Split wishbones/open drive+Torque Arm= NECESSITY!!!

I forgot about the torque tube.....Don't they use a coupler and not a u-joint at the rear? Then they could handle force.....

 

Gee old age and bifocals just caught up. Tman I got the original post and your reply mixed as one. If you have a good roll center right now you might not need a panard rod but it would really make a slotcar with it. Yes I'd agree that it is not a good idea to try to use stock ford radius rods with an open drive. You guys have a nice evening.

 

****, your concern on the rear mounting bracket is a valid one. I think on the next car (closed cab A pickup) I will weld the tabs on top of the housing, on theleft side axle tube. Where it is now, it follows the driveshaft in its path. And, I havent been kind with my 348 and 3.89 gears so it is plenty strong.

Like I said, It needs delrin or UMHW bushings on the TA, the urethane ones are deforming under load.

I would like to see some other solutions? Choprods gusseted his bones, I have seen others done this way.

I have also seen the bones used like mine and triangulated upper links added for control and twist. I was going this route until I ran out of room.

I dont think it is a big issue on a mild flatty with bias plys, hell when I got on the ROcky33 it would barely hook up! Spin city if you will.

 

In addition to all the excellent info in this post I'd like to add that ALL rear wishbones are NOT created equal.

The ones that bolt to the outer bearing housings of an axle and do NOT have the spring shackles as part of the wishbone ***embly are weak and shouldn't be used as the sole axle locating device.

The proper ones (I forget the exact years covered...36 for sure) that can take limited amounts of power and traction are the ones with the spring hanger locations cast as part of the wishbone itself.
They bolt to the bottom of the rear axle with large, dedicated mounting tabs and bolts.
They can also be gusseted easily to make them even more reliable.

Just wanted to include that for safety reasons...

 

I have the Rear Radius rods on my [buggy sprung] roadster mounted at the outside of the frame and at 90 degrees to rear axle....It will kill me.........

I have written Tman into my will. I left him my largest balance credit card to pay off......
I will race Tman ar the Hamb Drags and he will beat me.
I hope the bolts on his TA
[at the differential] are stong enough to hold under that launch -as I will be in harms way ,being behind him like that.....I think Ill place a cowcatcher over my radiator/grille to protect me from flying shrapnel......

Trent -are you gonna drive or tow[389 ratio]?

 

I've seen some cool "traditional" looking four bar setups done as you are talking....using wishbones for the lower two links (with some kind of joint instead of solid mount) and then some triangulated upper links to prevent side to side movement. Still keeps the old style split bones look but works better.

 

Tman,

As a result of your previous posts (and others) I am planning to use my '48 rear with open drive and unsplit bones. I plan to pivot the bones directly under the driveshaft pivot and run a torque arm / brace from the top of the banjo housing along above the drive shaft and connecting to a saddle that straddles the drive shaft and connects to both sides of the wishbone. Probably use a front wishbone ball to locate it all.

Only in my head so far so it'll probably change a bit but the theory will remain the same... Unsplit bones mounted rigidly to the axle housing and a rigid support from high on the housing and a single pivot point. I think Henry thought of it first though.

Pete

 

Question #4,734:

80's Camaro's have a torque arm that's solidly mounted to the rear. No bushing, no movement. Just a bracket bolted to the rear that pivots about five feet forward at the tail of the transmission. Never owned one of these cars, but I've "appropriated" a few of thier transmissions so I'm very familiar with the arm.

So here's the question - TMan, why does your torque/control arm have a pivot at the rear and why doesn't the Camaro. Both arm three link setups with similar geometry.



Thanks,
Ed

 

Yeah, add the hi RPMs that W motors arent 'suposed" to handle and it should be carnage by the 60 foot mark!

I do need better pics but the car is too damn low! You can see it next week at this time.

 

OK, for Grim. I dug through my pics and lightened a couple. They areent the best but give a better idea of the relationships of the arms. (sounds ***** )

 

The ideal situation would be to have pivot point of the torque arm on the same plane as the mounting points for the wishbone (radius rod). Can a torque arm be shorter than the wishbones? How much shorter before things get weird? Will the fact that the torque arm being shorter actually cause MORE twisting like Tman said his first setup did?

I wanted to use '36 radius rods and triangulate 2 torque arms that mount on top of the rear end housing to replace the panhard bar and solve the twisting problem, but in my pea brain I'm thinking that the two eyelets (per side) on the radius rods might be torqued more if they aren't the same length.

???

 

My TA is almost the same length as my bones. I found through experimentaion that the shorter the arm the worse the axle wrap. The extreme was the shorty link I made. in 3" of travel, the pinion angle went from level to 30 degrees. It also has some to do with where the arm is mounted, on top of the 3rd member vs in front like I have it.

As for your idea, just copy a Triangulated 4 bar setup. They work pretty well and the thinking has been done for you.

 

Another big problem alot of people don't realize is when you solid mount the axle end of the split wishbones they not only have to take the axle torque from gasing it and braking but they also have to act like a large sway bar trying to prevent body roll.

