My 64 Comet 3 link build

First a disclaimer of sorts.... I can't find my other post on this subject.Im too old and dumb.

I researched around the web looking for a pre fabled 3 link kit,set up,or pile of parts and never found one. 
We are talking 3 link, NOT torque arm,NOT truck arms,not triangulated 4 link,but......

I found that Ridetech has a triangulated 4 link for the FALCON so I decided I'd just go with that after all Falcon=Comet.....well that's not close to true in the back! Too many details to list,let's just say the mistake $$, was trying to make it fit. So baby with the bath water I'm using the lower axle mount and shock mounts as well as the lower arms and HQ shocks,If a single 3/4" threaded arm is strong enough I'll use those for the upper arm. I'll use a Fays 2 Watts to hold it side to side.

The above is in NO WAY a slam on Ridetech I tried to use one application on a car it was not designed for,totally my fault.

So we come to the dumb questions.

In my reading around Ive found it fairly universal to say in a front engine rear drive car the horizontal CG is roughly the cam shaft height (V8) Let's say 20". Then the 100% anti squat line is drawn from the contact patch of the rear tire to the point the CL of the front tire intersects the HCG Line.

side trip... X= Horizontal,Y Vertical,Z Longitudinal

(front to back)? Have I got that right at least?

In side view,plane view(?) we are only looking at X and Y.

In my research I've read to limit rear steer,or minimize it we want the lower bars fairly long,I'm using the Ridetech lowers at 21.75" and parallel to the ground at ride height OR no more than a 5deg angle up. Front higher than rear.

Now to get anywhere near 100% AS with a parallel to the ground lower the upper arm would have to be angled very steeply down to get anywhere near our 100% line. Being we don't want 100% AS in a hanlding application that's not a problem. Am I anywhere near correct on this up to now? 
 

Again in my "research" I've read anything above 0 to no more than 30% AS seems to be a good compromise . So 0 would be both upper and lower parallel to each other and the ground  then from there the upper bar angling down in front to increase AS?

So with the lower effectively "flat" does the upper arm lower/ arm junction stay within my 114" wheel base at 30% AS or end up out in space somewhere in front of the car?

Im thinking my design goal should be a maximum 30%AS with adjustability to 10%.

This is Mainly a road driven Autocross car with a very limited (very) open track capability. In time it may get a roll cage but for now it's going to have chassis bracing that I have found work very well in early  Mustangs. Mainly triangle bracing the front aprons and shock towers as well as "jacking rails" and subframe connectors and cross members.

Im working around a 255/40 17 tire squared on a 9.5" wheel. Minor flare. My original goal was a 275 square combo but the front torque box will not allow the wheel angle with a tire that wide. Sounds odd but I don't want to cut the car up (too much more).

As you can tell I'm sure, I need more rule of thumb right now with a few "it works well for me's" tossed in.

Maybe a I would go with at least "this size" upper link as well.

Oh I've had a Watts link on my autocross 68 Mustang for several years so I have a pretty good idea on the effect of rear roll center and roll couple effects. Higher tail happy,lower safer for everybody.

Thanks for reading, I'll try to get a few pictures up as the project moves along.

I built my own 3 link/watts link for my cutlass. Covered pretty well in my build thread and on my YouTube channel.

My best advice is make brackets with lots of adjustment holes. And a very strong 3rd link mount. Like seriously...I broke a 3/16 thick one, probably shouldn't have done the lightening holes...but now it's 1/4" thick and extra gussets. 

It transformed my car's drive on corner exit compared to the stock triangulated 4 link.

Don't worry about the math too much. Just get yourself an adjustment window because you will want to play with it and feel the difference it will make in hiw it handles

In reply to Asphalt_Gundam :

So off-road type 1/4" bracket for the upper. The lowers have 3 holes starting 5" from the axle tube center line to 7". The lower rod ends are 3/4" with 5/8" bolt holes. 

So will  upper rod ends at 1" thread with 3/4" through bolt be good for strength? Beefy enough or bigger?

Ive seen off road brackets with 3 holes each.

My thought is at ride height every thing parallel with the rods at the closest position on axle end. Then 3 holes avaiable at the forward mount using the upper hole as 0-0 base line then be able to adjust the front down and/or the axle end up to increase the upper angle down at front.

does that make sense?

Thank You

Have you looked at Street or Track and their 3 link system for vintage Ford products?  Heavily Mustang based but Shaun offers a number of kits and uses 3 link with full floating rear ends and Fays 2 Watts link assemblies.  I've got a boat load of his stuff on my Cougar and it works well.  

In reply to wawazat :

SoT, nothing for a Comet,no interest at this time.

I have his spindles ,two set actually,one on my Mustang another for the Comet.

i also have his big brake set up for the Comet.

