How To: PML Fully Explained!

robcarync

Sliders
Location
Raleigh, NC
I know all of this information is covered around here, but I found that it was fragmented in different places. I am going to give a full explanation of all things PML and hopefully help a few people understand a torsion bar suspension system and the purpose of the bump stop gaps (two things I have found confuse a LOT of people). Read on, let me know if I missed something or if you have any questions. Really try to understand the mechanics of what is going on if you are new to this stuff because that makes the actual 'doing' a lot easier.


If you know nothing, start here:


http://en.wikipedia.org/wiki/Torsion_bar_suspension




===========INTRODUCTION============




PML = Poor Man's Lift = ~1.5" Suspension lift


Front: Stock torsion bar suspension is adjustable to an extent. This stock adjustment is used to gain an alleged 1.5". Free front end lift.


Rear: Shackles connect the leaf springs to the bottom of the frame. Longer shackles will add about 1.5"


Purchase rear shackles:


The typical ones are the 1.5" shackles:


https://www.4x4parts.com/nissan/xterra-rear-lift-shackles-p-145.html


Some people have complained about not getting enough lift in the front end, and so I decided to go with the adjustable shackles so I could use a lower lift setting in the rear if I needed to. I eventually plan to get upper control arms to add more lift to the front, and then can max out the adjustable shackle at 2 1/8":


https://www.4x4parts.com/nissan/xterra-adjustable-lift-shackles-p-5612.html


If you are curious about how much lift you can get in the front end, place a jack under the front differential, and raise both front wheels at the same time, watching the bump stop gap. Once you have between a 0.5-0.75 inch gap between the upper control arm and the bump stop, you have reached PML ride height, and this will give you a good estimate of you front lift.




===========PREP WORK============


Prior to lifting anything, find a FLAT surface to work on (evenly laid garage floor is nice!). Ensure your tires are properly inflated. Ideally your tires should all be about the same tread height too.


Take preliminary measurements with a tape measure of your current ride height and write them down so you know where you are starting off at! Measure from the ground to the bottom of the doors right near each wheel well (not the wheel arches)


Measure the front:
7219971082_9dc94de921.jpg



Measure the rear:
7219971202_4e85e82660.jpg



Locate the rear shackles and the torsion bar adjuster bolts and nuts. Grab some PB Blaster or my favorite, Freeze Off! Drench all the hardware with some chemicals to keep them from being rust welded and breaking off. I started about a week before I was going to do the lift because mine looked really bad. I sprayed them all once, waited about 5 days, did them again, and sprayed them again on the day I did the lift. Maybe over board, but it definitely made things much easier.


Chemicals:
7219971842_e802ee6567.jpg



Front torsion bar location and functional diagram:
7219971262_6f0bef911f_b.jpg



Adjuster bolt, near mid section of truck. Spray bolt head, and both nuts above cross member.
7219971658_4690a1d113.jpg



On top of adjuster bolt, through cross member...two nuts...top nut is just to lock the bottom nut so it doesn't rattle loose.
7219970892_fbf83d6ac6.jpg



Rear shackle location:
7219973316_8493a67141.jpg



Spray shackle hardware:
7219973794_0c97befcc2.jpg
 
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robcarync

Sliders
Location
Raleigh, NC
===============LIFTING FRONT WITH TORSION BARS==================


Using a jack under the front differential, raise the vehicle slightly, but leave both tires firmly on the ground. You are essentially letting the weight of the suspension and tires droop on the torsion bars some, and letting the jack hold the weight of the vehicle. This makes it easier to crank them so you don't have to overcome the entire truck weight.


Using an open end wrench (I think 3/4"), loosen the top nut, which is just a locking nut. Back it off the bottom nut a little bit.
7219972340_1668f9613a.jpg



Now, use the same wrench to hold the bottom nut in place. Use a socket wrench to turn the bolt head. Laying on your back under the car,the bolt head faces down at you, and the two nuts are above the cross member. Looking at it, turn it clockwise to tighten it. It can be useful to have two people for this! If you are holding the bottom nut, and tightening the bolt, the bolt will thread into the nut, raising the lever arm of the torsion bar towards the cross member. The bolt head should go higher into the cross member, and the gap between the two nuts should get larger, as the nut you are holding will thread down the bolt while the top nut stays in place:


7219972732_05b4bf79e4.jpg



Make some shims that are between 0.5" and 0.75". I used 3 paint stirring sticks taped together.


