View Full Version : Rubber Bushings for 3-link.

11-17-2004, 08:41 PM
After perusing my Howe and Lefthander catalogs and reading up on some 3-link theory I found a few circle track suppliers that offer rubber bushing ends for UCA on 3-links. Such as:




The theory I have read is that these will allow the acceleration/braking torque to be applied progressively to the rear suspension. Does anyone have any opinions or experience with this type of end link.

And I know that the UCA on a 3-link should have little to no lateral forces applied to it, so would a UCA with rubber bushed end links be acceptable? Such as this:


Thanks for your thoughts.

11-17-2004, 10:01 PM
Im running johnny Joints made by Currie real tough stuff. Edelbrock uses them in there adjustible rear UCA's. Lubeable, sealed and rebuildable. Alot less deflection than bushings and easier on the car than spherical ends.

Norm Peterson
11-18-2004, 06:09 AM
RJ - As long as the rubber bushings are stiff enough to keep you out of wheel hop, that looks like it might be a better arrangement for street duty than rod ends. After all, that 3rd link isn't in the most easily accessible location for I & M. Just guessing that this stiffness probably needs to be somewhat greater than twice whatever a 25 year old OE rubber bushing is good for. Ummmm, the quality of the welds is kind of important, as they will be carrying all the UCA tension under acceleration and a smallish amount of bending while cornering (a consequence of the lateral force and Z-axis moment developed in the bushings).

I suppose that in theory, acceleration/braking loads might be more progressively applied. But there's the practical issue of bushing compliance being nonlinear, meaning that while the initial 'hit' might be less given instantaneous application of such loads (which may not be an appropriate assumption for comparison purposes, BTW), that says nothing about what happens after the bushings have compressed a bit and suddenly get lots stiffer. Best I can guess is that overall it's close to a wash in most road course or auto-x driving, an improvement in more moderate driving (where the loads are smaller anyway), and with an overall gain in less NVH finding its way to the chassis all the time. And that dragstrip starting line issues are unique enough that you'd compromise differently if that were the priority (read: all rod ends).

Perhaps jonny joints in all 6 rear link locations?


spanky the wondermuffin
11-18-2004, 07:48 AM
there are a few styles of tourque absorbing upper links,the rubber bisquit type would be easy to use.not the same as rubber bushing.cushioning the blow on the upper link will help with foward traction(but only if you were having a problem with a solid link)but won't affect brake hop.for that you need an axle damper shock mounted above the upper link but angled upward 5 degrees.that is going to be more (too?) intrusive into the cabin.i suggest steve smith autosports book #s239,paved track stock car technology.road course set up tips are included,stock cars can and do turn right.

11-18-2004, 12:36 PM
Interesting. I see your logic Norm about the bushing compliance being nonlinear. The Johnny Joints are interesting. Vince, are you using them just on the UCA? And are you using the STD sleeve?

Or the welded stud style?


With the sleeve style, would you have to build an arm with a cylinder that the full Johnny Joint would go into? I would think that if you were to weld the Johnny Joint sleeve to an arm it would distort.

The fact that they are suppose to be impervious to weather makes them a nice option to rod ends.

11-18-2004, 06:06 PM
Hey guys, at first I was going to run spherical ends on the chassis side but I think JJ's at all points is better. Im running the welded stud JJ's on all points on the Chevy II.Im going to use the weld on JJ's on one side and studs on the other for my Camaro. They don't offer a left hand thread so I see no point other than adjusting length.If designed correctly only an inch of adjustment is needed.One studded JJ gives you 1 1/2" of adjustment.
Jon's right I suggest the Steve Smith book. Very good stuff. If you want I could scan a few pages but its good reading to buy the whole thing. It was like $25 and shipped in a week.
I plan on running a dampner in conjunction with the UCA for taking care of the brake hop.On the positioning of the UCA, im running my UCA rear mount 2 inches behind axle CL so an 18" UCA doesn't take up any backseat space.Since your running an a body having the rear frame cross member makes packaging very easy. A bracket that uses the bushing mounts on the rear housing is very easy to make.I will be putting a 3 link kit together for a 68 Chevelle but that job doesn't start till March. let me know what you come up with.
If you go with the weld on JJ's use a tig. I have tapped threads into the DOM pipe and it was easy but time consuming.About 20min each side. The 2 1/2" JJ uses 3/4" threads and the 3" JJ uses 1" threads.I have notes on the DOM tube size if you need them.

