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Old 07-27-2012, 10:19 PM   #1
scott mckelvey
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Default Rear suspension: 3 link with transverse spring?

I decided that I cannot live with what's under my '31 model A right now (quite possibly literally).

I've searched and read just about everything out there and I understand what are some "ideal" setups, etc. I did see a few specific references to a 3 link but they were different.

Additionally, this is in part based on what is on the car already and I deem usable. So, the idea is to reuse as much of what's already there as possible.

Currently (two attached pics but they are hard to see):
Proposed (see attached drawing):
  • use the existing front mounts on the frame rail w/ heim joint for 1/2" bolt (single shear)
  • use only the bottom part of the rear axle brackets w/ heim joint for 1/2" bolt (single shear)
  • Modify 32-34 Ford Radius rods for the lower links by adding threaded bungs for said heim joints
  • Top link using 1" DOM w/ .120 wall and threaded 4-link bushings on the ends. 3 degrees lower and about 5.5" shorter than lower link.
  • Weld in double shear brackets for top link to both a frame crossmember and top of axle.
  • Driveshaft would be 3 degrees higher than the lower link and is about 11" shorter.
So, my questions are as follows:
  1. Generally speaking, is there any reason I can't do 3-link with a Transverse spring and no panhard bar? I understand there may be a limited amount of sway b/c of the spring/shackles and the fact that I'm not using a dead perch.
  2. If yes, are there any issues given my specific angles and lengths?
  3. Lastly, is the hardware and mounting sufficient (Heims with single shear 1/2" bolts, modified radius rods, and DOM tubing)?
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Last edited by scott mckelvey; 07-27-2012 at 10:40 PM.
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Old 07-27-2012, 10:48 PM   #2
exwestracer
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Default Re: Rear suspension: 3 link with transverse spring?

The side play issue would be the main concern. With 'bones, you have a little help holding the axle in place. The 3 link is a much more "free" design. Could be a noticeable thing, depending on your driving habits.

I'd recommend a Watts link to go with the buggy spring, but that's getting kind of complex and not really "period"...
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Old 07-27-2012, 10:57 PM   #3
krooser
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Default Re: Rear suspension: 3 link with transverse spring?

Can't you just fab a rear panhard bar?
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Old 07-27-2012, 11:01 PM   #4
rottenleonard
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Default Re: Rear suspension: 3 link with transverse spring?

Well, correct me if i'm wrong(I'm sure no one would do it unless I offer), But Isn't the main idea of a three link that you don't need a panhard rod, the triangle of the third link takes care of it....ya? Don't know why it wouldnt work.
And the shackles on the transverse spring should negate any binding that would occur, I don't see a problem, but mayby I'm not seeing it.
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Old 07-28-2012, 12:06 AM   #5
a boner
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Default Re: Rear suspension: 3 link with transverse spring?

On my modified, the upper/center bar is next to the drive shaft, in the drive shaft tunnel, with a length about the same as the drive shaft. I also run a panhard bar. All the bars have a heim joint on each end to allow for twist.
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Old 07-28-2012, 12:46 AM   #6
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Default Re: Rear suspension: 3 link with transverse spring?

This-

http://www.jalopyjournal.com/forum/s...source=message

3-link would look goofy and the set-up you have now will break something eventually.

Or turn what you have into a ladder bar set-up.
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Old 07-28-2012, 12:59 AM   #7
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Default Re: Rear suspension: 3 link with transverse spring?

3 links are one of the best ways to get enough compliance in a street situation where bodyroll cannot [ or should not ] be eliminated.

You don't need a panhard bar if it is designed correctly with a triangle shaped 3rd link [ 3 mounting points on the rear-end and 4 mounting points on the chassis ]
If drive tunnel clearance is minimal use a triangulated center link under the rear-end center and 2 parallel upper links on outsides

This method lowers the roll-center height [ a good thing ] and was very successful in the "Lotus Cortina" in the 60's
They used it for "Road Racing" and didn't need a panhard bar or any lateral location device.
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Old 07-28-2012, 01:00 AM   #8
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Default Re: Rear suspension: 3 link with transverse spring?

