Rear shock questions

[nhtc33d]

I am having issues with my shock setup. I can't seem to find a shock in the lengths i need. When the truck is aired up the shock length measures 23" when it's laid out it measures 8" when i air the front up and the rear down it measures 5". I have yet to find a shock with a compressed length of 4.5" and a extended length of 23"! what am i doing wrong?

[chevy_mike]

Maybe I am missing something but if you are aired out to the point the axle is hitting the notch, in the rear, why does it change with raising or lowering the front?

[nhtc33d]

I don't' know either But it does! This is the first thing i have "tried" to put bags on and have a lot of success with getting help from the great people on this forum.( insert butt the smooching here)

[LONGHAIR]

You need to re-think your mount locations. You are never goingto find a shock that can travel more than it's collapsed length.
You really need to measure the total travel of the suspension, at the axle. Then you need to find a place to make shock mounts that can accomodate that travel. The more vertical you can keep it, the better. Shocks work best when they travel the same direction as the suspension itself.

[nhtc33d]

Originally Posted by LONGHAIR

You need to re-think your mount locations. You are never goingto find a shock that can travel more than it's collapsed length.
You really need to measure the total travel of the suspension, at the axle. Then you need to find a place to make shock mounts that can accomodate that travel. The more vertical you can keep it, the better. Shocks work best when they travel the same direction as the suspension itself.

Thanks for the reply. So the measurement i show in the photo's is a different measurement than you are talking about? Where should i be taking the measurement from?

[chevy_mike]

Originally Posted by nhtc33d

I don't' know either But it does! This is the first thing i have "tried" to put bags on and have a lot of success with getting help from the great people on this forum.( insert butt the smooching here)

Not that I want to insult you or anything, so don't take this wrong, okay.

You say this is the first thing you have "tried" to bag. Is this the first thing you have tried to 4 link as well? What concerns me is, if I am reading what you wrote correctly and from your pictures, the space between the frame notch and top of the axle changes 3" because you raise or lower the front, something does not seem right with this.

Based on all the info I have ever read and all the vehicles I have worked on, this doesn't seem to be working correctly. In my thought, if you air out the rear so it is sitting on the axle, raising or lowering the front should cause it to pivot on the rear tires (actually around the centerline of the rear axle). To me, something in the rear suspension is not setup correctly and rotating the frame (by raising and lowering the front) is putting something in a bind or dermatically changing the rear geometry.

Do you have any more pictures of the whole rear and whole front suspension and a description of what you have done? I just want to make sure something is not totally out of whack and going to cause major harm or damage. Remember, I might be the one next to you on the road when something lets go.

[LONGHAIR]

Thanks for the reply. So the measurement i show in the photo's is a different measurement than you are talking about? Where should i be taking the measurement from?

You are in the right place...but that can't be your total trave numbers. The first one shows frame to axle contact, you should not do that. You need a "bump stop" in there somewhere. That metal to metal contact is very rough on stuff.
The second pic is only showing about 3" of upward travel. What is the full lift measurement?
chevy_mike has a point, it sounds like something is "rotating" somewhere in the travel.
Some pics from farther away showing minimum and maximum travel would be helpful.

[nhtc33d]

Thanks for the replies. I will get some more pics and post for you to see. The pictures i posted earlier are #1. total truck aired out. #2. rear aired out and front aired up fully. It would not let me post my picture of rear aired up due to sizing issues. But the measurement is 23" for the rear aired up. That is from the same spot i measured everything.

[nhtc33d]

Heres some more pictures. Hopes this helps. Thanks again

[LONGHAIR]

That appears to be a normal "truck arm" 2-link with a sliding wishbone. I really don't understand why it would move at all when the front is raised?

When you did this (lift the front) are you sure that there was nothing under the rear section of the frame, jack stands or something?

[chevy_mike]

Actually I think I might see the problem. I think the geometry of the links is wrong.

If you look in the one pictures where it up, the wishbone link is pointing up, away from the lower arms, at the front of the wishbone. When it's aired down, the links are paraell.

