When I first built my truck (78 K20 all 1 ton gear) 6 years ago I striped it down & blasted the frame and did over every body panel as nessecary to have a rig with no fill. In the years since the truck has received a few minor dents (rocks & trees) and I have just left them. I'd rather the truck had alittle charector then bondo falling off the side. One of the little things that has annoyed me is the dimples in the box over both rear wheel wells where the truck has been flexed too much. Like the dents I have just left those figureing that if I pull them they will just return the next time I get her twisted up, and there's always a next time.

Now in the middle of my winter upgrading blitz I have pulled off the skid plates to steam off any mud sticks or crap that have accumulated up in the chassis and discovered that the dimples in the box are not the only damage caused by this twisting. The crossmember thats over the front spring hangers for my rear axle has snapped in 2 and the the passeger side frame rail is beginning to crack.

I'm considering replacing the factory crossmember with rectangular box tubing. This should be much stronger and would also give me a good mounting point for my anti-spring wrap bars I plan on installing. I'm concerned that there may be bad sideaffects to stiffining up this one section of frame though.

Has anyone else had this proplem, and has anyone found a good solution ??? Should I use tube or a factory replacement. If iI use tube is there other crossmembers I should replace too. I'v heard the one under the motor can be bad too.

I kinda got lost reading your question - but I myself have a lot of frame flex. I check my truck after each ride and tighten up all the bolts ( t-case mount like to work loose) and I have found some stress cracks ( not in the frame, but to the new motor mount cross member and winch plate I used to box in the front)....I simply welded these up and have not worried about it.

I am in the process of putting a exo cage on my truck - this is the best option I would give you to stop frame flex........But actually I would not worry about it to much.

be careful if you weld your frame right there around the spring hanging points. A welded spot won't be as ductile as the factory frame. If you continue flexing it out, a potential for trouble. If you don't really care a lot about the rig, weld it and keep a close eye on it after every trip.

I agree with JIM. A full exo cage stoped it for me. A good inner cage tied into the front and rear will be just as good.

Sorry the question was so long winded Jim, I get lost some times myself. I'v never had any problem with the crossmembers "loosing up", but when I first built the truck I cut out all the factory rivets and reassembled the frame, crossmembers & and mounts with Grade 8 hardware and locking nuts. I once broke the mount on the adapter between the SM465 & the NP205, but this is the first time I'v snapped a crossmember.
Exo cage is probly not an option for my truck but a good inner cage is a great idea I had'nt considered.

Blacksheep, I understand what your saying about the welded section being brittler. I do care about the truck even though I use it hard. I had considered putting a plate on the inside of the framerail over the spring hangers (like the one most of us put on where the steering box bolts on). But I can only do that if I swap out the crossmember for box tubing. But I'm curious what the negative affects of stiffing just 1 section of frame will be.

http://www.whiteknight.ca/jim2.jpg

I used to have a lot of frame flex - But I have added additional crossmembers and am currently building exo cage

This is a good thread!
A also am having major frame twist problems, so bad that I have to readjust my door after a wheelin trip just to open them. I also have lost 4 tranny x-member bolts in the last 3 mo. and snapped 2 body mount bolts.
As you can tell it has become a big problem to me. I think to box the frame and tie the cage to it would almost eliminate any more twist.
:D

im curuois about what to rplace this x-member with myself.. the one on my shortbed has some rot, the frame itself is nice, just part of the crossmember is rusted aout badly... i was plannin on just cuttin another one form a frame i have, but id rather do the tube method myself

I've run the same frame for the past 16yrs('75 Subruban) and have always considered the flex to be a good thing. With a flexy frame and a long wheel base you can get quite a bit of articulation without having a lot of suspension travel. The down side is that it tends to break things. Things have changed a bit since I built my buggy and I'm in the process of rounding things up to put a new rig together and I will make the frame more rigid and add a lot of suspension travel so that I will end up with more articulation and should end up with less breakage since you have controlled movement with the suspension and not much control over the movement of the frame. The "C" channel frame needs some serious mods to control the flex. Boxing the frame is good but a lot of work. Cage with lots of bracing will help. My frame is a Suburban but I would have destroyed a Suburban body a long time ago. This is what the body looks like now.
http://www.montypics.com/pic.php?url=/speedo/2003-10-28/1067367897_2001_Hunting_trip_096.jpg

It is on a trail even if it doesn't look like much of a trail, its more than a hundred miles from the highway and very few people ever
get to see this place.

