howdy
Ijust put a 454 in my 67 conv. My wife tried to order me subframe connectors (bolt in) from Jegs they told her that they wont work with a conv.? Has any one done this I didnt realize there was a difference in subframe or floor pan from hard top to conv.
any help would be appreciated. Also this car is a 4 speed and the bell crank bar that the rod that goes to the clutch fork hooks to is to close to the hole the oil pressure gauge goes to .this is a 1976 truck block and this is the only oil pressure out let I can hook to I have "over come the problem but still would like to know if that is what the difference is in a bbc bellcrank and sbc.

The BB clutch z bar is different and will give you more space for the oil pressure sending unit. I had the same problem with my bb when it had a small block Z bar and frame mounts installed. Get the BB z bar and you should be fine. Hopefully, you have the BB frame mounts installed. You may still have to run a 45 or 90 deg elbow at the block to have clearance with an electronic sending unit.

Kent Wissman
67 SS 427

The convertibles have extra bracing welded to the floor pans. To put frame connectors on you will have to cut the braces where the connectors will be. You can then fit them tight up against the floor and just weld the braces to the frame connectors where you cut them.

My subframe connectors were cut in the middle to get over the extra bracing in the floor pan. The connectors still fit tight and the floor is not cut up. I noticed a big difference in body twist (lack of) after they were installed.
Rick

Your WIFE was going to order you subframe connectors! WOW, she's a keeper.

Just what is the difference between big block bell-cranks and smallblock ones? I had a 409 in my car back in '69 or '70 and everything bolted up fine if I recall when I used the small block one. I'm not too sure that I didn't add 1/2" nuts as spacers at the frame where the frame bracket for the bell-crank bolted to the frame. I do remember "standing on my head" fastening the hardware to the frame.

Is the distance from the block end to the clutch throw arm shorter on a big block one or what? pdq67

Rickmac, can you explain in a little more detail how you put these in. I also want to install these, but do not want to cut up my floor. What kind did you use and how did you cut them. Did you weld them back together with a modification of some sort.

to pdq67 what I have found out is that the sb zbar bends to the front of the engine more then the bb does what I did so as not to spend about $70 was to lengthen the rod from the pedal 1.25" then done by the oil hole I just ground it out about 1/8" this gave all the clearance I needed You put a 409 in a f body Bitchn

Bruce,

You would be supprised how a 11.5:1 C.R. .060 over 409 with a three-two manifold modified to take three big 2GC carbs. off a 348 will run if you put the old NASCAR solid cam in it. Boy, this again brings back the memories. pdq67

I actually bought the subframe connectors used from a guy that had them on his 69 convertible. The previous owner had used some bolt on subframe connectors that look like the Competition Engineering "Bolt-on" style in the Summit catalog. He cut out about 5-6" from the top side of the connector to fit over the floor brace. The previous owner had welded them to the bottom of the floor brace. I just bolted them into my subframe though without welding them. The cuts go down about 3/4", just enough to clear the floor brace. So, the cut is about 3/4" deep and about 5-6" long. Works great.
Rick

I am gussing on the dimension above, its been a while since I really studied them.

RICKMACK, Wouldnt you weaken the subframe connector by cutting it. Ultimately the whole strenght of the piece is alot weaker because similiar to cutting a beam. its only as strong as the thinnest part. Did you pass this by the manufacturer of the subframe connectors? Personally I would try to find an alternative way rather than cutting pieces out of what engineers speced the size of these connectors to be. Just my opinion.

Whenever a structural member is cut on its outermost edges the bending strength of the member is greatly reduced. Bending strength is a function of the shape of the member and distance from the bending axis to the outermost stressed fiber. The more "meat" you have distanced from the bending axis the stronger the member will be. Think of an "I" beam, the bending axis is at the center of the "I" but the bulk of the steel is distanced away from the center. Building codes typically do not allow holes for piping/electrical to be drilled within 2" of the edge of a floor joist and notching is strictly forbidden.

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Carl, you bring up an interesting point, but would it not be better to have a subfame connector which is slightly cut than to not have one at all. I looked and these subframe connecters measure 2"x1.5". Assumeing you cut the 2" by 3/4" you would still have 1.25" of material. Yes this is not as strong and you would have to make sure you do not create any stress concentrations, but it has got to be better than not haveing one. Your thoughts???

Rick,

That's a hard thing to decide without numbers. For both bending and torsion the key factor is the distance from the bending axis the outermost fiber. Both bending and torsional calculations use this distance in a fourth power formula, in^4. Hence, slight changes on the strong axis of a member can have large effects on strength. For circular shafts a doubling of diameter will result in an 8x increase in bending strength. Tubes are a bit more complicated but I hope my explanation helps to make sense of the math.

In your case, assuming the tube is 0.125" wall and another piece was welded in to cover the notch (making it a smaller rectangular tube) the bending strength of the connector has been reduced by at least 68% on the strong axis and the torsional strength reduced by 60%. This does not include factors for stress concentrations (both from notching and the reduction in cross-sectional area) and losses due to welding/patching.

Just as a visual, a std. 2"x6" is 3.9X stronger in bending than a 2"x4" and is only 2" taller.

If the bar were solid there would be a 75% reduction in bending strength.

I wish I could get a look at a convertible x-brace. From the explanations that I've read it seems the problem is that the x-brace is in the way of the connector. Would it be possible to cut the x-brace, install the connector, and weld the x-brace to the sides of the connector?


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Guys,
I'm getting ready to put subframe connectors in my car and if I have to cut them any to clear my floorboards, I am going to "fish plate" both vertical sides and contour the top side to fit the cut section so that everything is still boxed. I don't have access to a welder so I will pay to have it done by a professional welder for strength purposes. pdq67

They probably are weaker than the ones that are not cut. Would welding them to the brace help?