I'm going to keep this simple as I can. I want to cover the round bar weight distribution hitch. The square bar are trickier to adjust ...you can google your instructions if you wish. I would like to say that the Hensley arrow and the Pullrite systems are the best. The main drawbacks to these are they extend so far past the bumper, its hard to get any good equalization out of them. The farther behind the bumper the ball mount is, the higher the load on the spring bars to get the weight transferred from the rear to the front of the tow vehicle and the trailer tires. So they work best if your not trying to distribute a huge amount of weight.
Even if you have heavy springs, overloads, airshocks and the like...your putting weight behind the axle and your going to get lift in the front. That lift changes the stock suspension alignment settings, allows the front to bounce when traveling and lifts the headlight beams. First lets get some terminology:
Weight distribution hitch- The ball mount, shank,spring bars, and hangers for the trailer frame.
Undercar reciever- that which bolts under the tow vehicle.
Combo bar- old school term for the square tube part of the reciever that the hitch slides into.
Ball height- measurement from the ground to the top of the ball onthe tow vehicle. Also the heigth that the trailer requires.
Ball platform- The flat area on top of the ball mount where the ball mounts.
Spring clip- the flat spring and pin located in the ball mount that holds the spring bar in place.
Bushing and shims- Located between the ballmount and shank to maintain proper pitch on the ball mount.
Shank- solid square bar which inserts into the combo bar and mounts the ball mount.
Coupler- located onthe tongue of the trailer where the ball goes in.
First let me say that if you have simple combo bar bolted to a bumper of a truck, your not going to get any equalization if the combo bar just allows the ballmount to rotate up with the spring bar tension when applied. You need a ridged mount.
Trailer ball height- you can level the trailer on level ground and then measure from the ground up into the coupler. Or...measure from the ground to the bottom of the frame between the axles. Makes no difference the angle of the trailer. Call this A. Measure from the bottom of the frame to the inside of the coupler(usually the frame thickness). Call this B. A+B= BH. Add any differences in bottom of frame measurements fromfront to rear. I developed this technique and it has served me well. Now we have the calculated ball height of the trailer. We can shift this a little if we have tanks in the back to protect or levelers up front...the shank has the ball mount holes spaced 1 1/4" apart so we wont be exact. The ball mount ball height will be the trailer ball height plus 1/8" for every 100 pounds tongue weight. OR...1/2" for a smaller trailer, 1"+ for a larger trailer. I'd use a 1000# hitch for anything 23' and up. You also get to distribute weight thats in the back of the tow vehicle as well. So we got the height set...now for the pitch. The platform shoud be pitched down 4 to 7 degrees so the bars are at 9 to 13 degrees down so that when they are tensioned for travel...they are level. I use 4 to 5 degrees for a new hitch, 6 or 7 for a used set. I put the shank in the combo bar and figure which holes in the shank give me the proper height with the ball mount. Then I start putting shims onthe bushing to get my pitch. I lift the ball mount assembly while in the combo to remove slack and check my pitch. I use an inclinometer to measure this. Tighten the bolts( the flat washers go on the slotted holes) and set screw when complete. The chain hangers mount on the tongue so that the chains are vertical when the whole rig is straight. This is usually 30" back from the ball center. You can shift an 1" either way if there is interferance. Now..were ready to couple the trailer. Back the tow vehicle and lower the coupler onto the ball where you are just able fasten the coupler and no more. Install the bars into the ballmount by just shoving them in till they snap. Now use the hanger bar to fasten the chains into the hangers. Watch for twists and dont pinch the last link in the hanger either. You should try the 3rd link from the end of the chain on both sides. It should be tight but not dangerous to do. You can go up or down a link to get the proper tightness....otherwise we need to recheck measurements or just change pitch. I usually come out right at 3 links. ONLY after you bind the chains do you lower the jack the rest of the way down! You remove the bars the opposite way you installed them. By taking off the weight first with the jack, then releasing the bars. To remove bars from head...just rotate them forward and they will drop right out.Do not pull on the spring clips...you may hyper extend the springs. They should always rest flat against the ball mount. If they dont, the bars might fall out. High end trailers(airstream etc...) usually have the axles biased back so they need extra equalization but tow better when equalized. Be sure to deactivate load leveling or at least equalize load before starting vehicle. I just grease the holes in the ballmount and the ball...but, that good motorcycle chainlube with the moly lube has a film that wont break down and is not too messy...I might try that someday. I just googled WD setup and viewed the top 4 links. Um...yeah so I'm glad to have wrote this....