3-Link - The missing link!

[dv/dt]

I went out the other day to weld the banana bracket to my axle. As I was welding it I was thinkingg it would be a pain if I didn't have a welder. Would be nice if there was a bolt in solution for transmitting the torque into the axle. Well here's what I came up with. Puts a link directly from the 3rd link bolt to the unused four link upper bushing mount on the axle. Still needs to be trimmed to length and the forward bolt changed out for a grade 8 bolt. The forward bolt may seem small but a 3/8" grade 8 is good for 10,000 lbs in shear. The link is put in compression under acceleration. I have talked to William at VPM and he would be willing to make up a kit if the interest was there. We have discussed and alternative that would be a straight bolt in and would not require any drilling. It would be very strong but would be more expensive since it would involve some machining work on his part rather than just off-the-shelf parts. Let us know what you think.











And here is the concept drawing for the bolt in kit.



Cheers, Rod

[NAGA]

Typical engineer!!

You don't really want to finish that car do you Rod?

Another nice mod buddy. Only question I have is why do you think that link's in compression? The third member is trying to move forward in relation to the body. That would put the link in tension, but only if the banana bracket broke. Otherwise, there's probably no load on it.
The FFR link? It would be in compression as the rear end is trying to drive it forward into the frame.

Here's a challenge for you. IF you can figure out how to statically preload your new strut into tension, it would preload the banana into compression which would offset some of the live load tension. Maybe add a turnbuckle into the new link?

d

[dv/dt]

Hi Don,
Under load the front of the differential is rotated up as the pinion tries to climb the ring gear. This means the axle is trying to rotate the banana bracket rearward not forward. This puts the new link in compression since it would be pushing back on the banana bracket. The upper link is in tension and tries to lift the front of the car remember.

If you look at the bottom drawing of the production variation it is essentially a turnbuckle and would allow you to preload it (in compression) as you state.

Actually I'm waiting for an order from Summit so I can finish up the engine, etc. Besides, if I finish this what the heck am I going to do for fun!!

Cheers, Rod

[CraigS]

I like your solution as is.The rod end one is pretty but, like the other one you developed,those rod ends increase the cost about 10 times.I'd use the square tubing and weld on a plate at the forward end like the one at the other end.Drill the hole so the owner uses it as a guide for the hole in the big ear on the diff housing.Good job

[dv/dt]

Hi Craig,
One of the problems with the first setup is that drilling the hole in the 4-link ring can be tricky if the car is already together. It has to be centered and square on the ring for best strength. You would need to use an angle drill from the passenger side wheel well if the trunk sheet metal is already done. So the installer would need some special equipment and a level of skill above the second solution. But it is possible and does provide better mechanical advantage for the link.

The price difference for the rod ends isn't really that clear cut if you factor in the time to manufacture the parts. Throw in a couple of hours labour to make up the pieces/weld them up and it adds up. The rod end solution also gives you the added benifit of adjustability to fit variations between cars. Even slight variations in the banana bracket and it's installation will affect the bars length and angles. So even if William goes with the first version I think he would use a rod end set up. The other benifit of using the rod ends is that you could pre-load the rod slightly as NAGA pointed out.

Cheers, Rod

[Stinson Pilot]

Wow, and you think a lot of engineering thought goes into a production car...

You guys are awesome. Keep it up.

Do most guys with 3-link do some spot welds to transfer torque to the banana bracket or just leave it clamped as is? Will the clamp slip on the axel if you don't?

Always seems the simplest solutions are the best.

[thebicman]

Rod, get to work on finishing car. You know I'm way behind you in the build and I need to live the dream by driving in yours. Now come on, get cracking. Bert.

[Jim_Miller]

Originally posted by Stinson Pilot:
Do most guys with 3-link do some spot welds to transfer torque to the banana bracket or just leave it clamped as is? Will the clamp slip on the axel if you don't?

