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11 Posts
Discussion Starter #1
I am finally getting off my tail and been working on my project. Second generation Camaro. Sure you will see me asking a few questions from time to time. My question is should I bend it for drive shaft clearance or can it be a straight piece? My initial thought says straight...but watching these radial cars hike up in the rear now has me thinking. The bottom of the entire chassis will be pretty much at the bottom of the pinch welds of the body. 4 link..rear. Seems if I bend it it will wind up being really close to the ground. Want the finish product to be as low as I can get. These body styles not really meant to be slammed because of the curves of the rear fender...but I have tires and wheels mocked up under it and it will be pretty low. Thanks fellas

67,719 Posts
Is the rear crossmember you want to install, rectangular or round tubing? You will have more driveshaft clearance if you were to go with round tubing.

If you have the ride height of the car "pretty low" as you say --- tough to quantify without pictures --- the driveshaft will actually be higher at the rear section of the tunnel.

839 Posts
If you are talking a rather low car, it would seem you are going to need to be making the U upside down...going up or a ring that is favoring the top of the crossmember. The driveshaft would be considerably higher than the bottom of the rocker to get hooked to the pinion where it would be passing that crossmember. Not sure on the size of tires you are running, but think about some quick math...29"-30" tire, centerline of the housing would be roughly 13"-14" off the ground...the pinion would be a couple inches below that. My Thoughts, Lorne

11 Posts
Discussion Starter #4
It Round Tube. Complete gut out and back half. I have a straight piece tacked in at the moment. The bottom of the tube will be roughly 4 1/2" or so off the surface. So with 28" (the smallest one for figures) I will have approx. 4" from drive shaft to the tube. That be enough or should I try and bend it?

67,719 Posts
That bar -- the bar that spans the width of and welds to the inner rocker panels, that bar should be welded in even with the bottom edge of the inner rocker panels .. or as close to the bottom edge as possible. If you're asking to determine if the driveshaft has enough vertical distance to travel when the car is launching off the starting line, it does. With a 28" tall tire, you shouldn't have any issues being able to lower the rear to remove the tires.

11 Posts
Discussion Starter #6
That bar -- the bar that spans the width of and welds to the inner rocker panels, that bar should be welded in even with the bottom edge of the inner rocker panels .. or as close to the bottom edge as possible. If you're asking to determine if the driveshaft has enough vertical distance to travel when the car is launching off the starting line, it does. With a 28" tall tire, you shouldn't have any issues being able to lower the rear to remove the tires.
Thanks!! I have it like you described. Its as low as I can get it and be able to weld all the way around.

9 Posts
9" Ford has a 2.25" vertical pinion drop from the axle centerline.
So take ur smallest tire diam.
Divide by 2.. then weather its a raidial or slick u remove the remainer of clearance in ur math.
So lets take a 30" slick. Its gonna be about 14"/14.5" from track surface to axle centerline, depending on ur final wheel width vs tire size.

U then have an additional 2.25" on a 9" , of ur driveshaft CL being below ur axle CL.
( on a GM dana its less.bout 1.5" of vert. pinion drop below axle CL.

If ur using a steel driveshaft u will likely beok w/3" to 3.5" diam tube. In Alum. , it could be necessary to use up to a 4" diam to align w/ur critical speed calculations of proper torsion diam.

So if ur using a large shaft for calculatiions sake of 4", and the smallest tire diam. Of 28".
In a radial u dont loose much when divided by 2 vs a slick.
So ur 28" radial axle CL should be no more than about 13.5" at the pinion yoke.
Then subtract ur pinion drop at 3rd member from axle CL.
Again, 2.25" on a 9"
1.5" on a 12 bolt or dana.
We use the 9 inch @ 2.25.
Divide ur 4" diam alum driveshaft by 2, leaving u a 2" underhang at ride ht.

