78 Chevy 1/2 ton still has shudder, any help??

Hey all,
I 've posted a few times when i run out of ideas so I thought i'd try it again. 78 chevy 1/2 ton 4x4, has a vibration at 35 mph when you brake/accelerate/coast through it. if you brake hard, it does it worse,
doesn't do it as bad with some weight on the back (I.E. trailer or something), new rear end(did it before) rebuilt transmission (did it before) new ujoints, driveshaft's tight, still does it. could it be in the transfer case? it's the fulltime Tcase with the part time kit put in it. I'm running out of ideas and thought there could be a fitting or bushing in that old Tcase that could cause a vibration at a particular speed. Anyway, thanks in advance for your help
TB
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Trailblazer,     That sounds like a driveshaft that is bent, running off-center, or out of balance. If you had the driveshaft balanced earlier, it is possible that now, one of the balance-weights has been lost. Another idea: the U-joint caps may not be driven in equally now (missing any C-clips?), which would let the driveshaft run off-center. Badly worn splines could also let the driveshaft run out of true.     That full-time Tcase would make it possible for the front driveshaft to be the problem, if the front driveshaft is always turning as fast as the rear driveshaft.     Any good driveline shop can check if each driveshaft is running true (not bent or off-center at the splines or U-joints), and balance it, if necessary. That is specialized work, but it is not too expensive. Get some bids, first, to avoid surprises. Run the truck on a frame lift, and when the speedometer reads 35, any driveshaft problem should be easy to locate. Cheers, Red -- ************************* Replies will bounce, unless you remove the letter A from my email address.
Trailblazer wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If it's an automatic:
Look if any weights broke off of the flexplate?
Refinish King
PS A cracked or worn at the center flexplate can also do that!

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
someone mentioned me have the flexplate checked, so i went back to the guys who did it and they said it was fine, it did it before and after the rebuild so I figure they would have caught it. I'm guessing the only thing left it could be is the driveshaft like red mentioned?
thanks for your help, i think you posted about the flexplate and why i went back to the guys to have it checked.
TB

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.