Salt Racer
11-19-2004, 07:40 AM
Here's another good alternative to Currie's JJ.


Rubicon Express Super Flex Joint (http://www.rubiconexpress.com/dynamic/mainpage.asp?folderid=788)

It's basically the same thing, but unlike Currie JJ, it has threaded adjuster on one side (adjustable preload), which makes the use of harder durometer bushing material possible (nylon, in this case).

Downsides? Maybe price...I don't know how much Currie sells JJs for. These are designed to replace late model Jeep's susp. bushings, so bolt sizes are kinda goofy - small one takes 10mm, and the big one takes 9/16" fasteners. And you'll have to either rig up or buy adjusters. Nylon bushings make these less susceptible to bind than polys, but NVH would be worse obviously.

These are only offered in weld-in style. But it looks like Currie just welds a bolt (with milled or ground head) to the sleeve and sell it as threaded style, so you can just buy sleeve style and weld on a LH bolt (and get it plated or coated, if you're so inclined).

I used RE's joints on a Bonneville race car I built last year. I welded the sleeve on a 2x3 tubing with TIG. No distortion problem (at least I was able to assemble them w/o any problem after welding). I intend to use them again when I build new LCAs for my Riv's 3-link.

Running my car at a track made me wonder at what point brake hop would really become a problem. I didn't have any problem, and I was really pushing the limit of the car.

11-19-2004, 07:55 AM
Hey Katz, yeah those are nice but pretty pricey... if I remember and I don't offen, they where about $90 each for the 3" (9/16 bolt) and are bullet proof.Jon A recommended using step spacers to run the 9/16" bolt with 3/4" bracketry. Im goint to run the cheap stuff till I get serious on the track...or at least get on the track seriously.
I wonder of the reason you didn't get any brake hop was due to the weight of the car and components? Maybe the bend in the UCA? Any ideas? Sounds like you had a blast and Im sorry we didn't get to meet up with you...next time.

Salt Racer
11-19-2004, 08:24 AM
Yup, it's too bad but I'll be back in CA next year for sure. I really want to try Thunderhill and/or go back to SOSW with better setup (more springs, home-brew drop spindles, 275/40R18 KDs and rear stabar).

Anyways, RE joints aren't that expensive. Big one costs roughly $40 each. I sure wouldn't spend $90 each on something like that. You know I'm cheap (yet demand high quality parts - the worst kind of people).

Using spacers is a good idea. Riv's LCA bolts are 1/2" on axle end, so I can just drill out the holes on my brackets.

Probably static SVSA of 69" was long enough to keep the brake hop minimum (or none), but there are other factors as you mentioned. I thought about sprung/unsprung mass ratio, but the ratio is probably close to typical Camaros, etc. The Buick 9.375" rear end probably weighs 50% more than Ford 9" (BTW, I finally found a used posi centersection. It's very similar to Dana PowerLok). Rear coils are rather stiff at 300 lb/in, but then again, you can probably think of the whole assembly as oversized muscle car. The shocks work surprisingly well, so maybe that's a factor. I suppose I can set them to the softest and see what happens on street.

Mean 69
11-19-2004, 11:13 AM
Hi guys,

I just wanted to add a couple of points for consideration. Make sure that whatever you use for supension links is capable of handling the loads that you will expect see, scaled for a safety factor. If you are not certain what they are, contact a skilled mechanical engineer. Failure of these parts is not something you want to have happen. I saw a similar type of busing end on a different site that had failed by splitting the outer shell, it was similar to one shown here in that a stud had been welded to it. Scary.

A good quality rod end has a very, very high radial load capacity. If you are looking for a good value, QA1 units are really nice, and cost about $30 from Jegs and other sources. Teflon lined, forged, nice pieces. If anyone has the load rating on the JJ's or the other pieces, it would be great if they could post. Also make certain that the hardware you use to retain the control arms is suitable in terms of shear strength, again, if you're not certain contact a professional to look over your design.

