GM a-body best driveline angles?

[gearbanger]

I have read a good bit about driveline angles and I understand about equal and opposite angles and about the pinion raising under launch conditions and allowing for that. But what I am doing is a frame off on my GTO and at this point I am trying to figure out what the "best" angles are and build the rest of the car around that. I currently have the engine setup at level. The driveshaft is about a half degree down to the pinion, and the pinion is level. So in other words I have equal and opposite angles and I have the working angle at 1/2 degree which I have read is about the min for proper u-joint operation and long life. I also have learned that the pinion on the a-body is about 5/8" off center, which if you calculate the angle, comes out to just a little over a 1/2 degree of offset. So I figure I could lower the tailshaft a little and raise the pinion a little and have everything in a dead straight line, while getting my u-joint reliability from the 1/2 degree offset angles.

What is the best driveline angle setup????

[gearbanger]

No one?

[gearbanger]

I have been reading some more about this and something I hadnt really thought about was carburetor position. I sat the intake I am using on the motor and checked the level again, and it appears I would need to have the motor about 3.5 degrees down in the rear to have the carb base level at ride height.

How important is it for the carb to be level?

It seems like on a launch or under hard acceleration, it may be better to have the carb tilted forward some amount. That might make fuel distribution better under power.

[andrewb70]

Will this car be lowered?

Essentially, if the car is lowered, you will want the transmission as high as possible. When a-bodies are lowered, the centerline of the pinion actually goes above the transmission output shaft. So by raising the transmission, you make the driveline angles much better. Your limiting factor will the hump of the transmission tunnel. The back of my trans is so high that I have about 1/8" clearance between the slip yoke and the transmission tunnel.

Andrew

[Vegas69]

You have probably read one of my responses on intake plane. Without the body on the car it's going to be hard to set it as close to the tunnel as possible. I'd shoot for 3 to 3.5 since that is clearly what GM spec was. You can always shim your transmission up once you have the body on the chassis.

[gearbanger]

The car is lowered 2-3 inches. If the tranny and rear are dead level, I will have about 1/2 degree of driveshaft working angle front and back but my carb will be going downhill toward the front of the car by about 3.5 deg.

But if I set the carb level, then the motor will have to be going down toward the rear at about 3.5 deg. So the pinion will need to go up about 3.5 degrees and that will cause driveshaft working angles up near 4 to 5 degrees.

I would rather have a perfect driveline than worry about the carb. I could even angle mill the intake some to level the carb a couple of degrees if it is pretty critical to have it level.

[Vegas69]

Something to keep in mind here is under accel you could flatten out your anlges and have no working angle. Also, you subtract your driveshaft angle from your tranny and pinion if the pinion is higher than the tail shaft. I'm running 4 driveline and 3.5 pinion with no issues. I still think you will have tunnel issues with no driveline slope.

[andrewb70]

The car is lowered 2-3 inches. If the tranny and rear are dead level, I will have about 1/2 degree of driveshaft working angle front and back but my carb will be going downhill toward the front of the car by about 3.5 deg.

But if I set the carb level, then the motor will have to be going down toward the rear at about 3.5 deg. So the pinion will need to go up about 3.5 degrees and that will cause driveshaft working angles up near 4 to 5 degrees.

I would rather have a perfect driveline than worry about the carb. I could even angle mill the intake some to level the carb a couple of degrees if it is pretty critical to have it level.

As I recall, my GTO had the carb sloping down when it was stock. The manifold was actually machined slightly down. I really don't think it is an issue as long as you set the float levels properly.

There is very little room in the trans tunnel. You should really be doing all this with the body on the frame. Also keep in mind that some accessories, like the power steering pulley, may hit the powere steering box. When you start moving things around you would be surprised at the chain of events.

Andrew

[gearbanger]

The body will be going back on soon, but as I originally said I am kind of wanting to make the body fit the chassis if necessary to have the best driveline. If it is going to require something stupid looking in the car then that would be different but if it involves cutting the tunnel off and raising it an inch or two, I would do that no problem. I alread have to modify the floor brace that is right in front of the rear u-joint because it will hit now if you hit a good bump in the road. So If the tunnel needs to come up too, no biggy.

