Making "the old girl" Handle

[Truckstr]

Posted this on another board, but thought it might better belong here.

I recently acquired a 1967 C10 short-wide bed pickup. I've had a 1972 C10 long-wide bed as my "second car" for almost 17 years and the '67 just rides A LOT stiffer.

The '67 originally came with a six banger and 3 on-the-tree. It now has a 350 with auto (looking for a 700R4, BTW).

I have a set of 2-1/2" drop spindles (Early Classics) and a front anti-sway bar to install (along with 5 bolt pattern wheels and front disc brakes off of my '72). These two mods alone should be a big help in the handling department, although I'm not under the illusion that she'll ever beat a 'vette through the twisties.

I was contemplating modifying the front suspension geometry by changing the upper A-arm to cross-member mounting plates to allow for more adjustability and optimization of the instant centers and roll center.

So, the question is: does anybody have any experience with this type of modification? and also, why does the '67 seem to ride so much "harsher" than the '72? The front springs look to be the originals on the '67 and they are the same as the small-block equipped trucks. Right?

Thanks,
Jeff

[crazy longhorn]

I cant help with the alignment question, but on the stiffer ride, Im sure it has to do with the shorter wheel base. the longer they are, the smoother they tend to ride.

[Truckstr]

Thanks, I thought about that myself. I'm not so sure though. I'll check it out more deeply when I make the spindle switch. The front coils MAY have been cut. Can't swear to it yet.

It's not really an alignment "problem". I'm more interested in trying to optimize the geometry. I spent a bunch of time in Engineering school working on the front suspension for a Mini Baja vehicle (if anybody has ever heard of that). I suppose one might say that I have just enough knowledge to be dangerous - LOL.

Looking forward to getting some more responses.

Thanks in advance,
Jeff

[Fast68Chevy]

sway bars- defintely find a 3/4 or 1 ton front sway bar and maybe even get rear bar kit too. wont help on the ride harshness though. is your rear leaf or coil ? coil rear normally alwayts ride nice and soft, they are two stage coils in design, the middle three coils in the rear ones are close ot contacting each other at all time and actually do over certain bumps, then after that there is a lot of resistance and load handling capability comes in. Ppl think that the middle three arent supposed to touch, but in actuality thats how they are designed to be,

i can get you the GM technical description of the coils and how they work if needed,

[Truckstr]

Thanks for the reply, Fast68Chevy. I presently have the Early Classic supplied front sway bar. I'll have to check, but I think that it's 1-1/4 inch diameter. If it doesn't suffice then I'll go for a bigger one out of a 1 ton truck (up to '86, right?).

The '67 is coil spring rear suspension. I want not too harsh, but good handling. I'm from the school of thought that says bigger sway bars (vs. stiffer springs) is the way to go for handling - up to a point (too much of anything can be "ungood").

I'm still working out the math on the optimum A-arm mounting. I should have something pretty close - in theory - in the next few weeks. I'm just wondering what else (snag?) that I might hit - that's the reason for wanting to pick somebody else's brain/experience.

Thanks,
Jeff

[jiggs]

I think that the sway bars help out a lot, but progressive rate springs are also a must for good handling/good ride. Eibach are progressive. Shocks have a lot to do with it as well. Koni, QA1, Bilstein, KYB or others will diffinately help.

I know lowering the engine and moving it back would give better weight distribution in turn giving better handling. From what I have read, the 64-87 front suspension design is very capable. Lowering with shorter springs will give better roll center, but the camber gain is still positive during bump. Too short of springs is also a concern dealing with bottoming out. This is a problem that every GM suspension from the 60's has. The idea of having the front go into negative camber gain during bump is something that I have been thinking of as well. How to do it is a mystery. I think that moving the upper contol arm inner pivot lower would give good results, but bumpsteer would be an issue. Making the upper arm longer would then be the cure. IE: tubular upper control arm. That would take some design. Another thought is to use a 1st Gen Camaro mod. A spindle extender. This will move the upper ball joint pivot up giving the same result as moving the inner pivot lower. The only problem would be wheel clearance. Basically in my mind, the lower control arm has to be near parallel with the ground and the upper has to be pointing to the sky, a few degrees. This will allow negative camber gain. The more it points to the sky at rest, the more neg camber gain will be experienced.

