'52 Chevy pickup rear suspension question...

Truk52 · June 13, 2004, 07:31:22 PM

Hi all,

I haven't been here in a while.

Yesterday I saw a picture of a friend's '48 GMC 1/2 ton frame. The rear suspension on his truck has the springs mounted outboard of the frame whereas mine are mounted under the frame. Why is there a difference and which year did it occur in?

The only information I could find in my Shop Manual and other books I researched was that 1/2 tons came with screw in shackles and bigger trucks came with clevis type shackles.

Can anyone shed some light on this subject for me as I think it would be easier for me to lower the rear of my truck if the springs were mounted outboard of the frame like my buddy's truck.

Thank you all.

Truk52

threefive · June 13, 2004, 08:13:56 PM

Quote from: "Truk52"Hi all,

I haven't been here in a while.

Yesterday I saw a picture of a friend's '48 GMC 1/2 ton frame. The rear suspension on his truck has the springs mounted outboard of the frame whereas mine are mounted under the frame. Why is there a difference and which year did it occur in?

The only information I could find in my Shop Manual and other books I researched was that 1/2 tons came with screw in shackles and bigger trucks came with clevis type shackles.

Can anyone shed some light on this subject for me as I think it would be easier for me to lower the rear of my truck if the springs were mounted outboard of the frame like my buddy's truck.

Thank you all.

Truk52

GPster · June 13, 2004, 10:09:11 PM

According to the "King" the 1/2 ton frame is different from the 3/4 ton frames. If one of the frames you're looking at is 34" from side to side then it is a 3/4 ton. My memory is that the 1/2 ton frames are not parralell to each other in the rearand they're wider accross behind the rear end than they are at the back of the cab, This would account for the different spring hangers and you might only notice the reason if the original rear is still in place. GPster

1FATGMC · June 13, 2004, 11:26:03 PM

Quote from: "Truk52"

Yesterday I saw a picture of a friend's '48 GMC 1/2 ton frame. The rear suspension on his truck has the springs mounted outboard of the frame whereas mine are mounted under the frame. Why is there a difference and which year did it occur in?

Can anyone shed some light on this subject for me as I think it would be easier for me to lower the rear of my truck if the springs were mounted outboard of the frame like my buddy's truck.

I wonder if you need to move them out much to get the truck low. My truck sits pretty low and they are almost under the frame.

I used the front mounts from a '73 Camaro I stripped and I tried to set the front and rear mounts at the same ride height above the ground as the Camaro. This is suppose to help braking and dive I believe. I used some square tubing under the frame and above the front mount and did move it out slightly.

The rear mount is a piece of pipe up in the boxed frame that is the right diameter for the hanger rubbers (camaro). I moved this out slightly also so that I could use the camaro gas tank between the springs. I really couldn't have moved the springs much more as I only have 1 1/2 inches of clearance between the spring and the side of the tire/wheel (275X60X15). Be sure and check for your clearance for your tire/wheel combo.

Now all of this might not help you much as I built the bed from scratch and mounted the fenders where I wanted them so the back of the pickup isn't at all like a stock one.

There are more frame pictures ( HERE ). Hope this helps some.

c ya, Sum

enjenjo · June 13, 2004, 11:39:37 PM

I have modifed the frame on these to be parallel, by bending them in under the cab and shrinking it, and bending it out at the rear just a bit. If you set the rails up 34" apart, you can use 73 to 87 rear springs and hangers with the axle mounted on top of the springs. The stock shock brackets will still work.The rear shackle hole in the 73 to 87 rear hanger lines up exactly with the stock rear hanger hole., makes it easy to locate.

It soulds like a big deal to do this, but it's not that difficult. Where you want the frame to bend in, heat both flanges in a V, and pull into place with a bar clamp. The flange will bulge at the V, no problem at this point. When you have it where you want it, hold it on place with several clamps and bars, reheat the bulge in the flange, and dolly it flat. After shortening the crossmembers, reinstall them, and reheat the worked areas to relieve any stress, and you are done.

