3 link parts

[Nate K]

I am getting ready to install a 3-link and I need to know what materials you guys recommmend using for the joints and bars. I searched and cannot seem to find the info I need.
Nate

[Lowend]

have you looked at www.stockcarproducts.com yet? they pretty much build it for you

[Nate K]

I was looking more for advice on what rod ends to use or to avoid. Also what size of tubing is needed. I figured people on here have had experience with them and could help me out.

[mongoose]

i'm going to be running just some sweged tube... and johhny joints...

people seem to love the joints... and the tubes are cheap... 20 bucks... and strong.

[Damn True]

I suggest you get yourself a copy of the Pegasus catalog. Go straight to the back and order all of Carroll Smiths books. Read them first. They will answer the majority of the questions you have now and many that you have not thought to ask.

[Nate K]

I ordered the books but they seem to be on chassis setup and design my three link is already designed I just need to build it. I made the brackets out of 1/4in plate which is a little overkill but it was free. It is setup to use 3/4 by 3/4 heim joints. I was just wondering what joints you guys recommend and what tubing you normally use.
Nate

[35spline]

I used Johnny Joints and 1 3/4" DOM tube.

[The WidowMaker]

jj's with DOM 1.5 .120 lowers and DOM 1.25 .120 uppers.

Tim

[Nate K]

Which size johnny joints are you guys using and why did you use them instead of heim joints.
Nate

[parsonsj]

My 3 link uses 3/4" hybrid heim joints (3/4" threaded part, 5/8" hole). The brackets are made from .188 mild steel, and my tubes are 1.25 x .090 4130 (lower) and 1.5 x .090 4130 (upper). The panhard bar is also 1.5 x .090, though I've been told that a 1.25 bar would have been fine.

Johnny joints are unnecessary for a 3 link, since it has no inherent tube redundancy (aka bind). Jj's are needed in most 4 link street setups to reduce roll bind.

Good luck... and be sure to post some pics of your fabrication!

jp

[Denvervet]

Another reason I like the Johnny joints vs heims is they have a poly type race which can be greased and replaced. The knock I hear about heims is they aren't real durable or greasable and thus become loose and noisy.

[The WidowMaker]

john - why the 3/8" brackets? ive heard of the offroad guys using 1/4" so the holes dont go egg shape, but i havent heard of 3/8". are they a single shear mount?

also, i chose the jj's over the heims for the ^^^^ above reason as stated by "denvervet". the poly race will significantly lower NVH. they are very heavy though, and because of their width, i couldnt use them for the watts. i have the teflon lined heims in use on the watts.

Tim

[parsonsj]

Oops. I meant 3/16. .188. Double shear.

Good catch Tim! I fixed my post.

jp

[Nate K]

My 3 link uses 3/4" hybrid heim joints (3/4" threaded part, 5/8" hole). The brackets are made from .188 mild steel, and my tubes are 1.25 x .090 4130 (lower) and 1.5 x .090 4130 (upper). The panhard bar is also 1.5 x .090, though I've been told that a 1.25 bar would have been fine.


JP it is great to hear from you, your car is freakin awsome. Will 3/4 x 3/4 joints be ok. I would need to remake my brackets to use the hybrid joints. Where did you get the 4130 tubes and bungs.

Nate

[parsonsj]

Nate,

Thanks! Glad you like it.

For your heim joints, 3/4 x 3/4 will be fine. No worries there. I got my tube and threaded adapters from Art Morrision. Give Kevin Kosir over there a call (ext. 222).

jp

[Nate K]

I just ordered some stuff from kevin about 2 weeks ago. Should I use teflon lined or just metal joints.

[The WidowMaker]

the teflon lined are much better than just a plain joint, but the ballistic joints or jj will stay much quieter. there are mixed reviews on how long a tradional heim joint will last before the infamous "humming" starts.

[Damn True]

I ordered the books but they seem to be on chassis setup and design my three link is already designed I just need to build it. I made the brackets out of 1/4in plate which is a little overkill but it was free. It is setup to use 3/4 by 3/4 heim joints. I was just wondering what joints you guys recommend and what tubing you normally use.
Nate


Engineer to win covers the hardware side of things pretty well.

[Nate K]

Cool cant wait to check it out.

[JRouche]

I am making a watts link and gonna use QA1 ends. their 3/4x5/8 are stronger than the 3/4x3/4. And a 5/8" grade 8 bolt has about 8000 PSI in strength on shear, plenty. JR

[Damn True]

I am making a watts link and gonna use QA1 ends. their 3/4x5/8 are stronger than the 3/4x3/4. And a 5/8" grade 8 bolt has about 8000 PSI in strength on shear, plenty. JR



....and the above is why you guys ought to be reading Smith.

