bad vibes

[ilikemud]

I just picked up an 85 blazer bone stock, 350sm465/208 2.73 10 bolts. when i shift into 4th the truck shakes like it spit a ujoint. i can run it to 60 in 3rd gear and have no vibes at all as soon as i shift into 4th ive got problems... cant hear a bearring whine and it isnt hard to **** of pop out of 4th any ideas? bent mainshaft? tcase issue? anythoughts would be helpful. thanks

 

[Monster512]

motor and tranny mounts good? dont really make sence since you can run it to 60 in third with no vibes.

 

[shaun89]

im not a tranny guy but i dont see any other reason for it except the tranny.

 

[Hogback Fabrication]

im not a tranny guy but i dont see any other reason for it except the tranny.

Yep, its probably the trans going out

 

[ilikemud]

the trans mount has play in it and the crossmember is bent, but that has no affect on it in any other gear so i figured that shouldnt be the issue. ha sometimes when you ask a question you hope no one will answer what you had been thinking... figured it was in the trans thank you

 

[Monster512]

could be that trans mount and crossmember, when you are in the lower gears there is enough engine torque to keep everything tight, or not vibrating anyway, when you hit yer hi gear the ratio changes and there is less torque and letting all the loose stuff "loose". Id fix the mount and crossmember before tearing into the tranny.