In reply to Asphalt_Gundam :

Dang Cody,have you maybe thought about modifying your Cutlass?

Some feelthy peekchurs would be great.  If it still exists, Corner-Carvers was good/great for obscure suspension diatribes; you can also find plenty of home-made 3-links on pro-touring.com and lateral-g.net.  See also Cortex Racing (and their crazy 1965 Mustang).  It's all been done.  The best solution would just be to slam a C5 Corvette rear end in there, but that's just my bitchin' stout talking . . .

Anything that fits on a Mustang of 1965 will fit on the Comet, but you might need to cut an inch out of the middle if it crosses the car.  That said, you probably don't actually want anything made to fit on a 1965 Mustang . . .

In reply to rustomatic :

I thought the same about "anything that fits....will fit a Comet...

we'll sort of. 
I can say the rear frame rails are not the same,they diverge behind the shock mounts much more gradually for one,besides the shallower angle at the floor.

The rockers are also taller,floor and firewall.

I went with a coil over set up for a Falcon,even with drop spindles the front will be higher than my 68 Mustang by close to 2 inches ,shocks bottom out.

Many,maybe even most, of the "hard parts" are interchangeable but for sure the steering drag link is not the same as Mustang.

Ive done several Mustangs over the years including my friends 70 Boss 302 vintage race car ,I've got a pretty good handle on making Mustangs turn stop and ride pretty good doing it....this Comet will not fall into the bolt on category.

All that said,yes I could stay with leafs,a Watts link,double adjustable shocks and do all the normal Mustang stuff and it would all work like it does on every,about 11 now,Mustang I've done but I wanted to go out there a bit on the Comet.

Yup I'm almost clueless which is why I can't communicate with Corner Carvers average posters....I have the books ,and I've read them,I understand the theory ,but it's always helpful to talk with somebody who has been there done that.

I think I may speak the same language as the group here.

Ill get some picks up in a few days.

LOL on the just....Corvette...

My buddy and I always say "why are we screwing with old cars,just push the easy button,sell it all and buy a new 'vette."

BTW a 'vette rear in a 64 Comet would have 2/3 of the stock tires out of the fenders. Track width is about 65".

Yep, them dang Corvettes are so wide.  My '63 Falcon has a 1992 Corvette underneath . . .

Cyclone03 said:

In reply to Asphalt_Gundam :

 

Dang Cody,have you maybe thought about modifying your Cutlass?

 

I dabble 

Here's a pretty good visual of where I ended up with my setup. Each adjustment hole is noticeable in the way the car handles.

It may not be ideal or perfect but its where I like the handling. IMO the upper could use more angle and the lowers a little less, IF....i could get the same grip on throttle and do other adjustments for the rotation into and through corners 

So I'm not proud of my work at this point to post pictures....it's all at the ugly point.

Ive almost completed my subframe jacking rail project.

The forward lower mounts are welded to the subframe connectors ,this positions them 1" below the frame rail mount location I mocked/eyebald it at before. The mount is also moved forward 1/2".

Lower arm is 21.75".

Ive purchased a chunk of 1.5" .25 wall DOM for the upper arm and weld sleeves for 3/4 rod ends.

From Ruff Stuf I have 1/4" thick brackets that come with 3 holes but I'm going to add 2 more.

The brackets have back plates as well. I also bought a gusset kit from them with 45,90,120degree angles. All 1/4"

My plan is to use the same bracket on the axle as body,frame(lol), frame end upside down.

Im also offseting the upper 5" to the right from center to save a bit of floor and possibly allow the front upper to be a bit lower. A pure center position has the front mount lowest position limited by the driveshaft and tunnel .

Im going to set the axle bracket off the back of the housing allowing the upper to be 2" longer than if it was centered. I'm shooting for 80% of the lower ,about 17" (to early for math). Offseting the upper will allow a higher arm position without crashing into the floor .

Now if it was centered the upper forward mount would more or less be fixed as well as inside the cabin. Not a huge deal as I think I can squeeze it behind the seat back,I want to keep the seat for now. But the rear floor would have a 8-10" hump from the axle forward.

All of that....better to spread the axle mounts vertically or is it ok for them to be close?

I have 3 holes for the lower axle,one at the front.

Upper can have 4 holes available with a possibility for 5 with an offset mounting. 4 if centered,arm will most likely hit the front of the housing on full compression.

If I use an offset mounting I see no reason to have a mounting lower than the center of the axle at ride height . If it's centered I can't go lower than the driveshaft.

Thoughts,comments,criticism welcome.

pictures one day I promise 

Offset to the right side of centerline in the car is fine. Lots of 3 links are done this way and it does play into counteracting torque forces on throttle. However there is next to zero info about how much, so go with what fits/feels best. I thing I ended up with about 1/2 gap between the center section and the inner side plate. Enough for a good weld and it was also where I had good room up on the frame crossmember for the chassis side mount.

