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PhatNBad

4L80E crossmember

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Hi folks.  I’m having a 4l80e built for my 70.  Will a turbo 400 xmember work?  Or is any fabrication work needed and how involved is it.  Thanks I appreciate it.  

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Sorry that no one has replied. I will be doing the same swap in the future but not for another year. From what I have gathered so far the stock crossmember can be used by cutting of he mounting tab from the front and switching to the rear. You will probably need to slide the crossmember back also. If it doesn't match up with existing holes in the frame then new ones will need to be drilled. The mounting tab will need to be welded back on. Make sure to keep the 4l80e on the same height as the old set up to maintain the proper drive shaft geometry. Easiest way to do this is to use an angle finder at the back of the transmission. You should be able to download an app for your phone. As a last note make sure that your engine and transmission mounts are in good shape while making measurements, both old and new transmissions. This can throw of the angles and drive shaft vibrations aren't fun.

   

Edited by zmanabba
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14 hours ago, zmanabba said:

Sorry that no one has replied. I will be doing the same swap in the future but not for another year. From what I have gathered so far the stock crossmember can be used by cutting of he mounting tab from the front and switching to the rear. You will probably need to slide the crossmember back also. If it doesn't match up with existing holes in the frame then new ones will need to be drilled. The mounting tab will need to be welded back on. Make sure to keep the 4l80e on the same height as the old set up to maintain the proper drive shaft geometry. Easiest way to do this is to use an angle finder at the back of the transmission. You should be able to download an app for your phone. As a last note make sure that your engine and transmission mounts are in good shape while making measurements, both old and new transmissions. This can throw of the angles and drive shaft vibrations aren't fun.

   

Thanks for the reply.  I did hear that before about cutting the mounting tab off the front of the factory xmember, flipping it over and welding it to the backside.  I do have a question in my head about it.  Would the new location for the tab be in the same exact spot (height) as when it was on the front, except on the back of the xmember?  I guess what I mean is the mounting point on the 4L80E at the same height as the turbo 350 (to keep the pinion angle the same)?    

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The important part is retain the same angle. Unfortunately I haven't done the swap yet on mine but I have done a few other cars. From what I have found out there is ample tunnel clearance so moving things around to get the proper angle won't be a problem 

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