After a few months, most bugs are worked out with my 36 coupe. Runs great, good fun. One challenging issue is a pesky drivetrain vibration problem. As speed increases this becomes more and more noticeable. I am running a T5 trans, new professionally fabbed driveshaft, '36 banjo rear, transverse spring, and stock radius rods attached to the crossmember with a heim joint setup about 3" lower than the stock location. Includes a Hot Rod Works triangulation brace. The trans angle is 1 degree down. The pinion angle is 1 degree down (shaft centerlines not parallel). On a modern setup I would look to have minus 2 degrees of pinion angle like this (trans and pinion not parallel), maybe more for a drag racing setup. All my collective knowledge says this should all work great. But it doesn't. Looking the brain trust here for input, as I need to cut and weld the radius rods to make any change. My guess is the pinion wants to be parallel to the trans at rest, or maybe minus 1/2 or 1 degree down pinion angle to compensate for movement under driving forward forces. Thanks!
Drivetrain vibration issue-open drive banjo
- Thread starter PGBuick
- Start date
40cpe
Well-known member
I have personal experience with installing non-stock rear ends. I have always read to install the rear angle so the trans and rear angles are parallel, and have done so. If you have solid stabilization of the rear angle, such as radius rods, I don't see it moving much with driving forces as you would see in parallel leaf suspension.
tubman
Well-known member
I'd be surprised if you didn't have a vibration if the numbers you posted are correct. The above poster is correct in saying the rear end and transmission angles should be parallel. I've always found this video to be quite informative : https://www.youtube.com/watch?v=Idk3BVDVHq4.
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Great video. Thanks for the feedback. More work to do. The real issue is the setup sold for open drive conversion. There's no way to mount the front point of the radius rods high enough because the driveshaft is there. I can't be the first person to have this issue. The advice I've seen repeatedly about using parallel leaf springs is good, however, I'm determined to keep the banjo and make this work.
tubman
Well-known member
Cut the rear radius rod mounts from the rear axle housings, rotate the front of the pinion up, and reweld the mounts back on? It sounds like it only needs to rotate 2 degrees (-1 to +1), which ain't much
I realize there can be reasons why this can be impractical in the real world (thus the question mark).
I realize there can be reasons why this can be impractical in the real world (thus the question mark).
V8COOPMAN
Well-known member
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SIMPLICITY of the BUGGY Spring Suspension & TORQUE TUBE Theory
Ah YES ...."THE SIMPLICITY OF THE BUGGY SPRING SUSPENSION"! You almost couldn't say it any more simplistically. But there are a lot of "modifiers" in our ranks that still do not understand the totality of that simplicity. There are two basic elements that must be remembered when evaluating just how Henry's "buggy sprung, torque tube system" actually works, and what is required to remain fully, and safely functional.
The first element of the system is that the whole rear end/torque tube assembly articulates about TWO points in two dimensions. The assembly is able to ROLL about the longitudinal axis defined by the point in the center of the rear crossmember where the buggy spring is securely clamped, in addition to the front end of the torque tube assembly joint approximating a point slightly in front of the torque tube bell, essentially in line with the center of the U-joint.
The REAR end of the whole assembly is able to move up and down in a PITCHING motion via buggy spring action and constraint, about the same point at the front end of the torque tube and center of U-joint as discussed above. The 'captured ball' surrounding the U-joint at the front end of torque tube serves to anchor-securely that end of the torque tube, yet allowing full articulation about that point in the center of the U-joint.
The SECOND element that is often overlooked is that the TORQUE TUBE is the member which transmits the driving force that moves the vehicle forward, or rearward in the case of reverse. The torque tube actually pushes the vehicle forward, and pulls the vehicle in reverse. The torque tube is also the member that resists any control over the rear axle housing's propensity to twist upward at the front while transmitting torque to drive the vehicle FORWARD. While driving the vehicle in reverse, the axle housing tries to twist downward in the front. This "torque-induced" movement is normally contained and controlled by the torque tube. Once the torque tube is eliminated, as in an 'open-drive-conversion', those two radius rods (formed from rolled sheet-metal) now have their work cut-out for them trying to control the TORQUE-rolling of the rear axle assembly. You've gotta remember that these two wimpy rods are now what is left to PUSH the vehicle forward, or pull it rearward as in REVERSE. And if you 'GET-on-it' hard, all bets are off! Those radius rods can fold-up like spaghetti. They were originally designed ONLY as a means of reinforcement for keeping the TORQUE TUBE at an angle of 90º to the banjo housing, via simple triangulation.
Many times when modifying an old Ford's torque tube system to subsequently perform "open-drive" duty, some of these elements are overlooked, or even totally mis-understood. If the modified system overlooks any element of the original design, the vehicle will likely drive like crap, especially when traversing odd changes in road height, like driveway entrances, and pot holes. And heavy acceleration can be especially destructive if rear axle torque is not adequately controlled by substantial members specifically designed for that function. The entire rear end suspension must function in it's entire range of movement just as well as a stock torque tube rear end.
One more thing usually seen during these modifications is radius rods being "split", spread-out, and anchored to a frame rail by a bracket of some kind. In a case like this, whenever the rear end (or front axle) is raised or lowered at one end, as if you drove one rear wheel into a deep pot hole, anything that causes the rear end (or front axle) to ROLL in alignment with the longitudinal axis of the vehicle, you are actually TWISTING those radius rods. They are only going to 'TWIST' so many cycles before they break or fracture at a mounting point, or anywehere along their length. This does not occur when the radius rod is mounted to the torque tube. NO COMPONENT gets twisted with the normal movements in a torque tube rear end assembly. If you don't understand ANY of the above, trying to SUCCESSFULLY MODIFY a torque tube system to function properly is likely not going to end well.
In short, Henry designed all of those MINUS 1 degrees and all of those PLUS 1 degrees into this magical torque tube/banjo/radius rod assemblies back when he originally built these parts, and it is going to take some really imaginative engineering to modify what he originally designed to work perfectly with our OPEN DRIVE T5s DD