Look for the bump stop gap in the front of the wheel....Right inside here:
7219972922_86d556087b.jpg



Use the shims to measure the gap. You need at least 0.5" gap between the upper control arm and the bump stop:
7219970706_03302fa4ee_b.jpg



A better pic from RacerXXL...aftermarket UCAs and the bump stop gap:


pYO7YI4.jpg



As indicated in my picture captions, understand these bump stops. When people say there needs to be a 0.5" gap, it is not because there needs to be physical space between the UCA and bump stop. It is because that gap is the easiest way to measure the angle of the upper control arm. If the upper control arm droops too low, the camber will be way off, wearing the outer edge of your tires very fast, and the stock camber adjustments will not be able to compensate for it. If you have after market UCAs, crank away on the torsion bars with low profile bump stops and all. Lifting control arms don't actually lift the vehicle, they simply have modified geometry so that even with a higher lift, the camber can be corrected.


Repeat this process on the other side, and aim to have even bump stop gaps on each side. It requires some guessing and checking and raising and lowering. Once you think you have it where you want it, don't quite tighten the lock nuts just yet, as you may want to make adjustments after the shackles and when the suspension settles some. I did the front end lift first so I could max out my torsion bars, and then choose an appropriate height within the adjustable shackle.


=====================================


A note on the infamous 're-indexing': Re-indexing does not offer more lift or better bump stop clearance. Re-indexing involves removing the torsion bar from the adjusting lever, and adjusting the initial position of the lever/adjuster arm. This is only done for two reasons:


1) There is no more room to adjust the lever upwards. As in you have room in the bump stop gaps to continue lifting, but the physical lever arm that the bolt goes through interferes with the cross member, or the bolt interferes with the body. When you re-index, it separates the torsion bar from the lever arm, allowing you to start the lever arm lower so you have a larger range of motion for the lever arm to raise into the cross member.


2) Your bump stop gaps are already at 0.5-0.75" but the lever arm and bolt head are below the cross member. You want the bolt head and lever arm to be inside the cross member to avoid having it snagged on terrain. Separating the torsion bar from the lever arm allows you to start the lever arm higher so that when you reach your desired lift height, the bolt and lever arm ends up inside the cross member.


I did not have to do this, but if you think you need to, check the DIY:


http://www.clubxterra.org/forums/showthread.php?t=2554


http://www.clubxterra.org/forums/showthread.php?p=505782&posted=1#post505782




REMEMBER: THIS ONLY CHANGES THE FINAL HEIGHT OF THE ADJUSTING LEVER. IT DOES NOT HELP BUMP STOP GAPS OR LIFT HEIGHT.


Another note on suspension lifts and the bump stops: A suspension lift does NOT add room for a larger tire. This only changes the ride height. The suspension system allows the tire to raise up when hitting a bump, but also droop lower. Adjusting the position for the tire to sit lower only trades up travel for down travel. Think of it like this: When you are jacking the front of the vehicle up to take a tire off...the tires do not immediately raise off the ground. The body and frame raises as the tire droops down. That magic point where the tires lift off the ground is the theoretical amount of maximum lift. You can have your vehicle ride that high, but now when raising the vehicle with a jack, the tire immediately raises off the ground, as it has no droop left. Of course, it can take a huge bump in the road as the tire has a lot of room to travel upwards. That point where the tires quit drooping is also when the UCA makes contact with the bump stop...IE the bump stop making contact with the UCA limits the droop of the front tire, so it can not droop any lower once it has made that contact.


Moral of the story: Regardless of your ride height due to a suspension lift, you can't fit larger tires than stock. You may have room for them while sitting in the drive way, but any amount of flex will cause them to rub whatever they would be rubbing if it was not lifted. If you want larger tires, the body lift is what you want as it raises the body (fenders) away from the frame, creating extra room regardless of suspension position. The suspension raises the frame (and body attached to frame), looking like there is more room, but once again, any flex in the suspension will quickly remove the extra room.
 
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robcarync

Sliders
Location
Raleigh, NC
===============REAR SHACKLES INSTALLED===================


Go to the rear of the car. Loosen those shackle nuts on both sides, but don't take them out yet.


7219973794_0c97befcc2.jpg



You want to jack the rear end of the vehicle up, and support the frame rails on jack stands with both tires removed.


1. Chock front wheels so vehicle doesn't run away from you
2. Loosen lug nuts on both rear tires
3. Use scissor jack to raise drivers side frame rail
4. Remove drivers side tire
5. Place jack stand under drivers side frame rail
6. Lower jack
7. Repeat for passenger side


7219974032_afb68b227a.jpg



Go ahead and lower the spare tire by taking the T end of the jack bar with the scissor jack and putting it through the hole in the bumper by the license plate. Engage it with the chain mechanism to lower the spare tire from the vehicle.