Since the main arms are solid mounted, when you rotate the frame, the upper link is pivoting but not the lower arms. Basically the upper link is then pushing and pulling the rotation of the axle in relation to the frame, causing it to change height.

I think you need to rethink your setup and actually use proper suspension geometry, based on correct math, center point, rotation, etc., etc.

As for the shock lenght, with your bags that far up on the arms, you will never find a shock that will meet the travel requirements. The closer you put the bags to the front pivot point, the more range in height you get at the axle. Bags need to move back. You typically only need 8-10" of total axle movement and you will find most shocks will fall into this range, until you get into lifted application but that's a whold different ball game.

Hope that helps.

[LONGHAIR]

If you look in the one pictures where it up, the wishbone link is pointing up, away from the lower arms, at the front of the wishbone. When it's aired down, the links are paraell.

Since the main arms are solid mounted, when you rotate the frame, the upper link is pivoting but not the lower arms. Basically the upper link is then pushing and pulling the rotation of the axle in relation to the frame, causing it to change height.

I think you need to rethink your setup and actually use proper suspension geometry, based on correct math, center point, rotation, etc., etc.

That should not bother anything. The wishbone slides, so it changes length to follow the travel of the lowers. As long as there is no bind, from the wishbone "limiting" something one direction or the other, there really is no load on the wishbone at all...except side to side to keep the axle centered.
Even at that, it is not going to change the pinion angle (rotate the axle) because the axle is u-bolted to the lower arms, like stock.

[nhtc33d]

Originally Posted by LONGHAIR

That appears to be a normal "truck arm" 2-link with a sliding wishbone. I really don't understand why it would move at all when the front is raised?

When you did this (lift the front) are you sure that there was nothing under the rear section of the frame, jack stands or something?

No, It wasn't but the more i think about this i think it makes for this to happen.. If i lay the truck out there is 3ish" gap between the top of the axle tube and the bottom of the notch. when i air up the front only the space decreases to 1ish". If you take a 2x4 and lift one end it put more force on the other end. So isn't this just the same principal? Its not really "moving" its just the weight is being distributed differently? Anyways, Any ideas on where to mount the shocks?

[nhtc33d]

Originally Posted by chevy_mike

Actually I think I might see the problem. I think the geometry of the links is wrong.

If you look in the one pictures where it up, the wishbone link is pointing up, away from the lower arms, at the front of the wishbone. When it's aired down, the links are paraell.

Since the main arms are solid mounted, when you rotate the frame, the upper link is pivoting but not the lower arms. Basically the upper link is then pushing and pulling the rotation of the axle in relation to the frame, causing it to change height.

I think you need to rethink your setup and actually use proper suspension geometry, based on correct math, center point, rotation, etc., etc.

As for the shock lenght, with your bags that far up on the arms, you will never find a shock that will meet the travel requirements. The closer you put the bags to the front pivot point, the more range in height you get at the axle. Bags need to move back. You typically only need 8-10" of total axle movement and you will find most shocks will fall into this range, until you get into lifted application but that's a whold different ball game.

Hope that helps.

The wishbone i built is a sliding type so there cannot be any push pull on the axle. I have seen many trucks built like this with the bags in the same place and they have shocks mounted in similar areas where i was thinking on mounting mine. I must not be too far off from finding a answer.

[chevy_mike]

Ah, true, I didn't account for the sliding part of the wishbone. My mind was thinking like a drag setup where it would be a soild pivot to help plan the tires better.

[GMBowtie79]

I have one question, in the top picture in post #9 is the front end dropped or not? It's hard to tell by the pic but the cab looks angled back like the front is up. If it is looking at the picture the lowest part of the frame is a bend. When you drop the whole truck to the ground does the frame lay flat on the ground? I may be way off but if you drop the back down and then the front you might be getting a rocking chair effect from that bend which could raise the frame off the axle that mysterious 3"when fully aired out. Just a thought. Well, maybe there's more than one question here!

