Square Body GM Guys...Need Your Expertise

[ClassicTractorProfessor 5,314]

I have always been, and will always be a Ford guy. I've had a few GM trucks before, but not nearly as familiar with them as I am the Ford F-Series. That being said, I recently purchased a 1981 Chevy C30 for my welding/service truck. Not exactly what I wanted, but it was the only big block 4 speed 1 ton truck I could find. So far I've been happy with the truck, but the front end is terribly loose. So going through and pricing parts to rebuild the entire front suspension and steering. Upper and Lower control arms, coil springs, shocks, pitman, idler, tie rods, you get the idea. I want everything under the front of the truck to be in new condition. 

 

My question for you GM guys is this...when looking up the upper and lower control arms, it gives me two options, one for standard duty suspension and one with heavy duty suspension. How does one go about determining which one he has. This is my only rig right now aside from our camper, so I want to make sure I get the right parts the first time, to avoid extended downtime on the truck. 

 

The truck does have the 10K GVW Camper Special package and is a cab and chassis model if that helps any

[ClassicTractorProfessor 5,314]

Here are all the RPO codes from inside the glove compartment if that helps any. I'm leaning towards probably the HD but want to be sure.

[Pullstart 62,916]

Camper special alone is telling me HD.  

[ClassicTractorProfessor 5,314]

3 minutes ago, Pullstart said:

Camper special alone is telling me HD.  

That's what I was sort of thinking, but wasn't sure. 

 

I just had a guy on a Square Body FB group tell me the easiest way to tell is by how the lower control arms mount to the truck, if they mount with U-Bolts it is standard suspension, if they mount with regular bolts it is the HD, and that those were mostly used on the P-Series trucks and motorhome chassis. Can anyone verify this? I'd like to think he knows what he's talking about, but I also know how people on Facebook groups can be . Mine mount with the U-Bolts, which according to him points to standard suspension.

 

[Darb1964 1,043]

It's not a four by four I'm guessing, in1981 I was thinking they were still leaf Springs in the heavy duty models. What's it have for a motor? 350 I think may be lighter than the 454. Did it ask what motor when your looked at parts?

[Darb1964 1,043]

After looking at the window sticker closer I think the guy from the other group may be right. Looks like a comfort package, that's why coils. Better ride but lighter.

[ClassicTractorProfessor 5,314]

1 hour ago, Darb1964 said:

It's not a four by four I'm guessing, in1981 I was thinking they were still leaf Springs in the heavy duty models. What's it have for a motor? 350 I think may be lighter than the 454. Did it ask what motor when your looked at parts?

Nope just a 2 wheel drive. 454 with 4 speed behind it. I'm pretty sure I've got it all figured out and a list of parts to order. Now just have to convince myself that the old clunker is worth sinking $1300 into  Should be good to go for a while once I do though. Planning on replacing everything suspension wise from front to back. I noticed earlier in the week when I was doing U-Joints that I've got a broken leaf in one of the rear springs, so gonna go ahead and replace both rear springs, new coils in the front, new shocks, and everything else. Should ride like a new truck once I'm done.

[ri702bill 8,345]

What I find to be handy is looking at the pictures provided on the major auto part websites - you can usually narrow it down that way. 

Some vehicles can be an uphill battle to find parts for no matter what - my father in law ran a small 2 bay repair garage back in the 70's - I gave him a hand to put a clutch in a mid 60's International Scout once. There were FOUR different clutch discs listed - we narrowed it down to a choice of 2 by the spline count and the diameter - the parts counter guy needed the build date of the vehicle - seems the was a mid year parts supplier switch .....gave him that, got the wrong one ....

Bill

[squonk 41,156]

Look at the brake calipers. HD are usually a Ford style with the funky block held on with a single bolt. Light duty will have 2 thru bolts holding the caliper on.

 

HD pads   LD pads    

 

Another way to tell is measure the front sway bar diameter. 1 1/4" is HD and 1 1/8" is LD

Edited December 21, 2021 by squonk

[cschannuth 3,816]

Depending on the return policy you might be able to order both types and then send back what you don’t need. As a sidenote, that thing was really optioned up for a 1 ton dually work truck back in the day.  Pretty cool stuff. 

[Pullstart 62,916]

1 hour ago, squonk said:

front sway bar diameter. 1 1/4" is HD and 1 1/8" is LD

his RPO codes listed a HD bar too.  

[squonk 41,156]

WGT is the weight rating Basically a ton and a half. Frt axle 1885 rear axle 1115 lbs.

 

[Darb1964 1,043]

15 hours ago, ClassicTractorProfessor said:

Nope just a 2 wheel drive. 454 with 4 speed behind it. I'm pretty sure I've got it all figured out and a list of parts to order. Now just have to convince myself that the old clunker is worth sinking $1300 into  Should be good to go for a while once I do though. Planning on replacing everything suspension wise from front to back. I noticed earlier in the week when I was doing U-Joints that I've got a broken leaf in one of the rear springs, so gonna go ahead and replace both rear springs, new coils in the front, new shocks, and everything else. Should ride like a new truck once I'm done.

I would do it with the price of trucks now and the near future cost of them. If the frame in that bad boy is solid, you can get everything else you need fairly easy. I'm assuming the motor is strong, if it's been maintained at all it should be. I'm envious, 454 with a stick, you know, pass anything but a gas station. The square bodies are very desirable, never have a problem getting your $ back. That truck around my area ready to work like you're talking, seven grand, lack of four wheel hurts it some.

Enjoy

[Jrain 276]

all you need to do is look in the driver side door at your axle rating tag , if I remember you are r going to see a front spring weight rate at 3800 pounds or a front spring weight rate of 4000 pounds   the 4000 rate would be heavy duty and the 3800 would be standard option , I might have the rating wrong it might be  3500  or 4500 but in general if its rated 4000 or above it moves the front specs in to heavy duty.

[Jrain 276]

On 12/21/2021 at 12:29 AM, ClassicTractorProfessor said:

Nope just a 2 wheel drive. 454 with 4 speed behind it. I'm pretty sure I've got it all figured out and a list of parts to order. Now just have to convince myself that the old clunker is worth sinking $1300 into  Should be good to go for a while once I do though. Planning on replacing everything suspension wise from front to back. I noticed earlier in the week when I was doing U-Joints that I've got a broken leaf in one of the rear springs, so gonna go ahead and replace both rear springs, new coils in the front, new shocks, and everything else. Should ride like a new truck once I'm done.

If you are doing the rear leaf springs take a real good look at the leaf spring mounts that is the week point the mounts rot out and the bushings wear and cease  , the rear bushing can be a big PIA to get , and invest in good shocks not cheep at least 50 percent of your ride quality comes from the shocks.