I've been reading the archives lately about pinion and drive shaft angles. After spending a few quality hours today with my project (LS6-4L60E) I found that some of the information that has been posted seems to be The post topics are based around changing the pinion angle to improve the dynamics of the drive shaft angle. The rear end of the differential is machined flat on both bottom and top to mount to the crossmember and the spring. Any adjustment to the front of the differential would result in a positive or negative twist at the crossmember and spring. I highly doubt that this is acceptable. It looks to me as though the factory set up is 0 degrees. The only way (that I can see) to change the angle without putting twist stress on the spring and crossmember is to make opposing wedge shape shimes for the top and bottom or machine the angles into the differential mounts.
My game plan going into today was to get my transmission angle to pinion reduced as much as possible. Looks like about 3-4 degrees down on the transmission/0 degrees at the pinion with a 1" passenger side offset.
If anybody has angled their pinion up to counter the transmission down angle, I'd like to hear how you did it. I also got a post last week about the differential being offset in the frame. I believe that is not correct. I have also seen different accounts as to why the engine is offset 1" to the passenge side. I'd guess part of it is to offset torque load under hard acceleration. Others have said it's to increase driver foot room and balance driver weight. Anybody know the facts???.....gp

 

I'm not sure if I am giving you facts, but we are in the process of doing a body off resto. In order to repair the rear kick up, I had to remove the rear cross member. Upon replacing the crossmember I refered to the frame drawings and noted everything is off center to the right. At first I thought this odd, until I looked at my differential. The yoke exits the diff, offset to the right. The diff is centered in the crossmember, this keeps both half shalfs the same length, the ring gear in the diff is centered, so the pinoin gear has to be offset. I really couldn't tell you why all this is that way, but the frame centerline can be really deceving until you realize it. If you ever find out the exact reason, no b.s, please post it.


Clyde

 

Clyde,
I originally though you were saying the differential was mounted off center in the frame. You are absolutly correct. The diff. is mounted on center and the pinion is offset to the passenger side. This compensates for the driveline offset. It's very deceiving when you stand back and look at it. Thank You for your input.
http://s187.photobucket.com/albums/x...t=DSC04103.jpg

Now, does anybody have any feed back about changing pinion angle?

 

I'm in a similar situation right now. I put a 1/4" aluminum plate between the crossmember and the diff cover to lower the back a bit so I could raise the nose more. I now have about a 1/4" rubber cushion, squashed to about 1/8", between the nose mount and the frame, and still have several degrees to go to get parallel with the trans tail which I have raised 1/2".
I feel I am putting too much twisting stress on the crossmember right now. I too have concluded the only way is to use tapered shims on the diff rear (1/4" to 0") and then relocate the holes in the front mount so a cushion can be used. I figured (roughly) that the diff yoke needs to rotate up about 6* which equates to about 1 1/2" pivoting at the crossmember. This puts the nose mount way beyond its limit.....I don't need to worry about the spring because I have the dual-mount, but I am wondering about the strut rods. I suppose they should have a tapered shim too to bring them back to stock angle....
All my "calcs" are very rough right now, and this project is going to have to wait several months, but I too would like to hear any input others may have. I know there will be more to it than this......

As to the engine offset to the side, the reason I heard is to give the car equal weight balance with one person--the race driver--in it.

John

 

 

I'm going to try to figure out how to modify my diff cover to accomodate a 2-3 degree pinion up angle while maintaining the stock mounting locations for the crossmember and spring. I have a new rear spring from VB&P. I wish I had bought the dual mount set up! I'll make or modify the front mount to as you suggested. I think I'll get a spare diff cover to play with so I don't mess up mine. I think it will be a combination of machining material off the diff cover and adding the wedge shims. The challenge will be to maintain the same centerlines at the half shafts. Is this stuff fun or what!

