Anybody have any experience with this? I’m sure crossmember location and driveline length require modification..would/does the angle cause vibration problems?

 

I had one in an A-body for a while. Crossmember bolts to the factory 400 location. Drive line does need to be shortened. No vibration on mine. The problem I had was after put in a shift kit, new seals, gaskets, pan, cut the driveline and actually bolted everything together, then I discovered there was no provision for a speedometer. The 68 Delta 88 that I pulled the 455/400 from used the front wheel to drive the speedo instead of the transmission.

 

Well that’s good news! Sorry you had to learn that way. I learned about the speedo issue myself awhile back..after I had It rebuilt as well: I pulled the TH400 from a 70 delta 88 and luckily it had the spot for the cable on the trans..don’t know if it was the original trans,but it’s what I need for my 72 cutlass.

 

I would convert the trans to short tail shaft

 

Converting the trans requires complete disassembly. The output shaft needs to be changed in addition to the tailhousing, and the output shaft is the very last piece to come out of the case and the first one to go back in. Buying a new output shaft and tailhousing will cost more than just buying a short tail TH400 core.

And as noted above, long tail TH400s that came out of 1965-70 Olds full size cars do not have provision for driving a speedo cable, since those cars drove the speedo off the LH front wheel. In most cases the trans case isn't machined for the cable adapter, so you can't retrofit those parts without putting the case on a milling machine.

And finally, the additional length is aft of the mounting boss. The trans mount is in the same place on every TH400.

 

Long vs. short tailshaft will not change the engine-transmission angle. However it changes the universal joint angles. It changes them proportionally, so this would not normally create vibration.

If your rear axle upper and lower control arm bushings are tired, the tailshaft change could possibly put you into a vibration.

 

It shouldn't, however other things might. For example, I have one car that was incorrectly jacked up under the open channel section of the frame below the rockers. This caused the lower flange of the frame rail to bend upward. Moving the crossmember rearward to swap in a TH400 would require the crossmember to sit on this distorted part of the frame, changing the engine-trans angle. Yeah, this is an obscure issue, but not impossible.