89 Chevy Astro Van 4.8 V6 Automatic, Air Power Steering

The pressure hose on the power steering broke just inside the fitting that screws into the back of the pwr steering pump. I replaced the broken line, but the new line broke in the same place the old line broke. I inspected the brackets for cracks and made sure the pump is securely installed and is not vibrating. What is causing the pressure line to break?

I checked the motor mounts as advised. The motor mounts and transmission mount are in good shape. There is no excessive torque when the engine revs. I installed a new pressure hose and noticed an excessive amount of vibration at the pump end of the hose. The engine doesn't vibrate and the pump and gear box are solid. The vibration in the hose stops when the engine is rev'ed up. I believe the vibration is what is causing the the line to break. I am in the process of moving the position of the line to try to reduce the vibration. Any other suggestions would be appreciated.

I found the problem. The original pressure hose failure was caused by the same problem. A nut on the back of the power steering pump had vibrated off over time and this allowed the back of the pump to vibrate more than normal. Luckily, the nut had fallen down on top of the cross member under the engine and was not lost. I reinstalled the nut and the vibration stopped. Thanks for your suggestion. I hope this bit of knowledge will help you in the future.