7219973568_71da2563ef_z.jpg



You should now have your vehicle with wheels chocked, no rear tires, spare tire dropped down, and shackle nuts loose.


The rear axle weight is now supported by the suspension, making it difficult to remove the shackles. Take a jack and place it under the rear axle, right in the middle of the differential. Raise the differential just enough to relieve the weight from the shackles. The shackles should be a lot looser and easier to remove. I still had to give them a little tap with a hammer and a punch:


7219975884_617a98ed0f.jpg



They come out in two pieces:
7219974280_3339aa323a.jpg



Remove both shackles. You now have the jack supporting the rear axle, jack stands supporting the frame on each side, and no shackles on! I had some issues getting the shackles out near the exhaust, but it was nothing a little pushing and pulling on the tail pipe didn't solve.


Go ahead and choose the setting in which you want to fasten the lower portion of the adjustable shackle (if applicable). I used jacks in the front and rear at the beggining to try and simulate the lift I could get, and my simulated measurements predicted about 1" in the front. I still did the 1.5" setting though...the front end looked much higher before the shackles. Plus my rake was a little low, so I figured I'd go for the high rear end. Based on the larger rake I have now, perhaps I should have stuck to the 1" setting.


Anyway, fasten the bolts through the bottom of the shackle on each side using the included hardware.
7219974542_8fb7a2ffbc.jpg



TJTJ recommends when installing all shackle hardware:


to clean up and then slather the threads/splines with anti-seize compound before reassembly would be nice too, as THAT makes the NEXT adjustments MUCH easier.


With both shackles connected to the leaf spring, you need to connect the top to the frame! However, with a longer shackle, you will realize they don't quite fit! Go ahead and lower the differential/axle so it can drop as low as the rear shocks will allow. Take the scissor jack and place it in between the frame and leaf spring. Raise the jack, which flexes the leaf spring down, widening the gap with the frame. This gives you the extra room to attach the tops. It is cumbersome and may take some time to keep it from slipping, but it will work.


Drivers side scissor jack:
7219974696_000c5bfb6c.jpg



Passenger Side scissor jack:
7219974910_6200a5b8cd.jpg



Alternatively, to get the proper spacing for the longer shackles, TJTJ suggests:


When FIRST putting the rear on jack stands to REMOVE the shackles (Getting the tension off them so you can get them off easily), the trick is to find that magic height where the shackles are loose/ can rattle a bit...and then go HIGHER by the length of the added shackle lift.


IE: If your shackles will be give 1.5" of lift...raise the butt ANOTHER ~1.5", and THEN set it onto the jack stands.


Then use the floor jack, etc, to lift the axle BACK to the "Loose" height, and remove the OEM shackles...


..and then just LOWER it again to install the new longer shackles.


If you do the axle lifting from the diff, it lets you rock the axle left to right, etc...which makes lining up the holes for bolts easier as well.

Personally, after doing a few more of these lifts now, I have found that unless you disconnect the shock, or unless it has been already upgraded to 3" suspension lift shocks, you will need the scissor jack in the springs. Also, if you have a hitch or heavy duty bumper, a high lift or farm jack works well to support both sides and let you keep your tire on. On a typically stock Xterra, going for its first mod, removing the tire lets you work within the limits of the stock scissor jack.


Tap the top of the shackle in place:
7219975138_10f5938be2.jpg



Install the shackle hardware, tighten in place, and reassemble! With the longer shackle, the hub will sit lower, so you may need to use a jack to raise the differential some, or raise the frame rail higher to get the tires back on!


Beware of tire shops that over tighten tire lugs....you will ruin the tire iron trying to get tires off!!!! That white line is an actual tear in the metal...
7219975382_bcec16ec26_z.jpg



7219975588_5855380e64.jpg
 
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robcarync

Sliders
Location
Raleigh, NC
Drive around some to settle the suspension, re-check the front torsion bars periodically to make sure the rake is even left to right, and about a 1-1.5 inch rake from front to back (front being lower). Get an alignment, but not to stock specification:


Quoting TJTJ


1. Set the Camber to 0°, or as close to it as
possible.


2. Try for getting the Caster to be between 0.3° and
0.6°, set differently between the right and left
side, with the left side being less than the right.


