55.2-59 subframe question

[dsraven]

quickly looking through the sgtusmc build there is mention of a guy who put a 4x4 frame under his task force and it was high enough to clear the step on the box with the front spring mount. I wonder if it would work if the body was spaced off the frame tall enough so it didn't hang down below the body but almost, like a newer truck has. these frames have a pretty flat rea section by the look of it in that thread. the body builder's frame drawings may help figure that out if interested. upfitters has a lot of info there to peruse.

[Nima]

I don't know if this was mentioned or not but why not just graft the complete front crossmember with all the suspension and steering component to the stock frame instead of the whole front clip from later model truck? That is what I wanted (and still want) to do with my 3/4 ton but since it seemed to involve for my skill set, I went another route.

[jmlloar]

Originally Posted by Nima

I don't know if this was mentioned or not but why not just graft the complete front crossmember with all the suspension and steering component to the stock frame instead of the whole front clip from later model truck? That is what I wanted (and still want) to do with my 3/4 ton but since it seemed to involve for my skill set, I went another route.

This wont work. the 55 to 59 frame is the same width front to rear, the 73 up is a lot more narrow in front of the cab to give room for independent suspension.

[dsraven]

ok, maybe just me but, I can't get my head around how you would splice the frames under the cab somewhere and still have the ride height you want, at something close to stock for trailer towing. if the newer frame is dropped down in the middle are you talking about a splice that involves one frame sitting on top of the other frame? that would keep your cab mounts where they need to be but really you could just use the complete frame from the newer truck, build new cab mounts to space the cab off the frame to where it needs to be, and shorten the rear section for where your axle centerline needs to be.
or, buy some rectangular steel lengths and build your own frame using dimensions from the assembly manual and the upfitters frame drawings. kinda like what lil tow rat has done, even if you just built the front section so it has a good long overlapping section for strength but then comes together and up to accomodate the front end of choice.
maybe a quick drawing posted would help us help you figure it out or come up with ideas you can use.

[jmlloar]

I'm not that far along yet. I still need to get the newer frame and do some actual comparison. Guesstimating it appears that the 73 up frame will be at least partially below the 55 frame. I'm not building a frame from scratch. just using part from one and part from another. cab is already sitting where it needs to be, this way all I have to do is mate the newer front piece square and at correct position to keep the truck and suspension at correct angles.

This is basically no diff than using a camaro subframe that has been done a million times before. I'm just using a heavier built truck front clip.

Going by pics it also appears that everyone seems to think the 73 up frame drops compared to the 55 to 59. I think this is only partially true. I would say its even amount of drop and rise putting the 55 to 59 about halfway between the two.

Pretty sure mr48chevy hit the nail on the head back at #14

[dsraven]

ok, thats what I was wondering about, the drop offset. if you can get some frame drawings, and a bit of time to get them somewhat at the same scale, you could lay one over the other and really see how it fits before you cut anything. then you can see the best way to go about it all. or, just cut and line up and go from there, box the inside when done-or not since you will have a nice long overlap. those lennox metal cutting discs work really well and don't wear down to be smaller diameter as you go. a plasma cutter is nice if you have one, a torch with a grinder afterwards also works just not as precise unless you like grinding. starting with clean metal is always good.
you alrady knrew that, sorry, don't mean to imply anything like that. just spitballing ideas mostly.
anyway, keep plugging away and posting so we can see how it works out. a few pics along the way.

[mr48chev]

[QUOTE=Nima;9045394]I don't know if this was mentioned or not but why not just graft the complete front crossmember with all the suspension and steering component to the stock frame instead of the whole front clip from later model truck? That is what I wanted (and still want) to do with my 3/4 ton but since it seemed to involve for my skill set, I went another route.[/QUOT

The main reason is that the TF frame is just over 34 inches wide at the front axle They are pretty well true "ladder frames" as they don't vary in width front to back enough to get excited over.

At the front axle line 60 / 87 full size trucks all run just over 28 inches wide outside of frame rail to outside of frame rail at the axle. Just enough so that with a spacer plate you can slip the frame off a 47 second series though 55 first series rightdown between the rails. A guy in Cali did a bunch of AD trucks with I'm thinking 64/66 front suspenson back in the 1980's.

We had a guy show up with the worst case of cobbled together TF with mid 70's square body front suspension and maybe the worst case of cobbled together chassis I have ever seen in All my years of being around modified rigs. A section of the square body frame was scab welded to the inside of the notched TF frame.

Everyone here knows that I am not a fan of frame swaps the sake of being a "cool guy with a frame swap but on this truck for what he wants to do with it I think finding a 3/4 ton donor with a solid frame and good running gear chassis wise. and doing the frame swap is the wise move.

There are a number of reasons that I believe that swapping frames in this case makes more sense.

First ease of finding chassis parts = bushings and suspension pieces.
Second: a rear axle that you can walk into any Napa and still buy parts for without a hassle. No digging into the rare parts file.

There is far less hassle in building cab and bed mounts to get the cab, nose and box level than there is trying to figure out everything to mate the front of the later frame and the back of the older frame together and get it all right.

[whitedog76]

Fatman has an IFS kit that uses 73-87 components for 8 lug trucks.

On another note, 03 and newer GM vans have a frame that's slightly over 34 inches. The problem with it is the track width is way too wide for an early truck. The factory track width is around 67" but they have positive offset wheels. The axle WMS is really about 70".

What I like about the 03 and newer van chassis is how the front suspension is configured. It looks almost identical to the MII kits that we're all too familiar with. It may be possible to narrow and graft the van suspension to an early truck.

[whitedog76]

Here's the frame layout of a Chevy Express. The core front end components are laid out just like the MII kits. Crossmember, spring hats, etc...

https://nemigaparts.com/cat_spares/e...g/07/tg07-706/

[dsraven]

if it interests you, try thr gm upfitter site for frame drawings and dimensions. not sure it it has them for the vans but most likely does.

