallel.

cardo0

 

Yes parallel on engine and trans is best - but not always attainable. Remember you are dealing with a fixed location IRS. The problem is vibration harmonics from the U-joints traveling at different speeds. They should be around the same angle, hopefully less than 1 degree difference. The monster truck does sometime have extreme angles, but it is not a high mileage vehicle. For best joint longevity you would want to be not less than 1/2 deg but not more than 3 1/2 deg.

 

74modified is absolutely correct. And this is how I built my driveline, with parallell but opposite angles. Also called Z arrangement.
What I am trying to say is that there is an alternative arrangement called the W arrangement where the out going and in going shafts are NOT parallell.This arrangement will give the same conditions as the Z arrangement and will work just as good. This is tested and proven technology since the beginning of cardan shaft design and used all over the world in different applications.
Before you all starts to flame me, please read the technical documentation from GWB (Gelenk Wellen Bau) that I am linking to below. You will find all engineering and design information starting at page 38 and the detailed explanation of the Z and W arrangement is on page 40. (Download the pdf document).

www.gwb-essen.de/cataloge.html

I hope this will give clear and good information on the subject.

/Daniel

 

What the heck, thought I'd try it for myself. Yes that is cardboard.



I cannot feel any difference between either configuration while turning by hand and a little math suggests a relatively minor lift of the differential will create equal W-arrangement angles (1.88 degrees each side) in my drivetrain. Hope that works.

 

Sorry for not replying sooner, but was away from computer.

My reference to raising the rear was quite literally raising the mounting of the differential with respect to the chassis, not altering the angle front or back. I did need to alter that angle, but that was related to getting the driveline angles correct.

I ended up with about 2.6 degrees down for tranny, and 2.6 degrees up for the nose of the diff. To get this in my config, I had to modify the front diff bracket, but I doubt you will need to go that far. Simply trimming the rubber mount to get the right angles should do it.

BTW, fun fact I learned. One of the reasons there is an angle (apart from needing one with universals to avoid flat spots) is to gain interior space. What I found most interesting is that this angle is pretty consistent across most cars and is about 3 degrees. Here's the cool part. Did you ever wonder why if you sit an intake manifold on level ground the rear of the carb mount is higher than the front? Yep, it's to account for the engine being mounted on an angle Accommodating this angle ensures the carb sits flat and that there is an equal distribution of fuel in the bowls.

Good luck!

 

Your values are almost identical to mine, I had 2.8° down on the trans and 2,8° up for the diff. I too had to fabricate an modified diff bracket (the one that bolts to the diff.)

The transmission:


The Diff:
(90-87,2=2,8°)

 

Yes. Before embarking on my diff I read all 26 pages of your thread on another forum since our drivetrain setups were similar.

BTW, you do outstanding work!

-Fred

 

Aahh, now I remember your user name from the other forum!!
Nice to hear from you, and thanks for the kudos

/Daniel

 

Hey IGNATZ, I have what sounds like a very similar vibration under load as well. This is how I measure the angle of the driveshaft (see pic). It's low tech., but should measure it correctly. Can anyone see any problem with method? The protractor is magnetic and just hangs on the bottom of the shaft. As you can see I only have about 1 degree of angle and I definitely have a vibration under load that starts being noticeable at about 65 or so mph and gets worse the faster you go, does not seem to be engine related. I have a leaf spring that is just about flat (no curve at all with no load and sitting level) and this may be contributing to my vibration also. Hope this helps..

 

These angles must be with respect to .... what? Local vertical? Most people seem to think the diff is factory set to around zero to the frame.

Like your digital protractor, my digital cube is pretty cool because of the zero function. That means as long as the angles are small I can measure differential angles by moving it around. So for instance I zero it on the frame rail, move it to the diff (reads zero again) and then move it to the transmission (now 4.4 degrees). It's all relative and I don't care much about local vertical.

Knowing the length of the driveshaft and the moment arm of the diff, I can calculate how much to move the diff up to get equal angles between the two ends for W.

