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Old 06-08-2017, 09:35 AM   #1901
robnolimit
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Re: Make it handle

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Originally Posted by Hop View Post
Not sure if this has been addressed. looking to add coil overs. Are new upper and lower control arms required or will the current setup met my needs. 64 Step Side 2 1/2 spindle w/3 in drop spring in front, 4 in drop spring in rear. I want to lower the vehicle another inch all around without changing much.
Before I say what I feel I need to, remember that I am really trying to help. OK. So, my first question is, "What are you trying to accomplish?" I.E. - What are your goals for the suspension and/or the truck? This information has a lot to do with the right answer. Here's why.

IMHO (or, my opinion being fairly well educated on this subject) Adapting to a coil-over is seldom the best choice. (this is different that using a coil-over from a fresh design standpoint) What could you gain from a coil-over. 1. Compact design. uses less space and weight than a conventional coil/shock. 2. Easy mounting, - from a fresh design standpoint. 3. Adjust-ability of spring height via the threaded spring collar. 4. Typically built with high quality shocks, and/or with some valving adjustment.
And for the down side, LENGTH. To get 5" of travel from a coil-over, the open and closed measurements would be around 12" closed and 17" open. (eye to eye of mounts) Travel = ride quality. The shorter the travel available, the higher the spring rate needs to be to stop the vehicle from bottoming out on compression (bump/dip). The worst offender in the ride quality game are the 'Hy-brid' or 'direct fit' coil-overs. The ones that bolt to the LCA and the spring tapers out to fit the OE upper spring cup, with the upper shock mounting into the OE hole. These typically have 3" to 3 1/2" total travel, and I will now ask anyone, "If you, or anyone you have ever known, or heard of, has ever swapped in a pair of these, on any vehicle, and been happy with the ride quality, please let us know. As they may be the Unicorn, the only one.
Now, if ride quality isn't an issue, and you just want it lower, and maybe some adjustment to fix other problems, OK, they will work.

On to real Coil-overs shocks. The video shown is the best way to fit in a pair. By raising the upper shock mount they have created room for a longer shock to get back to the OE travel range. (lets say 4" to 4 1/2" of shock travel) that shock would be 11" to 15" long (closed vs open). But, this is a fair amount of work. There are kits avail, like the one from RideTech, and if this is your goal, that may be the best bet.

Now, on to your desire for 1" more of drop. If you do a coil-over swap in 'kit' form, and then back off of the spring collar 1/2" to drop the truck 1", you are loosing potential compression travel. And you didn't have a lot to start with. If the shocks and springs - or - coil-overs are installed correctly, then they are NOT the limiting factor of the suspension, the actual suspension design is, say, bump stops. Again, you need a very stiff spring to stop the vehicle from bottoming out.

You could get the same from a 4" drop spring and installing a high quality adjustable shock, BUT, the OE C10 shock mounts don't allow for a shock when the suspension is that low. Porterbuilt has a raised upper shock mount for that. BUT, the suspension itself is still almost bottomed out. You can trim down the bump stops (please don't just take them out) But by now, I'm sure you have noticed the front crossmember smacking the ground from time to time as it is now, and dropping another 1" will make that even worse.

Sorry for the heart-braking. But I want to be honest, and to give you the knowledge you need to make a good plan. If you want a coil-over because of the cool factor, then great. If you want another 1" drop, just trim the spring that you have, but know you will loose clearance and ride quality. Please stay away from the direct fit type coil-over swap kits. OR, you can go farther. Raise the crossmember up, or consider an aftermarket IFS with more travel and clearance. Sorry again for going on, and being a bit harsh, but I hate seeing people spend money and get a lot less than they were sold. Keep Truckin!
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Old 06-21-2017, 08:25 AM   #1902
rapid49
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Re: Make it handle

