Make it handle

[no moa]

Originally Posted by robnolimit

I think we should really go back to the begining. Lets start out by looking at the basic types of rear suspension available for these trucks.

Leaf Springs These are pretty common, and one of the most used and sometimes under rated. Leafs are widely used because of the manufacturing costs, and vehicle packaging. Leafs do many jobs at one time. They are the locators, front/rear and side/side, and the spring. The 'Instant Center', where the force pushes on the truck, is right at the center oof the front spring mount - non adjustable. The roll center is appx at the same height, and non adjustable. There is some side/side motion due to spring flex. HP threshold is around 400, after that the spring wrap is a big problem. Sway bars, shocks, and bushins can help. Be honest with your build. Once you add traction bars, sway bars, shocks and bushings, you've passed up the cost of link style suspensions.
Leafs can ride great, and handle good. Mary Pozzi won MANY autocross championships with her leaf spring 72 camaro. Keep in mind that the Big three automakers are there to make a profit, and leafs are a low cost, effective way to get the job done.

Great info on leafs, thank you, i'm running stock HD 5 leaf set up in mine. 454/400 with around 400 hp. But i dont' plan to run it to hard. well maybe in a straight line.

[69gmcc10]

Originally Posted by robnolimit

The "Wrap-up" on leafs. Easy to understand, fairly inexpensive. They can have a good ride and handling. Mostly non-adjustable. Expected Hp/Tq limit, 400/400. The lower the front spring eye mount is, the lower the anti-squat is, this could have less traction.

When you said the lower the front spring eye mount is the lower the anti squat, in what relatino is that? Is that to where the shackle mounts on the frame or the shackle to the leaf? Would longer or shorter shackles make a difference? Is there a correct ratio people should shoot for? how do cal-tracs effect this? Thanks

[Conundrum]

Originally Posted by robnolimit

On 63-87 C-10's, this is pretty easy. For the lower arms, remove the arm, and drill a new index hole in the cross shaft. I usually rotate the shaft 90 deg., then drill a new hole 3/4" back. You may need to grind a small amount off of the rear lip of the crossmember (more comon on 73-87) so that the bushing clears fine. Then bolt the arm back on. For the uppers, knock all the rivits out, unbolt the upper A-arm mount and slide it back. Weld it to the crossmember, and drill out the mount to fit the frame. Use grade #8 bolts and washers to bolt it back to the frame.

Hey Rob,
I am thinking of doing this to another crossmember I have, and was thinking of sectioning the upper A-arm mount to drop the mounting points while I am at it.

Good idea?
How much should I drop the mounting location?

[68 TT]

Originally Posted by robnolimit

With stock steering, the inner TRE pivit is too high. Computor analisys shows it should move down about 5/8" to help eliminate bump steer. We usually focus on the inner TRE, because moving the outer TRE means modified spindles. - (or rod-end type and other mods)As luck would have it, "tipping" the spindle to gain + caster will also raise the outer TRE, so this could easily turn out to be a 'win-win' mod.

As far as wheel position, with a dropped spindle, the wheel will move about 1/2 the distance of the LBJ. So if we move the LBJ forward 1 1/4", the wheel will move about 5/8". Yes, different drop or stock spindles will move a different amount. The more the drop, the less the wheel will move.

Have you looked at using the early 90's C2500 light duty spindles? These came with 6-lug rotors but the 5-lug rotors of the same vintage will fit them as well so they can work for all of us.

They are about 9-5/8" tall so they would be about 1-3/4" taller than the stock spindles. They can be bolted on with the use of C20 lower A-arms once fit with the ball joints to match the spindles and the matching upper ball joints will bolt into the stock upper A-arm.

I have them on my 69 stepside but have quite a bit of work left to do before it is on the road so I don't know how it is going to work out alignment wise.

There are other board members who have done the swap too but I don't know of any that have the truck on the road with them yet.

It might be something to look into even if it might require moving the TRE attachment point a bit.

[gringoloco]

Originally Posted by 68 TT

Have you looked at using the early 90's C2500 light duty spindles? These came with 6-lug rotors but the 5-lug rotors of the same vintage will fit them as well so they can work for all of us.