You never want to use Grade freakin anything in a stressed suspension member.


Seriously guys, AN hardware only in that type of application.

[Nate K]

....and the above is why you guys ought to be reading Smith.

You never want to use Grade freakin anything in a stressed suspension member.


Seriously guys, AN hardware only in that type of application.

This stuff is killing me! Right when I think I have it figured out I ask what I think is a simple question and realize there is way more to it. Hopefully these new books will finally help me get it finished.
Thanks for your help.
Nate

[JRouche]

You never want to use Grade freakin anything in a stressed suspension member.

Seriously guys, AN hardware only in that type of application.

The folks over at AME are the ones that supplied me with all the grade 8 hardware for my 4-link rear. I just used what was given. JR

[The WidowMaker]

jim fay supplies grade 5 with his watts. i guess im not really understanding; gm supplied these cars with grade 8 (some say 5) in the factory control arm mounting locations. ive never heard of a lca arm bolt breaking, and thats with slicks and wheel stands.

Tim

[JRouche]

jim fay supplies grade 5 with his watts. i guess im not really understanding; gm supplied these cars with grade 8 (some say 5) in the factory control arm mounting locations. ive never heard of a lca arm bolt breaking, and thats with slicks and wheel stands.

Tim

Hey Tim.. Glad you popped in with that.

Really, you wont find a guy saying a "real" grade 8 bolt failed in a set up. LOL They are way beyond the needs of any car suspension. If the fastener is appropriate for the size and the system is engineered for the bolt.

Example: A 1/4 bolt isnt put into play where it doesn't belong.

But Im talking about 5/8" grade 8 (not knock offs either) bolts. Haaa. You could hang yer entire car off of one, in shear, and put a couple gravities on it and it will NOT shear. And we are talking about one of them taking a fraction of the force that the car has to give. Im sorry but theres no way yer gonna shear off a 5/8" grade 8 bolt on yer link suspension.

Not with normal driving, or even race. If you let off on the peddle on the turn and let the rear hit the bank I am sure yer link bars will bend well before the fasteners (yeah, grade 8) even start to bend much less shear apart. I dont wanna get into a fastener argument though. Crap, I just bailed from a bearing issue that didnt need to happen.

I have grade 8 bolts holding my entire car together. Every shock, link, bumper and brake. Everything cept the engine, but thats entirely ARP.

I have what I have and till it doesnt work thats whats in place. JR

[Damn True]

This stuff is killing me! Right when I think I have it figured out I ask what I think is a simple question and realize there is way more to it. Hopefully these new books will finally help me get it finished.
Thanks for your help.
Nate

Nate,

I'm at work right now and don't have access to the materials to quote them verbatim but let the following suffice until I can get to it.

Carroll Smith prepared the GT-40's that won LeMans in 1966, 1967, 1968 and 1969. He prepared the 1969 F5000 Champ. He prepared the 1978 Aussie Touring Car Champ and he was a consultant to the Ferrari F1 team. Ferrari paid him to help THEM prepare F1 cars.

No disrespect to the people at AME or to Jim Fay, but I'll take the advice of Carroll Smith over theirs (let alone some internet e-genius) every time and twice on Sunday.

[JRouche]

No disrespect to the people at AME or to Jim Fay, but I'll take the advice of Carroll Smith over theirs (let alone some internet e-genius) every time and twice on Sunday.

I didnt even mean to ruffle any feathers. No doubt the best fasteners you can get are gonna be good. Just trying to give some other ideas. Nope, Im far from being any type of wanna be genius, far from it. Im just a hack in my garage STILL trying to get my own car down the road :) JR

[The WidowMaker]

I'm at work right now and don't have access to the materials

gotta love being at work, getting paid, and still wasting time. im currently doing it too. :cheers:

i see where youre coming from, but i still would think that in a race application, with a nearly unlimited budget, they are going to do things differently. hell, i could build my car out of carbon fiber too, but thats a little costly and the steel will do just fine.

i too respect what has been said and written, but i also cant afford 3x+ for a fastner.

Tim

[Damn True]

i see where youre coming from, but i still would think that in a race application, with a nearly unlimited budget, they are going to do things differently. hell, i could build my car out of carbon fiber too, but thats a little costly and the steel will do just fine.

i too respect what has been said and written, but i also cant afford 3x+ for a fastner.

Tim

A couple of points to think about.


It is illegal, ILLEGAL, to put an SAE bolt of ANY grade on an aircraft that is to be flown in any airspace under the control of the FAA or US Military.
Smith wrote his books based on experience gained in preparing the GT-40 which weighed only 2000lbs, the F5000 which weighed a mere 1250lbs (1105 for 3000cc cars), and F1 cars at roughly 1267lbs.


