47-55.1 Driveshaft Fit

[Jbrenyo]

Is it possible for a driveshaft to fit TOO tightly? We put the driveshaft back into my sons' project yesterday (1953 Chevy 3100 on a Code 504 S10 prepped frame with an LS1 and Tremec T56 six speed) and in order to get it in we had to rotate the rear end upward, slide the U-joint into the yoke, and then lower everything back down. The rear end stayed in place but the fit seems (to me) to be VERY tight. Everything moves okay but I'm wondering if this is going to cause a problem later? The "fix" of course would either be to have the driveshaft shortened by 1/8" or loosen the motor and transmission mounts and shift the engine and tranny forward a little. I'm reluctant to do that if it isn't necessary. All opinions/thoughts are welcome. Thanks!

[jwhotrod]

the slip yoke should have 3/4" to 1" from the end of the tailshaft housing to the shoulder on the slip yoke to allow for assembly and the movement of the rear end up and down in in the suspension travel. Yes, you are too long by probably about 1"

[joedoh]

its likely already too tight to use, and here is why:

if you look at the angle of your leaf springs and where the axle mounts you will see it is angled forward slightly, and when you lift the weight off the wheels the wheel centerline will move back slightly, and when weight is put on the wheels it moves forward slightly.

so that means that even if it fit with the axle loose and no weight on the wheels, you have taken up any slack in the slip yoke at the trans by just putting it on the ground. whats worse, when you hit a bump it will try to jam the yoke even further, and you will break the tailshaft of the trans.


I tell people the same, 1" of stickout, but make sure you are measuring yoke to yoke with it ON THE WHEELS. sometime when you measure yoke to yoke off the ground, the droop of the springs fools you and it ends up being too tight. I HAVE DONE THIS. its embarassing to pick up a new driveshaft from being shortened and drop it off the same day to have another inch taken out.

if you dont have a driveshaft shop around you, try a big rig service center, usually they dont care about your driveshaft being a "toothpick" (what they called my little bitty driveshafts) and shortening is fast and cheap in the driveline shop.

[mr48chev]

Both answers are correct but you have to measure it the way Joedoh said with the weight of the truck sitting on the tires or at least on the axles supported on stands.

It might be perfect with the weight on the wheels.

[Matt_50]

If I can add to this... with the weight on the ground and the yoke pulled out 1 inch... how do you measure?

[edgeleycanuck]

Here's what I was told by a driveline shop. With the weight of the vehicle on its wheels, measure the yoke length, insert all the way and pull out 1/3 of the way and measure the length of shaft you need based on that . I haven't had a shaft made yet but I would think that whatever shop you use should be able to give you proper advice.

[MiraclePieCo]

I've learned the hard way that 1" out sometimes is not enough leeway to get the rear joint assembled. Depending on your rear u-joint cup size, 1-1/4" out may be better. Yep, I've had to shorten a couple because I cut them too close.

[Jbrenyo]

Thanks everyone for the great advice. I'm glad that I asked folks that know what they are doing. We're going to measure the driveshaft as suggested and have it shortened.

Now, if losing weight was only so easy....my weight is actually fine. I'm just too short!