We have a 1988 Volvo 240 wagon. It’s start to shake badly when you get above 35. Rack and pinion? If so should i replace it? Or rebuild it. Thanks

 

Start easy by balancing and properly inflating the tires. Then there are other possible remedies before replacing the steering. Ball joints, tie rod endings, bushings, etc. Have your son turn the wheel while you safely inspect the steering system for loose play.

 

A quick first step would be to rotate tires front to rear, and while you have the front jacked up, do as Tom K suggests and inspect bushings etc

 

Yes we jacked it up the whole assembly has some play. Tires are balance. The shake is so bad you feel something might break.

 

Try to put a little weight up front (tires on the ground). Inspect again while turning the wheel. You should see the source of free play with the weight. The alternative is randomly throw new parts at the system until something sticks.

 

when i had a 'severe shake' it turned out to be badly worn ball joints. replacing both sides made the shake go away. nothing to do with the wheel
balance or the rack. as with the OP's situation the shaking started above 35-40mph.

 

You might have an out of round tire due to tread separation. Might still be in balance but no longer round. Your rack will not cause shaking - might amplify the shaking but not cause it.