I had noticeable vibrations before at interstate speeds, and I am just wanting to make sure and get it as close to perfect as I can while I can.

That is a good tip on the PS pump. I had the headers on already to make sure everything would be clear, but I hadnt thought about the ps pump. It has and electric fan so fan to shroud alignment is not an issue.

[gearbanger]

I did some more measuring and it appears that in order to set the engine level, I will need to raise the trans mount about 1-1/2". That will definitely require redoing the entire length of the driveshaft tunnel. Probably about 2"

So you think that if I run 2 deg down on the motor and 2 deg up on the pinion, that I can have a silky smooth drivetrain at high speeds?

I think that will give me about 3 deg of working angle on the driveshaft front and back.

[andrewb70]

I did some more measuring and it appears that in order to set the engine level, I will need to raise the trans mount about 1-1/2". That will definitely require redoing the entire length of the driveshaft tunnel. Probably about 2"

So you think that if I run 2 deg down on the motor and 2 deg up on the pinion, that I can have a silky smooth drivetrain at high speeds?

I think that will give me about 3 deg of working angle on the driveshaft front and back.

You can't figure out the working angles without know the angle of the driveshaft. Check this out:



http://www.chevelles.com/forums/showthread.php?t=213271

Andrew

[Roadbuster]

You can't figure out the working angles without know the angle of the driveshaft. Check this out:

http://www.chevelles.com/forums/showthread.php?t=213271

Andrew

Andrew, great post timing on this topic! I just used that thread to calculate my angles as I put in new rear control arms. I dug it out of your GTO build thread

Here is what I measured:
Engine and trans 2.8 up
Driveshaft 0.2 up
Pinion 1.2 down

So like Gokou I am going for a down angle on the pinion of about 2.8. The angles will be matched and opposite. I got the arms in last night late, so since today is a family day I will make measurements later this week.

Jon

[ponchopwr70]

Funny I'm going through the same thing now. The best I can get is -4, -1 and -3. My pinion is higher in the car than the trans. Also I have a gear vendors and can not go higher on the trans. I always had a slight vibration before but after the gear vendors and driveshaft shortening my car is worse. I adjusted the pinion angle with no change in vibrations from -4,0,0

[gearbanger]

You can't figure out the working angles without know the angle of the driveshaft. Check this out:


Andrew

The tranny is 2 down, the drive shaft angle is 1 degree up and the pinion is 2 up, so that gives me 3 degrees of working angle. Would that be smooth, or would the other scenario be worth pursuing.

I was looking at the tunnel again and then biggest problem I can find with raising it is the back seat bottom center mount will be raised and that will require a little reworking of that clasp in the seat itself.

ponchopwr70 , you need to get the pinion angle up so that it is parallel to the tranny, but that is also going to give you 5 degrees or more of working angle on your u-joints which may cause vibration itself. You may have to settle for that unless you are willing to cut the floor and reduce the trans angle somewhat.

[ponchopwr70]

Yea its not real bad just not perfect. I had the driveshaft re checked and its perfect. Ill put u-joints on the list to change every 10,000 miles along with valve springs and everything else.

[PhillipM]

You know I have read so many things before setting up my new drive line angles.. I followed the figure 7 to the "T" on this documentation from Inland Empire Driveline. But from what most others have told me it will vibrate. What do you guys think?

[andrewb70]

Figure 7 looks good to me.

Andrew

[PhillipM]

Okay cool. I'm just tired of cars vibrating so I hope that this one doesn't. I have lots of room to move the trans up and down to help out. Originally this car had a parallel engine that was a 0 with a driveshaft at 0 and a rear pinion at -1. It vibrated your teeth out above 70.

[gearheads78]

I followed the link Andrew put in is build thread. I don't remember the numbers I ended up with but the transmission was spaced up about 1/2" at the back. I have no driveline vibration at all.

[PhillipM]

Next time you are under the car would you mind checking the numbers? Thanks.