They are about 9-5/8" tall so they would be about 1-3/4" taller than the stock spindles. They can be bolted on with the use of C20 lower A-arms once fit with the ball joints to match the spindles and the matching upper ball joints will bolt into the stock upper A-arm.

I have them on my 69 stepside but have quite a bit of work left to do before it is on the road so I don't know how it is going to work out alignment wise.

There are other board members who have done the swap too but I don't know of any that have the truck on the road with them yet.

It might be something to look into even if it might require moving the TRE attachment point a bit.

Don't they net a bit of drop, too, due to spindle 'nub' location? There are drop castings available as well. It would be cool to use thesse in conjunction with the R&P kit with stock style TREs, for those that are leary of rod-ends. The downside I see to them, if the geometry is good, is the lack of brake upgrades available for the 88-98 trucks...

[68 TT]

Originally Posted by gringoloco

Don't they net a bit of drop, too, due to spindle 'nub' location? There are drop castings available as well. It would be cool to use thesse in conjunction with the R&P kit with stock style TREs, for those that are leary of rod-ends. The downside I see to them, if the geometry is good, is the lack of brake upgrades available for the 88-98 trucks...

If we can figure out the geometry so they work well to make these an attractive upgrade for the older trucks then maybe the aftermarket will step up and make some 13" or larger brakes for them.

One nice thing about these as they sit is that they work with 15" wheels so they are a good upgrade even for those who wish to use stock rally wheels on their trucks, even if only occasionally.

I'd like to see an aluminum bearing hub designed for these spindles that will use some off the shelf large Wilwood slip on rotors and good calipers. I'm sure the 88-98 truck guys would appreciate that too.

[robnolimit]

Lets talk Anti-Squat. For the most part, this is a comparison number. A way to say, "this is where the rear suspension lifts the truck". You may not know exactly where your 'anti-squat' is, but understanding it, and using it as a chassis tuning tool, will help. To understand anti-squat, we need to define a few things. CG (center of gravity), this is the balance point of the truck, both front to back, and top to bottom. As an estimate, say 58% of the wheel base (58% nose wieght) appx 68", and for hieght, say the center of the cam, appx 24" for a dropped truck. IC (Instant Center) this is the point where the suspension forces push on the chassis. For a leaf suspesion, we use the center of the front spring eye, for trailing arms, use the center of the front pivit. CC (contact Center) The center of the contact patch of the rear tire. Now that you have these 'points', draw a line from the CC, throught the IC, and contiue on that line until you pass the front/rear balance point. So, what do you do with it? First, you need to 'scale' your CG line. At the ground, you have 0% anti-squat. At the CG, you have 100%. You need to calculate where your 'force line' crossed your 'scale'. I try to set most projects up at close to 100%, with tuning room on either side. Below 100% = more lift on the front of the truck, the rear will sink some, more force pushing forward. Above 100% = more lift on the rear of the truck, the tires plant firm, but less force is pushing forward. The goal is to get all the downforce you need to keep the tires planted, and still push the truck forward as hard as you can.

[taank]

I am on pins and needles for the trailing arm conclusion.
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[jimmydean]

Originally Posted by taank

I am on pins and needles for the trailing arm conclusion.
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Me too! Man, Rob, leave a guy hanging why don't you.

Personally, I am sold on the trailing arm design for both ease of use and cost. After seeing the NASCAR style setup with the adaptability to variations in courses with the slightest adjustment, it just makes sense.

But I am waiting to hear what Rob has to say. Seeing how I blame him for me wanting to add more performance to my build.

[robnolimit]

OK, OK, - now that your all gettin a grasp of this, I'll throw in the curve ball. At the monent, these drawings are static, but in real life, Anti Squat (AS) in dynamic, it moves as the the truck moves up/down. Think about the pictures of old drag cars. Remember the long shackles to raise the rear? Well, this also raised the front leaf mount, or IC, and raised the AS. Not as dumb as it looked. Drag racers have evolved from this trick, but it did work. With trailing arms, The front eye of the arm is the IC, and it's pretty far forward. So, low trucks can have low AS %'s. I hear it comin', NASCAR uses these, and their mounts are low?? Yes, but their smart. They use air pressure to plant the rear tire, and the low IC give them more forward push, less energy waisted. BTW, ever see a cup car leave the pits? Smokes the tires without any hesitation, IE - not much bite on the tire from the suspension.

