[kevin1522]

When towing brakes work fine until pedal decides to go to floor & steering locks up and can't be turned. New master cylinder tried but no change. P/S pump or Hydroboost unit causing this?

 

[Crawdaddy]

It could very well be either the power steering pump or the hydroboost booster unit. Those are the only things that the brake and steering systems have in common. If it's only braking that causes the loss, I'd be inclined to start looking at that. But first, the obvious; have you checked the fluid level in the power steering resevoir? It might be low, or get low when the brakes are used a lot. Run the truck, cycle the steering and brakes a few times, then immediately check the level. If it's low, that might be your issue.

 

[kevin1522]

P/S system just flushed & refilled with new fluid. Shop gave truck back to me not wanting to change one or the other with not correcting the problem. Mine can't be the only one this has happened to so I decided to ask here. I'd rather not change both neither. Thanks to all in advance.