How low is too low for my panhard bar? What are the advantages / disadvantages of lowering the bar. I am going to install a Fat Bar 4 link on my 56 GMC. I currently have a 25 gallon blazer tank installed with little room between the tank and my rearend cover. I would prefer not to change the tank and can fab new mounts for the panhard bar. I can make more room for the bar by mounting it lower. I need to know what effect this would have on the handling.
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Old 06-21-2017, 08:48 AM   #1903
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Re: Make it handle

OK. EVERYONE should read this. (smart question BTW) The location of the PHR will determine the rear Roll Center. This is easily mapped out. The RC will be in the center of the bar (left to right) and at an elevation equal to the average of the two mounts at Ride Height. had to say it that way to include bent bars. If the bar is straight, it's the center of the bar. There are a couple of basic PHR rules we try to follow.

** Try to keep the bar level (mount to mount) at RH.
** Try to keep the center of the bar in the center of the WMS (Wheel Mount Surface) - or, center of the car/truck.

*** Some adjustments to these rules are commonly made for weight balance and track condition, but let's stay with the basics.

So, What about RC height. ** Lowering the roll center increases the Roll Angle of the chassis. So, a lower RC will increase body roll. (that's the bad part) BUT, the increased body roll puts more load on the outside tire (good for light back trucks) and may increase traction. (up to a point of diminishing returns) On the other side, raising the RC will reduce body roll, and keep tire loading more even (good if you have even ft/rr weight balance and sticky tires).

I think you would be OK to drop the PHR, but you will need to brace the dropped chassis mount. Please post up some picts when you are done.
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Old 06-21-2017, 06:42 PM   #1904
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Re: Make it handle

Thanks Rob for your quick reply . I will definitely post pics I'm looking for all the feedback I can get. I'm getting an education on this thread , thanks to all who share .
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Old 06-25-2017, 10:10 PM   #1905
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Re: Make it handle

I ended up lowering the panhard bar about 5" After the dust had settled I realized I probably could have done 4" Nothing is welded out at this point . I am also guessing at ride height. It came with 200# springs . How much can I expect the shocks to compress at ride height ? Any opinions on lowering the roll center this much ?
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Old 06-26-2017, 09:12 AM   #1906
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Re: Make it handle

Looks Good. One thing to check is the bar at R.H. Those coil-overs should be appx 14 1/4" at R.H. (appx 1/2 of the shock compressed.) Here's the quick way. Right now the shock is full extended, with 5" stroke. Measure the distance from the top of the axle housing tube to the bottom of the frame rail (notch) just above the housing tube. - looks to be around 6 1/2" or so. Subtract 2 1/2" from that measurement (1/2 of the shock travel) Cut two pieces of 2x4 to that length. Place a jack under the axle housing/gear set and remove the coil-overs. Put the 2x4's on top of the housing tube and use the jack to lift the housing until the 2x4's hit the bottom of the frame rail. Now the housing is very close to Ride Height. Make sure that the bar is level in this position.

But the looks of it, rear R.C. height will be around 8". (total guess, but, 27" tire = 13 1/2" to the axle center from the ground. Bar looks to be about 4" below the axle C.L. subtract another 1/2" for tire squat, and your at about 8") Your front R.C. will be around 4" to 5", so this is fine.
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Old 06-26-2017, 11:41 AM   #1907
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Re: Make it handle

Once again thanks for your quick reply Rob. You mentioned the front roll center. The front is a 81 Camaro clip with Hotchkiss springs and a 1 5/16" sway bar. It has circle track upper control arms that are moved back 1/2" for added caster. I am also running the original 15/16" front sway bar on the rear. Can you explain the relationship with the front and rear roll centers.
I also want to thank you for the quick shipping. I ordered the fat bar kit mid morning Tues. and it was waiting for me when I got home from work Thurs. afternoon .
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Old 06-29-2017, 09:32 PM   #1908
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Re: Make it handle

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Originally Posted by robnolimit View Post
OK. EVERYONE should read this. (smart question BTW) The location of the PHR will determine the rear Roll Center. This is easily mapped out. The RC will be in the center of the bar (left to right) and at an elevation equal to the average of the two mounts at Ride Height. had to say it that way to include bent bars. If the bar is straight, it's the center of the bar. There are a couple of basic PHR rules we try to follow.