Not speaking from experiance with a FF5 but from experiance with a 69 fastback stang and stock spring pads and also from what I can tell from page 3-4 of this Collegiate.pdf weld it. Add a Posi and some good tires and the rotation on an axel housing can be extreem.
Spun my rear housing up 90 degrees inside the leaf springs years ago. messy

[MJN]

Another effective and simple solution. Nice job [img]smile.gif[/img]

[dv/dt]

Doug,
Here's a post from last year discussing a failure and the welding issue. http://www.ffcars.com/cgi-bin/ultima...t/011653.html?

Currently the banana bracket relies on the clamping force in the main mount and the forward 3/4" tube that is in pure bending. Neither is a very efficient means of transferring the torque from the axle to the banana bracket. Not saying they don't work, just that they are not efficient and are subject to several variables (correct torque and clamping force, layers of paint or corrosion on the axle).

Bert, As soon as the Summit order comes in I plan to go nuts and get er done. Time to cut some grass!

Thanks Mike!

Cheers, Rod

[KevinM]

I still think you should be charging FF a consulting fee for all of this.

Very good solution.

Kevin

[quicksand]

rod, step way from the welder and get some sleep..nice innovation especially considering you're likely living in sleep depravation

[CraigS]

Rod-Ok, you convinced me. I keep thinking about your prototype which I could make up myself from bits in the garage and, of course my time is at no cost.But to do this as a business, and allow some adjustability, you are right.Once again-good work! Some day when I get good tires I'll definately need one.
Craig

[Vegas]

Rod,

How many Afco rods are you going to have me install before you are done?

[ONEBADSN8K]

It seems that everyone is worried about the three link. I have roasted the rear tires off and have seen no stress cracks or any sign of either twist or any thing else.It seems that most of the things I have seen are geared for the MKII as the MKIII is very well enginered. Have not seen any one even post about a MKIII breakage. I have built stock cars both dirt and asphalt for years that use a 3 link that is just as strong as the FFR with no failure.So much of this seems like overkill and over enginering. Remember this is just my opinion.

[AC4ME]

Rod, I did mine the way the drawing shows, except I used a aluminum rod turned down to fit in the ear hole, with bolt and washer to hold it in, but it was 1 1/4" long out on the pass. side. Then I milled that on a angle so the rod end could bolt straight in the side.
Can you tell me how to put drawings, either from AutoCad or hand drawings on the posts so I can show you what I did? Thanks
I have a little concern about the twisting or rotating force that these links will cause at the top of the banana bracket. What do you think?

[ June 05, 2006, 08:29 AM: Message edited by: AC4ME ]

[stroked]

ONEBADSN8K

Later MKII and the MKIII have the same 3 link setup. Earlier 3-link setups lacked a cross brace on the upper link bracket that helped reduce breakage at that point. In this discussion, the strenghtening is at the bannana bracket on the axle tube, which is the same design as it has always been. So in this case, the discussion applies to anyone with a FFR 3- link, including MKIII's. Do a search and you will find people with MKIII's with 3-link issues. Reality is that high HP + wide sticky tires + unmodified 3-link = broken parts. The 3-link upgrades are not hard and should make the setup more able to handle the high HP sticky tire combo.

[ChrisH]

Depends on the cost for me Rod. I liked the first upgrade, and this one looks promising as well. Let's see how much.

I think you would have a lot more interest if suddenly a bunch or banana brackets started to fail. I think it will take time to see if this upgrade is overkill or actually a needed component of the whole 3-link upgrade package. However, depending on the cost I would be interested in some "cheap insurance".

[dv/dt]

AC4ME,
I get what you are saying. To post drawing from AutoCAD I take a screen pic of the AutoCAD window (select the window and then hit Alt+"PrintScreen". You can then paste it into MS Image Editor (Paste as new image) or any other image tool and save it as a JPEG. Then crop it so just the stuff you want shows and you can post it here as you would any other pic. For hand drawing (like mine above) I took a digital pic of it but you could also scan it.

