Hi!
Not fluent in English, so bare with me

I suddenly noticed vibrations from my Chevy while accelerating from 60-80 km/h (not sure what that’s in miles), roughly around 3500rpm. Drove in 2Hi.
Parked the car to troubleshoot with the drive shafts in mind.

Found that the yoke of the rear drive shaft was cracked, and thought woohoo, that’s the problem.

Had to replace the whole rear shaft as the front multi joint (cross shape) was welded to the shaft after the workshop bended the claw.
The new shaft was a used part, but looks whole with no dents and bends. Replaced the cross joints with new ones.

unfortunately this didn’t solve my problem. Can’t quite figure out exactly where the vibrations comes from, it’s like driving over something rugged on the road.

still slight vibrations between 50-60 km/h, and worse when reaching 120km/h. Even had the engine warning lamp flash for a second when pushing the 120km/h uphills for a time.
the vibrations comes and goes.

I’ve checked the bearing hubs, and the wheel bolts, and they’re ok. The wheels were balanced a couple of months ago, and I can’t see any weights missing.
Brakes work fine, and there is no abnormal heat from the rims after driving.

The rear cross joint of the front drive shaft seems a bit sketchy, but I have my doubts that this is the cause of the vibrations as the vibrations are very much noticeable in 2Hi (haven’t tried the 4wd yet).

Tried to switch to neutral when I feel the vibrations, of course during that drive the vibrations weren’t very hard, but I didn’t notice any difference from in drive.

Problems I’m aware of:

Must drain the coolant because of an unfortunate mixture of red and green

Cable connection to the minus on the battery is a bit loose

Right upper ball joint (not sure if that’s correct) must be replaced as the rubber bellow is worn out.

Allso these vibrations happened after pulling a slight overweighted trailer for a very short distance.

Any suggestions of what to troubleshoot next? Any similar experiences?

I am grateful for any response

 

New used shaft could be out of balance.
Front U joint binding or bad can make vibrations even in 2wd as it does turn in 2wd.

 

Thanks! Might be worth trying to replace the u joints then They are the original ones, so probably about time.