Make it handle

[AJohn6]

Originally Posted by robnolimit

I'd go with a 1" splined bar and arms. I tried a 1 1/4", and even at .065" wall, it's a little stiff. Once you're set up with the 1" bar, you can change bars easy. I'd start with a 1" solid.

Thanks Rob, I appreciate the advice.

Adam

[jlsanborn]

Originally Posted by robnolimit

I'd go with a 1" splined bar and arms. I tried a 1 1/4", and even at .065" wall, it's a little stiff. Once you're set up with the 1" bar, you can change bars easy. I'd start with a 1" solid.

He Rob,
I had asked earlier but I think it got blown buy. In regards to the front swaybar, If I were to bone-yard one, which is the best one? I found a 3/4t burban with the optional heavy-duty unit. Keeper? I've got your panhard rod kit and shock relocate. I'll be getting your rear swaybar next week (still in stock?). I'd also like to get the Monroe shocks from you, but I'm not sure what I need with the drop I've got. Still offer 10% to board members?

Thanks!

[robnolimit]

On to Master Cylinders It's all about line pressure. And that means numbers. The first thing we all have to agree on is how hard to push on the pedal. The DOT standard is 30 to 40 lbs foot pressure. But we need a standard that everyone can agree on. I like to use 30 lbs on street drivers, and 40 lbs on race/performance builds. If thats OK with everybody, we'll start there. So, for the street, lets say 30 lbs of pressure comes from your foot. This would be multiplied by the pedal ratio. ?? What? I'll work on a picture for this. But for now, lets say you truck has a pedal ratio of 7-to-1. So, 30 lbs from your foot, times 7 from the pedal, = 210 lbs of force pushing into the master cylinder. Now to covert that into P.S.I. (line pressure) we need to know the size of the master cylinder. The area of the piston in the master can be calculated using the formula for the area of a circle. or, Area = 3.14 x R x R ( thats the best way I can type it in.) R being the Radius, or, 1/2 of the diameter. So, a 1" bore master has a 1/2", or .5" radius. 3.14 x .5 x .5 = .785 sq.in. of surface area. To get line pressure, we take the input force (lbs) and divide by the piston area (sq.in.) For our example, 210lbs / .785sq.in. = 267 lbs of line pressure. Not much. This will not stop your truck very well. So, what to do.

[gringoloco]

Originally Posted by robnolimit

So, what to do.

Um, add a booster, piston area, and pad friction coefficient? Good info! Timely, too What's the pedal ratio on a 67-72 pedal assy?
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[mongoose]

my square is only 3.5:1.. dunno if the 67-72 is the same.

[robnolimit]

Boosters This is the most common way to gain pressure. A power brake booster is like a stereo amp. It takes the the signal coming in and amplifies it on the output side. Bigger Boosters are like bigger amps, - more power.
The other key item is vacuum. Gotta have some. We use 18" as a test standard. Over the years we have tested a lot of boosters, and of coarse, we gathered all of the info. So, it's kinda like this:
For a givin size of a booster, you can have an approximate multiplier, based on 18" vacuum. This multiplier can be factered into the line pressure calculation.
A 7" single diaphram booster has a 1.7 to 1 multiplier
7" dual diaphram = 1.95 to 1
8" single = 1.9 to 1
8" dual = 2.25 to 1
9" single = 2.15 to 1
11" single = 2.45 to 1
Now these are averages from years of collecting data. **your results may vary**

If we go back to our example, at 267 psi. and add an 8" dual diaphram booster (267 x 2.25) we can expect to get 600 lbs of line pressure, givin 30 lbs of foot pressure on the pedal, and 18" af vacuum.

With this information, you can figure out the results of changing ratio's, boosters, and bore size.

[Mechanic77]

Great information on the vacuum brake boosters Rob, but do you happen to know the approximate multiplier for a hydroboost? Some of us like to run big cams that don't make much vacuum

[robnolimit]

Oh yes, I was gettin to that. Hydro-boost units use the pressure from the power steering, (hydrolic pump) And have a great amplifier advantage. There are many factors here too, such as p/s pump output, hydroboost bore size, and the pressure loading of the acumulator. As a general rule, I would use a multiple of 3.5 to 1 for most hydro units. The downside is a loss in pedal feel, some of this can be gained back by lowering the pedal ratio.

Next up, the good, the bad, and the ugly of all these items.

