Suspension Bind

[bobs66440]

I'm very new to the T-Bucket world and as such have no experience with the hairpin style suspension design. But I have to say, after beginning the final assembly process of the rolling chassis (in the rear) after painting, I am amazed at the amount of bind that seems inherent in the design. Straight up and down there is no bind at all, but try to lift one side and the whole chassis follows. I didn't quite understand what was going on at first, but after some experimentation I saw that as one side is going up, it's trying to pull the radius rod out of the mounting bracket. Yikes! What a terrible design, lol! Now I see why the 4-link and 4-bar design is preferred.

And, now I see why the original wishbone setup like in the Model A (pivoting in the center) works well with no bind until you "split the bones" and move them out more parallel to the chassis.

I suppose it's not so critical since the suspension travel is so slight, but still...

 

[bobs66440]

I'm thinking I may be better off with bushed rod ends here?? Unfortunately I would have to completely reconfigure all the brackets and everything...

I used spherical rod ends figuring that they would free up any bind, but it seems to have made little or no difference...I suppose moving the front mounts out (to clear the body) doesn't help but I can't imagine it making that much difference...

 

[bobs66440]

Now I see why Spirit (others may also) has such beefy (3/8") brackets...because the radius rods, frame & rear (or front axle in that case) all become stressed members and act as a pseudo "sway bar".

I used a long 2x4 as a lever to see how much twist was available and there is a decent amount. More than I would expect, so I don't think I will be shearing bolts and brackets. After all, these aren't rock crawlers with huge amounts of articulation, but it just seems a little unnerving...

 

[choppedtop]

I had 4 bar on my 33 coupe, and really liked the way it worked. Also had regular coil springs instead of coil overs. It road smooth. Now I have the same set up that you have. It is ok, a little rough riding. I have switched to 150# springs which helped a bunch. If and when I build another, it will have 4 bar, and coil springs.
Lee

 

[Francis Blake]

You have figure out the way the hairpin suspension works it is a little rough riding but it works because there is not a lot flex in these cars. There is no trouble with the way you did the rear it would be the same as a wider fame.When you are on the road I'm sure you will find this suspension to be adequate. Have fun with your car.

 

[fordsbyjay]

To me this is one of those things where the original design works ok for everybody but could it be made better??

I wonder if running a johnny joint would give you more articulation?

http://www.summitracing.com/parts/cur-ce9112n75-14/overview/

 

[Hackerbilt]

To me this is one of those things where the original design works ok for everybody but could it be made better??

I wonder if running a johnny joint would give you more articulation?

No...the problem is the back end of the ladder bars being attached with two bolts at the rearend on either side and fighting each other.
Unless you have some articulation available there, the style of front attachment doesn't make a difference.
You could gain a slight amount of articulation by replacing the Heim joints with rubber bushed rod ends (and adding the additional rearend plates for double shear mounting) and they will help a little bit...but I don't know if its worth it at this stage.
LOTS of T's going around with the same bind and no issues, mostly due (in my opinion anyway!) to the cars lightness not stressing the suspension bind points to the critical levels you might see with a much heavier car with similar ladder bars.

 

[bobs66440]

To me this is one of those things where the original design works ok for everybody but could it be made better??

I wonder if running a johnny joint would give you more articulation?

http://www.summitracing.com/parts/cur-ce9112n75-14/overview/

I don't think so, because the problem seems to be that as one side goes up and down, it mostly pulls the rod end fore and aft. Those, like spherical rod ends, have no give that way. Rubber bushed rod ends would have some give, but I imagine the rubber would eventually wear out from constantly being compressed.

 

[bobs66440]

No...the problem is the back end of the ladder bars being attached with two bolts at the rearend on either side and fighting each other.
Unless you have some articulation available there, the style of front attachment doesn't make a difference.
You could gain a slight amount of articulation by replacing the Heim joints with rubber bushed rod ends (and adding the additional rearend plates for double shear mounting) and they will help a little bit...but I don't know if its worth it at this stage.
LOTS of T's going around with the same bind and no issues, mostly due (in my opinion anyway!) to the cars lightness not stressing the suspension bind points to the critical levels you might see with a much heavier car with similar ladder bars.

I agree. I think that the inherent strength of the attachment points (if done correctly) is stronger than the force trying to pull it apart under normal conditions. I would think that the radius rods would bend before a bolt, heim joint or bracket broke, in my case anyway. Because I'm using super strong chromoly heim joints (18,000-19,300lb static load), grade 8 bolts and the brackets are really heavy 3/8" thick.

And as you say, the proof is in the hundreds or thousands of T's running around the same way.

 

[Keeper]

Shouldn't those mounts on the back be clevises? I have never seen a heim used on the rear like that at least not in single sheer.

What does the front mount look like inside? Did you use spacers to allow that heim to move?

 

[TriodeLuvr]

No...the problem is the back end of the ladder bars being attached with two bolts at the rearend on either side and fighting each other.