Now then there's a complication. Besides the up and down stuff there's the left to right stuff with the motor offset to the passenger side. Running a string fore and aft I take the arrangement to be of the W variety, that is the centerline of the diff is NOT parallel to that of the transmission. I am thinking there is some rotation of the driveshaft which will accommodate both misalignments but I don't see how to make this measurement with the body on. Alternatively I suppose I could view the drive shaft as a space diagonal but I don't want to. Did see a lot of math in the pdf but this is already way more of a science project* than I want.

_______________
*as my boss in my engineering job used to say, "don't turn this into a "science project"!

 

If you level the frame with the weight on the tires, you should take measurements from a true vertical axis.

Don't worry about how the factory set it. I had a completely stock setup and I ended up having to trim the rear bushing to get rid of a vibration a long time ago. If you notice, the diff x-mamber is secured to the chassis by the rubber top hat bushings, these will pivot the unit as you change the front diff bushing thickness to get you the angle you need.

The horizontal offsets are a different matter. You should work in the two planes independently. The motor and transmission are offset to the passenger side by 1 inch. The rear diff is offset to the passenger side by .85 inch. If your top hat bushings are good, I would bet your diff is close already. Be sure to check the tranny as the holes are slotted. This is where most of the adjusting needs to be done.

Also, I would not worry about the angle of the driveshaft itself, this (on its own) is irrelevant as it will change as the transmission and pinion angles change and will not guarantee that both angles are equal and opposite to each other, which is the most important part.

As each shaft rotates, the center section of the u-joint moves back and forth to accomodate the change in angle of the shaft. So, the front u-joint will rotate at a specific frequency as the shaft turns and introduce a force. The u-joint on the rear of the shaft (if the angles are opposite and equal) will also introduce this force, but since it is in the opposite orientation, that force is 180 degrees out of phase with the front force, so they cancel out (no vibrations). If one moves more than the other, the force is greater and the other's cancelling force is not sufficient to cancel out the full force. The resulting left-over force ends up being felt as a vibration. The smaller the difference, the smaller the vibration, and consequently the larger the force, the larger the vibration. That's why being close counts here as well as in horseshoes and hand grenades I've never done anything with configurations where both point in the same direction so I really can't comment on that setup.

Make sure your transmission and diff angles are equal and opposite, and then check the horizontal offsets after that. If those are good, you are good to go.

Cheers.

 

I had a similar problem and I know I was close because the vib would only happen when torque was applied over 50mph. I was able to tighten the pinion mount 2 turns and it went away. The bolt did loosen back up and the only thing that held it was a second nylon bolt to lock them in place.

I know it this might not be the tech way of doing it but ill wait until I blow the back end apart for all new bushings before ill bust out the angle gauge plus it's fixed

 

I think slvrshrk summons up everything
very good above. Get your angles equal on both sides and check the offset acording to his figures. Then you will be good to go.
As an information, the numbers you se on my photos are in respect to a completely level frame but that is really of no importance as long as they are equal on both sides.

 

I want to thank everybody who contributed to this, esp. 427Swede who provided something some of us didn't appreciate, i.e. the other driveline configuration. That considerably simplified my fix. I bumped up the diff by cutting the poly bushing way down, zero'd my gauge at the diff and got 4.35 degrees at the tranny and 2.15 on the driveshaft with the wheels on blocks, i.e. angle right in the middle. Little test run just now felt smooth. Since there is very little actual bushing there now I will probably modify the mount to angle it so I can replace it with a proper size bushing. This fix was a whole lot better than the major amount of shim I would have had to install to get the axes parallel. You guys are great. Way cool!

 

Glad to hear things are better! Just a quick question and thought. Is that 4.35 degrees at the tranny pointing down? I know you are thinking of leaving it and not shimming the tranny any more, but check the angle of your carb to see how much it is angled down in the back and make sure you are comfortable with it.

Shimming the tranny is no big deal. Once you find out how much you need to add, just buy a small piece of stock on ebay and drill the holes.

