advice on grafting 90 front frame section to a 82?

JeffP1167

JeffP1167

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Dec 21, 2009
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Location
Yucaipa, CA.
While this is a 74 frame its all I could find closeup pictures of. I would like to add a 90 front cradle and frame rails to a 82 frame and retain the composite spring as well.

A few questions I have since I have an idea on making a lugnut mounted jig and center it using the body mounts.

What kind of welder would be good for performing the welding needed?

Would I retain the stock 82 motor mounts?

Would you eliminate the spring pockets and weld in material verses grafting the c4 front frame section? Or would it be best to use the c4 front frame section to eliminate cradle mounting issues?

will the stock 82 motor mounts get in the way of hooking up the steering column to the c4 rack and pimion?

being all weight is off the suspension how do I ensure proper ride height again before welding in the frame section?

Would I use the c4 or 82 motor mounts?

In these pictures where would be the best cut points?

Lets hear your ideas on how to make this look like a nice grafting job as well as making it very strong. I cant afford a pre modified frame nor feel like it would be worth it considering value of car verses money invested and the worst thing that can happen is the frame is ruined.

My idea for a jig is this, buy some old steel 15x7 rims and cut out the centers and then weld square metal tubing to them to get the wheel base correct. then wrap around the front and rear of frame and connect to the bumper horns so that when they need to be welded back on they are in the right position as well. After everything is mounted I can then cut my frame and remove the cut out section from the jig and bolt the c4 suspension to the jig and it should exactly centered as the 82 suspension was and then begin welding it in place. Basically to complete my c4 suspension I just need a 90 batwing and dana36 differential and front composite spring. Aside from that I have everything else.

so let's hear you ideas for better success.

74frame2.jpg

74frame1.jpg
 
This is a 88-96 front frame section. Looks like if the 82 frame is cut right about the engine mount area this section after positioned properly could be grafted there. Then cut the 90 frame rail in front of that cross brace and graft in my front bumper brackets.

Then simply bolt the suspension cradle in place and bolt all the suspension up.

Anyone see problems in doing it like this? I'm sure a competent welder could reiforce the graft area for extra strength.

90framerail2.jpg

90framerail1.jpg

90framerail3.jpg
 
Copy%20of%20VFS-55T-96.JPG


This is a kit we used to put C4 suspension in a 67 Mustang. It uses a rack out of a Fox Mustang and welds to box type rails. Coilovers are required. It is narrower than a stock C4 track and lets you run a more classic wheel.

The problem you may have with welding the C4 cradle to the C3 frame is the resulting ride height.

If you have a complete cradle, remove the shocks and spring. Collapse the shock to ride height, typically 1/3 of total travel, and measure eye to eye. Make and install fixed "shocks" to that dimension (We used angle iron) Lock the spindles straight (more angle iron) and install the wheels and tires you plan to use. You should now have a rolling cradle at ride height. With your C3 frame set where you want it, you should have a pretty good idea of what needs to be done.

I'm sure real engineers are laughing their a$$es off right now, but this is the hotrod way.

Rob
 
MrForce said:
Copy%20of%20VFS-55T-96.JPG


This is a kit we used to put C4 suspension in a 67 Mustang. It uses a rack out of a Fox Mustang and welds to box type rails. Coilovers are required. It is narrower than a stock C4 track and lets you run a more classic wheel.

The problem you may have with welding the C4 cradle to the C3 frame is the resulting ride height.

If you have a complete cradle, remove the shocks and spring. Collapse the shock to ride height, typically 1/3 of total travel, and measure eye to eye. Make and install fixed "shocks" to that dimension (We used angle iron) Lock the spindles straight (more angle iron) and install the wheels and tires you plan to use. You should now have a rolling cradle at ride height. With your C3 frame set where you want it, you should have a pretty good idea of what needs to be done.

I'm sure real engineers are laughing their a$ off right now, but this is the hotrod way.

Rob
Click to expand...

Well, FWIW, I'm a real engineer, and I did it pretty much the way you mentioned (I was a hot rodder before I was an engineer). I welded up a crossmember very similar in appearance to your crossmember (although your welds are prettier than mine :thumbs:).
I made a fixture using 4" channel to set/fasten 4 steel ralley wheels at the correct trackwidth (I retained the stock C3 trackwidth in my conversion) and wheelbase, and fastened (welded) the fixture to the frame with the wheels at the desired ride height. I bolted the suspension to the wheels which then allowed me to measure the dimensions I needed to make the front crossmember (to bolt the suspension A-arms to). I did the same for the rear which showed me where to make the front bracket attachment point for the dogbone trailing links. The stock C4 dogbone bracket bolts to a welded in plate in the space near where the original trailing arms bolted to.

On the front I tried to retain as much of the original frame as possible (only cutting away as much as needed) but eventually I ended up removing all of the front spring pockets as they were in the way of the new crossmember. I welded in a new straight frame section to bolt* the crossmember to, and duplicated the shape of the front frame horns that the radiator and bumper brackets bolt to.

* I bolted the crossmember and upper A-arm brackets to the frame so that they would be easily removable in case I screwed up the wheelbase/trackwidth or wanted to change the suspension anti-dive geometry.

I had a custom rack made to be compatible with the narrowed trackwidth. I also put coilovers on after spending a day narrowing a front spring to fit, and deciding I did not want to go through that same headache every time I wanted to change the front spring rate.

I ended up using a modified '93 Firebird tubular sway bar to fit the new suspension.

That's the major high points.
 