So that puts the 4" driveshaft at about
(13.5" - 2.25"= 11.25".)
Then subtract half the diam of 4" driveshaft which is another 2"..= bout 9.25" at rear u joint. * Not at lower 4 link crossmember*

That location of said driveshaft w/vary based on ur crank CL Ht, and the angle of your eng.
Here is an example;
105" wheelbase car w/eng at 80" from bk of block to axle CL. Eng Crank CL at front is 10".
Eng angle is @ approx 1.7°. Back of block being hire than front by 1.7°.
So if u dont use CAD.
DRAW on shop floor several things
1st a track surface ht or the ground .
Then axle CL at rear upward to match your tire diam loaded..
Then go forward to where ur eng is located in distance and locate youe front Crank CL,
Then length of ur block bk to rear main seal,
But wait to place that rear block ht location until u strike a line from the front of block at CL of crank to your rear end CL, ( minus ur vertical pinion drop, plus u must move that position forward the length of the u joint CL on pinion as it relates to the actual axle CL which is gonna be about 10" in front of axle CL dependin on rear end choice and yoke style ( yoke length).
Get your rear end in a straight like to the angle of your eng block.
Draw that line on the floor or in CAD without any pinion angle.
The impose your driveshaft diam. Above and belove your driveline parh based on ur driveshaft diam. 2 " below the path for a 4" shaft.
Then go forward ( if its a 4 link car) whatever ur design is. Usually 23" from axleCL to lower 4 link crossmember on a normal small tire build, and no more than about 25" from axle cl to rear lower 4 link crossmember.
23"/maybe 24" being most probable
Then draw your 1.625" round tube up off track surface the same ht as u can install ur 4 link lower crossmember by creating a circle of 1.625".
( that sounds like its likely gonna be about 4.5" off track surface to bottom side if i understood ur description correctly.
Otherwise just put it where its looking the most promising is not at 4.5".

Assuming your rear shock is about 6"-7" behind your axle centerline, u should now be able to simulate dropping ur rear end down like u have raiaed up the car, and for a given length of open shock travel u should be able to "see" where ur driveshaft come to in proximity to the 1 concern of obstruction u have, the lower 4 link crossmember.

Keep in mind, the eng crank CL ht can be what u want, but the more pwr u have, the lower u will want it.
How far out u place the eng will vary w/either ur cars constraints of a stk firewall u must deal with and u may still want to be further forward than that anyhow based on Power.
So the 1.7° eng angle is only a guesstimate,
As i do not know all the constraints of your cars parameters.

When running an alum driveshaft it is VITALLY IMPORTANT that when the rear endvis hanging from the shocks, the driveshaft does not hit the 4 link crossmember, EVER.
NOT BECAUSE u will start the car and run it in gear w rear end hanging.. which u do not want to do anytime.
But rather, u do not ever want an Alum. Driveshaft to touch the crossmember at 4 link.. or hit any tubing or driveshaft loops for that matter..EVER.
Because once u accidentally dent that driveshaft u created a problem u cannot fix.

A steel driveshaft can be gently set onto a crossmember without damage as long as u dont spin it by running eng w rear hanging down and rubbing on crossmember or another improvised driveshaft loop that rubs before your rear shocks go to full open upon hanging the rear when car is off the ground in rear.
U take all ur design parameters front to bk.
Draw them in CAD, or on a sheet of butcher paper, or on your shop floor.

But if you want to truely know what u can, and cannot get away with.
Short of a full mock up on the jig of all this, u can lay it out pretty easily by measuring all pcs of the puzzle, and placing them in all the correct locations in the X, & the Z axis.
( left to right. = X axis)
( up & down off track surface is your Z axis)
Y axis only comes into play on rare occasion where u are offsetting either the eng from true CL of chassis or your pinion yoke vs rear end brackets that are welded onto the housing, in rare but still possible occasions, when looking downward from the ceiling either in your minds eye or on your CAD drawing, to make sure your driveline is where your ""constraints "" require them to be.
This Y axis is a left and right, or drivers to passenger alignment of congruent-cy..
Or lack of if ur working with a used rear end outbof another car or using stock eng location on anything newer than about 1960, since pre 1960s cars the engs are in center of chassis / engine bay.
Post 1960 on most cars, whichvary w/manufacturer and w/model, can be a 1/2" off center stock, and up to 1 3/16" in the case of some of your mopars of the late 60s or early 70s.
Point is. U can, with just a large pc of paper or cardboard, ir CAD, or your shop floor.