[jimmydean]

So from a NASCAR perspective, the suspension is set up so the air pressure created at speed by the aerodynamics is what creates downforce for traction and why they spin out so quick when they aren't doing 170.

OK, so what about the setup for a road course. Certainly they aren't creating nearly the downforce in a road course that they do in an oval. So do they raise the IC to create more AS at the lower overall speed?

<edit> Hey Rob, can you just set up an online course to cover all this material? Or better yet a weekend class with track days?

<edit2> Might be a dumb question, but do the bends in a trailing arm matter, or are you looking just at the mount points when drawing your lines? Or does the bend in the back of the arm only for mounting surface? I want to plot out my suspension now and see where it turns up on the scale.

[taank]

So from a drag racing perspective what is the best way to get this heavy old ***** to hook?
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[69gmcc10]

Rob thanks for the "diagrams" to go with the words, it helps solidify the ideas you discuss. So for a vehicle that is at stock height or closer to stock it is less important to flip the trailing arm brackets, blocking the rear is just a tactic to maintain ride quality and the lower you go the more important these factors becomes correct?

[KQQL IT]

Truck Arm looks the easiest. Although leafs and cal trac bars do a great job...
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[68 TT]

Originally Posted by taank

So from a drag racing perspective what is the best way to get this heavy old ***** to hook?

Increase anti-squat until you get it to hook. Use as little anti-squat as you can to get it to hook so more of the force is used to move the truck forward instead of lifting the nose upward.

Move as much weight as you can to the back of the truck and lighten the front end as much as you can too. Put the weight as close to the rear axle as you can. It will react quicker this way. If you put it further back the reaction will be slower and the front end lift will be more profound wasting energy.

You need tires with the largest contact patch you can fit on the truck and the softest compound you can get your hands on to start with though. A set of rock hard street radials won't hook in a nose heavy truck even with 150% anti-squat.

You can make one of our trucks hook like it has claws on a set of 28x10.50 slicks but a set of 325/50-15 drag radials work pretty well too if you need to drive it on the street and the track. Slicks will also require aftermarket axles so that may influence your choice as well.

My favorite pic

[taank]

Originally Posted by 68 TT

Increase anti-squat until you get it to hook. Use as little anti-squat as you can to get it to hook so more of the force is used to move the truck forward instead of lifting the nose upward.

Move as much weight as you can to the back of the truck and lighten the front end as much as you can too. Put the weight as close to the rear axle as you can. It will react quicker this way. If you put it further back the reaction will be slower and the front end lift will be more profound wasting energy.

You need tires with the largest contact patch you can fit on the truck and the softest compound you can get your hands on to start with though. A set of rock hard street radials won't hook in a nose heavy truck even with 150% anti-squat.

You can make one of our trucks hook like it has claws on a set of 28x10.50 slicks but a set of 325/50-15 drag radials work pretty well too if you need to drive it on the street and the track. Slicks will also require aftermarket axles so that may influence your choice as well.

My favorite pic

how do you increase anti squat on a truck arm. i wouldnt mind lifting the wheels a bit

[taank]

Also who owns that truck?
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[hairlesshobo]

Originally Posted by 68 TT

Increase anti-squat until you get it to hook. Use as little anti-squat as you can to get it to hook so more of the force is used to move the truck forward instead of lifting the nose upward.

Move as much weight as you can to the back of the truck and lighten the front end as much as you can too. Put the weight as close to the rear axle as you can. It will react quicker this way. If you put it further back the reaction will be slower and the front end lift will be more profound wasting energy.

You need tires with the largest contact patch you can fit on the truck and the softest compound you can get your hands on to start with though. A set of rock hard street radials won't hook in a nose heavy truck even with 150% anti-squat.

