Driveshaft yoke movement.

[Colt45ws]

So I decided on a whim to install my police Aluminum driveshaft in place of the stock steel unit. This piece is shorter than the steel one and in the PIs is paired with a extended output shaft and extended housing. The yoke is longer on the PI shaft as well, 6.25" in length instead of 5". With a small detail; The stock yoke is splined to the end, and the extended yoke only has splines on the bottom 4".
I made a diagram of how it fits in the stock short housing and output shaft.

My thought is that it will probably have reduced critical speed, due to the shorter housing providing less support. However, Critical limit with my final drive is over 160mph, so even if I clip 25% off thats still faster than I would want to go.
Anyway, so I was messing with it today, and grabbed the driveshaft at the front u-joint. I found the yoke moved around about 1/16-1/8" all around inside the trans. Is that excessive? I didnt play with my OE shaft before I pulled it so Im not sure of what normal is. It does not vibrate or anything, even up to 80mph. Ive played with putting it in different gears, so I change engine and exhaust noise to kind of listen for what doesnt change, but Ive got nothing.
Thoughts? My thought was to pull the yoke off the stock shaft and put it on the Alum shaft. Its shorter, but has full splines so actual contact is higher; around 3.25". Then, putting on a .75" driveshaft spacer will bump it to almost identical with stock.

 

[Donald]

And the reason you are doing all this?

 

[OtisBlkR1]

Originally Posted By: Donald
And the reason you are doing all this?


exactly my thoughts..

 

[expat]

1/16th + seem excessive!
I would check to see what the OE slack is.

 

[Colt45ws]

Originally Posted By: Donald
And the reason you are doing all this?

Because its shiny, and I like shiny things.
No really, Im going to be putting in gears (either 3.73 or 4.10) and I will need the Alum shaft. The steel shaft is not safe above 60-70 or so with 4.10s.

 

[George7941]

Agree with expat, 1/16 is excessive. In fact any perceptible play is excessive. My experience is mainly with trucks but I think the no perceptible play rule would carry over to cars too.

Some vehicles have a bushing on the output shaft and not a ball bearing and the bushings do wear out. They are easily replaced.

 

[Charlie1935]

Originally Posted By: Colt45ws
Originally Posted By: Donald
And the reason you are doing all this?

Because its shiny, and I like shiny things.
No really, Im going to be putting in gears (either 3.73 or 4.10) and I will need the Alum shaft. The steel shaft is not safe above 60-70 or so with 4.10s.


I've ran steel drive shafts over 6000 RPM with no problems.

 

[Colt45ws]

Originally Posted By: Charlie1935
Originally Posted By: Colt45ws
Originally Posted By: Donald
And the reason you are doing all this?

Because its shiny, and I like shiny things.
No really, Im going to be putting in gears (either 3.73 or 4.10) and I will need the Alum shaft. The steel shaft is not safe above 60-70 or so with 4.10s.


I've ran steel drive shafts over 6000 RPM with no problems.

Ive seen pictures of transmissions after someone ran a steel shaft to 80mph with 3.73s. Completely blew the tailshaft housing apart. Cracked the transmission. Of course the driveshaft fell out and beat the heck out of the bottom of the car as it flopped around.
Good reason the police cars got an Alum shaft. There is actually a better shaft used in MY2000 CVPIs that used Alcoa Aluminium Metal Matrix. This was due to 3.55 being only final drive offered that year so they went with the better material to bring the limiter back up to 130mph. Limiter with 3.55s is 115 on the normal Alum shaft.

 

[morris]

iam running 4.1 gear in a 2001 dakota V6 stock O.D. trans. BUT i never drive over 50 mph. no trouble. at speeds of 35- 45 mph i gained 4 mpg. but like i said i never drive over 50 mph. i really was not wanting to get better mpg, just a side benefit. it let the trans go to a higher gear. running 1400 rpm at 35-45 mph. i think the same thing could be done by adjusting the shift points to shift sooner, on a stock gear, just an ldea.

 

[expat]

Originally Posted By: Charlie1935
Originally Posted By: Colt45ws
Originally Posted By: Donald
And the reason you are doing all this?

Because its shiny, and I like shiny things.
No really, Im going to be putting in gears (either 3.73 or 4.10) and I will need the Alum shaft. The steel shaft is not safe above 60-70 or so with 4.10s.


I've ran steel drive shafts over 6000 RPM with no problems.


Same here, I never gave it a second thought.
I thought that's why center bearings were installed?

 

[SteveSRT8]

Any competent Drive Shaft Specialist can help here. Mine has a fixture like a giant lathe to spin the shaft for balancing.

He balances them WAY beyond factory specs.

And there is always a reason when the OEM's make a change. My car has factory 3.06 gears and a 180 mph top end speed. It's driveshaft? All aluminum with a center bearing.

And re: slop at the tailshaft, that's an inexpensive fix for most cars. Many can replace just by pulling the shaft out.

 

[mechtech2]

When installing any driveshaft, measure the angle of the front and rear U-Joints. [car weighted on the ground!]
They should be the same . Less vibration and long life are assured.
Shims are used on the tranny mount or maybe the rear end.

A gravity angle measuring device for $5 at Sears is good for this.

 

[Colt45ws]

Okay, want to know something WEIRD? I checked it tonight and it was SOLID. My friend was with me when I first noticed the behavior in the OP. We both checked it out and thought it was more slop than should be.