Crossmember Drop Help

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SteveAle

SteveAle

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I am installing a A518 transmission in my 70 Duster. I would like to know about how much drop I should use on the transmission crossmember. Most universal kits come 0-3-6 inches. I am thinking prob around 3, but wanted to see if anyone has already done the math. :cheers:
 
I thought most modified the floor pan and the cross member has an extension to the rear for the extra planet section. I am curious about what else is posted on this subject as I plan on an A-518 behind my first gen Hemi in an E body. Any drop will have negative effects on shaft angle and ground clearance.
 
I should have added more information. I wont be using the factory crossmember. I have aftermarket front suspsension and plan on getting rid of the torsion bar mount completely. I have connected the rails already and see no need to keep the torsion mounts.
 
Sorry don't understand the question. Drop "from what?"

As others have said, you are going to have to hack up the original crossmember AND the floor to get that monster 518 up in there.
 
SteveAle said:
I should have added more information. I wont be using the factory crossmember. I have aftermarket front suspsension and plan on getting rid of the torsion bar mount completely. I have connected the rails already and see no need to keep the torsion mounts.
Click to expand...

Be careful. That Torsion bar crossmember does a lot more than just hold the torsion bars. Its structural support for the middle of the car, and strengthens the firewall, dash and door pillar/windshield section of the car. I welded mine completely to the floor, have factory torque boxes front and rear and installed the complete US Cartool chassis stiffening kit in the car including subframe connectors. Are you going to run a full cage?

The 518 is basically an inefficient design with the overdrive added onto the back of a 727. It takes a lot more power to spin than several of the alternatives. If you are going to do a lot of highway miles, a lock-up torque converter is nice too.

I love the built 200R4 and 3000 stall Torque converter with lock-up in my '68 Barracuda. It's almost like having a 5 speed automatic, and I only had to notch the driver's side of the crossmember to fit it in the car. The floor remains untouched. These transmissions can be built to handle 1000+ hp. The engine and trans sit at a zero degree angle. I didn't have to change my pinion angle to get the rear-end at a 2 degree nose down angle in relationship to it either. Just saying.

For those who trip on parts brands, I did paint the transmission black and drew a Mopar Pentstar on it. I draw the line at engines and rearends, as Mopar makes the best, but you can't see the transmission anyway. It it sure works great with my injected Mopar Magnum stoker and 3.91 rearend combo.
 
Cant really give you any kind of answer in this situation. The only way to tell what you need is to install the motor/trans at the proper angle and measure it.
 
SteveAle said:
I am installing a A518 transmission in my 70 Duster. I would like to know about how much drop I should use on the transmission crossmember. Most universal kits come 0-3-6 inches. I am thinking prob around 3, but wanted to see if anyone has already done the math. :cheers:
Click to expand...

I think I know what you are saying now. I've seen those kits where they sell you a crossmember that lowers the transmission mount way down so you don't have to cut out the tunnel portion of the crossmember. They require you to tilt the engine/transmission WAY down in order to clear the existing torsion bar structure. You would want the "0" inch drop, mount, since you are going to remove it.

If you opt for the 3 or 6 inch drop, you will likely have to reposition your spring perches unless you are adding a four-link or something like that.
 
jbc426 said:
I think I know what you are saying now. I've seen those kits where they sell you a crossmember that lowers the transmission mount way down so you don't have to cut out the tunnel portion of the crossmember. They require you to tilt the engine/transmission WAY down in order to clear the existing torsion bar structure. You would want the "0" inch drop, mount, since you are going to remove it.

If you opt for the 3 or 6 inch drop, you will likely have to reposition your spring perches unless you are adding a four-link or something like that.
Click to expand...

I can't imagine this with a "stock stance" car. If you were doing a tube front axle "gasser look" they yeah. That 518 is BIG "back there." I cannot imagine hanging it down from a stock upper crossmember and not having problems
 
As mentioned you do not drop the cross member. If you do that you'll put the driveshaft at a terrible angle and tear U-joints up left and right and most likely damage the trans too and it'll probably vibrate because of the bad angles you created. You HAVE to hack the top side of the torsion mount and raise the A518 to where the engine and trans are level or just slightly above. Your aftermarket front suspension has nothing at all to do with the engine and trans angles
 
So my plans of totally removing the torsion bar crossmember and installing a tubular crossmember connected to both frame rails wont work then?

I assumed that since the tubular coil over front suspension and connected subframes would be rigid enough to just install a crossmember between the frame rails like any other car would have it done?

I was hoping to clean it up under the car, since my subframes are connected in 1 piece it would look alot cleaner to remove the mounts and just install a crossmember like the ones pictured below
 

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If you don't put the engine back to factory position/angle
headers will hit the steering linkage, plus headers will drag the ground

I choose to split the torsion bar cross member in the middle,
section the sides , so i could widen and raise the TB crossmember
Then I bent 2 1" tubing to reinforce the sectioned area
was even able to use the original bolt holes to install the trans cross member

maybe these pics will help make sense.. lol


002-5_zps52f2bdc7.jpg




yuoo_zps46cc82a2.jpg



floor is raised 4"
025_zps71b26119.jpg


this crossmember (68 "b" body) does set lower, but no lower than the oil and trans pan
I could have made a custom cross member,so, that it wasn't lower but just used what I had laying around (quicker)
eng is set at 3*down(toward rear end)
012_zps3bec2cb7.jpg


the other 2 u bend pieces are connected under the floor to cross members that serve as drive shaft safety loops and stiffen the frame connectors

034_zps8c61b6fa.jpg
 
Hate to ruin your safety thought.... Break a shaft going thru the traps and it'll rip right thru that, and you.

It's why nhra made certain classes use scatter tubes, as they witnessed a car cut in half and it cut thru a cage and the left side of the driver and helmet. Safety loops are so they can PUSH the car off the track and the shaft not interfere with that.

A 30 lbs shaft at 5000+ rpm is equivalent to a shredding plant

Loops don't serve a safety issue when they break at speed, or when broken from over speed.
.
 
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