drcook

If I can get to the point of buying another one (after the 1991 big block K2500 4x4 is finished and sold) I will most likely get a M6 89-91.

Tom400CFI

You were originally right; the frame "rail" does run from front bumper to the rear wall (b-pillar) but it's not one piece; it's make up of something like 10 pieces....all spot welded together. The rear rails are made of two pieces, spot welded together. The C5 & C6 use a single piece of tube steel, pressed into shape and cross section, that runs from the front of the car, to the rear of the car. Better. Stiffer.
Anyway, the door post does indeed, "straddle" the frame rail.



I don't think the sections bend much. IOW, the rocker rail, from the door post to the rear wall...I think is stiff. *I* think all the deflection is in the welded seams/joints. I think I have devised a way to confirm that. Stay tuned.

I haven't tried the other side, but I can, easily enough. I'd bet it's the same, but I'll check. I have only found a couple broken spot welds and they were on the mounting ears for the right bat wing mount. K-bars are tight....And I even added some missing bolts; where the square tube braces run from the hood latches to the forward frame rail? You can see them in this pic:


See where there are two bolts that run down through the flange (at the bottom of the brace) into the frame? The flange though, wraps down around the in inside of the frame rail. On that inner part of the flange, there is a slotted hole, and the frame rails both had a corresponding threaded hole...but no 3rd bolt on either side. (?) Paint had no marks like the bolts had ever been there, either. I added those bolts and tightened everything.



The wonder bar came on all C4's...it got bigger/thicker in the later car.

Who thinks the LT1 is better? No changes in frame, late L98 - any LT1.

GREGGPENN

OK...OK....the LT1 is better. OTOH, my choice back in 1999 was an 89 and a 93. If I'd bought the 93, I may not have pulled the motor and built a stroker. I may not have ended up with a car that's as fun (or more fun?) than a "Z". L98's = more dissatisfaction with top-end performance = more likelihood of modification = home-made Z. It's a toss-up! LOL

You didn't mention the K-brace....Absent or bigger in later years. (I actually think that brace would be more beneficial/significant than the wonder bar...but then again one of the original design team "wondered" what good it served!

I guess they didn't have the technology to manufacture/bend the complex shape of our side rails back in the 80's? So, it had to be made is pieces/sections?

Most importantly, the article (above) said the frame was designed for a 20yr life span. Does that mean my frame is out-of-warranty?

Tom400CFI

No, no.... I said that there is no difference in later L98 frames, and any LT1 frames. From '88 on.....the frames are all the same. No change. The LT1 frame is no better than an '88 L98 frame.

The size of the K brace was increased in later cars. It was there in early cars, but the cross section was increased for all '88^ cars and some early Z51 and convertible cars.

I guess either the technology for one piece frame rails was either non existent, or not cost effective. Or maybe it was simply too much new tech to integrate into an already very new and complex car (like the tq tube that showed up later in the C5). The technology, used first on the C5, and then on truck frames was "hydroformed" frame rails and as I understand it, the key feature of this method in the C5 was that the entire rail started as a single, seamless piece of tube steel, pressed into a single, seamless square tube with all the right bends in it to fit the car. WAY different than all those gaps and janky welds you see to make up the rail in the C4. Whatever the reason it wasn't used, Hydroformed frame rails isn't mentioned in Corvette from the Inside until late in the book when discussing the "new C5" as it related to Dave.

Here are some C5/6 frame rails, right out of the hydro forming process. Seamless....one piece...



Here is a drawing, showing the number pf pieces used to make the C4 Frame rail....6 pieces, and that doesn't include the "rear wall" that connects the rear rails to the rocker rails...




Now compare the final results:

Tom400CFI

Interestingly, when searching for those pics, I found THIS article. Scroll just under 1/2 way down and they cite the source of the issue:

"The C4's two side framerails consisted of three pieces that were welded together to form one beam; engineers discovered that these welds were the source of the flexing.
The C5 design team found a clever solution to this problem: It made the new frame out of a 14-foot-long, 3mm-thick steel tube. The tube was closed off at each end and filled with high-pressure water. The water bent the steel into the correct shape without welding. This new process was named hydroforming and was introduced in 1997. Frame strength proved so high that when the convertible was introduced in 1998, it didn't require any extra bracing."


Accurate info? Who knows. It's SuperChevy.

drcook

We all have to keep in mind the lead times required to get a car into production -vs- the technology of the day. In order to hit the showroom floor, knowing how long it takes to make tooling, I am sure we would lift an eyebrow as to when they first released the orders to start building the tooling, both internal and external to GM. The technology reflects what was current then, ie: stampings and spot welds, and even those had to be tweaked.

Add to that GM's notorious lack of adequate real world testing, and you end up with a car that creaks and moans. Our cars are good cars, with the C5 frame, they would have been great cars.

You might disagree with me on the statement of lack of real world testing, but GM is GM. I have another one sitting out in the drive way that I had to fix. The 04.5 LLY diesel was a notorious overheater. I installed an extra radiator down behind the bumper (the design was worked out by some bright folks that experienced the troubles early on) along with a bunch of other changes. If my life had been different at the time, I would have jumped on the lawsuit train and forced a buyback but we had other issues in our lives going on. However, it is now fixed.

Tom400CFI

That is a PITA. Our CST-V has had numerous issues where I or someone else (other than GM) had to engineer a proper solution. Lame....BUT you can at least be glad your LLY isn't an '03 -'10 PowerJoke.

drcook

One of the changes was to install a larger transmission cooler. I don't know how to weld, but I can fabricate bolt together stuff pretty good. This is what I did.