[INSIDIOUS '86]

Originally Posted by robnolimit

Oh yes, I was gettin to that. Hydro-boost units use the pressure from the power steering, (hydrolic pump) And have a great amplifier advantage. There are many factors here too, such as p/s pump output, hydroboost bore size, and the pressure loading of the acumulator. As a general rule, I would use a multiple of 3.5 to 1 for most hydro units. The downside is a loss in pedal feel, some of this can be gained back by lowering the pedal ratio.

Next up, the good, the bad, and the ugly of all these items.

So how would one go about lowering the pedal ratio? I gave some stainless braided lines on my truck and fit the first time I can feel the brakes but I'm switching to hydro boost so if feel is affected how do I change this? Mines an 86 Chevy shortie
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[NPilot1975]

Rob, I was looking at a manual pedal setup with a 5.75:1 ratio that is floor mount. Do you think this would be safe on the street with some getting used to?
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[robnolimit]

Well now, if we all wanted safety we wouldn't be hanging out here. But, yes, I think this is do-able. If you run a 7/8" master, you will end up with appx 391 lbs of line pressure at 40 lbs from your foot. Then look for an aggressive brake bad. You'll have some brake dust, but she'll stop. If it is a tandem master cyl set up, try a 3/4" bore (front)and a 13/16" bore (rear)

[robnolimit]

Two big events today. GoodGuys @ indy, watch out for Brad Coomer and the Summers and Sons C10 on the Auto-X. It's Brads Birthday, and he wants a Pro class trophy in a bad way. In Ohio, @ the Lingenfelter Performance Nationals, Chris from Smitty's has his fresh C10 build out on track. As of last night Chris was only 2 sec. off the overall leader, and this is his first full day of Auto-X in the new truck. BTW, Chris recieved an invite to the Optima OUSCI, Great job Chris, watch for a feature on this truck soon.

[gringoloco]

Any tricks of the trade for stabilizing a solid axle over mid-corner bumps?
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[robnolimit]

Originally Posted by gringoloco

Any tricks of the trade for stabilizing a solid axle over mid-corner bumps?
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Front or rear? what year?

[gringoloco]

Originally Posted by robnolimit

Front or rear? what year?

Rear, in a 67-72. I know this is an inherent issue with a solid axle vs IRS, just wondering if there is anything that can be done to 'tame' the unsettling on less than perfect surfaces mid corner. Seems like the other modifications made to increase handling (poly arm bushings, longer panhard, anti-sway bar) will reduce articulation of the axle and contribute to the 'skipping' feeling.

[jayman68]

Originally Posted by gringoloco

Any tricks of the trade for stabilizing a solid axle over mid-corner bumps?
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Originally Posted by gringoloco

Rear, in a 67-72. I know this is an inherent issue with a solid axle vs IRS, just wondering if there is anything that can be done to 'tame' the unsettling on less than perfect surfaces mid corner. Seems like the other modifications made to increase handling (poly arm bushings, longer panhard, anti-sway bar) will reduce articulation of the axle and contribute to the 'skipping' feeling.

Good question!

Thanks for the info Rob, let us know about the 'A' body springs.

[robnolimit]

http://youtu.be/OWnW2VkgfVY Hellboy in action.

[robnolimit]

OK, some yes, some no. First off, I'll say that I'm not a big fan of urathane in the trailing arm bushings. It's one of the only spots I'd say no to. If I was going to change the front pivit, I would fab in a uni-ball (steel) or a Monster-ball (delron lined) This would allow full articulation without any axle shift. If you don't want to do that, stay with the rubber here. Second, almost every spring and shock I've seen is too stiff, WAY too stiff for a goood handling vehicle, of any kind. Lets face it, we're not going to the high banks at Daytona. Food for thought, a stock rear spring has appx 600 lb/in, where as my Hellboy truck currently has 150 lb/in springs. I am looking into 'A' body springs to check out compression hieghts vs. spring rates, to see if we can make use of them. The longer panhard rod, especially if it is a low mount unit, will help eliminate the side-skip. And, if the springs and shocks were correct, then the swaybar could do it's job, and you'd never feel the bump. A mercedes 550 can do it, why not us?

[gringoloco]

Ok, what you're saying makes sense--especially considering my recent experience in swapping from 'bags to drop coils on the rear of my truck--definitely a stiffer ride. I may try to buy back some of the articulation by swapping to rubber bushings. Can you expand a little on the advantages of the "soft spring, big bar" theory? Also, how will this affect load capacity? Does this hold true for the front, as well?

Thanks for the info!

