Correctly Determining Rear Shock Mount Placement for Maximizing Shock Utilization

Update Feb 11, 2019: If you don't want to read this thread, the determination is captured in this post:

How-To: Toyota Tacoma Rear Shock Relocation - Determining Leaf Spring Cycle and Mount Positioning​

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Whew, quite the thread title! And this is a long-ass first post, sorry.

Background for people who find this in the future
Here's the deal - as we wheel, we find ourselves wanting to upgrade stuff on our trucks. One of those things is often suspension. That means new shocks and leaf springs in the rear, and eventually, sometimes, relocating the rear shocks to allow for longer shocks (thus more travel), etc.

We were having that conversation (my fault) over here in the awesome
1st Gen Shock Relocation 2.5" - Outside Frame Rails thread, but that clearly wasn't the right place because we were only sort-of on topic.

I've tried to capture a bunch of our conversation from there, for starting context here.
/Background

So, this thread.

The question is - how to correctly determine where to place the shock mounts so as to maximize utilization of a shock - i.e. maximize nearly 10" of a shock that has 10" of travel/stroke?

I'm also reserving the second post for (hopefully) the conclusion that we come to for the right way to do this - for posterity. Plus, it'll be a great education for me (and I'm selfish that way).

OK, conversation so far:

This all started when I read the following:

@Willbeck - i still see a full leaf pack underneath, are you cycling the suspension before you mount the towers?

@erice - Negative. The Alcan leafs are voided if i disassemble them. Not ideal​

Having just done a relocate with Alcan leafs myself, I replied with:

@turbodb - I found in my recent rear shock relocate that cycling the suspension (I too have Alcan's and removed all but the top leaf - I don't care about warranty, I'm going to wear them out ) is not the right way to go about figuring out travel/positioning.

I have yet to write this all up and post in my thread, but the more I think about it, the right way to figure out placement is actually to load up the truck as it'd be on a trip, and then position the shock so that it's approximated at the midpoint of it's travel at resting height.

So, with a 12" travel shock, you want 6" of shaft showing when the truck is fully loaded. Doesn't matter (or matters a lot less) where you are in your leaf spring cycle.​

I knew that would draw some opinions out, and it sure did!

@Blackdawg - While yes this makes some sense. It still doesn't.

If you cycle the pack, you should be able to calculate the mid point of the travel and that is how you go about determining where to place the shock. It would be wise to measure your ride height as well to figure out where you sit in terms of your suspension travel. If you pull 9'' at the leaf pack lets say and you figure out that your ride height loaded down is only 3'' up travel. Thats a problem with spring capacity. Your shock mounting point should not change as 3'' up is still only 3'' up you want the shock to go and that means you have 6'' down to cover as well.

@Squeaky Penguin - Monte's right on this one. (can't believe I just said that)

The leafs have a certain amount of travel, doesn't mean you're sitting in the middle of that at ride height.​

These responses matched with what I've always heard (and essentially what @Willbeck said previously) so I still wasn't understanding. Since I like to understand, I added:

@turbodb - Interesting. Zane and I did the single leaf, full cycle on mine when we did the relocate. We then mounted everything based on that and the shocks were exactly at mid-travel (5" of shaft showing) when the springs were in the midpoint of that full cycle.

The problem is that once we loaded everything back into the truck, the leafs compress (as expected) and so ride height is much lower (say ~3" lower than empty, but still ~3" above stock), giving me only 2" of uptravel before the shocks bottom out. (10" travel shocks)

So are you guys saying that this is a problem with the leafs, and they should be holding the truck up more at ride height? I feel like the back is already as high as I'd like it...​

With that extra info, Brett replied with:

@Squeaky Penguin - Just a facet of the setup.

Your options are more lift, a willingness to let your leafs go more negative, or spring under.​

This was probably totally correct and someone with a better understanding would be like "duh, of course." But I'm not that guy - I want to be that guy but I'm not yet. So I said as much to Brett, hoping he'd educate me:

@turbodb - I don't follow, sorry (my fault, I'm sure). Since the shocks are at mid travel when the leafs are at unloaded mid cycle, how do I account for the fact that the springs cycle even more when the truck is loaded?