It doesn't matter what the Caster is, just as long as
you get the most Caster you can on the right
side, then set it so the left side is less by 0.3°
to 0.6°


Camber = 0.0°L.....0.0°R


Caster = 0.9°L.....1.2°R


Toe in = 0.08"L...0.08"R


Total toe = ...0.16"


Pre PML
6996832072_d32c4dc40f_c.jpg



I am still driving around some to settle the suspension and plan on making some more adjustments to the T-bars. However, it really does not look like I got much lift from the front T-bars. I know that the 'lift' is defined by the bump stop gap, and so by definition I have 1.5" over stock, but it makes me wonder how low was stock to begin with...because mine seemed low to begin with, and I barely got an inch in the front thus far. Looks like UCA's are in my future :)


Lastly, it appears that simulating the PML with jacks under the front differential and raising the rear frame/body was an accurate representation of my results...As the jack experiment predicted about 1 inch lift in the front...and that is what I was left with.


EDIT: Final Measurements and Reflection


Before I adjusted anything, the measurements I took were at the seam right below the doors:


Front Left: 19.5" Front Right: 18.5"
Rear Left: 21.5" Rear Right: 20.5"


After some final adjustments and negligence with the bump stop gaps (As I said, UCA's in the very near future, plus my tires are already bad...so I'll let the bad camber slide temporarily until I get both together) I got the ride height to:


Front Left: 20.5" Front Right: 20.25
Rear Left: 23.0" Rear Right: 22.5"


Interesting observations to note: The front to back rake was a bit large at 2 inches starting out. I should have gone with the 1 inch setting on the adjustable shackles. Oh well... I also began with a left to right rake of 1 inch. I tried to adjust the ride height to even it out. However, the front left tire, when maxed out at the bump stop gap, was much higher than the front right tire, when maxed out at the bump stop gap. I found it odd that the same ride height would have different bump stop gaps. I tried to even the front ride height to the same height the best I could (front right bump stop gap maybe 1/4 inch), which in turn brought the rear ride height closer from left to right, but not quite the same.


Lastly, using the jack under the front differential and raising the front end while monitoring the bump stop gaps gave me a predicted max front lift of:


Front Left: 20.5" Front Right: 19.5


This ride height was exactly what I had when maintaining the correct bump stop gaps.


So, in conclusion, if you are concerned about how much lift you can get from your stock torsion bars, raise the front differential and watch the bump stops. Measure before and after. You now know how high your front end will be after your PML.


After final adjustments and settling:


7250628998_d902882410_c.jpg
 
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xterra terrestrial

Test Drive
Location
canada
just did this. really easy to do. have an extra jack around for re-positioning the spring to get the bolts in is a must. my question... the top bolt wasn't long enough to make it all the way through the nut. made it about 95% of the way through. got the kit from 4x4parts. is this normal? seems like the bolt should be longer.
 

robcarync

Sliders
Location
Raleigh, NC
just did this. really easy to do. have an extra jack around for re-positioning the spring to get the bolts in is a must. my question... the top bolt wasn't long enough to make it all the way through the nut. made it about 95% of the way through. got the kit from 4x4parts. is this normal? seems like the bolt should be longer.

Agreed after doing another PML...you need a 2nd jack to re-position the springs. I tried to use a high lift in the trailer hitch and lift both sides at once, but you have to disconnect the shocks to allow the axle to droop enough to fit the extra length of the shackles. Without disconnecting the shocks, even if you jack the rear end up some more, the shocks pull the axle up with it. Granted it is just one bolt to drop the bottom end of the shock, but it was just easier to wedge an extra scissor jack in there and push the spring out 2 inches.
 

SLWZ4

Test Drive
Location
Utah
So I have been thinking about doing the PML for a while and decided to look into it today. My question is how much space should there be between the bump stops before the lift? I made a 1/2 inch spacer guide and when I put it up there I only have a little over 1/2 inch gap to begin with. I put a jack under the front diff and raised it up until I hit the 1/2 inch gap mark and it only resulted in about a 1/2 inch lift when measured at the bottom of the door. I am running slightly larger tires (265/75r16) would this make a difference? I am not the original owner and I wondered if the previous owner had already done this but the back leaf springs and shackles look stock. The height measured at the rear door is about 2 inches higher than the front and I would think that they would be about the same height if the front had been raised but not the back. Any ideas?
 
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harryron

The Grumpiest of Mid-Westerners
Location
ohio
Sounds like you need to index your torsion bars. You should have about an inch to a inch and a half rake from front to back.
 

SLWZ4

Test Drive
Location
Utah
Correct me if I'm wrong but I thought reindexing was only necessary if you have run out of room to crank the torsion bar adjuster bolt more. Will reindexing increase the gap between the UCA and the bumpstop?
 
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