I also like to use the one ton rear cab mount in the center of the rear of the cab, it makes it easier to shim the cab so it set level, and keeps any frame twisting from tranfering to the cab

Phat · June 15, 2004, 09:32:50 AM

3/4 frame is straight and a lot nicer frame to work with. But i agree i dont think you need to do much to the stocker other than lowering blocks and put the rear on top of the springs to get it low. Been running one for about 15 years thats dragging on the ground with bags and stock springs. Dont think i would go bending the frame and heating it up just to put the springs on the side. Not a real smart thing to do. Also the rear center cab mount lets the cab twist any way it wants ....so i would go with the later model ones on both sides and adjust them to get the cab straight as they are not so good from the factory. But what would i know i have only built 15-20 AD trucks in my life...LOL If you do heat the frame please box it as that is something you just dont do if your going to drive it a bunch of miles. Its also in a real bad spot on these trucks.

enjenjo · June 15, 2004, 09:57:57 AM

Uh... bending frames is a big part of what I do for a living. Bending them back after an accident. I have done a couple a week for over 20 years. Yet to have the first one fail.

Phat · June 15, 2004, 10:02:04 AM

Ah what do those truck frames say on them....You know the big sticker LOL Done my share of Petes and freight shakers But a 50 year old 1/2 ton truck is just not a smart thing. Besides you almost dont have to use heat on a 1/2 ton frame.

On this side of the world we most times just chan ge out the rail on big trucks. If you were to heat and bend a rail on my tri axle dump truck after a hit you would own it... LOL It dont work. I presume you are talking 80,000-180,000 gross trucks ?(mich train) Maybe a UPS frieght truck but even they would not let us heat and bend em back.

PeterR · June 15, 2004, 10:32:49 AM

The only frame repairs I have seen fail have been where an over enthusiastic repairer has fitted a heavy reinforcing channel inside the frame without taking care to provide a gradual transition. Invariably the frame fatigues just outside the channel where there is a sudden change in section modulus.

Setting the cab on a centre point mounting saves it from a huge amount of punishment as the frame twists. Just park with one wheel up on the kerb then stand behind the truck and eyeball the twist in the fame, you will wonder how it ever straightens out again.

And one more thing I just remembered, do not be concerned at having spring hangers on the outside of a channel frame, that is the ideal place for them. The shear center of a channel is outside the web, so mounting the hangers on the outside minimises torsion effects in the rail.

enjenjo · June 15, 2004, 10:33:46 AM

So how many of the triaxle dump trucks in your area started out as road tractors in their first life? Around here a lot of them did. I have stretched many frames too. And did tandem cuts, added third axles, hydraulic trailers, sleeper boxes, droms, and I'm not the only one doing it.

Phat · June 15, 2004, 11:39:05 AM

First one on the block years ago to put a pete airleaf under my B-model but i sure as heck did not weld or bend it. (i stretched it at the same time to 260 inches) All bolted. Tri axles around here are mostly brand new. Not kidding . Lots of work for them and the DOT guys are real stone crushers so old stuff dont cut it.. But the only way we stretched was bolt and double or triple frame. Heck brandnew Petes were bending frames around here and had to have rail replacement. Having worked in your area code i guess if you work for a fleet outfit that hauls no weight they could and have to get away with it. I sure as heck would not do it as i used to come out of cleveland and flint with 100,000 plus all the time for the 500 600 mile ride home.. I guess i am the only one that has seen frames bent that were fixed wrong. They twist and sag and do all sorts of bad stuff after repairs. But i guess thats kinda O/T as we are talking 50 year old 1/2 ton frames. We all have our ways... guess i have seen more failures and have formed and opinion. Come see me after you have hauled a load of ship anchor chain that weighed 135,000 lbs and the welded frame on a company trailer broke.(it was straped and arched in Ohio) LOL Not a lot of fun. I was lucky too have built and driven Over the road trucks and you can tell the diff in one thats been fixed. Like i said just and opinion from real exp. Got to be a reason that sticker on the frame says use no heat do not weld or bend this frame....Why do you think that sticker is on there?