Said another way - with a single leaf, the furthest "up" my axle can go (starts lifting the truck off the jack stands) leaves ~3" of space before the bumps hit. However, loaded and flexed, the full pack cycles even further - I can get into the bumps. Obviously, this means the pack is going more negative on the trail than we can cycle with the floor jack...

How do you account for that?​

At the same time - we were all now typing furiously because "whoever yells loudest on the internet wins" , Shane mentioned:

@desertjunkie760 - My first reaction is why are your shocks your limiting factor on bump? Shocks should never bottom out. That’s why you cycle.​

This I totally get, and I agreed! Look at that, our first agreement!!! . The question for me is how to convert this agreement into practice.

@turbodb - I agree - they shouldn't be the limiting factor and I don't want them to bottom out. The question is how to ensure that the case. Cycling the suspension (just the top leaf) clearly didn't work for me... Because it suggested that my leafs wouldn't flex as much as they actually do.​

So, that's were we'll pick up in this thread - there's been a bunch of commentary about what I must have done in the other thread, and I'll start by replying to that.

My bumps (I have Plastics Guy's 4.25" bumps - essentially 2" taller than stock) don't totally limit negative arch with my Alcan springs. My understanding is that a bit of negative is OK - from my conversations with Bill at Alcan.

So - you are both correct - we cycled by taking out all leafs but the top leaf, and then using a floor jack under the axle (on one side at a time) to push it up until the entire back of the truck was lifted off of the jack stands (under the frame just in front of the rear leaf hanger). When we did that, the single leaf was

• not yet negative
• still had several inches of travel (3-4") until it would have allowed the bump to contact the frame.

However, the truck was "lifting" at that point so no matter how much higher we went with the floor jack, the distance between the frame and bump wasn't changing.

I definitely see more cycle with the leafs when the truck is loaded. This makes sense to me because that extra weight in the bed creates a lot of momentum (larger mass) when going over a bump, and so as gravity pulls it back down to earth, it has "moves further down before being stopped" by the shock/leafs.

This is as compared to a floor jack pushing up on the axle and having only the mass of the frame (bed was off) pushing back down.

Agree, or am I being dense?

Makes sense. Actually, as it turns out, my leafs go flat right when the top of the leaf pack is 4.5-5" from the frame bump location. So, about .75-.25" before the bump makes contact.

So, the bump is contacting just as the arch becomes negative.

OK, so I think this is what we actually did. Sort of. I mean, we didn't have the bump actually hitting, but we did think of that place (flat leafs) as the place where they should hit. My plan was to build a short tower for the bump to move it up to that position when I got back home.

The problem that I discovered with this setup is that at normal ride height - when the leafs were more flattened out by all the weight - that meant I only had a couple inches of uptravel (I think I'm using that correctly - the wheel could only move up toward the frame a couple inches) before hitting the bump (or in my case bottoming out the shock since I hadn't raised the bump yet).

Yeah, loading the back end is what I tried to say at the very beginning of all this. But that seems to "contradict" the whole point Brett is making that you want to find out the full range of motion of the leafs in this next post:

So here you mention ride height again in your follow-up to Brett, which it seems like Brett is saying isn't the issue:

Thanks, same question I asked of Monte and Brett above.


OK, and lastly - I'll include some pictures here (sorry for the crappy drawings, I'll clean these up and update the post as time allows:

When we cycled the leafs, we did the following to determine travel of the leafs - again, with no weight in the back.

​

But then, when I went on my first trail ride, I discovered that this was possible:

​

 

For the full set of steps, and links to parts if you're doing this on a Tacoma, use this printable sheet:

How-To: Toyota Tacoma Rear Shock Relocation - Determining Leaf Spring Cycle and Mount Positioning​

Summary (cliffs notes version)

Steps to determine shock mount placement (by fully cycling leaf springs):

Note: assume that as part of this, you're adding new upper and lower mounts vs. just using the OEM ones. That means you're removing the bed in order to fabricate.