[nhtc33d]

Originally Posted by GMBowtie79

I have one question, in the top picture in post #9 is the front end dropped or not? It's hard to tell by the pic but the cab looks angled back like the front is up. If it is looking at the picture the lowest part of the frame is a bend. When you drop the whole truck to the ground does the frame lay flat on the ground? I may be way off but if you drop the back down and then the front you might be getting a rocking chair effect from that bend which could raise the frame off the axle that mysterious 3"when fully aired out. Just a thought. Well, maybe there's more than one question here!

Thanks for the reply, Yes, That picture the front is aired up. That could be were the 3" is going! Good eye! I still need help finding a shock and/or a mounting position that i was looking for help on in the original post so if you have any suggestions let em rip!

[GMBowtie79]

First get it so its level when aired out. put some bumpstops in or blocks of wood. Where you planning on bridging your notches or not? If you bridge it you could mount from the bridgedown to below your axle. You can look at www.balisticfabrication.com in there brackets and tabs, or www.speedwaymotors.com look under race parts (rear suspension) they both have parts you could work with. you have alot of travel so you will have to find or make a mount rear end that hangs below the rear(like a coilover mount) I'd think somewhere around 4"-6" and run it up to a bridge and you might want put a shock mount that has multiple holes (like a front 4link mount for drag racing) so you can have some adjustability. That way you get some distance between your shock eye mounts when the truck is on the ground. The more distance between the eyes when the truck is aired out and the shock is compressed and the the more travel you'll get, but you still might have to figure out a way to limit that 23" when fully aired up. Hope these suggestions might help give you some ideas and good luck!

[nhtc33d]

Originally Posted by GMBowtie79

First get it so its level when aired out. put some bumpstops in or blocks of wood. Where you planning on bridging your notches or not? If you bridge it you could mount from the bridgedown to below your axle. You can look at www.balisticfabrication.com in there brackets and tabs, or www.speedwaymotors.com look under race parts (rear suspension) they both have parts you could work with. you have alot of travel so you will have to find or make a mount rear end that hangs below the rear(like a coilover mount) I'd think somewhere around 4"-6" and run it up to a bridge and you might want put a shock mount that has multiple holes (like a front 4link mount for drag racing) so you can have some adjustability. That way you get some distance between your shock eye mounts when the truck is on the ground. The more distance between the eyes when the truck is aired out and the shock is compressed and the the more travel you'll get, but you still might have to figure out a way to limit that 23" when fully aired up. Hope these suggestions might help give you some ideas and good luck!

Thats EXACTLY the kind of information i was searching for! Thank you!

[GRIMSS]

This may and may not help on shock placement.

mini truck mag had a tech on shock placement for what shocks you want to run.

it goes like this.

desired wheel travel / Shock stroke = X ( shock postion, measured from the frame pivot )

X is a % of the total lengh of the a-arm or the rear lower bar

here is the example they gave.

Rear
10" (travel) / 6.5" (stroke) = 0.65
the rear bar they mounted it on was 30.75. 0.65 * 30.75 = 19.9

so they mounted it 20" from the frame pivot. then collapsed the shock and made the upper fame mount.

the did the same on the front.

Don't know if it will help but I was wondering it myself.

[nhtc33d]

Originally Posted by GRIMSS

This may and may not help on shock placement.

mini truck mag had a tech on shock placement for what shocks you want to run.

it goes like this.

desired wheel travel / Shock stroke = X ( shock postion, measured from the frame pivot )

X is a % of the total lengh of the a-arm or the rear lower bar

here is the example they gave.

Rear
10" (travel) / 6.5" (stroke) = 0.65
the rear bar they mounted it on was 30.75. 0.65 * 30.75 = 19.9

so they mounted it 20" from the frame pivot. then collapsed the shock and made the upper fame mount.

the did the same on the front.

Don't know if it will help but I was wondering it myself.

That's some great information! I will look at trying this when I get started on my shock mounts. Thanks