If I keep the car an auto, I will fab up a mount for a fan cooled cooler and put it back where the spare tire sits, after I build a spare tire delete. A while ago I found one for sale on eBay and grabbed the pictures of it for reference. A fan cooled oil cooler will fit back there also.

The original trans cooler was half this size. The 2006's have this much area, just twice as wide and half as tall.

The A-brace was already there. I built cross braces and connectors. Actually this flexing a little is good (not being welded).

GREGGPENN

You might not have followed my joke -- comparing the L98/LT1 powertrains. Had nothing to do with framing at that point!

So...both braces existed all along. They both got PERMANENTLY bigger in 88 -- using specs from prior Z handling packages.

I thought the article posted on the prior page stated the C-beam was chosen over the torque tube to provide better access to the drive shaft.

Something in that page 11 article made me think the side-beam-to-Apillar was the major source of flexibility. I skimmed it again and didn't see it -- other than lots of effort with dash/front-end bracing.



Also....In the 3 pics you posted above, are you sure pic #2 isn't a C5? Or...maybe you weren't making it clear where technology landed after hydroforming?

I saw the last picture in my searches too. It links to restoration details about a ZR1 prototype. I almost posted that same picture because I couldn't find the raw frame pics on my PC. When you look at the right frame (of the 2 frames in your last pic), you can see how the firewall and "bucket" behind the seats SHOULD provide LOTS of resistance to trapezoidal distortion.

Any chance you plan to post a vid SHOWING the flex [point] you're talking about? Because their was quite a bit of discussion [page 11 article] about the need to improve welding for High Strength Steel, it might explain the weakness of that joint. The picture below shows only two sections built with HSLA (steel). Lamm's book (page 11) talks about the need to weld HSLA -- to itself -- but the pic below doesn't indicate that issue where it joins to the side rails. But, that doesn't mean that weld isn't a bit weaker?


It would appear HSLA was use to fortify front crashes and roll-overs.

Dr. Cook: I assume your improved cooler doesn't impede with air flow over the radiator? Nice work!

bill mcdonald

I have read all the same stuff about the braces for the Z51 as well. I always wondered why my car had them, and was non Z51. Clears that up.

The stuff you posted about the C5 frame is all the stuff I have read as well. Also the balsa wood sandwich floorboard

There is also a plate under the car, below the trans tunnel. It has like 100 bolts holding it in and attaches the left and right side together. Some after market people made one that was thicker. Suppose to help.




Also, on my 01, the trans tunnels is steel and solid, front to rear.

Lots of changes happened between the 4 and 5.

drcook

THese types of discussions send me off looking to research and understand. Hydroforming has been around for quite a while.

https://en.wikipedia.org/wiki/Hydroforming

Sometime in the last year and half there was a thread on here about a build of a race car. The folks showed pictures where they had to go in and do rust repair of the frame. I would like to see some more of what was done to that car frame wise (if any) while the repair welding was going on.

While looking through old postings, I found this:

https://www.corvetteforum.com/forums...nterested.html

Seems like it petered out and went nowhere.

Tom400CFI

That's my understanding, from what I've read.





It was. I'll post an excerpt from "Corvette from the Inside" that explains the reasoning:






....with more time, the could have made the tq tube work. And with more time, they did -in the C5.




In post #224, pic #2 is a drawing, showing all (many, not all) the individual stampings required to make the C4 frame rails. Pic #3 is a C6 which is the same as a C5 and the purpose was to show the seamless nature of the frame rail as compared to the tacked-together-pieces of the C4's frame. Which you can see in pic #4.





I do plan on making a vid of any isolating of flex points that I can identify.




.

Fastnail

Dave,

I have a spare delete and if you need any other pics, dimensions or measurements, let me know. It is currently in my 96, but I'm going to put it in the 88 track car. Let me know if you need any pics of it in the car.

Cheers,

Mark

JoBy

Both were there from the beginning. I have an early 1984, serial no 903 of 51547 built, probably in the second or third week of production.

Tom400CFI

Great pic....all the parts are there, except for the inner rail gussets.

Here is that pic of the "late" frame upgrades again for a side by side comparison;

v8vette84

I checked out his site and it looks like he was designing a brace that used the mounting points of an X-brace while attempting to utilize a part of the C5's tunnel design by tying both sides together using 3 bent braces. Designed to go up and over the driveshaft or under the exhaust based on the bends. Too bad he hasn't been active in years and his site is outdated too. Looks like attempts to contact him have bee unsuccessful as well.

http://www.riceperformanceproducts.c...ame_brace.html

dclafleur

The angle on this doesn't show how much bigger those angle braces that go into the k-member are. I first noticed it working on a friends 89 and they looked completely different from the ones on my 85. They're about two inches tall vs 1 inch on the earlier cars. I've thought about retro-fitting one from the later cars but it's oddly hard to search for (what do you call it?).

Tom400CFI

The photo is definitely not taken from an ideal angle....that's for sure. But you can tell if you look at Jonas' and then look at the late frame. Look at the flanges.

I wonder if, since going from ~1" channel to ~2" channel w/a much larger flange netted a gain, would boxing those help even more?

GREGGPENN

Assuming early owners aren't happy with frame stability: I'd be really, really inclined to find/install/make and x-brace [for early cars with the smaller K-brace and wonderbar]. An x-brace would definitely address strength in frame squareness -- like the K-brace. If you want to strengthen what the wonderbar accomplishes consider a camber brace.

This post also assumes retrofitting the later gussets/K-bars is more difficult than above.

drcook

That would be great. Now that my shoulder has healed up I am finally back up to working on the car.

I know of a source where some of those braces could be acquired. I pointed this thread out to him. If anyone is truly interested, send me a PM and I will give you his website. He is not a sponsored vendor here, so he has to be careful about trying to sell too much here on the forum.