Build 86 Xtra Cab Build (4Wheelunderground 3 link front, 4 link rear and 3.4 swap)

[aztoyman]

Good discussion and explanation. My frame rails are plated on three sides (4 sides on DS) with 3/16" from the front cross member to below the front cab mounts. Hopefully that helps rigidity. The engine is right in the middle of all this so no room for anything across the bottom or top.

I also realize that the shocks will not always be up or down equally on both sides but could be up on one side while down on the other. Lots to factor in.

 

[ntsqd]

The math doesn't lie, I'm correct. For the purposes of this analysis I'm holding the bottom of the frame fixed. And then looking at how the rest of the frame and the towers will distort when the forces are applied. How the frame as a whole twists is a whole other analysis that can't be looked at until what is happening to the shock towers is understood.

Assuming a 100 lbs/in spring rate, compressed 4 inches.
Assuming the shocks are tilted 5° inboard at the top.
That makes it 400 lbs force acting at a 5° tilt at the upper shock bolt hole.

Vector Math breaks that down into two composite forces, one acting exactly vertical and the other acting exactly horizontal.
Sin 5° = Opposite/hypotenuse; This is a force triangle rather than a length triangle but the math is exactly the same.
So, Hypotenuse * Sin 5° => 400 * Sin5° = 34.86 lbs force in the horizontal direction. That's the static loading per shock tower, but the dynamic loading is going to scale up in the same proportion.
Even if the force and the angle are both doubled that is still only 138.92 lbs force per tower in the horizontal direction.
Obviously the bottom of the frame isn't fixed, and the rest of the frame is going to distort from that loading. Which will consume some of that horizontal component in moving other parts around.
I contend that the brace is superficial only and won't do much at all.

 

[gnob]

The math doesn't lie, I'm correct. For the purposes of this analysis I'm holding the bottom of the frame fixed. And then looking at how the rest of the frame and the towers will distort when the forces are applied. How the frame as a whole twists is a whole other analysis that can't be looked at until what is happening to the shock towers is understood.

Assuming a 100 lbs/in spring rate, compressed 4 inches.
Assuming the shocks are tilted 5° inboard at the top.
That makes it 400 lbs force acting at a 5° tilt at the upper shock bolt hole.

Vector Math breaks that down into two composite forces, one acting exactly vertical and the other acting exactly horizontal.
Sin 5° = Opposite/hypotenuse; This is a force triangle rather than a length triangle but the math is exactly the same.
So, Hypotenuse * Sin 5° => 400 * Sin5° = 34.86 lbs force in the horizontal direction. That's the static loading per shock tower, but the dynamic loading is going to scale up in the same proportion.
Even if the force and the angle are both doubled that is still only 138.92 lbs force per tower in the horizontal direction.
Obviously the bottom of the frame isn't fixed, and the rest of the frame is going to distort from that loading. Which will consume some of that horizontal component in moving other parts around.
I contend that the brace is superficial only and won't do much at all.

Roger, vector.

 

[aztoyman]

WAY beyond MY math skills. Or lack of. I'll stash my tubing couplers for another project.

Would my rear shock hoops require a diagonal brace for the cross brace to be effective? I was also thinking I should add a tube gusset where they are welded on. I'll have to go back in my thread and grab a pic.

 

[ntsqd]

Roger, vector.

Doesn't that quote go "Roger, Roger"?

If you make part of a structure really rigid while the rest of it is not you run the risk of cracks where the rigid meets the flexible. Better to make it all slightly flexible so it doesn't kill itself in use.

 

[Broski]

But perfectly in line with the common sense factor!

 

[bkg]

The math doesn't lie, I'm correct. For the purposes of this analysis I'm holding the bottom of the frame fixed. And then looking at how the rest of the frame and the towers will distort when the forces are applied. How the frame as a whole twists is a whole other analysis that can't be looked at until what is happening to the shock towers is understood.

Assuming a 100 lbs/in spring rate, compressed 4 inches.
Assuming the shocks are tilted 5° inboard at the top.
That makes it 400 lbs force acting at a 5° tilt at the upper shock bolt hole.

Vector Math breaks that down into two composite forces, one acting exactly vertical and the other acting exactly horizontal.
Sin 5° = Opposite/hypotenuse; This is a force triangle rather than a length triangle but the math is exactly the same.
So, Hypotenuse * Sin 5° => 400 * Sin5° = 34.86 lbs force in the horizontal direction. That's the static loading per shock tower, but the dynamic loading is going to scale up in the same proportion.
Even if the force and the angle are both doubled that is still only 138.92 lbs force per tower in the horizontal direction.
Obviously the bottom of the frame isn't fixed, and the rest of the frame is going to distort from that loading. Which will consume some of that horizontal component in moving other parts around.
I contend that the brace is superficial only and won't do much at all.

But "only" x# of lateral force is still lateral force, as I mentioned... The broader question is if that's enough to worry about for crawling. 95% absolutely no. Is it enough to worry about for DD? 90% no. Is it something to worry about for high-speed dezert whomping... I'd say yes.

Does the brace, as designed offer *SOME* protection? Yes. Does it hurt anything? Absolutely not. So why not add it?

 

[aztoyman]

@bkg I already reinforced the mounting point on my towers and I have the tube couplers on hand so I might add it later. I don't have any tube at this time and I'm having trouble even getting to work on this truck. $hit keeps popping up that takes priority.

I'm curious now about how much the towers move with my usage. I thought I had enough room around my steering shaft but I was told early on in my build from people with more experience than I that it may become an issue. It has had my attention since, so if I see any evidence of contact I will add a .250 wall tube across and see if it provides any reduction in movement.

I'm also wondering if I made it with mitered and welded joints (straight tubes) if it would be any less likely to bend VS a one piece tube with 70 degree bends on each side.

