TT...Thanks for the interesting link. I haven't read it all or digested it yet but it looks informative and valid so far. I'm sick and tired of the vibration in my car and have replace everything including the fan, motor, motor mounts, universals, drive shaft balanced, clutch, etc. I'm in the middle of a 5 speed conversion from Muncie and want to get to the bottom of it so this may help. I still suspect the left to right angle of the transmission tailshaft is not correctly in alignment but have to measure to prove it.

Good information from everyone on this subject...thanks.
Bill

 

I don't want to jack this thread but I do want to take advantage of the knowledge base that has responded so far. I have been chasing a vibration that occurs at about 70 mph and 1900 rpm's (5th gear). So far I understand the transmission rear end UJ phasing. So my question has to do with halfshalf alignment. What is an aceptable angle from centerline of the side yoke to the CL of the wheel spindle?. Inspecting my halfshaft UJ's I found the needle bearing wear pattern to be heavy on one side of the pinion and light on the other. Would this be caused by to much halfshaft angle?. I also found that the inside knuckle of the UJ was causing a ware pattern on the side yoke on the passenger side of the rear end but not the dr side. Again to much HS angle?. With the car on level ground I measure 6 degrees drivers side and 3 degrees pass side, if I adjust camber to bring the HS into +/- 1 the pass side tire is to far in at the top. I'm not a math major or alignment expert, so if I'm doing something wrong please point me in the right direction. The noise has to go.
Thanks
Russ

 

Great link TT, that is some good reading there, thanks!

 

With all the 5 and 6 speed conversions its good to see this info gets out there. And i continualy read threads where someone tries to get the diff pinion to tailshaft straightend and after many frustrating hours ends up with speed sensitive vibration. Yea most trans conversions get the trans tailshaft pointed at the diff pinion after hours of grinding and prying before installer ever asks why - no research. And i don't know why this info ain't provided with the fancier trans upgrade kits. Geez, for a $3k or $4k trans kit u would think the vendor would have something so help with this alingment question?

Not to say that if one may have a straight shot alignment and may not have vibration. But look at all those trucks running lift kits these days. Big drive shaft angles and not even close to straight tailshaft to pinion alignment. And for high power applications how 'bout those monster trucks. Ever look at monster truck drive angles? Maybe over 45 degrees while pushing thousands of hp?

BTW i read the Chevy Power Manual too - though i don't have it availible right now - and i don't recall any chassis information at all - let alone driveshaft alignment. I don't know why anyone would quote the Power Manual for a chassis topic? It discusses sb and BB engine building and GM performance parts.

IMHO i would leave the stock angles as is and for a trans conversion i would try to maintain the original angles if possible. The only reference i have is a book called "Practical Engine Swapping" and it preaches the parrallel installation - no straight shafts.
cardo0

 

If you put an alignment tool on the tailstock of the transmission you would find it points off towards the passengers rear wheel, it doesn't run straight back.
Now place the same aligment tool on the pinion yoke and you see the pointer pointing off towards the passengers front wheel?
Where is the parallel but offset here? Where is the universal equal but opposite? Theory is great but if your car doesn't match the THEORY what do you do?
I rotated, I did NOT offset further. I rotated the rearend housing and it takes very little to bring the pointer into alignment, I rotated the rearend slightly in the bolts until the pointer on the pinion pointed to the output shaft of the trany. At the same time I moved the tailstock just enough so it too pointed the the pinion.
My drivershaft no longer forms a VEE but actually all components are aligned.
I too have the Chevy Power manual and read the engine sections and the corvette section, didn't see the section on driveshats? could be there? I just haven't run into it but again I haven't read the book cover to cover, just the parts that interested me. That included all the corvette section.
Again I believe if you have a vibration problem, you try all the balancing tricks, new bushing and nothing gets rid of it maybe your power train is forming this weird angle like mine and with it straightened out you suddenly loose that shifter vibration or any other vibration.
My rearend is not suddenly moved over that one 1/2 shaft is too short and one too long, the rearend only needs the nose moved a degree or so to get it pointed forward, the 1/2 shaft doesn't suddenly run crooked because the pivot points are almost above the universal, very close anyway and the nose is far away so the effect is greatest out front.
As for advice from my friend Roger, a Richard Petty around here with an unparalled winning streak, over 50 races wins in a row I still trust his advice about getting my drivetrain aligned.
I am giving my opinion, it is not necessarily right and I don't need Jerks jumping all over me.

