Strange problem help please

[Ont67shortbox]

I was out on the weekend with the truck,ran pretty good for the first time out. I got home and was checking things out and where the drive shaft passes through the cross member there is a line like it was rubbing all around.the shaft is centered in the crossmember hole and I have no idea what would cause this?I know the truck is not caged but could it be twisting on launch and causing this? its a 427 bbc with around 450 hp,runs low 12s not like its a torque monster or aything but this is something new its doing.I have stock motor mounts with the good trans mount,baffled thanks for any help Brian

[Super73]

Questions...

Have you double checked u-joints?
Are the caps secure in the yokes?
Any slop in them?

How deep is the yoke in the trans?
IE when you pull the shaft, how much enguages?

Is the shaft straight?

[Marv D]

And are you sure it wasn't there before the trip to the track. Depending on the setup,, my shaft gets real close when I I jack it up and drop the shocks to get the stupid steamroller tires off.

[Rannos]

I know with my old setup my driveshaft was not centered when the truck was sitting on the ground. It was almost touching the right upper side of the loop in the cross member. It never touched the crossmember and the truck ran high 11's low 12's with a lil' SBC. That was with solid motor mounts and a ploy trans mount. Mounts are important. The less the drive train and truck flex the more power you can put down and the quicker it will react to throttle. Like Marv asked are you sure it had not touched before? To make sure it is touching now, spray the shaft in some black paint in that area and go back to the track this weekend. Fresh wear ring means you have got a rub, clean paint means your good. Hope this helps.

Jay

[vin63]

Originally Posted by Ont67shortbox

I was out on the weekend with the truck,ran pretty good for the first time out. I got home and was checking things out and where the drive shaft passes through the cross member there is a line like it was rubbing all around.the shaft is centered in the crossmember hole and I have no idea what would cause this?I know the truck is not caged but could it be twisting on launch and causing this? its a 427 bbc with around 450 hp,runs low 12s not like its a torque monster or aything but this is something new its doing.I have stock motor mounts with the good trans mount,baffled thanks for any help Brian

To answer your question, yes, the chassis can flex enough under certain circumstances. From your description, is the driveshaft making contact with the crossmember all the way around the opening, or just one area of the opening?

[BR3W CITY]

My guess is it would only have to contact one side, even for a moment so score the DS all the way around, considering the speed at which it rotates (would act like a lathe). Have you checked the trans mount again? I know you said its "a good one" but is it STILL good or has it suffered damage? BBC on stock motor mounts can move a good bit...bbc+stock mounts +chassis flex and I could see it happening.

[Ont67shortbox]

Thanks for all the good replies,I will take it out and check the engagement this weekend and then respray the shaft and see what happens,I know the motor mounts and urathane trans mount are new,it is centered at ride height.

[vin63]

Originally Posted by Ont67shortbox

Thanks for all the good replies,I will take it out and check the engagement this weekend and then respray the shaft and see what happens,I know the motor mounts and urathane trans mount are new,it is centered at ride height.

As I mentioned earlier, it would be important to find out on which side or area of the crossmember the drive shaft is making contact.

[El Campo]

Mine did that same thing. Is your panhard bar tight and have good bushings? This could make it rub upon turning etc. Also I would make sure that my trans mount bolts were still tight. Have had them do crazy things before (or else I forgot to tighten them, not sure which)

[74 shortbed 406]

I would also like to suggest something. I have a go pro, it is a very small video camera, and in the right case, waterproof and very hard to mess up. It is fairly cheap, and can be mounted almost anywhere. I bring this up because you can mount it anywhere. It has helped me find a multitude of problems on my truck, good video when on Atv, waterproof for float trips, pretty much anything. A couple minutes to mount under truck, like strapping a person to the underside to take a ride, launch a couple times, see what happens, and see what it needs to cure problem. Digital images can be broken down frame by frame if need be on a comp at any time. Just a thought. But I have heard these frames referred to as pretzels, they bend everywhere.

[TexasArtist]

I'm having a very similar issue. After putting the bb in my truck, and getting a longer driveshaft(larger diameter too)I lost a ujoint, replaced u jointswhich i shoulda done first, but still didnt know if it was going to fit. The driveshaft is really close to the loop, maybe a 1/4" from rubbing. it looks as if it has rubbed and is going to cut it in half, but only on one side of the driveshaft. I painted it this morning but havent looked at it yet, i will try a gopro next. With a groove in the ds is it now out of ballence? And is it safe? How much can the yoke stick out of the transmission? Im going to try the old/skinny ds with a longer yoke again, its an issue thats seriously bothering me.
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[TexasArtist]

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[Marv D]

I would pull that shaft and cut me some clearance ASAP!!!
Something ain't right! The shaft (even being oversized) should be more clear than that!

[TexasArtist]

Thanks, thats what i thought too, so i switched to my old one with a longer yoke, now im worried because i think the yoke is only in about 2.5" how much yoke needs to be in the tail? It drove to work ok
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[Super73]

Texas, is your truck lowered?
If so, did you buy an adjustable pan hard bar and recenter your rear end?

Not sure what year your trucks are, but when I lowered my 63, I had to put and adjustable pan hard bar in to square up the rear end. On the later 67-72's the pan hard bar is shorted making rear end shift even worse.
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[TexasArtist]

No it isnt lowered and the ds i put in tosay is skinnier and has plenty of room for now. I do want to lower it but i think im going to wait till i get some welds or something
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[Super73]

I would be curious to know if your motor and trans tail shaft is centered in the truck along wit the rear.
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[TexasArtist]

Originally Posted by Super73

I would be curious to know if your motor and trans tail shaft is centered in the truck along wit the rear.
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Its not 😳
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