I was once told the more adjustment you build in the better...and that has been good advise.

I built my upper link mounts with 5 holes each so there was a level at ride height option at each height. And...have never run a level setup. Imagine you're looking at the tire from the side view. When the throttle or brakes are applied that causes and opposite rotational force on the rear axle housing which in turn is only kept from spinning by the control arms. So those forces go into those arms. The distance from axle center, angles, and weight transfer of the vehicle all play into how much force goes through which arm and how that transfer of force affects the chassis.

For example: The lower mount on the axle is 3" from the centerline and the upper is 6" from centerline. Leverage says that the upper arm is going to be transferring a much larger amount of the rotational force into the chassis. On throttle this is a push on the bottom arms and pull on the top.

So lets say that the upper arm chassis side is lower than the axle side and the lower mounts are level. The level lower mounts will create a neutral strait forward push on throttle (assuming no change in ride height to keep things simple). The angle of the upper arm however will create a lifting force in addition to the rearward pulling force. The greater the angle the greater the percentage of lift while lessening the the rearward pull. That lifting force is trying to raise the rear ride height while the weight transfer is trying to lower it. Both of these forces wind up at the tire making more grip by placing more weight on the tire.

Now if we put an upward to the front angle on the lower arms we are doing two things. First we are creating a lifting force with the lower arm also. More angle equals more lifting force. Too much lifting force with at some point will overload the tires and cause traction loss. The second thing that happens is rear steer. More angle is more rear steer. As the outside wheel in a corner compresses, the ride height lowers, and the rear axle move rearward on that side as the arm comes to level. The opposite is happening on the inside as the ride height increases, the axle is pulled forward, pivoting the axle relative to the centerline of the vehicle. The axle steers outward (against the corner) increasing rotation into the corner.

I'm remembering I also made a basics video about a bunch of this stuff. So here's that

In reply to Asphalt_Gundam : The housing I'm using is one of the fabricated ones from Quick Performance that has nice flat areas for mounting and gusseting the upper bracket,offsetting also gets it away from the fill cap. 5" right of center give a good solid mount surface.
Does the upper axle mount need to be braced side to side as well as for and aft? Did your upper fail due to the lightening holes in the bracket for/aft or did it roll to the side? I purchased the housing with all 1/4" wall tubing so it's heavier than it needs to be I'm sure. Unsprung weight be damned. 

Can you see any reason the upper forward mount needs to be lower than 5" from the axle center? That would result in the lower and upper being 10" apart at the axle. With that the forward chassis mount would also be 10" apart vertically. All arms level at ride height during assembly/fabrication. I could mount the upper forward with adjustment for a lower setting as well. Maybe 5 holes with set up using the center hole allowing 2 up and 2 down?Or forget about up at the front and go all down but that would have the forward upper below the center of the axle.

The only fixed position is the lower forward. Then lower aft has 3 positions.

Ive actually watched all your 3 link stuff a few times,I just like the idea of bouncing ideas around.

Have you had any axle hop during braking with higher % of anti squat?

From what  I've heard it's a real code brown moment when it happens.

It definitely failed due to the lightening holes the first time. But it was repaired and plates welded on the sides over the holes and it still later failed again. After a redesign in 1/4" thick plate and adding a front gusset I haven't had problems. My front gusset had two slots for fitting around the bracket sides and is a trapazoid shape for the most part being wider on the axle top and tapers to the bracket. My reasoning being that spreading the loads out would be better than if they were focused on smaller area. This gusset does give support to the bracket side to side.

I can't really give you any hard numbers on locations and to be honest I didn't care with my stuff. My goals were plenty of adjustment and getting a longer upper arm in there. I put my car at the desired ride height and started measuring. For the axle side upper it was the trunk pan minus full compression travel for the top of the bracket. Figured out where the highest hole could be and added as many below it as the axle would allow. Similar process was used for the chassis side but I cut myself off adding a crazy amount of holes going down because I didn't want a big bracket hanging below the frame that could be a dangerous catch point if it bottomed out in a bad way. I settled for matching both brackets in distance from the ground for multiple level options. My ride height this worked out. Yours it might not. Rough guide of reference I can give you is my setup works best with 5.25" drop to the front. If that's on the aggressive side??? I don't know. There is no instance where you'll be wanting uphill to the front so figure that in. **the exception to that statement is rearends with birdcages (bearing mounts). They do not transfer rotational torque forces into the arms because there is a bearing between the arms and tubes. Creates totally different tuning scenarios**

Long story short....definitely do the extra adjustment holes lower on the chassis side.