From what I have read, this suspension is not prone to bumpsteer, so if re-designed properly, it should not be a concern.

Caster is also something that has to be addressed. To get the opimum caster, you requires too many shims. That is OK for regular driving, but at the limit, there will be a lot of stress on the alignment bolts.

Unsprung weight is also the ememy in handling. Looking at the sheer size of the suspension pieces, I think it is doomed. Also the cast rotor, spindle and caliper add killer weight.

Polyurethane bushing are also a must. The ones that have graphite in them won't squeek.

Dropped spindles do nothing as far as geometry is concerned, but they do lower the center of gravity.

The rear coil suspension is a good start, but lowering is essensial. The trailing arms are at too great of an angle. Getting them level with the ground would help out a great deal. Again, good springs like Eibachs, good shocks and a moderate size sway bar is all you need. Look under a Winston Cup car. It looks really similar to our trucks. 7/8 diameter bars from 3rd Gen Camaros and TA's work great.

Boxing the frame would give a lot of needed rigidity.

High center of gravity, as far as the gas tank and passanger seating position are concerned is not great. There is nothing you can do with the seats, but put the tank low in the frame. Between the wheels would be great, that way the center of mass is not at the ends of the truck, but there is no room. Baffles in the tank would aid in swishing during cornering.

If the tires you are running are crappy, you will never see what everything else will do. Also don't goo too large of diameter, wheels get really heavy after about 17".

Please PM me with your ideas or design for the upper A arm. I am very interested in what you are thinking. I too want my truck to handle.

Thanks,
Tyler

[Truckstr]

jiggs, thanks for your response. It appears that you and I are on similar trains of thought.

The similarities in the suspensions between our trucks and Winston Cup cars hasn't escaped me. Adjustability? Well, that may be a different thing entirely. I have a spare frame (bare at present) from a '69 GMC (leaf spring rear suspension) that I have been sand blasting and measuring, etc. That frame has all of the mounting holes for switching it over to coil spring rear suspension. Repositioning the front trailing arm mounts has crossed my mind. I'll know more as I spend more time with my '67 (I've only had it a week).

I've considered "notching" the front cross member to lower the center of gravity without upsetting the front suspension geometry. I am a little concerned about the roll axis angle. I don't want to change that angle and thereby impart a tendency for the truck to want to "swap ends" on hard braking in a turn. More math to work out, I guess.

I've been taking several measurements of the front suspension components ("king pin" angle, A-arm pivot points and their relation to the upper and lower ball joints, track width, etc., etc.) and I'm still working on a graphic representation of it so that I can see what it'll do as the A-arms travel through thier arcs. I have access to Pro-E CAD here at work, but finding the time to use it is proving difficult. We're in the middle of a design cycle right now (which reminds me, I should be working. LOL).

I'll keep you in mind and PM you when I have something worth sharing. Thanks for your input. I certainly don't have all of the answers. As the old saying goes, "two heads are better than one".

Later,
Jeff

[jiggs]

Jeff;

Another thing that has to be addressed is the rear panhard bar. Its location, length and angles are not very good. It allows for a high roll center for the back. The fact that it is out on two planes is not a good thing either.

To have a low roll center on the back, the bar must be at least as low as the center line of the diff. This is a problem, simply because the bracket that would be needed for the frame would be very long and would have a lot of leverage on it. That is another reason for a lot of lowering.(Get the frame closer to the diff. This is also why boxing the frame would be a good idea. Mors support around the frame bracket would also be a nessesary thing.

The bar should be as long as possible, be parrallel with the ground at rest, and be perpendicular to the frame, (or parrallel with the diff.)

Another thing is that this bar has to support the entire weight of the rear while the truck is cornering. This would mean that the bar should be quite a substantial size to support that. The brackets as well, ecspecially the one on the frame must be beefy. I would use at least 1/4" plate for them. For the bar 1" seamless, schedule 80 pipe should be strong enough.

Because the rear trailing arms form a triangle (looking from the top, down), they do take some of the load off the panhard bar while cornering . How much is the question.


Having both the front and rear roll centers low should increase the cornering ability of the truck by a lot. It should also help the roll axis. Now all I have in my head is theories, the practical has yet to see the light of day. This is why I am so interested in what you are thinking.