** Try to keep the bar level (mount to mount) at RH.
** Try to keep the center of the bar in the center of the WMS (Wheel Mount Surface) - or, center of the car/truck.

*** Some adjustments to these rules are commonly made for weight balance and track condition, but let's stay with the basics.

So, What about RC height. ** Lowering the roll center increases the Roll Angle of the chassis. So, a lower RC will increase body roll. (that's the bad part) BUT, the increased body roll puts more load on the outside tire (good for light back trucks) and may increase traction. (up to a point of diminishing returns) On the other side, raising the RC will reduce body roll, and keep tire loading more even (good if you have even ft/rr weight balance and sticky tires).

I think you would be OK to drop the PHR, but you will need to brace the dropped chassis mount. Please post up some picts when you are done.
When you say to keep the center of the bar in the center of the WMS, do you mean left to right? I think going from the frame to the trailing arm on opposite side is the best that can be done for the in a stock type setup, right? That would put the bar off center to the drivers side?

Last edited by clemsonteg; 06-29-2017 at 09:57 PM.
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Old 06-30-2017, 09:06 AM   #1909
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Re: Make it handle

Yes, it would be nice if the bar were centered left/right. Usually not 100% realistic with a lot of fab work, or shortening the bar (bad). So, it is acceptable to have the PHB center 1" or 2" from the vehicle CL
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Old 07-10-2017, 10:23 PM   #1910
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Re: Make it handle

So this is off the current topic a little, but I remember rob saying something about flipping the leaf spring shackle hangers on the 73-87's. What is the reasoning behind this?
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Old 07-12-2017, 10:03 AM   #1911
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Re: Make it handle

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Originally Posted by Ddkeeler View Post
So this is off the current topic a little, but I remember rob saying something about flipping the leaf spring shackle hangers on the 73-87's. What is the reasoning behind this?
With the weight of the truck above the shackle instead of below it ,gravity is working for you instead of against you in regards to the leaf spring being able to flex therefore letting the suspension work more freely.
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Old 08-03-2017, 11:23 AM   #1912
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Re: Make it handle

Hey Rob,

FRAMES

I wanted to ask you about boxing frames and adding X-braces. I understand we want these frames stiff to handle the HP and let the suspension work better.

Is it needed to box in the whole frame or just some key areas? I have 3/16" x6" steel plate to box in the frame and a 20' stick of that stuff weighs 76 lbs. I remember my auto shop teacher saying that it takes 10 HP to move 100 lbs. At what point is boxing the frame and adding X-braces slowing us down?

Thanks
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Old 08-23-2017, 02:53 PM   #1913
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Re: Make it handle

Yes. Any more information on the X-Braces?
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Old 08-29-2017, 01:08 PM   #1914
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Re: Make it handle

Boxing, X bracing and weight. The best weight-to-performance saying that I know is this: 100 lbs = 1/10th of a second. Now, this not an absolute, but if you have a 10 to 13 sec car, it's really close. On the flip side, Weight down low, below the Center of Gravity, will help the base handling. Also, the stronger chassis will help in traction, braking, handling and a big improvement in ride quality. So, in total gain, I would add 100 lbs of chassis stiffener weight with no thought about a negative to the weight.
So, yes, box the whole thing, but make sure it's square and level when you weld. Standard crossmembers make squares, or ladder frames. - not very strong. Try to make triangles. They are strong. We do sell the X member from our Pro-Tech chassis for $595 that can be fitted into the OE chassis. (not a 100% drop in, but not too bad to fit). I know that PB also has a pre fab X kit.
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Old 08-31-2017, 03:09 PM   #1915
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Re: Make it handle

Hey Rob,

Anymore tips with making X Braces? Should they cover a certain length? Type of steel used?
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