Driveshaft angles - where to compromise?

[Guest bluex_v1]

I have worked out my driveline angles, but I'm not sure whether I should stop while I'm ahead or not.

Currently I have both transmission and differential centerlines almost perfectly perpendicular in both planes, but the u-joint angle will be 4 degrees on one end and 4.1 degrees on the other. I could raise the tail of the transmission a little further and reduce both angles a little, but one will be affected more than the other…resulting in something like 3 degrees and 3.5 perhaps. The Diff is already angled down as far as it can go. So the question is, would I be better off reducing the operating angle at the cost of a little bit of perpendicularity (word?) but still within the recommended 1 degree difference, or keep it as is with an almost perfect perpendicularity but a slightly higher operating angle?

 

oh yeah, does anyone know where to find fine thread 14mm nuts for the mustache bar studs on the r200? the area fastener supplier didn't even have them and I hate to just take them off of r200 in a JY since someone else might need them if they take the diff. Are there any other parts on the cars that use 14mm fine thread nuts?

[Tim240z]

and I hate to just take them off of r200 in a JY since someone else might need them if they take the diff. Are there any other parts on the cars that use 14mm fine thread nuts?

 

Hey...all's fair in love and Junkyard wars

 

Mcmastercarr.com should have them.

 

Tim

[Mike kZ]

You want 3 degrees or less:

http://www.streetrodderweb.com/tech/0203sr_driving/

 

http://drivetrain.com/driveline_angle_problem.html

[Guest bluex_v1]

Given my tire size and diff ratio, at 75 mph, my driveshaft will be rotating at 3700 rpm. At that RPM, an angle of greater than 4.5 degrees should be acceptable according to the table on the http://drivetrain.com/driveline_angle_problem.html page...which does contradict their 3 degree rule of thumb, which also contradicts the 'length of driveshaft divided by 5' rule, so I'm not sure which takes precedence.

 

Tweaked my transmission a little more;

Calculated with a 19.75" driveshaft, the angles are:

+ 3.1* (vert) +0.7* (horiz)

- 2.8* (vert) -0.3* (horiz)

 

A 0.3* difference vertical and 0.4* difference horizontal.

Is this going to be close enough without getting too far from parallel?

 

-McMaster Carr only has nylock nuts in 14mm fine thread...is the back of the diff going to get hotter than 250*F?

[Pop N Wood]

Is it just me, or does that second article only measure driveline angles in the verticle plane? Where did they measure the side to side angles?

 

bluex_v1, the numbers you give show the total angle difference between front to back to be 1/4 degree. That is better accuracy then they tell you to measure the angles to begin with. You're total U joint angle on the front is 3.178 degrees. That is awful damn close to 3 degrees to me.

 

I would be a little weary of lining up the angles too precisely sitting flaccid in the driveway. I would try and visualize which way the engine is going to twist under torque and see if that will increase or decrease the driveline angles. Even under steady cruise there will be some twist.

 

Also, wouldn't a Z with the diff bolted somewhat solidly to the chassis have an advantage over a live axle car? Seems like we are going to get less movement so wouldn't that mean we could tolerate more angle? Working against us is how short our driveshaft is and how low the rear end ratios typically are.

[Guest bluex_v1]

I think the hotrod article did not address the 3d perspective.

You're total U joint angle on the front is 3.178 degrees.

Hmm, a^2+b^2=c^2 ...neat

My engine and trans is mounted very stiff with urethane suspension parts, each secured as far from the engine centerline as possible for minimal play, so hopefully any engine twist will be negligible. Even so, which way does the engine twist? opposite of crank rotation I assume, but which direction does the crank rotate?

Also, wouldn't a Z with the diff bolted somewhat solidly to the chassis have an advantage over a live axle car? Seems like we are going to get less movement so wouldn't that mean we could tolerate more angle?

Definitely an advantage over a live axle, especially if we're using one of the alternate diff mounting schemes. However, as I understand it, that doesn't literally mean that a higher operating angle can be tolerated. It just means that we don't have to make so much of a compromise where we choose to set the angles at rest.

[Pop N Wood]

Actually you gave your measurements in degrees, so I found the total angle via spherical trig:

 

total angle = arccos( cos(vertical angle) * cos(horizontal angle) )

 

Use it all the time at work.

 

As far as which way does the engine twist, just rev it a few times and watch. You know the front of diff will come up, but it too will twist a bit to the side. It is just like the one article said, for a street car put a little preload on the drive train and try and get this "average" position as neutral as possible.

[Guest bluex_v1]

total angle = arccos( cos(vertical angle) * cos(horizontal angle) )

Never seen that one! ...its cool when these different formula relationships show up though.

just rev it a few times and watch.

Easier said than done

I will also be using my aluminum mustang driveshaft, shortened, which should be a little more tolerant too. We'll see how it turns out and at least have one more solid data point out there for future reference.