Answer your own question to within a 1/16", pretty easily, tohelp u chose a shock length that does not ever allow ur driveshaft to to the rear 4 link crossnember , regardless of ur driveshaft diam. Or your eng location.

What could get u in trouble most likely is an incorrect shock length for the rest of your constraints.

I could tell u it will all be fine.
But if your willing to take the time and effort to build your own car, why not do the same thing a professional would do and map out all the constraints for your combination.

I do mine in Cad.. and have shown others how to do it on a concrete floor or on a large rolled out sheet of butch paper or car painters masking paper.

Its a good exercise for any 1st car build.
Especially since you clearly care about your clearance.
So why take my word ir anyone elses word for what you do or do not have for clearance, and instead just map it out yourself?

Just use each pcs of the puzzle that u own to define your constraints.
Ur block type, ur tranny type, since the front u joint pivots off that tail shaft and not the back of the eng block.
And measure from ur spool to your yokes U joint to get out in front of the axle CL the correct amt as well.
All while defining your chassis constraints as well tosee it all in a real, and tangible drawing.

Or not?
Myself. Ive built a few cars.. and can say i never do any build without knowing my constraints before laying any pipe.

1 more pcs of advice.
Just cuz u plan to run a 28"x ? Or 30" x ? Size tire. Doesnt mean u have to build ur chassis to only accept that size tire.
If for nothing else but resale value wise.
Anytime u build a car, ushould at least ponder the possibility of either yourself or someone else wanting to put a wider or larger tire on the car later.
Narrowing a rear end and new axles are both pretty easy in the big picture.

Trying to nartow the chassis of a 10" tire car to fit a 14 x 32 or a 34.5 x 17 in the future.
Well.. its very costly, and the next guy who may want it might decide he doesnt want to balk half the car to get a bigger tire on it.
Going smaller in tire is always easier than going bigger.

If u never had this issue, u hav no idea how much u may hav wished someone would hav planned a lil ahead for the future of your car.
Whether its u or the next guy.
Just a lil advice.
That advice, & $1.09 might get u a burger on the dollar menu...
Take it for what its worth.
Good luck on ur build.
if for no other reason, just to appreciate the craft from more than a 30,000 ft elevation, looking down.

11 Posts
Discussion Starter #9
Oh I have the whole build in 3D model. To know where everything will be located. To be more specific I was just wondering what would be the most separation to plan for. The answer would lie in someone that has a radial set up that knows about how much that will be. Then I could move in CAD to simulate the movement. Cause no doubt I could make it hit no matter where I put it. Bend or no Bend...I think where I have it laid out it would have to separate a great deal for the drive shaft to hit the cross member. I do believe everyone should do it once. I like to learn....I ask why....I like to know I did it...I like to understand things. I just wish it could go faster...I had more time in a day..more days in a week. But one thing at a time and on to the next.

9 Posts
Ur shock drop out is what dictates your clearance. Once u have constraints created
( aka~ CAD drawing )

Nothing else is gonna cause it interfere,
if everything is bolted together,
and your biggest concern is when rear of car is off ground.. rear only drops to the full shock opening or the limit of your anti roll bar.
Which ever comes first. Shock preferably.
Cuz anti rolls defining rear end drop are a receipe for arms going ""over center"" and binding upon setting car bk down..

If ugot it all drawn in CAD u know to the thousand of inch if u got clearance.

Guess we did not understand your question .
Our mistake.
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