With my TKO600, I had to add a full inch of shim to get it into alignment. I wanted to keep the exhaust hanger so I added 1/2 inch under and 1/2 inch over the bracket and it worked out fine.

Whatever you decide, nice work on sticking with it.

 

Hi guys Ive been watching this topic closely as Im in the middle of a ls swap to c3 myself. I have experience with other motor/car alterations and just wanted to ask something if you dont mind. I agree with everything you have said but unclear as to your information about your "horizontal plane". Are you saying that if you look straight down from the sky through the body that the centerline of the motor/tranny doesnt have to centerlined with the rear housing and pinion? My understanding is they do or thats where the most vibration comes from under load from torque of the motor(wanting to twist) and the rear being held in place. Sorry to step in last minute but I wanted to see if theres something I missed. Thankyou

 

That's correct for a C3, if the motor is centered in the car by the factory by default, then that's where it goes. It could vary by car and I don't have enough experience to comment on other cars, but in a C3, the motor is offset. The motor/tranny is offset to the passenger side by 1 inch and the diff is offset by .85 inch to the pass side. The same rule applies to that plane, as long as the angles are equal and opposite they will cancel out. In the case of the horizontal plane, the motor and tranny need to be parallel to the diff. Take some measurements of your motor mounts and you will find they are offset by 1 inch to the passenger side. If you center the tranny mount, you are actually mounting the unit on an angle. This condition will make the angles from the diff to the shaft and the tranny to the shaft unequal.

While the difference in offset is tiny (.15 inch), having the two units parallel makes sure that the angles, however small, are equal and opposite.

Hope this helps.

 

Here is a photo I took at the U-joint connection to the transmission. The string runs from the diff shock mount bolt to the front of the motor.



The silver thing is just a flat magnetically clamped to the driveshaft to make an angle measurement. The driveshaft is 26", I think this offset is a lttle exaggerated from maybe not being exactly straight up. I don't know if the diff is aligned along the center of the car, I suspect so and I didn't take a lot of time to make more measurements so I can't guess at any of these angle magnitudes. This doesn't look tiny but I can't stand behind the picture very well either. Suffice to say there is some offset. Thing with the tranny is if you slot some mounting holes you can improve this.

If you search this forum you should be able to find pictures from a guy who used a laser to shoot a line from front to back. Saw that a while back but can't remember the details. And I think it was with a factory motor.

As to the carb SLVRSHRK, yes I have one and can kinda see some slope with the air filter on. My carb has sights in the bowls and I've set front and back individually. Going to leave it at that. If I shim the transmission there is going to be upward movement of the exhaust and I will end up either hitting the crossmember holes or stressing the pipes or both.

 

Ok thanks guys, slvshk I thought thats what you were saying .Adding to what you said if you look were the haromic bal sits, theres a recess for it in the cross member and you can defintely see the offset.Most of the swaps I had done have went the same way with centering the motor tranny and rear reguardless of position in the chassis. Vettes are new to me. Ignatz Even though you use string its a proven method and as long as your pickup points are right it works fine. I just pulled everything off the chassis again to clean and paint so ill put my rearend locating crossmember back in temp and see how it looks. ill try to snap a couple of pics then put everything back in and do the same. Thanks again for clearing that up.

 

Rather than start a new thread I'm going to chime in on this one that addresses the things I'm experiencing. My pinion angle started out at 2.8 down with the engine/trans angle being 2.0 down. In order to achieve equal driveline angles I cut the front diff mount 5/8 of an inch which reduced the down angle to 2.3 and gave me equal angles in a W-arrangement. I'm still experiencing the noise, (it's not a vibration) and I was thinking that in order to achieve a parallel arrangement (since it moves half a degree per half an inch) I'd have to raise the pinion 4 1/2 inches! That is obviously absurd, so the W-arrangement is my only option. The only thing I can think is that the offset being .15 off is causing a compound angle misalignment and that's where the noise is coming from. This has been the most intractable mechanical problem that I've ever experienced.