 

Palamesa,
I figured the diff & trans are off by about 8* or more in opposite planes, with the stock set-up. I never really had a vibration problem until 85-90 MPH, and even then it was not bad.
My idea is to make two tapered shims, one between the crossmember and diff mount surface (I don't think I like the idea of machining material off of the diff mount....!) and another smaller one of equal angle to go inside the crossmember to keep the boltheads true to the diff mount plate. And yes I guess a third shim for the strut rod mounting plate to keep it true also.
A shim tapering 1/4" in 3" equals 4.7* which is raising the diff yoke about 1", which with raising the trans tail 1/2" (almost 1*), gets it pretty close.......There is still more to get, but using the nose mount /cushion it should be doable....
The vertical change in halfshaft location I would not think would be enough to worry about, it is the relationship between strut rods and halfshafts (which developes the roll center of the car) which is important and varying that is a popular mod anyway.

Just thinking out loud here......More as I think about it.....

John

 

I dont understand how anyone can intelligently play with this sort of stuff with the body on the car, and I been reading these type threads and seen most of the ideas/concepts, and fail to see how they can be executed with any precision, body ON.....

All I know is whit my putting a 700 r4 into my Muncie '72, the vibrations were rather noticeable....all I did was shorten the driveshaft, and measure the offsets, muncie to 700, and alter the mount accordingly...
bolt it up, and so had the vibration in the shifter, as it was still tied to the frame, modded stick shifter....well, when going to the 200 4r I notice that vibration is gone....dunno the source, or reason...angle?, driveshaft?, tranny?....no clue....

 

The angle the shaft leaves the tranny and meets the diff need to be the same. Most people adjust by adding or subtracting shims (I used washers)under the rear tranny support. The engine is not centered in the frame, it is offset to the right to accomodate the steering linkage. This is the reason for the offset. I installed a Mustang T5 manual tranny in my 79, replacing the 350 auto. I had no vibrations whatsoever.
Bernie

 

See my above post with photobucket link.....Body Off.

The point of this is that the factory set up is less than ideal. When you go with non stock transmissions that are longer, it amplifies the problem. The stock set up for the pinion is 0 degrees. The stock location of the trans tailshaft is pointed down. All the drive shaft experts say these need to be parellel. The only way to do this is to jack up the tail shaft (limited by tunnel) and point the pinion up. This discussion is about pointing the pinion up.
I know some guys have done lowering of the differential. I'd like to hear your thoughts....gp

 

Bernie,

I believe that simply adding shim the the crossmember mount will cause the crossmember and spring to twist when you tighten up the front mount. As JPHIL and I were discussing, the shims need to be opposing wedges to create the diff up angle while maintaining flat mounting surfaces. We are working on figuring it all out if you'd like to join us....gp

 

It has just stuck me that the angles could both be zero and still work fine, as long as there is a "correct" amount of angle at each end of the shaft. Think about it... If the CL of the driveshaft and pinion are parallel but not concentric, with an equal but opposite angle of 2-3 degrees from parallel to each point, wouldn't that introduce the desired dynamics into the U-joints?

Further, it would appear alltogether possible to have the crank and pinion set at opposite but equal angles, and end up with zero degrees at the joints if those CL's happen to be concentric.

Excuse my hasty grafix...

 

Skunk,
Yes that is exactly what we are after.
The OEM set up has both trans and diff pointed down, we want to rotate each to raise the yokes into a parallel yet offset plane.

John

 

Also, it is not feesable to raise the transmission tail shaft enough to get it parellel to the pinion. It will hit the tunnel long before you get to 0 degrees. The idea is to get it as high as possible, then match that angle at the pinion. Lets say for example that I am able to raise my trans tailshaft to about a 2 degree angle where it is tight against the tunnel. I'd then set the bracket for the trans. to settle down at about a 3 degree angle to have a little room between the trans and the tunnel. I now need to angle the pinion up 3 degrees for the "optimum" set up. I realize many have made swaps and have no vibration problems. JPHIL and I are working on making it as mechanically correct as possible.

 

Here are a couple threads i recently posted. My original and then one answering someones questions. May long and drawn out, but you may find some info helpfull.