Gus

I had a 78 1 ton that did the exact same thing as yours, Smash-K20, and I did what you are thinking about doing and caused both sides to crack. I used 2 pieces of 2" x 1", one verticle and one horizontal welded to 1/4" plate that was cut to fit the frame. I used the 4 gearbox bolts plus 2 more towards the rear and used five bolts on the other side, 2 at the front and rear, and 1 in the middle to bolt it in. it still flexed great but i think the extra rigidness in that area put my frame through hell.

Well after doing alot of checking around the general idea i get is this.

1- If I just repair the factory frame and crossmember the problem will come back.

2- If I just replace the one crossmember and stiffin one peice of frame it will snap elsewhere.

3- I could fab new crossmembers and replace them all, plus add a couple and keep the 26 year old factory frame rails. But to me this is like alot of foreplay without getting laid, I will do alot of work and in the end I'll lend up with something thats hard but not really usefull.

So I have decided I will patch up the factory stuff to last for now and begin making myself a full tube steel frame with an inner cage. In the process I'll convert her from LWB to SWB. I figure this will take close to a year considering I just spent most of my upgradeing allowance building a new 454 that I'm installing. The wife will have a bird if I come home and tell her " Honey, I just ordered $1500 of steel tubing" .

Thanks for all the input guys, now does anyone have any advice on making a tube frame from scratch?

I have had the same problems.
Currently, I am building a new truck and I don't want to
have these problems again. I'm not confident enough to build
my own tube chassis, so I decided to start with a stronger
frame to begin with. I am using a stripped down, shortened
C-60 frame. (from a med duty straight truck)
It has 10" C-channel straight rails that are 1/4" thick
It can't weigh more than a 1-ton frame that has
been boxed in and cross supported, But I bet it's stronger.
I know this isn't the answer for everyone, But I think it's
an excellent solution for my problem & it only cost me $200.
If anyone is interrested I could post photo's.....

Originally posted by SOFA-KING BIG
If anyone is interrested I could post photo's.....


I'd be interested in seeing just how big that looks? Sounds like an interesting project...

I'd love to see some photos of that as your doing it. Will you be using factory cab mounts and exc... or will you be custom making this stuff? If your going to adapt the factory mounts and brackets I'd like to see how you do it.

Here are some quick pictures.
Sorry they are not the best, I'm using the frame as
a tool & junk table for assembling the rims and tires right now.
Oh ya & I know my camera is a POS....

I've got the springs bolted in place using all OE stuff.
Most is from the C60, some from a 1 ton chassis.
The rear of the rear spring hanger originally was the front
of the rear springs when it was a C-60.
That's how much I cut off, 6'-7 Ft. of frame rails off the back.

a little blurry.... But for now, you get the idea.
Check out the drop hanger I fab'ed up.
Rear of the rear spring.

That's the front of rear spring
It's from a 1 ton chassis...
I also changed all the original 7/16" to 5/8" Grd*8 bolts.

Thats a nice Job Sofa, it's similar to how i began my truck except my main rails where just 6 inch c channel and I replaced the factory rivets with 1/2 grade 8 hardware as a opposed to your 10 inch rails and 5/8 hardware. That crossmember that you can see in your first picture is Identical to the crossmember that snapped in 2 on my rig. You might want to think about beefing them up.

Oh a little note, when I did mine i rented a magnetic base drill press from a local rental company. It made drilling frame rails soooo much easier. Now is a great time to drill mounting holes for skid plates on the bottom of your C channel if you don't already have them too.

I can't wait to see when you get the body mounted. Any idea how your going to attach the bodymounts to the straight frame when they are all ment to be at differing heights on the factory frame? You must have a factory frame there to measure for comparison.

Here is the front half....
I used C-60 mounts for the front & rear hangers
A Nice chance to use some OE drop brackets...
Those are my tires laying next to the frame...
And It looks about a 85* approach angle.

Here is the front end of the frame...

As for a body I've got a complete '92 S10 4-dr blazer.
Most of it's body mounts are at the same height.
I plan on using mostly OE cab mounts, from the C-60,& S-10
And I also got some more from The junkyard.
After I finished the frame to a rolling chassis I was going to
mock-up the body to the frame then Fab all the mounts in place.
But I want to do all the work on the frame & the mechanicals
without the body in place. So that will be almost last....

What are you guy's opinions on a 10" channel?
Do you agree the 10" is more rigid than the 6" stock?

Any helpful ideas are appreciated!


:beer: :beer:

it is still just a ladder frame
if you can get a roll cage that ties into the spring mounts it will add a vertical component to combat twisting

Thank You M.J. for your constructive feedback.:beer:

I planned on building a rollcage, I will remember to tie it into
the spring mounts.

Does anyone else have any good ideas or feedback?