Exactly right. One side is attempting to rotate the axle, the other to keep it the same. There's a simple solution to this, but it requires an asymmetrical radius system. If one side of the suspension is built as usual (radius rod), that's sufficient to maintain the axle at its correct attitude (rotation angle). The other side then only needs to maintain the correct (and identical) fore-aft position of the axle. This could be accomplished by converting one side to a modified ladder as below. Of course, this means the two sides of the vehicle no longer look the same, and it might also weaken the rotational rigidity of the axle in straight line acceleration. It does solve the binding issue, though.

Jack

 

[bobs66440]

Exactly right. One side is attempting to rotate the axle, the other to keep it the same. There's a simple solution to this, but it requires an asymmetrical radius system. If one side of the suspension is built as usual (radius rod), that's sufficient to maintain the axle at its correct attitude (rotation angle). The other side then only needs to maintain the correct (and identical) fore-aft position of the axle. This could be accomplished by converting one side to a modified ladder as below. Of course, this means the two sides of the vehicle no longer look the same, and it might also weaken the rotational rigidity of the axle in straight line acceleration. It does solve the binding issue, though.

Jack

Yes, and also I was thinking, if you just disconnect one rear mount bolt, effectively making it a 3-link, it would be able to rotate also. But as you say, who knows what else it will effect.

They run a similar setup to what you drew in some dirt stock cars. The radius rod connects to a "birdcage" bracket that has a bearing in it to allow it to turn freely on the axle tube.

 

[bobs66440]

Shouldn't those mounts on the back be clevises? I have never seen a heim used on the rear like that at least not in single sheer.

What does the front mount look like inside? Did you use spacers to allow that heim to move?

I was originally going to use clevises, but I figured the heim ends would allow more freedom of movement and may be stronger since the clevis bolts are only 3/8". The heims use 1/2" grade 8 bolts.

The inside of the front mount is like a double shear bracket with the heim end captive, and also has spacers on either side so the joint can move freely. I didn't see a problem with having the rears mounted in single shear because most of the ends that mount to the frame I've ever seen are mounted that way. I don't really see how it can go anywhere unless a bolt breaks, but I can't imagine a 1/2" grade 8 bolt breaking due to these stresses...but I've been wrong before...

I have a large washer on between the bolt head and heim joint to keep the joint captive in case it separates.

 

[TriodeLuvr]

I had no idea anyone was using an arrangement like that, I was just thinking out loud. In fact, I realized after posting that the same thing could be accomplished with a single bar on one side, effectively a 3-link like you mentioned. Your heims should be fine in that location. It's just an additional cost compared to bushed rod ends (that's what came on my car). You know, I'd have to think really hard about replacing that setup with 4-bar, now that you've done all the work. The 4-bar might be useful if these cars had more compliant suspensions, but the rear on mine (and I assume most buckets) just doesn't travel much over bumps. For vehicles like these, the benefits might be more theoretical than anything else. One thing, is it common for the front attachment of the rear rods to be offset from the frame like that? Not saying it's wrong, just asking. Mine is directly under the frame.

Jack

 

[bobs66440]

I think you are correct regarding the theoretical benefit. These cars have so little suspension travel that the stresses are very minimal. I suppose if it was a real issue, there would be cars breaking all over the place and the design would have been shelved long ago. But in these days of the sue-happy public, manufacturers are still building and selling them. That says something I suppose.

The only reason why I moved the mounts out was to clear the body. I lowered the chassis 2" from normal, which in effect, raised the axle and thus the radius rod mount. That put it up into the body. I didn't want to cut up the body to clear the tube, so I moved the mounts out instead.

You can see by the photo, I would have to really chop up the body to clearance them...

 

[Keeper]

Couple things I see.

1 - you may need some "misalignment" spacers on the front mount, that will allow that heim to twist a lot more. If you disconnect the rear bolts, and twist that joint, you will probably see its hitting very early in the rotation.

2 - those hiems bolted like that on the rear probably only move side to side, which is what the panhard bar will prevent,so they probably won't be any different then the clevises. They do sell clevises with 1/2 holes, they just cost a bunch more, I picked up one up at speedway, for $19!

http://www.speedwaymotors.com/AFCO-10491-Steel-Clevis-5-8-18-RH-Male-1-2-Hole-3-8-Slot,23917.html

Those rodends, might be another option to give you a bit of movement in the rear. Though you will get the single sheer argument again.


Oh yeah, that front mount will make a great spot for a step!

 

[Hotrod46]

I've always heard that these cars have limited suspension travel. I wonder if the limited travel is due to the hairpins and tube axles more than anything else.

I have 4 bars on both ends of my car and it has plenty of travel. I can drive over curbs and speed bumps at an angle with no trouble.

Really not trying to "stir the pot", just wondering.

 

[Mike J]

I too had the same issue, changed my front end to 4 bar. All kind of travel now with no bind.

 

[old round fart]

It looks like your misalignment spacers are installed backwards. The small end should be at the heim end.

 

[TriodeLuvr]

I wonder if the limited travel is due to the hairpins and tube axles more than anything else.

I've had several discussions on this exact topic with several people in various bucket forums. It's my opinion that these parts - as a system - aren't stiff enough to have a meaningful impact on single-wheel suspension travel. I base that on empirical observations only, and not everyone agrees with me.

Jack