1. Remove bed
2. Support both sides of the rear frame AND rear axle and remove wheels
3. Remove u-bolts holding leaf pack to the rear axle.
4. Disassemble the leaf pack (you can do this in-place), by removing all leafs except for the top leaf.
5. Place a spacer the same thickness as the missing leafs between the top leaf and axle. Reinstall u-bolts and whatever bump stop you'll be using.
6. Jack the axle up (ideally, both sides at the same time) until your bump stops compress after hitting the frame (note: if you can't compress them, estimate their full compression), or until you reach your desired maximum leaf spring compression (should be at least slightly past flat; starting to frown).
   
   IMPORTANT NOTE: Make sure you have enough weight on the back of the truck (this could be a lot of added weight, since the bed is off) to keep it from lifting off the jack stands that are supporting it while you do this.
   
7. Place the upper shock mount AS HIGH AS POSSIBLE and tack it. (You can actually probably fully weld it at this point - you really want it as high as possible on our trucks)
8. Install the shock in the upper mount.
9. Compress the shock so that you have just enough shock shaft left showing to account for the compression of your bump stop, plus 1/2" as a safety buffer.
10. Place the lower shock mount where indicated by your compressed shock and tack it.
11. Install the shock in the lower mount.
12. Cycle the suspension. Droop it all the way out, and determine if you are risk of over-extending your shocks. If you are, install a limit strap that is 1" shorter than full extension (to compensate for stretch of the strap).
13. Remove the shocks to complete fabrication.
14. Fully weld the upper and lower mounts if you haven't already.
15. Paint everything to inhibit rust.
16. Reinstall the shocks in the mounts.
17. Reinstall the wheels.
18. Reinstall the bed.

For the full set of steps, and links to parts if you're doing this on a Tacoma, use this printable sheet:

How-To: Toyota Tacoma Rear Shock Relocation - Determining Leaf Spring Cycle and Mount Positioning​

 

Excellent write up on the subject and I look forward to the input.

I love the commentary as well.

As for now, I’m going to enjoy my Moscule Mule, watch my dog torment my cat, and watch Venom.

I was wondering if you would show up to the party.

 

You're being dense.


You're still looking at this the wrong way, Dan. The springs are the only thing that really matter here.

I'm a few beers in, so hopefully this make sense.

Ignore the shocks, you should easily be able to setup shocks to use all of the available travel of your leafs. Your leaf packs have x amount of travel available (for a 1st gen using stock leaf mounts, x will be 10" or less). Assuming you retain the same length shackles, this travel is always in the same position in relation to your frame. It's simply a geometry factor based on the length of the main spring. Got this tip for @jberry813 years ago: take a piece of string the exact length of your main leaf, tie it between the hanger bolt and shackle, and you can essentially simulate what your leafs will cycles. Will also tell you if your shackle is appropriately sized to the amount of movement necessary for that length of spring. If you were lifting the frame off the jackstands while cycling, that's an issue with how you went about cycling, and has zero impact on that available travel.

Ride height is NOT the issue at all, it just determines the ratio of up/down within that fixed range of travel.

Do not assume the bump stops your bought from whoever are the correct height for your application. You need to set that height based on where you're comfortable with the leafs going. This should always be set before measuring and mounting shocks.

 

From your list it seems like there should be a fourth option. Change the shock mount locations. Raise the upper shock mount or lower the lower shock mount or a combination of both.

To the collective, I am also curious about why letting the leafs go a little negative during max flex is a bad thing?

 

I know you've probably been through this a million times. Just one more is all I ask . hahahaha

I'm sure I'm being dense. Sorry for that.

"ignore the shocks"
I'm ignoring the shocks. Didn't even have them in my pictures .

"leaf packs have x amount of travel."
For me, that's right about 9", so that we're being concrete. Tried to show that in the top two pictures. And, I have OEM shackles. I like that string trick. I assume what you mean there is that pulling the string tight shows you the "top" of the cycle (flat springs), and letting it hang shows you the "bottom" of the cycle (full droop). Makes sense.