I have had a driveline vibration in my 81 and after new tires, suspension, u joints, driveshaft balance, rebuilt rear dif, (all needed anyway), i still had a vibration that would pickup around 55 and get worse right to 90. The shifter would rattle and seat of the pants. I was reading about driveshaft angles and all that. Its very involved and will elaborate if someone wants more info. But my angles even w new engine/tranny and diff mounts, were way off.

I had 3.5 deg between the diff and driveshaft, and .2 deg between the driveshaft and the tranny. Wicked vibration. I altered the pinion mount and brought up the diff so I now have 1.3 deg between diff and driveshaft and adjusted tranny mount down to get .9 deg between driveshaft and tranny. Now, ther is only .4 deg difference between the two u-joints instead of 3.3 and the largest is now only 1.3 deg.

All is smooth, real smooth, excellent.

A lot of work, 7 hours last night till midnite. measuring angles and made a nice chart and all. The idea is no angle greater than 3 degrees and the drive angle and the driven angle need to as close as possible so they cancell out the rythmic cycling of each u-joint.

I ended up removing the lower rubber differential pinion mount and removing almost all the rubber from it. Only 1/16" rubber left on the steel washer. That raised up my diff yolk and got my diff/driveshaft angle from 3.5 degrees to 1.3 degrees. Then space up or down the tranny mount to get the tranny/driveshaft angle as close to the diff/driveshaft angle as possible.

The simple universal joint, as used on most automobi-les, is basically two Y-shaped yokes connected by a cross-member called a spider. The spider is shaped like an X and arms that extend from it are called trunnions.

The spider allows the two yoke shafts to operate at an angle to each other, When torque is transmitted at an angle, through this type of joint, the driving yoke rotates at a constant speed while the driven yoke speeds up and slows down twice per revolution. This changing of velocity (acceleration) of the driven yoke increases as the angle between the two yoke shafts increases. This is the prime reason why single universal joints are not used for angles greater than three to four degrees. At four degrees, for example the change of velocity is .5%. At ten degrees it is 3%. If the universal joint were set at 30 degrees and the driving yoke were turning at 1000 RPM the velocity of the driven yoke would change from 866 RPM to 1155 RPM in one quarter of a revolution. In the remaining quarter revolution the velocity would change from 1155 RPM to 866 RPM.

On a one-piece drive shaft this problem can be elimi-nated by arranging two simple universal joints so that the two driving yokes are rotated 90 degrees to each other. However, the angle between the drive and driven yokes must be very nearly the same on both joints for this to work. This allows the alternate acceleration and deceleration of one joint to be offset by the corresponding deceleration and acceleration of the second joint. When the two joints do not run at approximately the same angle, operation can be rough and an objectionable vibration can be produced.

I used a digital angle indicator. Removed the drive shaft and used it on the differential and transmission yolks on the faces where the u-joint straps would bolt on, to measure those angles. (be sure they are straight up and down or the angle changes). Then install the driveshaft and measure it along its length. You will be taking the driveshaft in/out many times during this test and info gathering. Dont bother to bolt it in each time, place the trunions in the cups and slide the tranny slip joint back to secure in position. I had to alter the diff pinion mount to raise it up to get it right. Then raise/lower the tranny mount and find a combination that gives you nearly the same. Very important. My angles are within .4 of one degree of each other. Take good notes and make a chart of each angle each time you make a change.

Hope this helps

 

Frank,

Thanks for the detailed reply. This is the exact problem we are working on. I'm not sure you addressed the number 1 issue though. That's the twisting stress put on the upper crossmember and spring. The diff has a 3 point mount. Upper crossmember, spring and rubber pinion mount. The factory design on the rear mounts (diff cover) is they are flat and level. The front pinion mount keeps everything level. By simply cutting down the front bushing and tightening up the front, it puts allot of twisting stress on the crossmember and spring. When the front comes up, the rear mounts are no longer flat. I'm working on a design right now that lowers the diff.and provides a pinion up angle while keeping the crossmember, strut rod & spring mounts flat. I'll keep you posted as I have more time to get it modeled up in SolidWorks....gp

 

Palamesa,

I see your point. I would have to do the trig, but at first glance at the moment of rotation, when I pull up the pinion mount, doesnt look like the upper crossmember mounts would rotate much as they are located above the pinion mount. Dont forget that as the pinion is raised, it also wants to come forward as well. The pinion mount is located in front and below the two upper crossmember mounts. The axis between the upper mounts is the center of rotation when adjusting the pinion mount. When lowering pinion, it goes down and back, when raising, it goes up and forward.

