Any tips for 90 degree back in?????

Enough clearance and the proper angle is nice.
So, Get Out And Look - as often as needed.
Don't just rely on mirrors.

 

That's true. I just did these exercises in my CDL school the other day.

 

Knowing your pivot points... The tandems and the drives... Try pushing a shopping cart backward, same idea. Tandems are stationary and you have to push the front part around to 'drive' the cart. Well it works in my head anyway

You can also get a model truck and watch the movements of tractor and trailer from above as you move it around... That might help you get 'the big picture'.

 

Ive been watching youtube videos on how to back properly and stopped at some truck stops and watched some drivers do it there. Plus watching my dad do it over the years I have the concept, but practice is what is gonna be needed.

 

As far as the test goes just the trailer has to be right. It doesn't matter how the truck ends up. So when you start the back it should be about a 30* angle attack. Then when your tires are about 3' away from the cone line jack knife her in there and you should be close. Find you a little rock to cheat with, Place it where the left front side of the trailer should be. Then you can look at it from the drivers side to figure where to stop pushing the front around.

When ever you back try not to over compensate or you look like a snake wiggling around. It takes about half the angle to get the tractor back under the trailer. So when you first start that 30* angle the trailer about 15* your steer tires should be turned the other way. Then it's nothing but straight back until your tires are about 3' away from the cone line and then jack knife her in there and look for your rock.

Another thing you might visualize is the trailer is already in where it suppose to be. How would everything happen pulling the trailer out? Backing in should be just the opposite with your actions.

 

the biggest mistake students make is watching the end of the trailer
the pivot point for a turn is the tandems
if you are just practicing in a parking lot having the tandems all the way back
helps you match up what your eyes think they are seeing in reverse
but tandems to the back end take more room to maneuver
while tandems to the forward the back end of the trailer swings past the pivot point

 

Plus spend lots-of-TIME out on the practice range.
TIME = Things I Must Earn

 

Try it with a spread axle a few times. yuck.