"tell if your shackle is appropriately sized"
I don't get this part, sorry. [....thinking...smoke from brain area....]

Oh, actually - maybe I do get it. When 'pulling the string tight' in what I said above, I still need to use the full length of the string, as oppossed to just pulling it tight and ignoring the excess. That's because the leaf springs are a given length, regardless of position.

And so then, to use the 'full length' of the string at the top of the cycle, I'd end up moving the shackle to "take up the slack."

"lifting the frame of jack stands, issue with how we were cycling"
OK. But then, what's the right way to do it? I don't understand how there could have been any other way except to have a "more loaded / weighed down rear end of the truck." Is that where we went wrong?

"Ride height is NOT the issue at all"
I hear you, and I understand why you are saying this. Heck, it's what we did when we did the work on my truck. Now I want to hear from Monte @Blackdawg since he seems to be saying it (at least partially) needs to be taken into account.

"Do not assume the bump stops are the correct height for your application"
Totally. I assumed I'd need to move them when I started all this.

The one thing that made me question this was the fact that when I ran a trail without shocks (I removed them since they were bottoming out), I was able to snap these photos when the truck was flexed. As you can see, I'm actually on the bump. Perhaps that means the leaf pack is over-flexed though, and I don't want to go that far.

​

frame resting on bump stop. Note the lack of shock in the mount . And the slightly frowning 8-leaf pack.

​

fully stuffed rear passenger. frame resting on bump stop.

​

rear driver drooped down, when passenger rear is on bump stop.

 

Sorry been busy all night doing chores. I'll do a real chime in tomorrow.

That said ride height only matters in the sense that you either pick what you want it to look like..or lift it to get it closer to setting it to the right up and down travel numbers you want.

Granted that is not simple with leaf springs..

Pretty much everything Brett is saying is right.


@Digiratus nothing wrong with negative. I left mine go way negative because travel is good especially up travel. The down side is they wear out faster. Big whoop.

 

Your leaf pack looks fine to me, Dan. It'd be better to see the whole thing, as I'm curious about your shackle angle as well, but I don't see a problem with the slight negative arch of the leafs.

I would say your bumps are in about the right place, so all you need to do is make sure you have a 1/2" or so of shaft exposed on your shocks when they're mounted and you're stuffed (bumps fully compressed). That may necessitate adjusting your mount locations, but it looks like you have plenty of room to move the top mounts up before hitting the bed. And of course, doublecheck fully extended length vs. droop, but I doubt you'll have an issue there with 10" travel shocks.

Edit: I'll add that the only thing that could be improved about your measurement method is that you need to compress both leaf packs at the same time to get an accurate shock measurement. If you just do one side at a time, with inboard shocks you're not getting the actual compressed length, and you could bottom out. Ask me how I know.

 

Look at you adulting. You'll have a house soon too I bet. Sheesh, what is the world coming to?

I'm with you on negative. Don't care how fast they wear out, really.

Gotcha on ride height, I think. So, since I like the height I'm at now (I don't want to be much higher), the idea is to move the mounts to positions that work with that height. To me, I still don't see how I would figure that out with the single leaf cycling and no weight on the truck. When you have time tomorrow, I'd love you to list the steps to figure out where to place the mounts. For me, the place I went wrong was how to figure out full stuff without lifting the truck off the jack stands.

I agree the leaf pack looks OK. I've already moved the top mounts up as high as they can go (not pictured, obviously) and now the shocks bottom out at the same time the bumps hit - so I probably need to either:

• move the bottom mounts as well, which is going to be more involved, given the proximity of brake lines
• move the bumps up .75" - 1" so they hit first. Easier, but limits travel "unnecessarily."

At any rate, I'm drivable-with-shocks now so the decision between the two options isn't time-sensitive.

 

Move the lower mounts. Then get limit straps

And yeah. Laundry and cookie baking haha

 

Yeah, moving the lower mounts is the plan - you can see they are angled up slightly, so I have room to move them.