I'm planning on using 17x9.5 rims with 90'ish offsets so I can run J55 vette brakes that I have. One thing I would like to do though is figure out a way to mount my 82 dana44 to a C4 batwing so I don't have to worry about fabricating a front differential mount if possible.

I'm going to basically part out my 90 project vette and use the complete L98 and automatic in the vette. This will give me every possible part for the conversion. I also have the larger fe-7 32mm & 26mm sway bars for this conversion and Z51 2 1/4 lock to lock rack and pinion.
 
JeffP1167 said:
I'm planning on using 17x9.5 rims with 90'ish offsets so I can run J55 vette brakes that I have. One thing I would like to do though is figure out a way to mount my 82 dana44 to a C4 batwing so I don't have to worry about fabricating a front differential mount if possible.

I'm going to basically part out my 90 project vette and use the complete L98 and automatic in the vette. This will give me every possible part for the conversion. I also have the larger fe-7 32mm & 26mm sway bars for this conversion and Z51 2 1/4 lock to lock rack and pinion.
Click to expand...

I'm playing around with a somewhat similar combination. I currently have an adapter bracket on my C3 D44 batwing in the '69 to mount the rear toe bracket, but I'm looking at trying to use a lighter C4 D36 batwing in place of the C3 batwing. Once I get the bolt spacings and shape finalized with the plywood model I'm planning on making a copy in aluminum plate.

IM001780.jpg
 
Ok, I did some pretty close measurements

1990

tire height 275/40/17 25"
track width front 5'8 3/4
rear track width 5'9"
wheelbase 7'11 3/4

1982
tire height 255/60/15 25 1/2"
edge of fender lips front and rear was about 5'9"
wheelbase about 8'2"

So near as I can tell the 90 suspension should fit in the wheel wells without any modifications. with a 1/2" aspect difference between the two tires the 17" wheels should look perfect in the wheel wells. If there is any fitment issues could probably fix with spacers or a different offset rim.

I am thinking about using Z06 or ZR1 style rims. But will look around at what would look good on the car.
 
I saw this C4 rear cradle kit on a website and wondered what you all think of trying one of these in my 82 frame to kinda simplify the irs install.

c4cradle.jpg
 
I saw this what looks like a 3 gen f-body that a guy is putting a c4 irs in. Think mine will be much less hassle then what this person went through. I guess I have to read up on pinion angle and what not. I thought about using the c4 "c" beam but figure a universal pinion mount might be my best choice. I just don't want to deal with any floor clearance issues.

After the swap is complete all the original 82 suspension and steering parts will be for sale. All are still in very nice condition and I believe the differential is a 2.87:1 ... will also be selling the engine and transmission from this 82 as well.

c4install.jpg
 
That camaro is 1MeanZ's car over on thirdgen.org. He's also on frrax.org do a search there, pics are there. If you look up one of my old threads about the 82, I have a C4 dana 44 in there. Maybe use some ideas for mounting and pinion bracket.

Stay away from the flux welders. maybe score a used gas setup???
 
This is a picture I found again after Marck sent it to me. This is about what I have in mind for my car.

c4frontgraft.jpg
 
This garage jig kinda gave me a few ideas. Buy rolling my assemble 82 frame on it I could connect it to the rear bumper mounts and then to that front bumper frame extension piece. The after the C3 wheel base is established unbolt all it's suspension and bolt the c4 stuff in place and this should make a perfect wheel base. Then use the body mounts like this guy did to keep the frame rails aligned since they are bound to flex after the engine cradle area is cut out.

I'm not to impressed with how he center the hub surfaces and I feel a cut out of a steel rim would center better then just drilled holes in a piece of metal since the rim holes are tapered for the lugnuts and would provide a more precise centering method.

I'm curious though how ride height is re-established correctly or is unsprung ride height used or compressed ride height. Also how to compensate for difference in rotor surface to rotor surface width differences from c3 to c4 or is the rim offset where the difference is and they are actually the same or close to it?

As you all know I plan on using as much of the c4 frame rails as possible so I can use the c4 cooling capsule verses the 82 radiator support set up. So after grafting the whole c4 front section in Use the the jig to shorten the front tubular bumper support to allow the c4 cooling capsule room to fit and also fab new fender hood latch supports.

Since I don't have a real welder I plan on tacking everything good and then take the frame to a certified structural welder and have them really get everything welded up. I feel a jig like this to be capable of preventing heat distortion of the frame if it is strong enough and will also look into welding all areas of my frame.

Obviously my frame would not have the complexed bends as this frame has. But would like to go for a job that is clean and hard to tell it is a graft.

jig8.jpg

jig1.jpg

jig3.jpg
 
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I talked to one of my companies mobile trailer repair guys and he says he has a uncle who does mobile welding, so think is what I will do is just get everything aligned and tack it and then have him go over everything so my frame is very strong.

Basically after the car is back together since this one has been non op'ed for many years just quik register and take a trip to a referee for certification and then a quik smog test and start using it again.
 
I got these specification differences between a 82 and 90. How will the 1" track difference front and rear affect how the tires fit in the wheel wells?

1990
Wheelbase, inches 96.2
Length, inches 176.5
Width, inches 71.0
Track, inches front: 59.6 rear: 60.4
Curb weight, pounds 3,223

1982
Wheelbase, inches 98.0
Length, inches 185.3
Width, inches 69.0
Track, inches front: 58.7 rear: 59.4
Curb weight, pounds 3,345
 
I left factory motor mounts since C4 mounts are in wrong spot. I used a jig.
Worked great, car handles unreal. I did front and rear.
 
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