Mechanics

GMC TRUCK WHEEL PROBLEM

1980 GMC Truck • 50,000 miles

Im am going to be putting my 454 in my truck soon hopefully, I currently have a 350, is there anything I should do extra then the standard motor swap?
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Jessesandberg
February 25, 2013.



Stiffer front springs and larger radiator.

Caradiodoc
Feb 25, 2013.
I got a 4" lift in my truck so do you think the springs in the front would hold up?

Tiny
Jessesandberg
Feb 25, 2013.
I'm a suspension and alignment specialist and as such I do not get involved with lift kits or lowering kits. A very important part of my job is correcting ride height that is off as little as an inch from the design measurements. Lawyers and insurance investigators love to find those kinds of modifications so they can shift part of the blame away from the guy who ran the red light and caused a crash.

There are a number of things to consider when ordering replacement springs through the dealer. The two biggest factors are engine size and whether it came with air conditioning. Both of those affect the weight the springs must support. Even if you have a four-wheel-drive with a solid front axle, handling is affected by the added weight. With a heavier engine the stock springs are typically a little shorter but considerably stiffer to reduce body roll when cornering and diving when braking.

With the short-arm-long-arm suspension system, (upper and lower control arms), ride height has a major affect on tire wear. When old springs get weak and sag, the arcs the control arms go through changes due to changes in the suspension's geometry. You can have perfect numbers on the alignment computer but when that geometry is wrong, those numbers only pertain to a vehicle that is standing still, not bouncing up and down on the highway.

You also have to look at how the truck was raised. With a solid axle, all you can do is install taller springs or add a spacer to them. That will not alter the alignment but it will affect the relationship of the steering linkages to the wheels. A dropped pitman arm will reduce the error in the geometry but it still won't handle as well as it was designed to.

If you have upper and lower control arms and all that was done was to install taller springs, you and I have no idea what is going to happen. For sure handling will be miserable and tire wear will be greatly accelerated. The correct way to do it is to use "drop spindles". Those are spindles that put the center of the wheel, (the axle bearings), further down from the upper ball joint and closer to the lower ball joint. That does not alter the ride height of the suspension system. Ride height is not the same as the height of the body from the ground. Ride height has to do with the suspension system's geometry. Imagine driving onto a pair of 2" x 6" pieces of lumber. The body will be higher off the ground, but nothing changed with the suspension geometry.

Whatever is done with the pitman arm, the same thing must be done with the idler arm. Those two put the main steering linkage perfectly parallel to the ground. If that linkage is not parallel to the ground, the truck will dart from side to side when a tire hits any bump or hole in the road.

You also have to consider "scrub radius". Draw an imaginary line through the upper and lower ball joints. That line will intersect the road surface at a specific point on the tire tread. Altering ride height doesn't change scrub radius, but people usually raise their trucks so they can install larger diameter tires. That DOES affect scrub radius because it raises both ball joints while keeping the original angle. The larger the tires, the further out on the tread that line will hit the road. That's where the reduced handling and braking come into play that lawyers will use against you in the courtroom. They will convince a jury that you were less able to avoid that guy who ran the red light, and they will be right.

Drive shaft angle is another casualty of altering ride height. The motions the universal joints go through were carefully designed in to reduce wear and vibration.

Most trucks and minivans have height-sensing proportioning valves in the rear brake system because there can be such a wide range of loading in the rear from empty to fully-loaded. A one-size-fits-all proportioning valve like is used on cars would not meet all the different conditions. If nothing is done with that valve, it will always look to the braking system like there's no load in the rear so brake fluid pressure will be reduced to prevent easy rear-wheel lockup under normal braking. You can be sure the lawyers will see that.

As you can see there's a lot to consider when altering ride height or just installing different wheel or tires. The designers take this all into account when they design every car and truck. The braking and suspension systems work as a team. They are so well perfected that there isn't anything anyone can do later to improve those characteristics without at least degrading something else.

Caradiodoc
Feb 25, 2013.
You have just taught me alot of things I did not know before, thank you for taking the time to write all of that down, and im using this truck as a show crawler and its being trailered everywhere I want to take it so it will never see pavement for the reasons youve mentioned above. Again thank you for taking the time to explain all of that to me, I really appreciate and use all the knowledge I can get.

Tiny
Jessesandberg
Feb 26, 2013.
You're welcome. You don't have to worry about tire wear and handling issues. Suspension and alignment is one of my specialty areas. Bodywork is one the things I definitely do not have the talent for. I tried it once, and everything I did in six weeks my buddy redid in three hours!

Caradiodoc
Feb 26, 2013.
Hey I was just told il need a bigger flywheel for my 454 cuz im mating it to a sm465, im swapping it with a 350, do you think I will need a bigger one or no?

Tiny
Jessesandberg
Feb 26, 2013.
That is not in my area of expertise. I have been told that all Chevy engines will bolt up to all Chevy transmissions around that time period, but I've never heard anything mentioned about flywheels and flex plates. The issue is going to be the starter mating with the ring gear. Your starter is bolted to the engine, and logic would dictate it has to work with whatever transmission was available, and a transmission would have to work with whatever engine it was put behind, so my initial guess is the flywheels will be the same.

There are other considerations that I am not familiar with. I'll have to differ to my Chrysler experience. Some of their engines are "externally balanced" meaning they had cast crankshafts instead of forged, and there were two counterweights they couldn't cast as part of the assembly. They added balancing weights to the vibration damper and to the torque converter or flywheel. All of those parts interchanged but you had to use the right combination to prevent an annoying vibration.

Chrysler also had three different transmission housings for 6-cylinder, small block, and big block. There were two different transmissions for each engine group but those interchanged with no modifications. There was only one flex plate and only one size ring gear, so matching it to the starter was never a concern.

That's just some food for thought. What I would suggest is visiting a salvage yard and have them look up the parts in a Hollander Guide. That will list each part with a code number, then you look up that number in the back of the book and it will list all the applications it fits. If you come up with the same code number for two different applications, you don't need to modify or replace anything. Many public libraries have Hollander Guides too.

GM used to have a book in the '80s called "Chevy Power" that listed all the modifications and interchanges related to racing. It was about a half inch thick. You might check at the dealership to see if they have something like that yet, or if they have a mechanic who is familiar with what interchanges from that era.

Caradiodoc
Feb 26, 2013.