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.

[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

[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]

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.

[gearbanger]

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.

Wow, that is surprising. From reading driveline angles articles and such, I would have thought that to be a near perfect setup. I guess the best thing is to just experiment with each car and see that the particular components like.

[PhillipM]

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

[gearheads78]

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

I would be glad to but it my be a while. I borrowed the tool to measure. I will try to remember to borrow it again the next time I know its going to be on the lift with time to pull the rear springs so I can get the rear up to ride height.