You would need to measure the distance between the imaginary center line between the upper mounts to the pinion mount. That would be the radius that the pinion mount moves about. My car measures 18". I probably raised my pinion 3/8 to 1/2" max. At a 18" radius, using pie X diameter, 1/2" of pinion travel equals 1.6 degrees rotation at upper crosmember mounts. I dont think thats stressing the upper rubber mounts.

For the spring twist, the spring is mounted directly below the moment of rotation (being the axis between the upper mounts). So as the differential would rotate about that point, as in the case of raising the pinion mount, the area of the spring mount actualy moves forward and of less of an amount compared to the pinion hieght change because its moment arm, (distance to the axis of rotation) is far less that of the pinion mount. Mine is measures 7" . 1.6 degrees rotation at 7" moment arm equalls .38 of the 1/2" pinion change or .19''. So the area of the spring mount moves forward .19" which is not much when you figure the "hanging" type hardware used in these cars.

And to be real acurate, measure the distance from the axis between the upper mounts to the axis lined up between the lower spring mounts (on the hangers) with weight on the spring, and thats the true moment arm. Mine measures 8.5" from upper spring mount to point where end of spring meets the hanger. 1.6 degree of rotation at 8.5" moment arm equalls .47 of the original 1/2" pinion change or .24".

So to summerize my calculations. By raising the pinion mount 1/2" (and thats stretching it), we rotate the differential about the upper crossmember mounts 1.6 degrees. Moving the area of spring mount on carrier forward .19" and moving the lower spring hangers forward .24".

Considering the loosness in the hanger system design and the play in the hanger bolt holes, these changes dont seem bad at all.

Thanks for your time, I had a chance to excersize my mind, now I can go sit on the couch w a cold one.

Enjoy your project.

 

I Have been down this path in my 74r...firstly,the engine is mounted significantly to the rhs of the fore and aft centerline of the body,secondly,the engine is not even parallel to the centerline of the body,it is offset several degrees in the horizontal plane for the obvious reason that the output shaft at the end of the gearbox has to point at the diff which is in the center of the body.Just imagine how much fun you can have when you want to put a steering box and brake master cylinder and power brake unit on the rhs as part of a rh drive conversion....we centered and lowered the engine by cutting off and making new engine mounts,this was so the 700r4 would fit into the transmission space and the optimum 2* drop to the diff could be obtained in the vertical plane and to minimise the horizontal angle to almost 0*....worked out pretty well in the end,but it was far from easy...john

 

Frank,
I hope I didn't come across as acting like I know more about this then the rest of you. Sometimes I need to think out loud to get some feed back. To me, this is a very interesting problem to solve. I'll look over your calculations more closley when I'm at work tomorrow. I just came in from working on my car. I mocked up a shortened drive shaft to help get the angles right. Anyway, lets continue to share information as we all get this thing right. I'm not sure if your body is off but mine is and I will be spending quite a bit of time to get this right. If anybody is wondering why I'm spending so much time on this, here is the answer. I just got back from vacation with my wife. She spent ALL of my Corvette project mad money. Lets say I have allot of free time while I try to rebuilt the fund. The bottom line is that I hope we can all work together to solve this problem...Thanks...gp

 

The magic crucial factor seems to be to get the verical down angle at the gearbox end pretty much the same as the vertical up angle at the diff end with as little horizontal agle as possible and if there is any to try to the left angle more or less the same a the right angle....and in neither case more than 2*......it isnt as easy as you might think because the shape of the floor(inparticular the transmission tunnel )makes it very hard to adjust the gearbox position(particularly since i installed a 700r4 which is a different shape to the previous T400)...john