[Kopfjaeger]

I think I have my drive line angles where they need to be. 5speed LGD-700 trans, 2.7* down. 12 bolt rear with Currie control arms, adjustable upper, 2.1*, pinion yoke up. Did I leave enough difference in the rear angle? On hard acceleration the pinion yoke will move up, correct? How much with a coil spring rear?

My drive shaft will need to be 56.75” long. I was planning on a 3.5” diameter driveshaft but I’m not sure if that’s going to be enough with 3.73 gears, a .80 5th gear, and 26.65 diameter rear tires.
Thoughts?

Joe

 

[Blackhawk]

Run a string between your pinion and output shaft. The driveshaft angle needs to be considered for your U-joint angles as well, not just the component angles compared to level.

 

[Alwhite00]

Are you on stock suspension or lowered? A lowered A body opens a whole different can of worms if the pinion ends up higher than the trans output.

 

[chaze]

Al, not disputing your conclusions but why does that matter? Seems that as long as the trans output and rear pinion angles are correct it should not matter.

 

[Blackhawk]

Al, not disputing your conclusions but why does that matter? Seems that as long as the trans output and rear pinion angles are correct it should not matter.

If the car is lowered enough you would need the transmission to go into the floor for decent U-joint angles.

 

[Kopfjaeger]

Vehicle has coil overs on the front and 1” lowering springs on the rear. The trans is as close to the floor as practical. That angle will get no better. Actually, at less than 3.5*, I thought I did really well getting that angle reduced as much as possible. The rear, I can both increase or decrease that with impunity, although I thought the goal was to keep them equal/opposite. I get that the u-joint angle needs to be “happy” but there is only so much that I can do. I realize I’m handicapped by lowering (poly body mounts), that I’m running a 5 speed, and that it’s a 67, which has tight tunnel clearances.

I do appreciate all the replies. Critical speed has me perplexed. So I need to avoid exceeding the shafts max rpm, but what about 1/2 critical speed? Is it that I don’t want to be operating normally at that?

Oh, and I realized, after I sent this thread, that I put it in the wrong place. I’m asking the moderators to move it to the appropriate trans/differential section.
Joe

 

[chaze]

If the car is lowered enough you would need the transmission to go into the floor for decent U-joint angles.

Disagree. Typical A body car OEM tranny installation tilts down 2-4 degrees. So with the pinion adjusted to tilt up the same amount you would have them parallel at different heights. Same as if the car was at standard ride height.
The driveshaft angle relative to the ground is not a factor.

 

[Badd64]

Disagree. Typical A body car OEM tranny installation tilts down 2-4 degrees. So with the pinion adjusted to tilt up the same amount you would have them parallel at different heights. Same as if the car was at standard ride height.
The driveshaft angle relative to the ground is not a factor.

I have to disagree. Driveshaft angle to ground may not matter too much, but angle to each end is highly relevant
I know you will all go back to that video of the guy showing binding. In a stock car that is fine, but a lowered is different. it absolutely does matter if driveshaft is running uphill or downhill in working angles.
So take that guys video and turn it around, making his "rearend" the drive end and his motor the driven end..

In a stock height car, rear pinion is typically lower in height than trans output. You would want equal and oppsoite angles for best operation
In a LOWERED car, rear pinion is typically HIGHER than trans output. If you go equal and opposite angles you are Increasing the working angles (not good). So you go down on the pinion to minimize the working angle.

This is called broken back and only applies to cars with pinion HIGHER than the trans output.

 

[Blackhawk]

Disagree. Typical A body car OEM tranny installation tilts down 2-4 degrees. So with the pinion adjusted to tilt up the same amount you would have them parallel at different heights. Same as if the car was at standard ride height.
The driveshaft angle relative to the ground is not a factor.

The transmission and pinion angles are only half of the working angle. If the pinion is higher than the transmission and the transmission is angled 2-4 degrees down compared to level, your working angles will be beyond the recommended specs. Equal and parallel is an oversimplification.

 

[2/75NastyNewbs]

The thing about the driveline angle threads is the confusion between “up” and “down”.

For the sake of clarity, I’m assuming that everything is pointing down and rearward.

With a 1” drop and adjustable rear upper trailing arms, you shouldn’t have a problem with the pinion yoke being higher than the trans output yoke with a trans angle of 2.7 degrees with your car sitting level.

Equal and opposite is a good goal if not using the “broken back” method. You could stand the car on its back bumper and still have equal and opposite.

What’s your driveshaft angle? Spicer has a good calculator. Don’t use theTREMEC app on your phone.

 

[mrpaticular]

If you put a smaller diameter tire on either end it can through the pinion angle off.
Equal but reversed on each end.
SteveDeluxe300 on here turned me on to the tremmic phone app.
Rick

 

[Blackhawk]

If you put a smaller diameter tire on either end it can through the pinion angle off.
Equal but reversed on each end.
SteveDeluxe300 on here turned me on to the tremmic phone app.
Rick

Only in relation to gravity, not in relation to the other components.

 

[chaze]

Pinion height can be offset up, down or side ways from transmission.

Most cars have the differential located at a height lower than the transmission. The output of the transmission is roughly parallel to the differential pinion input.

If you reverse that (differential higher than tranny) and still have output and input parallel the result is the same.

 

[123pugsy]

Tranny down, pinion up, or, tranny up, pinion down. Same thing.

 

[Kopfjaeger]

Ok, my pinion yoke is not higher than my transmission yoke. The driveshaft slopes down from the trans to the differential. How much? That’s the million dollar question, what am I looking for as a number?

I can bring that angle down a little by pulling out a shim on my trans mount but that will put me over 3* down. I thought the goal was to keep the trans and differential angles close to 3*.

Joe

 

[123pugsy]

The goal is as little as possible on each, but never dead straight to each other, otherwise U-joints will seize up.
3° is OK if they are both the same. Weight of car on the wheels of course.

 

[lucifershammer]

The goal is to keep the working angles (the angle between the driveshaft and the transmission and the angle between the driveshaft and the pinion) as close to the same as possible.

You also want to keep the working angles to 3* or less if possible

Opposite working angles is not a requirement. Working angles equal to each other (or as close as possible) is.

I am currently running a 2.5* working angle at the transmission and a 2.4* working angle at the pinion. They are not opposite. There are no vibrations.

Chevelles from the factory did not have equal and opposite angles either.

 

[Alwhite00]

Al, not disputing your conclusions but why does that matter? Seems that as long as the trans output and rear pinion angles are correct it should not matter.

If the driveshaft is running uphill to the rear end it most definitely matters. It compounds the angle at the trans.

 

[chaze]

Never mind.............................

 

[123pugsy]

Uphill out of tranny means diff pointing down makes it exactly same.