Katz, when I looked at your car, I though that the rear springs were mouted on the LCA's? If so, what is the motion ratio, or more specifically, what is the wheel rate? I finally got my car back on the ground, and with the 225 lb-in springs (mounted lightly off vertical, to the axle assembly) the booty end of the car feels really firm. Granted, I do not have the engine in the car yet, nor have I adjusted the Penske's, but it is pretty solid. I don't recall your car riding harsh at all, in fact I recall commenting that I want to duplicate it when I build the 61 Impala to house my drag race motor! Your car is a bit heavier, but this is a pretty big increase in wheel rate over my setup unless there is a motion ratio involved. By the way, all, I am one of the fortunate folks that got to drive Katz' car during his recent road trip, and it is super cool, really impressive handling for such a big car.


Salt Racer
11-19-2004, 11:54 AM
Hey, thanks Mark! (BTW, I'll send reply to your PM by the end of the day).

You're correct that my springs are on LCAs. Can't remember what the motion ratio was on top of my head, but wheel center rate (w/ estimated 1500 lb/in tire rate) is 118.7 lb/in. Ride Freq. is 64.7 cpm, so it's close to factory pony cars? JFYI, the front Ride Freq. is 71.0 cpm. I'll probably have to go stiffer with wider KDs all way around, but I might experiment with soft coil/stiff sta bar approach with this car since I don't want to make the ride much firmer than it is.

So you're seriously thinking about Imp, eh? That'll be a cool ride! :smoke:

11-19-2004, 06:31 PM
thanks,good point Mark, I know the JJ's are made of .120 wall DOM,(also availible in chrome moly) I don't think we will have a problem there. Im more concerened about the welded bolt portion of the set up, although it is 1" x 3 1/4" fine thread bolt welded with full penetration. I have friends that rock crawl using the Currie trailing arms and they have had no failures. He beats the living sh!ot out of his jeep too but road racing is a different force all together.
Thats why im leaning more towards the weld on JJ's and running 1 1/2" .156 wall DOM for LCA's.Fish mouthing the tube to cup the JJ then TIG them for the next car. Right now im running 1 1/4" .156 wall DOM LCA's. Be nice to get a set out for testing. As far as hard numbers you guys like hearing I have nothing for you so right now its just speculation of its strenth. I suck at numbers.... for instance I figured the pricing was off.Not too much more for the super flex joints, I like the load adjustment.
Any word on Jon A's aluminum LCA set up on his Stang? I haven't been out at CC for along time.

11-22-2004, 08:40 PM
Jon and Vince, thanks for the suggestion on the book. I will pick up a copy at library tommorow. I can't buy a book this close to X-mas. That one was already on the wish list.

Katz, thanks for the Rubicon Joint suggestion. That is a nice piece of work.

Mark, I contacted Currie today about the load rating on a Johnny Joint and they did not give me a specific answer. The basically stated that the load rating would be limited to by the through bolt itself. And they suggested a 2.5" joint for a P-T type of 3-link based on the fact that threy use it regularly on drag applications which is more of an impact load than a road race car. So no real data, but another opinion. If anyone has a JJ that they could take apart and get me some dimensions, I could model it up quick in CAD and have my FEA guy at work give us an opinion.

11-22-2004, 09:00 PM
Another option to check out is Hotchkis JJ's. I dont think they are on the website yet, but they had them on their new tubular control arms for A-bodys and they looked pretty sweet. I talked to the guy on their design and he said they are urethane outers, but the inside had a delrin greasable insert to take on the point loads. Seemed like a pretty sweet design. I wish they had an exploded view to get a better idea. Maybe Ill contact them to try and get some pics.

Marcus SC&C
11-24-2004, 06:13 PM
FWIW we`ve used the JJs in a few applications now and been pleased with them. I have some "different" ideas I`d like to use them for if I ever get the spare time to pursue them. The similar ends used in some Edelbrock UCAs are very nice too. Marcus