I also didn't do anything with the lower forward point. I put more adjustment holes on the axle lower but don't need that aggressive rear steer that was how I got the stock stuff to work well. If I was needing to run a higher ride height then lower adjustment hole on the chassis side for all the arms would be better. If the car was to run even lower ride height then higher adjustment on the chassis might be needed. So basically how things worked out on my setup I have enough window that I was able to find what I needed and still will if I lower the ride height.

Yeah I've had axle hop, It's not fun. As long as you get off the brake pedal quick you can recover and only run a little deep into a corner. Keeping the rear bias on the low side of optimal helps. Give up a little performance but make sure the fronts lock first.

This is my subframe connectors and jacking rails.

Ive also mounted the forward lower control arm bracket to the subframe connector.

Dont look at the rear axle that's the next post.

Next the rear axle with upper 3 link tacked in place with all but the side gussets in place.

Upper mount is rotated so the upper mount holes are 3/8" forward.

Lower mounts tacked in place in line with the center of the forward mounts.

Next the axle in what I'll call mock up position ,ride height is most likely an inch high.

I have the lower arm in the closest to the axle position and connected to the forward mount.

For mock up the lower arm is level.

When the forward upper mount is positioned I'll use the hole closest to the axle then with the arm level I set the forward mount using the upper hole also level.

This will have the upper and lowers parallel.

I added one hole to the upper bracket,the pre fab brack only had 3 holes.

I haven't verified yet but I believe I'll have 5 holes available for the front upper mount.

as usual I welcome your comments.

Long week update,sorry no picks this time.

The lower forward mount wouldn't work,it was too low and I would end up with negative roll steer so I went back to forward spring eye mount with offset bushing to move the control arm inboard 1/2". That allows my 17 X9.5 wheel with 8mm offset to clear nicely.

The Watts link frame and upper coil over mounts and done and installed.

For the forward mount I made a doubler plate with a hole to allow the mount to go through the floor . I only have on hole above the floor with 3 down under the car. A crossmember ties the mount to the frame rails side to side.

The rear upper. axle mount goes through the trunk floor about 3" with the axle housing center hitting the floor. This is honestly too low,the axle tube are over 2" off the frame rails at this point. I'm going to install 3" bump stops. The coil overs just touch their bumper when the rear is rotated and still no frame rail contact.

its all coming along pretty well but slow,or I am. I've pretty much got a solid 40 hours in what I've done so far.

My buddy is coming over with his welder so we can hot glue the heavier tubbing tomorrow so it should be done except for a bit of lip stick.

I mock up with a PVC upper link it sure looks cool when everything moves.

Im thinking of painting the links white and having PVC pipe labels made,then put hose clamps near the ends....

That would be funny!

In reply to TurboFource :

I don't think "normal people" would get it.

But those in the know would die.....

Why didn't I see this thread earlier   I have been converting RX-7s to three link setups for about 16-17 years.

Lower links, the longer the better. 24" pivot to pivot minimum.  As close to parallel with the ground as possible when just below normal ride height.

Upper link, 3/4ish as long as the lowers.  Upper pivot an inch or so lower on the chassis than the rearend.  If this can be adjustable, all the better, because this is something to play with.  Increasing antisquat also increases brake hop so you can go too far.  1-2" down seems a happy medium.

Laterally, it helps to make the upper's chassis pivot slightly to the passenger side of the axle pivot.  This allows antisquat to favor the right side, to counteract driveshaft torque trying to lift the right wheel.  I have never seen any good math for this because it depends not only on the other angles of the other links, but also your rear gear ratio.  Taller gears lift the right tire more so need more left-right angle than shorter gears.  This is very much a "play with it and see" thing and you can play with it with different thickness spacers between the rod end and the mount.  Of course you also get this effect in braking, which you don't want, but there are always going to be tradeoffs (unless you go to floating caliper mounts).  I balanced this by running gearing in the 4.7-5.4:1 range to minimize how much driveshaft torque affects the rear.

On that note... rod ends, especially the upper, will make a hellacious clattering in short order no matter what rod ends you try.  I used to change them... then put up with all the knocking... then went bougie and replaced the rod ends with Johnny Joints.  Much much better.

Also, depending on how hard you drive the car, you really should look into a backbrace for the rearend.  With the torque loads going one way on the ends and the other way in the middle, you can bend the rear.  On one Mazda rear I had (banjo style, like a Ford 8/9") I split the back of the housing like cracking an egg.  So I started bracing them with tubing... and at one event, I broke a brace and then broke the axle on that side.  This directly resulted in my building a backbraced 9".

For future posterity, that Comet was more Fairlane  intermediate than Mustang/Falcon compact, hence why Falcon/Mustang stuff was not going to fit too good.  At this point, it doesn't really matter. 

Me playing with angles