[jmlloar]

Not sure in newer vans but older stuff like 71 up into the 90's is no different than the pickup. It uses all the same parts ecept the k frame is wider. and steering box is different.

[mr48chev]

I've seen several TF truck bodies sitting on 73/mid 80's 3/4 ton chassis in this area over the years. That was a fairly common swap in this area back in the 90's usually after someone rolled his square body in the hills.

I just flat don't see the productivity of cobbling frames together for this particular truck. All you seem to think about is scabbing something together because you think it is a cheaper way and that is hard to place any sort of wisdom with.

[Rickysnickers]

Whether or not we agree or disagree is immaterial, in the end, it's his truck. If that is how he would like to proceed, then that's his choice. I think we've beaten this horse passed death.

[mr48chev]

Originally Posted by Rickysnickers

Whether or not we agree or disagree is immaterial, in the end, it's his truck. If that is how he would like to proceed, then that's his choice. I think we've beaten this horse passed death.

It's been beat to death but I just want to see him build the safest truck he can build. In this case with this truck it is a full frame swap that would be the safest way.

[Rickysnickers]

I'm not arguing with you and actually agree with the point about building something that is safe. All we can do is give advice and let him make the ultimate decision. There's been plenty of advice, which is why I'm suggesting we move on to the next part of this build.

[jmlloar]

Made my decision. I'm splicing the frame. Guess I'll be unsafe just like all the other streetrods with camaro, volare, and mustang II swaps.

Got a friend who has been building street rods since the 70's. He also said this will work fine. If I splice, and fish plate the frame it will be just as strong if not stronger than original in that area.

There are tons of med and heavy duty trucks on the road that have had their frames stretched and shortened this way. it makes no difference if I use 2 different year frames. These two trucks are old enough to have similar design and mild steel frames. The newer pickups are spliced from the factory with a very smal overlap and are plenty strong.

I appreciate all the help making my decision and I will post picks of the build when I start cutting.
Thanks.

[dsraven]

glad you have made your decision. like snickers says, your truck, your decisin, just make it safe, which it sounds like you plan to do.
if fishplating and frame grafting is new to you or anyone lurking, google the topic as there are many ways to do the same thing but some provide a stronger seam and less apt to crack depending on how the fishplate is made and welded in. you could also drop by a heavy truck frame shop and see how they shorten or lengthen van body trucks and do their fish plating as those units are all over the place and you don't see them cracked in half, lol.
I recommend a digital level, even a digital torpedo level set on top of a longer level if needed, as they are going to be more accurate than the old eyeball from different angles against a bubble level. they are pretty cheap and some have a laser built in which can help you line up the front to rear down the middle. what I do is mark each cross member at it's center-side to side- then run the leaser or stringline down the middle to ensure all the parts are lined up before tacking. a plumb bob from the axle center lines with a correspondng mark on the floor and then cross measure is also a good idea. you probably have it figured out though, it sounds like it isn't your first rodeo.
hopefully you will post up some pics as you go, it will be interesting to see how it fits up and how the ride height will turn out.

[mr48chev]

The frame splice will work fine if it is done right and reinforced right. You will have to deal with having things square and on the same plane so it works and drives right but it can be done.

The problem for me is when someone starts throwing out different Things that may or may not work and make it sound like he was listening to the local spit and whittle club members or the face book experts who have never built a truck or car in their live but think they know a lot because they know someone who did one once.

[jmlloar]

Got another question going on the same topic.

Friend of mine has an 81 up suburban frame that might just fit the bill. Specs show it shorter than the pickup, so that helps.
My question is does anyone have an idea how much difference is in the middle compared to the pickup frame? Outside of wheelbase. I dont have access to it for awhile and trying to get an idea of what it looks like compared to the pickup.

[dsraven]

try the gmupfitter site to see if they go back that far for frame drawings and dimensions in their body builder area.

[jmlloar]

searching all morning
very little info

[dsraven]

have you looked here?
https://www.gmupfitter.com/wp-conten...uckUtility.pdf

sometimes I catch myself spending a whole lot of time researching something and then a little voice way in the back of my brain says "you could be doing something constructive with what you have". then I go work on something I have control over. lol.
moral: don't sweat what you can't control.

[jmlloar]

thats for 03.
I need 73 to 91

[mr48chev]

73/91 have a quite a bit wider tread width than the later trucks that Square body guys knocked as being "little trucks" when they came out in 1988 and burbs in 03.

You are looking at a 129-1/2 inch wheelbase. That means shortening the frame if you have a short box.

Tread width is the real issue. While it can work you can't really run a reverse offset wheel without it looking like a goat roper's 4x4 come to town.

Truth is there are just far better ways too do things than swap frames unless you don't have and original frame to start with.

[MARTINSR]

And if you are doing a sub frame mod to your stock frame.....little tip:


Remove the shocks on the sub frame, put a piece of "all thread" through there and tighten it up lowing the frame down to the expected right height. You can get this realistically by measuring the lower control arm to the frame on a stock car you got the sub frame off of.

Measure off all you can to have the correct wheel base. Tack the sub frame onto your frame then INSTALL THE FRONT SHEETMETAL! Yes, install the front sheetmetal so you can see the wheel in the wheel well to be sure you have made your measurements right!

DO NOT trust the measurement with the frame up high without any weight on it. The geometry of the suspension can make odd things happen like moving the wheel forward or back with the arch of the control arms.

Just a quarter inch off can make a hell of a difference! I have seen it, I have seen STUPID looking wheel wells with the wheel too far back and it stand out!

Just thought I would throw that out there. It's what I did so this mistake wouldn't happen.


Brian