As for twisting, this link will only come into play if the loads exceed what the banana bracket can take or partial loads even if you pre-load it a bit. Either way the combination should be able to take more than the banana bracket by itself before failing.

Cheers, Rod

[dv/dt]

ChrisH,
Pricing will be determined by William. I see this as an alternative to welding. Not everyone has a welder and there are some risks (bent axle housing) if you don't do it right.

Cheers, Rod

[AC4ME]

Rod, thanks for the help. I see what your saying about the twisting. I'm not sure, but we'll find out as I'm going to run it. If I can ever get it done.

[Ozona]

Rod:

The autoweld upper control arms might have some pointers on how to attach to the pumpkin w/o welding. They cut/build out a bracket that bolts through the "eye" for the bushing. Basically it's a solid steel bushing cut into halves that bolts through if that makes sense. It would be much stronger than drilling through the eye loop and through bolting.

HTH

[dv/dt]

Hi Ozona,
We agree that drilling through the 4-link ring would be the weak link (probably not too weak until you got to very sticky tires on a high hp car). Another issue would be to try and drill it centered and square on an assembled car. Those were the reasons for developing the production version shown in the bottom drawing. I believe it does, more or less, exactly what your mentioning but with a 3-piece bushing. William may in fact go with a 2-piece bushing.

Cheers, Rod

[William Mapstone]

Since this will be primarly for people who do not or can not weld the banana bracket, we want to develop a solution that will be very strong. Therefore we will be using 2 steel bushings sandwiched between the ear, similar to the hand drawing shown in Rods previous post. I hope to have a price soon, so I can gage interest.

[ChrisH]

Originally posted by William Mapstone:
Since this will be primarly for people who do not or can not weld the banana bracket, we want to develop a solution that will be very strong. Therefore we will be using 2 steel bushings sandwiched between the ear, similar to the hand drawing shown in Rods previous post.

OK...I think I'm confused. Is this a solution for the folks who can't weld the banana bracket to the axel tube? I thought that weld was to keep the tube from spinning insite the bracket? My understanding was that this fix was to help support the bracket itself in high strees stiuations to keep it from bending/buckling? I don't see how it could be an alternative to welding the banana bracket to the axel tube.

[William Mapstone]

It will keep the banana bracket from spinning on the axle tube. No one has had a banana bracket bend, as far as I know.

[ChrisH]

OK...I get it. I thought there was a guy not too long ago that bent the bracket. Can't remember who, but I'll dig around and see if I can find it. Could be just my feeble old mind playing tricks on me again!

[dv/dt]

Chris,
I have heard reference to bending the bracket but it was always talking about the 3/4" square tube which extends forward to the front differential housing. For the bracket to spin on the axle that brace would have to bend. The design above will do both however, it will keep the banana bracket from spinning on the axle and will also reduce the chance of bending (I also haven't heard of this happening but with enough power??) the banana bracket itself by taking some of the loads and giving them a different, and better, path to the differential housing.

Cheers, Rod

[RButton]

I broke my front bracket which allowed the entire rear end to rotate thus the "banana" bracket banged into the 3 link cross frame benting it. But the "banana" bracket itself never moved. In fact, it is what allowed me to keep rolling, as it rested on the 3 link frame holding the rear end "sort of" in place so I could drive slowly home.

My "banana" bracket is positioned by the rear end vent tube so even clamped on I think it will be difficult for it to move.

The new FFR front bracket is working out much better. 2 days of hard auto-x and it held up great... so far. BUT I really like the stuff Rod has come up with to help the 3 link system!! And the price for the addon's are really reasonable... just go out and price some good round joints!!

[jim harris]

William,
Sent you an email and know from past experience that you do not read your mail regularly so I also will tell you here that I want one of the banana bracket anti-rotation devices when you have them.
dr.j