My car will weigh more than the F5000 and the F1 car combined I can't afford not to use AN stuff in critical locations. (I would use though an ARP wheel stud or any of their engine hardware)

After further review, there is waaaay too much important info to actually quote. Google books has a few bits and pieces of it but in order to understand the whole picture you really have to read the books.

Prepare to Win - Chapter 1
Engineer to Win - Chapter 8
Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook - Chapter 4

Summarizing Smith; SAE bolts have a number of critical shortcomings.


Threads are often cut rather than rolled. Cutting threads fractures the grain of the metal and weakens the structure.
Thread shape is less than ideal due to hard angles resulting in stress risers.
SAE bolts are designed primarily for tensile loads and the shanks are slightly undersized for shear applications. (Your rod-end bearing however is most likely exactly the right size)
SAE specifications are stringent.....but there is no enforcement. Bolts can be made anywhere, in any way and marked as Grade-X and sold.

AN/MS/NAS hardware has a number of positive features lacking in SAE hardware.


Aircraft hardware threads are always rolled, after heat treating ensuring that the grain structure of the substrate is intact.
Aircraft hardware threads have the proper radius to mitigate stress risers.
Aircraft hardware has a true bearing surface beneath the head of the bolt. Similarly the shanks are absolutely true to the long axis of the bolt.
Aircraft hardware is drilled for safety wire or cotter pins at the correct angle and at the appropriate point in manufacture to ensure minimal (if any) loss of strength.

Aircraft hardware is muuuuuch stronger. The aforementioned 5/8" grade 8 bolt is rated at 8000lbs in shear. An AN bolt of the same dimensions (AN-80) is rated at 25,100lbs tensile, 23,000lbs single shear and 46,000lbs in double shear.

Knowing that a great deal of SAE hardware is manufactured in China, and knowing that Chinese manufacturers have no apparent problem putting toxic filler material in food products and formaldehyde on infant clothing......I am not entirely confident that they have elected to self police the stringent SAE specifications.....especially since there is no enforcement.

Aircraft hardware manufacturers are however subject to steep fines and imprisonment if they gundeck those specs.




Aircraft hardware can be bought in quantity, and dirt cheaply I might add from Aircraft Spruce. They sell them in huge sets with wide varieties of sizes and some even come with nifty little divider boxes to store them.

Seriously guys. I'm not trying to "win an argument" or trying to be right here. This is a matter of safety. If money is an issue maybe you ought to consider spending less on aesthetic elements like wheels and make the first priority the safety of the car. We are building really freaking fast (and rather heavy) cars here. Many of us intend to put them on a racetrack (HPDE or auto-x) and treat them in the same manner as a race car. Why would you prepare the car as anything less than a race car?

[Bow Tie 67]

True,

When I started with the airline in 90 we were going through inspections on our MD 80 fleet for incorrect engine fasteners. The engine is held on by three bolts and I did find black-market bolts. The tolerance on the threads were incorrect, kind of like an hour-glass, and right at the point the nut should be clamping the mounts vibration isolator the running torque would completely disappear. Some scarry sheet, when I fly I drink.

Matt

[Damn True]

Yep, it happens. CG-1427 crashed in 1988 due to faulty hardware (low-bid supplier found to have sourced hardware from Mexico) in the pitch-change rods killing 3 aircrew. The supplier is still at Ft. Leavenworth.

But the fact that there is enforcement ensures that the frequency of black market hardware entering the inventory is mitigated. With no enforcement at all of SAE hardware combined with the most likely point of origin (China) what do you reckon the odds are that the Grade-X stuff on the shelves actually is to spec?

Even if the Grade-X stuff is built to spec (often isn't) it is still inferior to AN/MS/NAS hardware.

[CarlC]

The detail that I really like about using AN bolts for suspension use is that the full diameter of the shank can be used in both shear planes. For OE spec. one thread is in shear. Even with the G5 materials spec. for AN airframe bolts if both planes are in full-diameter double shear it is, on paper, a stronger connection than a G8 OE. This does not take into account long-term corrosion effects on the G8 shear thread plane or the questionable quality of a hardware store bolt.

I've had to deal with some very frightening bolting jobs that support the rotating structures in steel mills, heavy construction, etc. There's a reason why there are spec's there as well, such as A325 and A490. But it is scary how often those specifications are discarded and/or not adhered to by the manufacturer.

[BillyShope]

The 3link spreadsheet at my site (Page 18) provides link loads for a 1G forward acceleration when the links are arranged to provide equal rear tire loading. Might be useful to you.

http://home.earthlink.net/~whshope
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