[robnolimit]

OK, lets think about spring rates. First, we need to imagine our basic truck, and how we want it to sit. I'll say that we have a trailing arm C10 shorty, dropped 4", no notch. There is now 4" from the axle housing (top) to the frame rail (bottom). So, from Ride Height (RH) we have 4" of compression travel available. - then it bottoms out. I'll also say that our truck weighs in at 3850 lbs. with 1400 lbs on the rear (JT's specs.). Looking at the rear only, thats 700 lbs per side. If you had a 400 lb/in spring, it would take 1600 lbs per side to bottom the truck out, 3200 lbs total. (appx 1600 lbs and a good bump would do it) But this will still haul a 1/2 ton load. Now if we put 200 lb springs on it, and get the same ride height it would reasonably only carry 800 lbs without bottoming out to bad. Remember that appx 1/2 of the driver/passanger weight will go to the back. So now your down to about 600 lbs load cap. - max, with 200 lb/in springs.

[robnolimit]

There are a lot of concepts out there about handling. Here is one thing i see a lot at Auto-x and track events. The problem is that the car (truck) is loose through the corner. The solution is to disconnect the rear sway bar. ?what? I see this all the time. OK, I get it the first time, but this is backwards. If you need more rear bite, lower the roll center (panhard mounting points) and/or softer rear springs. Now I'll ne honest, I n
know just enough to get into real trouble. When it comes to other suspension concepts, I try to understand why, and then look at the outcome. Porsche does very well with a 'stiff spring' layout, as do most exotics. - but their CG is VERY low. Mercedes and BMW have great handling and smooth riding cars with the 'soft spring' approach. -higher CG. There is no "one size fits all" answer. Trucks and Hot Rods (my arena) all suffer from a high CG. Using a soft spring and big bar set up makes sense to me. The weight will force the truck to lean over, so let it compress the outside corners of the suspension with soft springs, then use a large swaybar to transfer the suspension load to the inside corners.

[69gmcc10]

So, why do u reccamend 3/4 ton front springs for these trucks?... your logic would say that 1/2 ton springs would be the way to go. Is it because the fronts of these trucks are so heavy and gm undersprung the 1/2 ton truck to ride soft? I am honestly just trying to understand not be confrontational.

thanks

[robnolimit]

Originally Posted by 69gmcc10

So, why do u reccamend 3/4 ton front springs for these trucks?... your logic would say that 1/2 ton springs would be the way to go. Is it because the fronts of these trucks are so heavy and gm undersprung the 1/2 ton truck to ride soft? I am honestly just trying to understand not be confrontational.

thanks

Good catch! Your right on both counts. Yes, with the stock A-arms and suspension points, what we would think of as 'soft' is still a bit firmer that the OE 1/2 ton. The cut 3/4 ton spring nets out at about 1000 lb/in. This sounds like a lot, but the ratio on the lower arm is close to 30%, so the 1000 lb spring nets appx 300lb/in load rate at the center of the tire (hub face of the rotor)

[69gmcc10]

So, even with the cut 3/4 ton spring in the front and stock 1/2 ton springs in the rear the front has less than half the rate than the rear does? and there is nothing in the bed?

[robnolimit]

SHOCK MYTH Got your thinking caps on? Company A advertises thier new bad ass double throw down billit shock. It's the latest and greatest ever. Years of testing and technology have gone into them. - Now, this could be 1970, 1999, or today, it's been going on for a long time. So lets think about how good these are for YOUR TRUCK. They sell these new Brand-X shocks by LENGTH, and MOUNT TYPE. So, you need a 4.5" stroke shock in front, with a 10" spring, and a 6" stroke rear shock with a 12" spring. Now here's the really cool part, they have it all in stock!!!! This is so cool. They tell you you need a 500 lb front spring and a 250 lb rear spring. Good to go. Isn't this great? This is all set up just for your truck! ----- or is it??? Did you notice any information telling you a different part number for a front or rear shock? Well, no but the length does that right? Honestly, I don't know. But I do Notice Brand-X only seporates shocks by length. Thinking cap time. If the front of your truck weighs 2400 lbs, (1200 per side) and has a load rate of 30%, the shock would see almost 4000 lbs of force per inch of shock travel. Out back, the rear weighs in at 1400 lbs (700 per side) with the shock layed over at 20% you net a load calc around 88%, so the shock would see about 795 lbs of force per inch of travel. OK, once again, 4000 lbs force up front, 800 lbs force in the back. Wow, thats 500% difference! Here's the question of the day - How could you expect the same shock valve to work correctly in both places?