You can make one of our trucks hook like it has claws on a set of 28x10.50 slicks but a set of 325/50-15 drag radials work pretty well too if you need to drive it on the street and the track. Slicks will also require aftermarket axles so that may influence your choice as well.

My favorite pic

It's very impressive to me to see a truck with a fat @$$ front end like our trucks have pull of something like that. Now I don't think that would be good to see while driving down the expressway but cool nonetheless

[robnolimit]

great pict. and right on the mark. Anti Squat is like carb jetting. You want just enough to get a good plant of the tires, too much will waste energy and run slower. With a trailing arm truck, there are only a few ways to do it. I'm going on the assumption (I know) that the truck will stay at it's current ride hieght. 1) move the front trailing arm mount up. You can flip the stock mounts or buy aftermarket. This is the easiest. 2) More work here. Shorten the arms appx 6", use a 'johnny-joint' style pivit ball, move the crossmember back 6", and use adjustable mounts. This is for the serious guys. 3) move the CG down. Lower the motor/trans, and everthing else you can find. BUT, moving the CG back, while helping weight balance, will lower your AS. So, if you move wieght back, you need to raise the IC farther. Sinking in yet?

[robnolimit]

One more thing, if your going to do this right, you need to know where yor are. Its time to weigh and measure your truck.

[hgs_notes]

Originally Posted by 69gmcc10

When you said the lower the front spring eye mount is the lower the anti squat, in what relation is that? Is that to where the shackle mounts on the frame or the shackle to the leaf? Would longer or shorter shackles make a difference? Is there a correct ratio people should shoot for? how do cal-tracs effect this? Thanks

He is talking about the front leaf spring mount which does not have a shackle, which is why there is no adjustment. (unless the mount is modified for upwards or lower mounting of course)

The rear mount has the shackle. Shackle length in the rear will effect ride quality and the longer the shackle the more side to side flex there will be. On a truck a longer shackle will lower the rear, unless the shackle is flipped like the car style, which will then raise the rear. Think 70's car with giant m50's in the back and the gas tank showing because the ass end is sticking up. Longer shackles on jeeps was a common inexpensive way to get soe lift, but the shackle is weaker, so now those kits usually have a bar welded between the shackle plates to strengthen it.


Shackle flip kits for trucks are available through the off road after market as a common lift option. Othere will remove the front spring mount of the rear axle and swap it into the rear mount, so the shackle can point downwards. I have also seen pics of the regular rear spring mount with a hole cut through the bottom for the shackle to go through, but I think this would really reduce the strength of the mount.

Here is a typical shackle flip mount...

[hgs_notes]

Originally Posted by robnolimit

great pict. and right on the mark. Anti Squat is like carb jetting. You want just enough to get a good plant of the tires, too much will waste energy and run slower. With a trailing arm truck, there are only a few ways to do it. I'm going on the assumption (I know) that the truck will stay at it's current ride hieght. 1) move the front trailing arm mount up. You can flip the stock mounts or buy aftermarket. This is the easiest. 2) More work here. Shorten the arms appx 6", use a 'johnny-joint' style pivit ball, move the crossmember back 6", and use adjustable mounts. This is for the serious guys. 3) move the CG down. Lower the motor/trans, and everthing else you can find. BUT, moving the CG back, while helping weight balance, will lower your AS. So, if you move wieght back, you need to raise the IC farther. Sinking in yet?

Oozing in like molasses is more like it. Wouldn't tire diameter also affect this? Taller tire would raise the IC point while keeping the CC in the same spot.

[68 TT]

Originally Posted by taank

Also who owns that truck?

djracer currently owns the truck. He has reconfigured and rebuilt the truck since he picked it up.

http://67-72chevytrucks.com/vboard/s...d.php?t=151718

Previously it was Tom Durham's truck which is from the time frame the pic was taken.

[taank]

ok so to increase the anti-squat if i was to install something like this


wouldnt it change the driveshaft angle as well? would you have to add a drop block to correct it?.

if you flipped the brackets it would effectively do the same thing?


the higher the trailing arm is in the crossmember the higher the ride height in the rear would be?

[Grimee]

Raising the arms in the cross member will change the amount of anti squat and the pinion angle. the springs will set the ride hight