 

Why?? Because in the older copies of the Chevy Power book they devote a whole section to Corvette chassis preparation.....front suspension, rear suspension, transmission, rear axle and differential, brake systems, roll cage, frame preparation and modification.......alingment specs and roll bar size yet not a word about the diff being in crooked....
redvetracr

PS: this "jerk" can remember a time when a certain someone was measuring his bump steer with a tape measure and NOT a pair of dial indicators, the same person who said something would work because "it looked strong"......I wonder what Richard Petty would have to say about that.....

 

I have that chevy power manual. I read this section many times, complete drawings of roller cage, tube size, radius etc etc. Not a mention of setting up the drivetrain?
Take any stock corvette and bump steer is measured in inches, any one. Only when you get down to actual modifying it, changing tie rod length and outer tie rod positon is it necessary to get into dial indicators. 3/4 or 1 inch can be measure with a tape measure.
While I certainly have the money and the tools to do any job I please I still rely alot on my own ability and homemade tools if I am not convinced a more expensive way is not better.
I do teach engineering and lot of designs you can take one look at and tell right away where the weak point is. I trust my gut feelings alot.

 

doesn`t simple geometry tell us that when you move your pinion to the left one degree you are moving the right side yoke forward one degree and the left one back one degree??
...redvetracr

 

No. The pivot point on our rearends is at the back. If you have 1 inch behind the pivot point and 10 inches in front of this same pivot point moving the front over 1 degree would only change the back by 1/10 of a degree. It is not linear. Also the 1/2 shafts turn at 1/3 the rpm of the driveshaft so they are less affected by rpm.
It is like using a pry bar. You have to look at the distances and the fulcrum point.

 

Huh? If you rotate an entity 1 degree the entire thing rotates 1 degree regardless of the rotation center. The rotation center only has an influence on the 3D placement (coordinates) of "points" in the entity, if you rotate the diff 1 degree it rotates 1 degree, the pivot point does not matter. A change in rotational center for a given angular rotation only changes the resulting position in 3D, not the angle of rotation itself

A cirle has 360 degrees regardless of the radius/diameter. Sure, the resulting radial movement of a X degrees will be larger for a larger diameter/radius circle, still the degrees are the same..

 

Your right Marck. One degree is one degree. What I was getting at is actually a distance movement. If you move the front of the pinion over 1/8th or 1/4 inch the 1/2 shafts which are located very close to the pivot points move far less. This is of coarse a rotational distance and NOT actually moving the whole rearend over.
You are the man Marck.

 

Yes but Howard is talking about degrees and making a valid point, I mentioned the same issue some posts above that, when you are installing the diff crooked you are also messing up the suspension from side to side. Please red it all over again, we are not trying to knock on you or your car but rotating the diff is seriously NOT the way to do it. Please ask your race car friend Roger if he runs live axles or IRS cars and more importantly if he is running engine/trans offset and if so, offset the same amount as the pinion or not, the latest is what we have.

 

Marck you are right. Guys I appologize for giving you bad information. Howard and Marck proved I don't know what I am doing. I'll try and keep out of these discussions and my stupid ideas to myself.
You can't rotate a solid axles since it throws the wheel base out. But you guys already know that.

 

Don't be like that, why are you saying that? No one said you don't know what you're doing.

 

What makes us so sure that this diff is installed crooked?

Bear with me because I don't think I've read the full story in previous threads here, but it sounds to me like either the diff, or the engine, or both were crooked BEFORE, given that Norval's pointer tools formed a Vee.
The pointers appear to prove that the engine and diff are now on parallel (or even the same) axes, at least on the horizontal.
I know that for the UJ "work" properly the axes should be offset, but there will presumably be some offset in the up/down direction that will suffice?