 

[bkg]

@bkg I already reinforced the mounting point on my towers and I have the tube couplers on hand so I might add it later. I don't have any tube at this time and I'm having trouble even getting to work on this truck. $hit keeps popping up that takes priority.

I'm curious now about how much the towers move with my usage. I thought I had enough room around my steering shaft but I was told early on in my build from people with more experience than I that it may become an issue. It has had my attention since, so if I see any evidence of contact I will add a .250 wall tube across and see if it provides any reduction in movement.

I'm also wondering if I made it with mitered and welded joints (straight tubes) if it would be any less likely to bend VS a one piece tube with 70 degree bends on each side.

technically , mitered may be stronger… but I really don’t see issues with the bend. As stated above, the lateral force probably isn’t enough to worry about kinking the bend. I’m assuming you’ll be doing .120 wall.

Steering is likely more due to the body mounts than frame twist at the tower(???). My Tacoma floats a lot… and my steering shaft does rub the tower (it wasn’t clearanced as well as yours.) Pretty sure the hilux does t float as much, but it’s been a long time since I sold my 86

 

[aztoyman]

I'll be doing my cage in .120 wall but I'm not opposed to getting a piece of .250 wall for the tower brace IF it would be a better choice. (The towers are .250 if that matters)

I also don't know how much the pan hard affects the twist of the frame rail. This suspension is a first for me.

I understand your logic as far as it can't hurt, so why not. But now I'm really curious to see how much it moves. If touches the steering shaft at all, I'll put one on and be able to verify if it does anything or not.

Also, I was looking to see if I needed to add a guard to protect the bottom of my radiator and also if I had a way to use my winch as a suck-down............IF needed. I have NO idea if I would, just trying to plan ahead if I have issues on the steep ledges. I've had some scary close calls with the leaf sprung 88. More so with the rear on super steep descents though.

Well, anyway, It looks like I have "some" room to put something across the bottom of the frame rails if I need to for whatever reason. Obviously just forward of all the linkage. I have plenty of other things to get done first. It's just something I noticed while under the truck.

Thank you all for the feedback, experience and advice. It IS welcomed and appreciated.

 

[ntsqd]

At a worst case guesstimate of the lateral static force component being~139 lbs per tower, and in looking at how the towers are tied into the frame, and with consideration for how the truck will likely be driven I see no need for the brace. Said differently, if 139 lbs of force is enough to cause those towers to move at all then we're already in trouble and that brace isn't going to fix it.

IF the use changes to include desert racing or pre-running activities then I still wouldn't go over the top with the brace. I would go around both ends of the intake staying as low as possible, and likely running a tie-tube between the front and rear tubes parallel to both sides of the intake. And at that point be seriously considering an engine cage that the towers are part of because it is going to be the best bet for dealing with those forces.

 

[aztoyman]

I'm still running sheet metal axle housings (yeah with reinforcements) and 8" differentials, stock knuckles with IFS hubs hanging the 37" sticky 81# tires and 46# wheels further out on the stock trunnion bearings so I if I do any desert jumps..........ONE is probably all I can do. My shock towers would probably pop my intake manifold off. If I survive the attempt, any injuries would most likely be sustained from my wife channeling her initial fear into rage upon my skull.

Thanks for crunching the numbers,

 

[gnob]

I'm still running sheet metal axle housings (yeah with reinforcements) and 8" differentials, stock knuckles with IFS hubs hanging the 37" sticky 81# tires and 46# wheels further out on the stock trunnion bearings so I if I do any desert jumps..........ONE is probably all I can do. My shock towers would probably pop my intake manifold off. If I survive the attempt, any injuries would most likely be sustained from my wife channeling her initial fear into rage upon my skull.

Thanks for crunching the numbers,

sort of wish I had my stock housing destroying jump on video. i wonder how many of the other drivers that saw it still tell the story. ,

 

[aztoyman]

Say it ain't so gnob!!

 

[gnob]

Say it ain't so gnob!!

this is why I have diamonds meow

 

[aztoyman]

Not much time available for this lately but I wired up the JDM (?) marker lights/turn signals. Then realized I should have ordered an electronic flasher relay. For some reason I thought I had one since this harness is from my 88. I must have been thinking of my Tacoma or something. This one is still the original.

I have a larger air filter on the way. I couldn't find a way to fit the Donaldson filter housing I was hoping to use.

Since I have to post pics I'll show you the tower brace I came up with today for "test purposes". Once I get in the dirt, I will see how much tower flex I get. Only then, will I install it and see if it makes a difference.

Bkg mentioned that the body mount flex may be more of a problem with the steering shaft to tower clearance. I didn't think of that and was surprised to see how much some cabs moved in some videos I watched. Hopefully my poly mounts minimize my cab movement.

 

[aztoyman]

Here's more pics for inquiring minds. I couldn't make it symmetrical because of the intake. So it's a 50 degree bend on the passenger side and 55 degree on the driver side. One leg is slightly taller to compensate and come out level across the top.

The tube couplers are basically directly above the frame rails if that matters. The shocks are tilted 5 degrees. The tube is just .120 wall scrap I found in the shed. (Not DOM) It's just sitting on top for pics so it's slightly tilted.
This is the only way I can find to fit a brace. I understand it may not do anything. I was bored today.

driver

 

[jgranthevagrant]

You wrote that both bends are on the passenger side. Is that diagnostic port in its original spot?

 

[Mudder]

For what it’s worth, I picked up my electronic flasher relay from O Reillys. It’s been working great.

 

[aztoyman]

jgrant, thanks for catching that. I fixed it. It says Diagnostic on the cover. It is factory for the 99 4Runner the engine came from. I've never used it.