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#490072 - 02/25/08 09:51 PM
Re: diff enclosed converted to open drivetrain?
[Re: downunder pat]
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JohnD1956
Member
Registered: 03/29/03
Posts: 2207
Loc: New York
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This past weekend there was a spot on the NASCAR race where the announcer was standing in front of a car mounted to a rotisserie. The oiling system was the subject but I was looking at the rear axle mount. Here's what I saw.
The car had a panhard bar just like our Buicks. It also had the strut rods ( the rods which come from the outside edge of the rear axle to a center point on the torque tube, except for the race car the strut rods were mounted to a bracket attached to the bottom of the car.
I also noticed the car had a protective shield over the drive shaft, sort of looked like a torque tube system, but there were universals at the trans and pinion.
So I got to thinking just how caould this be done for us.
It would appear that the factory drive shaft could be cut and the rear female end could be fitted with the universal yoke by any driveshaft manufacturer. The front end is a bit different. Basically you'd have to have the driveshaft cut and a new yoke welded on.
The big question is what to do with the strut rods. And the answer might be to have a bracket made to cross the X frame and then have struts made to take in the new angles needed to bring them up to the new bracket. This would also require modification to the parking brake hookup, and a change to the rear brake hydraulics.
Then once you had the new engine and trans in place you'd have to have a custom driveshaft made for the length needed.
Like anything else, it's possible, but not very economical to do.
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#491092 - 02/29/08 01:20 PM
Re: diff enclosed converted to open drivetrain?
[Re: JohnD1956]
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Matt Harwood
Member
Registered: 10/09/01
Posts: 1605
Loc: Cleveland, OH
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As John pointed out, you're going to need some way to secure the rear axle to the frame/body of the car. Right now, the torque tube is doing that for you and the strut rods are just there to keep the tube and the axle aligned. The panhard prevents side-to-side movement, something required by the switch from leaf springs to coils. If you secured new strut rods to the body, you would have to use a Heim joint or something that would not only allow some rotational flexibility, but some side-to-side compliance as well. Otherwise you'll induce suspension bind which can cause spooky handling characteristics.
Here's the most basic suspension: leaf springs are used to align and locate the rear axle:
I think you would have to devise some kind of 3- or 4-link suspension to do an open driveshaft on one of these cars. Not only do you have to keep the rear axle following the rest of the car, but you have to keep it from rotating as the wheels try to turn it along the axis of the axles themselves. A u-joint won't do this at all and will fail the moment you put the car back on the ground. The upper control arms in a 3- or 4- link are designed to do just this, as well as to help keep the axle aligned behind the car. The panhard may or may not be required depending on which setup you use. But again, the more links you have, the more bind you're going to get and the more noise you're going to transmit to the body.
Here's a 3-link and a 4-link setup. You can see how they control both lateral (4-link) and forward location (both 3 and 4-links). The 3-link needs a Panhard rod.
4-link:
3-link:
The protective sleeve that John mentions on the NASCAR is called a torque arm, and pretty much does what the torque tube does--it keeps the transmission and rear end rigidly aligned and prevents the axle housing from rotating. It is either bolted directly to the rear of the transmission or to a bracket mounted near the transmission. In fact, the rotation of the axle under power transmits the rotational torque forward, helping to plant the rear tires even harder by moving the weight transfer point. It eliminates the need for upper control arms of any kind, but still requires lower control arms and a Panhard to function effectively. Late-model Camaros used torque arms & panhard rods in their rear suspension arrangements. Interestingly, the C5 Corvette switched back to a torque tube after having an open driveshaft with a rigid "sleeve" connecting the transmission & differential (which was possible because the IRS diff was mounted to the chassis, not live).
In the photo below, the two horizontal links that connect at the center of the differential cover are taking the place of a panhard, and are called a Watts linkage. You can see how the torque arm goes forward to a bracket near the transmission, as well as the two control arms that keep the axle following the body.
Torque arm:
I think getting an open driveshaft between the transmission and the rear axle would be easy. It's the suspension that would give you headaches. If you want to change just the driveshaft, I'd figure out a way to install a torque arm near the back of the transmission and the front of the differential housing, attach the strut rods to it, and leave everything else alone. Don't attach the torque arm to the transmission itself, however, because you're technically eliminating the universal joint from the rigid part of that assembly, even though you'll have one in the driveshaft on both ends. Attaching it directly to the transmission will break the transmission case as soon as the axle moves up or down. Does that make sense?
Hope this helps.
Edited by Matt Harwood (02/29/08 01:39 PM)
Edit Reason: added photos
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#491225 - 03/01/08 12:49 AM
Re: diff enclosed converted to open drivetrain?
[Re: Matt Harwood]
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Thriller
Member
Registered: 09/06/03
Posts: 2202
Loc: Winnipeg, Manitoba, Canada
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Thanks for the Suspension & Linkage 101 course Matt 
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#492915 - 03/08/08 02:25 AM
Re: diff enclosed converted to open drivetrain?
[Re: Thriller]
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downunder pat
Member
Registered: 12/26/07
Posts: 20
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Thanks guys for your reply and taking the time to explain in detail the issues involved with pics alway makes it easy to understand for the uninitiated.
I did not check my post for a little while. Things seemed a bit quiet but when i opened it today had a  VERY pleasent surprise indeed.Thanks again Matt and John C. I will be going ahead with the conversion just purchased 9"ford rear differential with disc brakes and driveshaft so onward ect.I must admit that if i lived in USA would not be even thinking of going to all this trouble. But do not have confidence in getting dynaflow fixed properly in Australia.Need second hand pump and bits ect.
Thanks again this guys regards Patrick Maiden BCAust 991 nsw
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