We all know these cars aren't exactly assembled to the nearest micron, you have to ask what kind of tolerances are present in the rear end of the frame anyway, and how much difference there is out of the factory between things like diff/engine angle, and trailing arm length?

So Norval, did you have a wobble before you did the alignment, which disappeared after?

 

Wow! I didn't think this post would generate so much passion. For what it's worth, I read all the replies with enthusiasm and am greatful for the information contained in them.

Keep smiling!
Ian

 

Just a complicated subject and everyone is trying to share what they think is good info - no-one here trying to be a jerk.

Norval please don't take it so personal as u have always been a great resource on this forum and we understand u have a lot of hard earned research to share here. And i am convinced of your honest efforts as if anyone can get it right u can. But there are other schools of thought on this topic and maybe it seems your fighting prevalent ideas/hearsay by yourself - i know i've been there too. We all can see you have worked very hard to get your vette right and no-one wants to take that away from u Norval.:o

redvetracr, yes, yes, yes i will have to dig out my Chevy Power Manual when i can find it and have anther look. But maybe i'm thinking Chevy Power Manual while there's a Chevy Power "Book" published also - maybe not the same book? Regardless now i need to take a look and thx for the reference.

Ian maybe we can all smile as there very well could be a way to make the driveline smooth using either method.
cardo0

 

A long time ago I had a vibration that came in at 60 left at 70. The shifter would vibrate and I would have to rest a hand on it to keep the noise down. The first time my wife was in the car she was shocked at how bad it was.
The vibration left at 79 only to reapear at 90 so bad you didn't take it much higher because you were really shaking the car badly.
The ONLY thing I did at the time was align the drivetrain. With Marck link my drivetrain looked like the 1st picture, the drivetrain formed a Vee. Both the motor and rearend seemed to be off, not pointing straight back but both pointing off to one corner like I posted earlier.
I aligned both the tailstock and the rearend.
I intentionally run my speedo gears 10 % low so I know I have an honest speed and second when the wife glances over I have this extra cushion on how fast I am going.
My son rarelly drives the car and we were out making a quick run. He was driving and I told him to pick it up. While running I told him to not look down but quess the speed we were running at? He guessed about 90 mph and then I told him to look down. The speedometer was sitting at 120 mph or a true speed of 132. This was a steady speed, the car is just loafing along, I know I drive at this often, but the car feels abslutely smooth, no shifter hand vibration, no dash, no nothing but a smooth feeling.
If that solved my annoying vibration who are a couple of know it alls to call me wrong, chevy power is only a guide, it isn't a bible. We all have to look at our own problems and hopefully work them out.
I know it worked for me, I spent probably a month going over this until I figured it out and made the adjustments.
No one knows my car like I do, it solved my problem of vibration and yes I get ticked when these so called experts tell me I did it wrong.
I am still the type of hot rodder that is not afraid to think for himself, I don't get any help on anything and am not restricted in my thinking to what the books say nor what alot of experts on here have to say.
This is the last time I will post on alignment because it seems to be the wrong approach according to the EXPERTS
I check my speedometer by running with my GPS. It is extremely accurate and records a run as to distance traveled, top speed and it reads out constantly the true speed with an accuracy factor. A great tool for training my horse Strider and checking speedometer accuracy

 

This thread began with a question about the offset (in a birdseye view) of the differential pinion offset. If this discussion is still about driveline angles in a "birdseye" view, I think you are correct cardo0. it really is splitting hairs. If you were to align the motor, trans, driveshaft and diff in a straight line, you would be talking about an angle of 1/4 of a degree in the birdseye view!

All in all, I think either method will work because they are virtually the same. Good call cardo0.

 

Hey man, it's not like I'm getting any help here either, in fact you can consult your racer friend, I'm 100% on my own here and I like to meticulously research before I start something and I know for 100000% that I am right. That doesn't mean I don't think for myself, damn I think I thought this stuff over more than most people here. Reading a book and taking the advice and methods explained in it is not restrictive thinking, it's applying what you learned to the task at hand.
How did you learn everything you know? If you don't trust what's in the books you must be 100% autodidact.