A watts link or modified watts link will make that work. Full articulation with lateral forces being controlled with the watts.
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Old 07-28-2012, 02:29 AM   #9
gnichols
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Default Re: Rear suspension: 3 link with transverse spring?

I've been thinking that something like this would be a nice to fit into a rod chassis. It's made for a Pony car, but seems adaptable. The Watts link is hard to see, but it's on the back side of the diff. Gary

http://www.bmrsuspension.com/?page=home
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Old 07-28-2012, 04:19 AM   #10
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Default Re: Rear suspension: 3 link with transverse spring?

I think the "Grumpy Jenkins" version was the first successful one that immediately comes to mind
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Old 07-28-2012, 05:52 AM   #11
pitman
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Default Re: Rear suspension: 3 link with transverse spring?

I was thinking of the setup that Kerrynzl mentions above. Then no parallelogramming
or side deflecting. You'll want to evaluate the best upper differential bushing type, perhaps a 'shouldered' urethane or hard rubber in double shear style of mount. I'd consider simply splitting the upper link as in his left hand diagram. If it helps the roll center too, so much the better.

Last edited by pitman; 07-28-2012 at 05:57 AM.
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Old 07-28-2012, 07:12 AM   #12
Jmountainjr
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Default Re: Rear suspension: 3 link with transverse spring?

If you stay with a three link, the triangulated top link as pictured in the left picture in post #7 solves your side movement control issue. The only downfall of that design in cars with limited verticle space is the extra height of the bar connection onto the top center of the rear axle housing. If you look at that style of top link, it's very close to the top bars on a triangulated four link except the bars come together at the top of the axle instead of two attachment points on either side of the center section. That difference does change some of the roll centers. But in a light car with limited actual suspension travel, you can use a triangulated four link with a transverse spring and gain some verticle clearance over the three link.
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Old 07-28-2012, 07:31 AM   #13
chopt top kid
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Default Re: Rear suspension: 3 link with transverse spring?

Scott, Your three link setup should work fine as long as you have proper preload in your transverse rear spring(rule of thumb = spring tension holds shackles at 45 degrees). Hot rods have been running transverse springs without panard bars for decades.
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Last edited by chopt top kid; 07-28-2012 at 07:58 AM.
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Old 07-28-2012, 07:51 AM   #14
F-6Garagerat
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Default Re: Rear suspension: 3 link with transverse spring?

Check my build thread below, like post 91 I think. I used a Uni Ball at the front of the bones. Way better than a heim. I have to add a torque rod still.
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Old 07-28-2012, 07:51 AM   #15
scott mckelvey
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Default Re: Rear suspension: 3 link with transverse spring?

Quote:
Originally Posted by Beau View Post
Seen it and like it, but don't like the idea of the ball in the rear.

Quote:
Originally Posted by Kerrynzl View Post
You don't need a panhard bar if it is designed correctly with a triangle
This method lowers the roll-center height [ a good thing ] and was very successful in the "Lotus Cortina" in the 60's
Quote:
Originally Posted by gnichols View Post
The Watts link is hard to see, but it's on the back side of the diff.
both the examples that you guys showed are coil sprung, and I get why that's necessary in that application, but not with a transverse spring. Am I wrong in assumption that the spring in this case will do the locating of the axle, with the understanding that there will be some play like during hard cornering. In which case my spring will located the axle side-to-side (not the links).
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Old 07-28-2012, 08:48 AM   #16
DICK SPADARO
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Default Re: Rear suspension: 3 link with transverse spring?

Just caught this post this morning, after looking at your pictures just what is wrong or what do you think is wrong with the rear installation you have now?
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Old 07-28-2012, 09:08 AM   #17
scott mckelvey
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Default Re: Rear suspension: 3 link with transverse spring?

Quote:
Originally Posted by F-6Garagerat View Post
Check my build thread below, like post 91 I think. I used a Uni Ball at the front of the bones. Way better than a heim. I have to add a torque rod still.
Seen that and equivalent joints (although I'd be more inclined to use the rebuildable Rubicon version if I went that route). Certainly an option if i triangulated some ladders or rods inboard, but at that point I'm completely removing and redoing everything, including adding additional frame cross members. If I go down that road then there's no limitations and I'll do exactly what I want. The point of this exercise is to see if I can make use of what's already there, safely and cleanly.