Thanks
Tyler

[70 Jimmy]

Couple of comments (remember, I'm no expert, but I'm no engineer either! LOL ).
-You might think about just clipping the front end with camaro or chevelle front clip. They make a ton of "g machine" parts for them.

-You can notch the crossmember into the frame. I did it for a 1.5" drop before spindles and springs. Don't forget to notch for the steering linkage at the front, center of the crossmember.

-You could also step the frame up at the xmember (then back down before the rad support. I've seen this and it works real well because of the head room for the engine. Of course your engine may be higher, raising your center of gravity.

-You could also make your own xmember using 67-72 suspension. That would fix any xmember clearance problems.

Also, I don't think your rear swing arms will just "bolt up". I believe the frames are different. I could be wrong, it's happened before... I think. Hehehe.

Just to give you some options. You think like an engineer and as a Mechanical/Electrical/Software Technician, it's my job to supplement the engineers thought process. Kind of a reality check. Hope that doesn't sound arrogant because the engineers do the same for me. Remember, never over engineer a project, someone has to live with it. In this case, that someone is you. Keep it simple and avoid re-inventing the wheel (unless you just love doing that). OK, no more soapbox bs. GOOD LUCK and have fun!

[jiggs]

Jimmy, you make a very valid point. What we are doing here, I think, is trying to iron out the inherent flaws of the front suspension that the factory cursed us with.

Now what we are talking about is to reengineer the movment of the "A" arms as they travel through their arc. It may be very simple or it may be useless to try. If no one tries, there is no progress.

Double "A" arm suspension is the best deal out there as far as handling is concerned. If you could make it better with a few pieces, you probably would. These could be the parts to make a truck handle closer to a sports car. Who knows. We may be wasting our time, but I think it is time well spent.

[srhart71]

Coming from another mechanical designer, it sounds like you guys are on the right track. I will he heading home for Thanksgiving so I can look through my old issues of Truckin. They did a project a little similar to this about 6 years ago that I thought I might want to try. They lowered a 67 (I think) swb with the intentions of getting it to handle better. About the only thing I definitely remember about the tech side was that the panhard bar was replaced with one that mounted to the right side of the frame and to the axle tube almost to the left trailing arm. I will look and post my findings when I get back.

[Slammed67]

I too am trying to improve the ride quality of my truck. I'm also about to perform a front cross member notch. I'm running air bags and am not happy with how "high" the truck sits at "ride height". It also rides too rough in my opinion. When setting up an air ride system, at "ride height" the bags should be at or close to their designed "installed height" or overall height of the bag. With my bags inflated to ride height (5" to 6" tall), the front of my truck sits higher in the front. To compensate I have to add more air to the rear bags to raise the rear of the truck. By doing this, I'm exceeding the recommended bag installed height, thus causing the rear of the truck to ride too rough. I could shim the rear bags up so the truck would sit level with the bags at ride height, but then I'd lose some overall drop in the rear. I considered modifying the lower a-arms to drop the front bags, but don't feel confident enough to make a safe modification to such an important part of the front suspension. So, the front cross member method seems to be the way to go. I like how high the rear sits with the bags at ride height, I think a 1.5” notch will lower the front enough to match the rear height. My engine is already in a lower, rearward position, as recommended above. Also, I have ECE's adjustable panhard bar which sits more horizontal than the stock bar at ride height. My goal is to have the truck ride low and sit even lower! I’d like to have the tops of the tires even with the tops of the wheel arches. I’d be interested to hear of any more improvements that can be made to the front-end geometry. Oh, I also had to lowered the passenger side mounting point of the panhard bar. I was experiencing some interference with the c-notch with the bags totally deflated. Don't think it really had any affects on handling. Here's a pic....

[Jesse 67 c-10]

One thing that would help in the rear, especially with a lowered truck would be changing the shock location so the shocks are more up and down, if you moved them to a further out position too this would increase roll resistance, an adjustable tubular A-arm setup with a 4 link rear would be awsome though! adjustable coil overs or air with good adjustable shocks, move some wight around, good sway bars, quicker steering ratio could have a great handling truck!
Jesse