Don't love that idea since it it's more work and more welding on the axle housing (which I probably over-fear is bad for the metal there / weakens it), but I know it's the right thing and you know I like right things.

Still though. I want to understand where I went wrong figuring this out the first time, so would appreciate you or Brett walking through how you'd have done it.

 

We

 

OK. Didn't want to be presumptive. I really do appreciate your help. Would do again.

 

It seems like most of your questions have been answered but I wanted to give a little input.

@Squeaky Penguin did a great job on explaining the concept even after a few beers. I appluad you.

With that said, when you go through this process, your finding "x" as your vertical travel, again eliminating the shocks as a variable. Once you find your droop and bump numbers, or where you want to limit that travel, then you mount the shocks to work within those perameters. It sounds like the cycling process was not successful for you because you were not able to figure out you full "up travel" numbers. Cycling with a single leaf still leaves variables, such as inertia, additional weight (tire), load, and articulation, but it gives you a general number to work with when mounting shocks.

If you were to weigh down the truck enough while on the stands so that it wouldn't "rise" then you could have figure out roughly what you full up travel numbers would be, exluding bump stop compression. (I have found that to be difficult to find if not using hydros and would love to hear some ideas.) At that point you can figure out where to mount the shocks to work within your perameters. Moving the lower shock mount would likely be your easiest solution here as mentioned about, however I would like to get more details of the upper shock mount if possible?

As far as negative leafs, thats user preference. Negative arc wears your leafs out quicker, as @Blackdawg mentioned, and thats totally up to the user if they are willing to do that. I personally like where your bumps are set now and a slight bit of negative arc will be fine, IMO. Just need to make the shocks work within you "x" amount of travel.

Edit: what shocks are you running?

 

Your fourth option would assume the shocks are the limiting factor. You should have already bumped it where you wanted it and set up shocks to match.





Anyways, you're getting closer Dan, but not quite there. Let me address a few things, but first something I missed last night:

You need to base all your measurements on vertical travel, i.e. the entire axle moving up and down. Leaf springs twist and bind during articulation and do not allow the full range of motion. You will always get more travel vertically than in articulation. Do not base your shock setup and measurements just off one side flexed.

How do you know? Previously you said you weren't able to get accurate measurements while cycling?



If you're basing your 9" off this picture, and that's where you wanted your springs to bump, you should of raised the bumps to stop there. If you wanted it to go up further, you need to account for that in your measurement. You can't just assume because you couldn't get there based on your cycling, that it will never happen. It seems like that is where your problem is coming from. You need to fix the uptravel stopping point where you want it to be.

The string is just an easy way to get an idea (not exact) of what your springs will cycle.

You're on the right track here. The leafs get longer eye to eye the more they flatten out. The shackle needs to have enough range of motion to account for the change in lateral length of spring as it cycles.

As mentioned previously, I think you did two main things wrong.

A) you needed to weigh down the back of the frame while cycling to get an accurate measurement
B) you didn't limit the uptravel to where you wanted before measuring and installing shocks

Don't listen to Monte.

I think all he's trying to say is that it is a trade off. I have a lot of lift, and therefore more uptravel, but have a crazy rake going on.

See above, I think you missed the mark here.

Couple things here. As I mentioned at the top of this post, this is really less travel than you would get with vertical travel. If you were bottoming out your shocks articulating, it would have been worse with vertical travel. I can not really get into my bumps flexing as my leafs bind first. That's kind of what looks like is going on here, as the bumps don't look very compressed, also means you would have more of a negative arch at full bump with both sides compressed.


Honestly, if I were you Dan, I would start over and do it right versus just moving mounts around hoping for the best.

Get the upper mount as high as possible - that should always be step one of any shock mounting.
Get enough weight on the back to accurately cycle the packs.
Set the bump height to where you're comfortable going. (would be helpful to know how much those bumps compress)
Mount the lower mount such that the shock travel matches the leaf travel. Ideally you wouldn't bottom out or over extend your shocks, but sometimes you can't get a long enough shock in a physical location. In which case I would mount the shocks to avoid them bottoming out, and add limit straps. That way you don't loose any up travel.