Quote:
Originally Posted by DICK SPADARO View Post
Just caught this post this morning, after looking at your pictures just what is wrong or what do you think is wrong with the rear installation you have now?
Like most everything on this truck, it was done quick and dirty w/ little attention to aesthetics, safety, or function.
  • it's using front hairpins, which in my opinion are not up to the task. Plus they have one measely bracket barely welded in the middle for strength.
  • they are mounted outboard on the frame rails, and bind obviously with any articulation (this truck will be on the street, not the track). aside from that, something will break in this configuration so I'd just as soon fix it now.
  • not addressed in this thread, but I already remedied it: it had narrower than stock perches w/ a stock A spring and the shackles were vertical at rest and bottomed against the perch brackets on the axle with little to no travel of suspension.


Quote:
Originally Posted by chopt top kid View Post
Scott, Your three link setup should work fine as long as you have proper preload in your transverse rear spring(rule of thumb = spring tension holds shackles at 45 degrees).
That was an issue (see above), but it's been corrected.

Last edited by scott mckelvey; 07-28-2012 at 09:16 AM.
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Old 07-28-2012, 10:33 AM   #18
DICK SPADARO
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Default Re: Rear suspension: 3 link with transverse spring?

Scott, what you have isnt as bad as you think, maybe the pictures dont show the quality of assembly but the concept is ok. If you are limited on equipment and cash this just needs a little TLC. From your post, you just need to clean up a few issues first by replacing the spring shackle mounts to the correct span, this will make a major difference. The wish bones are positioned Ok but should have a heim end or tie rod end installed at the frame mount to counter the twist from one wheel bump. If you want to see how much deflection in the rear rods, place the vehicle on stands at ride height while you are changing your spring mounts, remove the shackles and jack the axle up to simulate a 2" one wheel bump. You will see that it should not twist very much and most twist would be accepted by the moveable end. Clean up the welds, make sure the frame bracket is gussetted.

If you are bound an determined that you are not happy with this set up the simplest set up you can install is a split wishbone set up ( check Pete and Jake's design) that converges near center line of the car. It locates the rear axle and with the use of a transverse spring eliminates the requirement of a panard bar.

Good luck with your project .
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Old 07-28-2012, 01:32 PM   #19
davidfe
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Default Re: Rear suspension: 3 link with transverse spring?

Quote:
Originally Posted by scott mckelvey View Post
I decided that I cannot live with what's under my '31 model A right now (quite possibly literally).

I've searched and read just about everything out there and I understand what are some "ideal" setups, etc. I did see a few specific references to a 3 link but they were different.

Additionally, this is in part based on what is on the car already and I deem usable. So, the idea is to reuse as much of what's already there as possible.

Currently (two attached pics but they are hard to see):
Proposed (see attached drawing):
  • use the existing front mounts on the frame rail w/ heim joint for 1/2" bolt (single shear)
  • use only the bottom part of the rear axle brackets w/ heim joint for 1/2" bolt (single shear)
  • Modify 32-34 Ford Radius rods for the lower links by adding threaded bungs for said heim joints
  • Top link using 1" DOM w/ .120 wall and threaded 4-link bushings on the ends. 3 degrees lower and about 5.5" shorter than lower link.
  • Weld in double shear brackets for top link to both a frame crossmember and top of axle.
  • Driveshaft would be 3 degrees higher than the lower link and is about 11" shorter.
So, my questions are as follows:
  1. Generally speaking, is there any reason I can't do 3-link with a Transverse spring and no panhard bar? I understand there may be a limited amount of sway b/c of the spring/shackles and the fact that I'm not using a dead perch.
  2. If yes, are there any issues given my specific angles and lengths?
  3. Lastly, is the hardware and mounting sufficient (Heims with single shear 1/2" bolts, modified radius rods, and DOM tubing)?
Scott,

Hope you don't mind that I corrected the color balance in the pictures.

Interesting questions.

Regards,
David
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Old 07-28-2012, 01:46 PM   #20
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Default Re: Rear suspension: 3 link with transverse spring?

Toss it all and get a Jag IRS. It's already been very well engineered, and looks cool, too. Just my two cents. Very simple to install, aftermarket cross-members available. Google Jaguar rear suspension.
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