Drive line clearance

[Rwalkup]

Good morning, I am building a 1948 Chevy 3100. Put a 350 with a 350 transmission in it. I'm wondering how much clearance is a minimum for the driveline on the main center crossmember. I don't want to have to do any extra crossmember work if I don't have to. I have a static lowering job, drop axle in front with lowered springs and lowered springs and Blocks in back. Right now I have about 2 1/2 inches of clearance from the top of the driveline to my center crossmember that the center of cab sits on. Hopefully these pictures show up, this is my first post. Don't mind the broomstick, it was only way I could test my clearance before I got my driveline ordered. Thanks in advance for any of your suggestions.

[Rwalkup]

Here are a couple more pictures.

[Rwalkup]

More pics

[Keith Seymore]

Broomstick is actually pretty darn clever.

You are going to need to position the rear axle in full jounce (max upward travel), as defined by the jounce bumpers or whatever limits the amount of squat. Add the radius of the driveshaft (half the diameter of the shaft) to the centerline created by the broomstick; I'd add 1" to that for a clearance envelope between the shaft and crossmember. You could use styrofoam or that florist foam to mock this up. That should tell you where you want to be.

Unfortunately, based on what I imagine I am seeing in the photos - I think you are going to be doing some rework to that crossmember to provide the necessary clearance.

K

[Rwalkup]

Thank you for your reply. I have been struggling with how to modify the center of that crossmember. My particular cab mounts right there in the center not on the two outside corners.

[_Ogre]

my thoughts are to raise your axle all the way up to the frame to check for clearance
you don't really have a c-notch and you will probably occasionally bottom out on the frame
as in going down the highway at a decent clip and hit a low spot that squats your truck

anyone with an ad truck want to comment on the lack of c-notch in the frame?
i know that it no c-notch in a tf frame wouldn't work with a static drop

[Speedbumpauto]

You can do a modified notch to that crossmember and box the bottom of it out far enough on the legs to make it at least as strong as it was and gain 1 1/2" or so of clearance, by my eye. I wouldn't box it all the way out to the frame so that the ends have a little bit of "twistability" where they attach. Like the others have said, unbolt the rear shackles and jack the diff up as far as it will go to get your measurments.

[Rwalkup]

Thank you guys for your responses.

[Advanced Design]

Rwalkup, first off welcome!

I built my 48 truck on bags with a C notch and had no interference problem with that crossmember. My transmission pan was just above the plane of the bottom of the running board brackets. Perhaps your powertrain is mounted higher?

Yep, the broomstick is a great idea.

[Hawkerdriver]

I bought a piece of 3.5" PVC and cut it as the Driveline they want to build me is 3" that was how I mocked mine up a little more realistic size wise cost me $10 for piece of mind