I'm sure I missed several things in there...

 

That is what I'm saying. So yes listen to me haha

Frank has 5.5'' of up travel. Thus a LOT of lift too. I don't have much rake though when loaded down.

 

Totally. Thanks a ton for keeping going with me, appreciate it.

Makes sense.

I totally agree with you that this is where we went wrong and where the problem is coming from. Maybe I could have said that more clearly, sorry. Really what I was wondering was how to do it next time, differently.

I think this is the key / most important bit for me in your response, because I think it answers my question of how to do it next time, differently. For (A) we needed to weigh down the truck to counter the single leaf when cycling. This is essentially the exact opposite of what we did - we removed all weight from the truck when we were cycling, since that made for easier fabrication/access.

For (B), even though we didn't do it physically, we fabbed everything as though we had (with my plan being to do it later under less time crunch). So I agree with you that the right/non-time crunch way to do this is to set the bump.

I want to note one other bit though - probably obvious to you but to capture the point for me. Since we got (A) wrong by not weighing down the bed, we couldn't get (B) right and so it was a good thing we didn't actually set the bump stops when we did the work - they would have impacted way too early in the leaf cycle because we didn't realize how far the leafs really would cycle.

I think what was going in in the photo needs to be understood in context (which I didn't give) so let me give you that. I found this place on the trail with cross-axle whoops and realized it'd be a good place to check flex under load. So I eased the truck into position until I felt the frame touch the rear bump (side note: it was obvious that it did, and is something I've never had happen on the trail before when I had OEM bumps and shocks installed, so a cool experience).

So, I don't know that my leafs are bound at that point, and I know for sure the bump isn't compressed hardly at all b/c I just eased it into position.

But, I do know that I sort of like the position of the leafs in the photo - and so that means I need to move the bumps up so that when they are fully compressed, the leafs end up in that position. Essentially, if they compress 1", then they need to get moved up 1"

Where's the fun in that? If we just did everything right, our builds would be over so much sooner.

These are great steps. As I mentioned above, #2 is the one that I/we missed on the first go, and which led to what I've got now, so that's great to realize. Now it's just more work to get everything right...which is fine by me since I love the learning and doing part of all this just as much as the result.

THANK YOU.

Yep, you hit the nail on the head here - I didn't get the cycling right. I realized that early on (by early I mean "early in the trail run, the mistake was already complete" and is why I started asking questions here on how exactly to do it right.

It's making sure there's enough weight in the back while cycling. I didn't realize that was necessary with just one leaf. Amazing how strong a single leaf is, really.

Exactly. And actually - I'm totally curious about this now too:

New question: How do I figure out how much the bump stops compress?

The upper shock mounts are (now) mounted as high as they can go. You can see where they were previously in this photo I posted just after doing the work, and which Monte and Brett kindly pointed out was a huge problem at the time. I've since cut them off and welded new ones that are parallel to the bottom of the bed - and thus above the frame rail - which gave me an extra ~2" or so.

​

OK - thanks again everyone, really appreciate the patience here. It'll be a bit before I post it, but I'm going to write this all up, so hopefully someone can benefit from it in the future, and we don't have to explain it again and again (as you've likely already done...and for me, lol).

But hey, if it's all in one place, you could just link to it, right?

 

OK, so remaining questions:

1. How do I (does one) figure out how much the bump stops compress?
2. Specific to my situation: Should I be worried that I plowed a bunch of heat into the rear axle housing when welding on the lower mounts the first time, and now I'm going to cut those off and then plow a bunch more heat into the same area? (from a metal strenth/fatigue perspective)

For #1 - I guess that if the back is weighed down enough when cycling the pack, you can place spacers under the bump stop until it compresses fully and starts lifting the truck (weight and all) off the jack stands). Seems sketch.

 

When I measured how much my super bumps compress I put one on the jack pad and jacked up half the cruiser. That's approx 2500lbs. Then measured it's height.