You can also mount your links all above or below the axle line at the differential as long as you allow for enough vertical seperation and build the mounts beefy enough to handle it. This is commonly done these days with 4x4 rockbuggy's were they mount them all above axle center line to get mor clearance.

Heres a link to a 4x4 site were a few guys have setup some programs so you can enter in the numbers and get some ideas of what your antisquat and roll center numbers end up being for various link lengths etc

http://www.pirate4x4.com/forum/showthread.php?t=204893

 

"Another big problem alot of people don't realize is when you solid mount the axle end of the split wishbones they not only have to take the axle torque from gasing it and braking but they also have to act like a large sway bar trying to prevent body roll."

Yep.....and that's why they are trying to tear apart on turns. It makes no difference, in this case, whether you have a torque arm or not. Draw yourself a sketch looking at it all from the side. Drop the near side wheel a bit. You'll see that the housing has to rotate some in one direction. At the same time raise the far side wheel the same amount. You'll see that the housing has to rotate in the opposite direction. Well....a 3" diameter tubular housing can't do that and there are forces that are trying to tear it all apart. This happens whenever you make a turn and the ch***is wants to roll to the outside of that turn. The axle housing, which cannot flex, is attempting to act as a very large roll stabilizer bar.....!

 

No problem at all...

This is something that we've talked about before. I just wanted to say that I'd seen first hand what happens if you don't use a TA.

All this in-depth discussion is gravy!

 

The anti-sway/solid mounting is the reason why I didn't split the bones to 90 degrees from the axle and put heims on the front to allow some rotation. Otherwise the bones will have to twist....a three foot length of tubing is going to give before the large diameter tube that the axle is made of will twist. Round tubing is torsionally stiff.

As for the pinion angle changing through the travel.....it is completely a function of the placement/length of the links. You can think of a 3 or 4 bar setup as a SLA (short long arm) independent suspension (on one wheel). In the SLA setup instead of pinion angle change you get camber change through the travel. It isn't hard to check your work on paper (simply geometry) if you know where you want to place the connections. The pinion change is a combination of length and position of the links. You can have a short upper arm and get little change in angle of the pinion. The placement has to be right.....

There is a program called Mitchell WinGeo which is used for suspension design. It calculates the roll centers, camber, and steering angles through suspension and steering input. A little complicated to use at first, but it works well.

Tman- if you were using the short arm in the same location as your current TA, because it is not far above the axle centerline (which is what the axle rotates about), then through the travel, the short arm will swing a tighter arc (more fore/aft movement) which will rotate the axle more because of the short radius between the TA and the axle centerline. If the TA was higher, even with a short TA, the larger distance from the axle centerline to the TA will decrease the amount which the axle rotates. Maybe you already know this, I'm just saying that if some people have space constraints, a short TA can work depending on how it is mounted.

 

ah! beat me to the punch!

 

John, time to post your drawings of the "Ultimate" split wishbone set up.

 

Probably the slicks....I was going to just run bias plys but who knows maybe down the road I might want to put slicks on it.......It does sound like your setup was beefier than mine is now.....Were the bones mounted solid at the front or jointed?? Were they mounted on the outside of the ch***is???

 

Awefull fancy talk! I just tacked the short arm together and watched what it did, didnt need software for that! Like Jfast said, lots of this can be figured out with a quick sketch or mockup in wood or steel or even string to check the arc the members move in.

Also, I think the urethane bushed bones help me in this situation. There is enough flex in the ends that I eliminate lots of bind.

 

There is a book from down under called ENGINEERING STREEET RODS. The Holdens have a cool rubber pivot that could be used to connect bones or ladderbars in an semi/unsplit fashion. I have seen it done over here with a large oversized Heim.

 

The semi-unsplit with a heim is what I did.....The heim won't give like rubber though.....I'm leaning towards adding a TA for now and then if I ever want to do more (I was going to eventually put a Q/C in the car...money permitting) then I can change to a ladder bar setup.

 

I had the bones split to the underside of the frame rails so not totaly outside but close. They were mounted with large hiem joints 5/8 inch bolts. The rear mounting point was at the outboard end of the axles as close to the backing plates as possible. Looked real good but twice change the pinion angle so severe the u joints cluncked there way home. I did take off the slicks and put bias plies on but that was a fuction of the porta walls blowiing off at speed, went to real whitewalls now. The ladder bars work great but i know I should have mouted them as close to the center as possible but i didn't want to grind off the tabs I already had.

 

That's the same size joints I used.......my bones are only split about 18" apart, and they aren't as long as '36 bones.................still I don't know if that is enough to keep them from bending..........

 

Don't know if yours will work or not, but I see alot of folks running them and they seem to work. I don't know what I did wrong but I'm glad I changed them. Good luck.

 

Funny you guys are all talking about this. Anyone at the Milwaukee NSRA nats saw our new product. You'll be reading about our new torque arm kit in the pages of Rod & Custom soon, probably in the fall. And it's nothing like what has been shown in photographs in this listing. Should be for sale in the first of October.

 

well, show us some pics! If it was good enough for NSRA it should be good enough to show us hoodlems